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Cavity-enhanced channeling of emission from an atom into a nanofiber
Abstract
We study spontaneous emission of an atom near a nanofiber with two
fiber-Bragg-grating (FBG) mirrors. We show that the coupling between the atom
and the guided modes of the nanofiber can be significantly enhanced by the FBG
cavity even when the cavity finesse is moderate. We find that, when the fiber
radius is 200 nm and the cavity finesse is about 30, up to 94% of spontaneous
emission from the atom can be channeled into the guided modes in the
overdamped-cavity regime. We show numerically and analytically that vacuum Rabi
oscillations and strong coupling can occur in the FBG cavity even when the
cavity finesse is moderate (about 30) and the cavity length is large (on the
order of 10 cm to 1 m), unlike the case of planar and curved Fabry-Perot
cavities.
... E 2 (x) = E 2 (x, y) cos(β 2 z) exp(iω 2 t) [35,36], where β 1 and β 2 are the propagation constants of E 1 (x) and E 2 (x), respectively. The total electric field operator can be written as ...
... where ii is the relative permittivity in the i (i = x, y, z) direction in laboratory frame. This optomechanical resonator supports two fundamental orthogonal quasi-linear polarization optical modes [34] with the corresponding electric field profiles E 1 (x) = E 1 (x, y) cos(β 1 z) exp(iω 1 t) and [35,36], where β 1 and β 2 are the propagation constants of E 1 (x) and E 2 (x), respectively. The total electric field operator can be written as ...
... Considering Equ. (35) and Equ.(36), we know that ...
Optomechanical systems offer unique opportunities to explore macroscopic quantum state and related fundamental problems in quantum mechanics. Here, we propose a quantum optomechanical system involving exchange interaction between spin angular momentum of light and a torsional oscillator. We demonstrate that this system allows coherent control of the torsional quantum state of a torsional oscillator on the single-photon level, which facilitates efficient cooling and squeezing of the torsional oscillator. Furthermore, the torsional oscillator with a macroscopic length scale can be prepared in Schrödinger catlike state. Our work provides a platform to verify the validity of quantum mechanics in macroscopic systems on the micrometer and even centimeter scale.
... E 2 (x) = E 2 (x, y) cos(β 2 z) exp(iω 2 t) [35,36], where β 1 and β 2 are the propagation constants of E 1 (x) and E 2 (x), respectively. The total electric field operator can be written as ...
... where ii is the relative permittivity in the i (i = x, y, z) direction in laboratory frame. This optomechanical resonator supports two fundamental orthogonal quasi-linear polarization optical modes [34] with the corresponding electric field profiles E 1 (x) = E 1 (x, y) cos(β 1 z) exp(iω 1 t) and [35,36], where β 1 and β 2 are the propagation constants of E 1 (x) and E 2 (x), respectively. The total electric field operator can be written as ...
... Considering Equ. (35) and Equ.(36), we know that ...
Optomechanical systems offer unique opportunities to explore macroscopic quantum state and related fundamental problems in quantum mechanics. Here, we propose a quantum optomechanical system involving exchange interaction between spin angular momentum of light and a torsional oscillator. We demonstrate that this system allows coherent control of the torsional quantum state of a torsional oscillator on the single photon level, which facilitates efficient cooling and squeezing of the torsional oscillator. Furthermore, the torsional oscillator with a macroscopic length scale can be prepared in Schr\"odinger cat-like state. Our work provides a platform to verify the validity of quantum mechanics in macroscopic systems on the micrometer and even centimeter scale.
... Recently, nanofiber-based cavities have been developed as a promising candidate for CQED [29][30][31][32][33]. Due to * takao@waseda.jp ...
... Recently, nanofiber-based cavities have been developed as a promising candidate for CQED [29][30][31][32][33]. Due to * takao@waseda.jp the tight confinement of the guided mode [29], high interaction strengths can be obtained, even with moderate finesse. As these cavities can be directly integrated into a fiber channel, multiple cavity systems can be easily linked. ...
... By calculating the spectrogram of each transmitted laser, we are able to determine the time of the cutoff point for each higher-order mode and for each wavelength, and hence the corresponding fiber radius at that time [47,50]. We use three lasers with wavelengths of 682 nm, 633 nm, and 532 nm, corresponding to singlemode cutoff radii of 248 nm, 228 nm, and 192 nm, respectively, which were chosen to determine the radius of the fiber in the vicinity of 200 nm, close to the optimal nanofiber radius for experiments with cesium atoms [29]. These lasers are combined using dichroic mirrors to be coupled into the fiber cavity, and detected on three separate photodiodes after being separated by a diffraction grating. ...
We demonstrate the fabrication of ultra-low-loss, all-fiber Fabry-P\'erot cavities containing a nanofiber section, optimized for cavity quantum electrodynamics. By continuously monitoring the finesse and fiber radius during fabrication of a nanofiber between two fiber Bragg gratings, we are able to precisely evaluate taper transmission as a function of radius. The resulting cavities have an internal round-trip loss of only 0.31% at a nanofiber waist radius of 207 nm, with a total finesse of 1380, and a maximum expected internal cooperativity of $\sim$ 1050 for a cesium atom on the nanofiber surface. Our ability to fabricate such high-finesse nanofiber cavities may open the door for the realization of high-fidelity scalable quantum networks.
... Recently, nanofiber-based cavities have been developed as a promising candidate for CQED [29][30][31][32][33]. Due to the tight confinement of the guided mode [29], high interaction strengths can be obtained, even with moderate finesse. ...
... Recently, nanofiber-based cavities have been developed as a promising candidate for CQED [29][30][31][32][33]. Due to the tight confinement of the guided mode [29], high interaction strengths can be obtained, even with moderate finesse. As these cavities can be directly integrated into a fiber channel, multiple cavity systems can be easily linked. ...
... By calculating the spectrogram of each transmitted laser, we are able to determine the time of the cutoff point for each higher-order mode and for each wavelength, and hence the corresponding fiber radius at that time [47,50]. We use three lasers with wavelengths of 682, 633, and 532 nm, corresponding to single-mode cutoff radii of 248, 228, and 192 nm, respectively, which were chosen to determine the radius of the fiber in the vicinity of 200 nm, close to the optimal nanofiber radius for experiments with cesium atoms [29]. These lasers are combined using dichroic mirrors to be coupled into the fiber cavity and are detected on three separate photodiodes after being separated by a diffraction grating. ...
We demonstrate the fabrication of ultra-low-loss, all-fiber Fabry–Perot cavities that contain a nanofiber section, optimized for cavity quantum electrodynamics. By continuously monitoring the finesse and fiber radius during the fabrication of a nanofiber between two fiber Bragg gratings, we were able to precisely evaluate taper transmission as a function of radius. The resulting cavities have an internal round-trip loss of only 0.31% at a nanofiber waist radius of 207 nm, with a total finesse of 1380, and a maximum expected internal cooperativity of ${\sim}1050$ ∼ 1050 for a cesium atom on the nanofiber surface. Our ability to fabricate such high-finesse nanofiber cavities may open the door for the realization of high-fidelity scalable quantum networks.
... In this context, a tapered optical nanofiber (ONF) based cavity provides a unique fiber-in-line platform for cavity quantum electrodynamics (QED) [7,8]. Because of the strong transverse confinement of the ONF guided modes, even a moderate finesse ONF cavity can enable high single atom cooperativity [7,8]. ...
... In this context, a tapered optical nanofiber (ONF) based cavity provides a unique fiber-in-line platform for cavity quantum electrodynamics (QED) [7,8]. Because of the strong transverse confinement of the ONF guided modes, even a moderate finesse ONF cavity can enable high single atom cooperativity [7,8]. Moreover, based on the achievable finesse, the cavity parameters can be designed by choosing an appropriate cavity length ranging from tens of μm to few meters [7][8][9]. ...
... Because of the strong transverse confinement of the ONF guided modes, even a moderate finesse ONF cavity can enable high single atom cooperativity [7,8]. Moreover, based on the achievable finesse, the cavity parameters can be designed by choosing an appropriate cavity length ranging from tens of μm to few meters [7][8][9]. Based on this concept, the strongcoupling regime of cavity QED has been demonstrated using a 33 cm long ONF cavity with a finesse < 40, realized by sandwiching the tapered fiber between two conventional fiber Bragg mirrors [10]. However, the extremely long cavity length and the presence of the tapered section within the cavity limit the atom-cavity coupling rate (2π × 7.4 MHz) and the achievable cooperativity (∼3.3) [8,10]. ...
We demonstrate efficient interfacing of individually trapped single atoms to a nanofiber cavity. The cavity is formed by fabricating photonic crystal structures directly on the nanofiber using femtosecond laser ablation. The single atoms are interfaced to the nanofiber cavity using an optical tweezer based side-illumination trapping scheme. We show that the fluorescence of individual single atoms trapped on the nanofiber cavity can be readily observed in real-time through the fiber guided modes. From the photon statistics measured for different cavity decay rates, the effective coupling rate of the atom-cavity interface is estimated to be 34±2 MHz. This yields a cooperativity of 5.4±0.6 (Purcell factor=6.4±0.6) and a cavity enhanced channeling efficiency as high as 85±2% for a cavity mode with a finesse of 140. The trap lifetime is measured to be 52±5 ms. These results may open new possibilities for deterministic preparation of single atom events for quantum photonics applications on an all-fiber platform.
... In the vision of a quantum network, efficient integration of the quantum interface to the existing fiber network is also an essential requirement. In this context, optical nanofiber based cavities offer a flexible alternative platform [8]. The nanofiber is the subwavelength diameter waist of a tapered single mode optical fiber. ...
... Moreover a major part of the guided field propagates outside the fiber enabling interaction with the surrounding medium. In order to get insight about the interaction dynamics in a nanofiber based cavity we follow the formalism developed in ref. [8]. Based on the formalism, 2g 0 = 2 ηγc/L and κ = πc/(F L), re-spectively, where η is the channeling efficiency of spontaneous emission of atom into the nanofiber guided modes without a cavity, γ is the atomic spontaneous emission rate near the nanofiber, c is the speed of light in vacuum, L is the optical length of the cavity and F is the finesse of the cavity mode. ...
... Furthermore, we fabricate two photonic crystal structures separated by 1.2 cm on such a nanofiber using femtosecond laser ablation, thus forming a long nanofiber cavity. The cavity modes with finesse value in the range 200-400 can still maintain the transmission between 40-60%, enabling "strong-coupling" regime for a single atom trapped 200 nm away from the fiber surface [8]. For such cavity modes, we estimate the onepass intra-cavity transmission to be 99.53%. ...
We report the fabrication of a 1.2 cm long cavity directly on a nanofiber using femtosecond laser ablation. The cavity modes with finesse values in the range of 200–400 can enable the “strong-coupling” regime of cavity QED, with high cooperativity of 10–20, for a single atom trapped 200 nm away from the fiber surface [Phys. Rev. A 80, 053826 (2009)PLRAAN1050-294710.1103/PhysRevA.80.053826]. Such cavity modes can still maintain the transmission between 40%–60%, suggesting a one-pass intracavity transmission of 99.53%. Other cavity modes, which can enable cooperativity in the range of 3–10, show transmission over 60%–85% and are suitable for fiber-based single-photon sources and quantum nonlinear optics in the “Purcell” regime.
... High coupling efficiency can be achieved by confining the guided light along the ONF axis, namely, cavity enhancements [30][31][32]. Thanks to the well-established technologies of micro/nanofabrication, ONFs can be tailored, and the coupling efficiency can be substantially enhanced [33][34][35]. Various tailored ONFs with complicated structures have been proposed [36][37][38][39][40][41][42]. It is expected that the coupling efficiency exhibits the potential to reach 80% or more [34]. ...
... Various tailored ONFs with complicated structures have been proposed [36][37][38][39][40][41][42]. It is expected that the coupling efficiency exhibits the potential to reach 80% or more [34]. Experiments with solid-state quantum emitters and cold atoms have been accomplished, in which remarkable enhancements are demonstrated [15,[43][44][45][46][47]. ...
We propose a scheme to enhance the coupling efficiency of photons from a single quantum emitter into a hole-tailored nanofiber. The single quantum emitter is positioned inside a circular hole etched along the radial axis of the nanofiber. The coupling efficiency can be effectively enhanced and is twice as high as the case in which only an intact nanofiber without the hole is used. The effective enhancement independent of a cavity can avoid the selection of a single emitter for the specific wavelength, which means a broad operating wavelength range. Numerical simulations are performed to optimize the coupling efficiency by setting appropriate diameters of the nanofiber and the hole. The simulation results show that the coupling efficiency can reach 62.8% when the single quantum emitter with azimuthal polarization (x direction) is at a position 200 nm from the middle of the hole along the hole-axial direction. The diameters of the nanofiber and the hole are 800 nm and 400 nm, respectively, while the wavelength of the single quantum emitter is 852 nm. Hole-tailored nanofibers have a simple configuration and are easy to fabricate and integrate with other micro/nanophotonic structures; this fiber structure has wide application prospects in quantum information processing and quantum precision measurement.
... By creating a cavity structure on a nanofiber, mode confinement can be extended to the longitudinal direction, leading to a strongly enhanced light-matter interaction [3]. Obviously, such cavity induced enhancement is wellknown as the cavity QED [4]. ...
... However, the nanofiber cavity system can open a completely different operating condition from that for the traditional cavity QED systems based on free space Fabry-Perot cavities. For example, spontaneous emission can be channeled into fiber guided modes with an efficiency greater than 90% using a rather moderate cavity finesse of 100, which is 1,000 time milder condition than that for the traditional cavity QED [3]. Such moderate condition can remove a barrier to extend the cavity QED physics to future photonic technologies. . ...
Recent progress in quantum photonics with optical nanofibers (ONFs) is reported. Emphasis is on the photon channeling into the fiber guided modes for a hybrid system of an ONF cavity and a single quantum emitter.
... Finally, we briefly discuss about the alignment of the nanowire to the direction of the nanofiber. Figure 5a shows a schematic of the relative angle φ between the 40 ), and additional cavity-modified (based on the model in ref. 57 ) results, respectively. The nanowire radius r d = 85 nm and the nanowire length L d = 3.6 μm are fixed. ...
... The coupling efficiency is determined by the spontaneous emission rates of a two-level atom into the supermodes derived from the Heisenberg equations. In order to investigate the contribution of the Fabry-Perot resonance due to the reflection from the nanowire facets, we additionally modify the calculations by using the cavity-modified spontaneous emission rates based on the model in ref. 57 . For simplicity, we assume that the rate of the spontaneous emission coupled to only the nanowire-based supermode is modified by the reflection from the diamond nanowire facets with the approximate reflection coefficient ...
Nitrogen-Vacancy (NV) centers in diamond are promising solid-state quantum emitters that can be utilized for photonic quantum applications. Various diamond nanophotonic devices have been fabricated for efficient extraction of single photons emitted from NV centers to a single guided mode. However, for constructing scalable quantum networks, further efficient coupling of single photons to a guided mode of a single-mode fiber (SMF) is indispensable and a difficult challenge. Here, we propose a novel efficient hybrid system between an optical nanofiber and a cylindrical-structured diamond nanowire. The maximum coupling efficiency as high as 75% for the sum of both fiber ends is obtained by numerical simulations. The proposed hybrid system will provide a simple and efficient interface between solid-state quantum emitters and a SMF suitable for constructing scalable quantum networks.
... Various tools and techniques are being used to make fiber Bragg grating (FBG) [20][21][22] and photonic crystal (PhC) cavity [23][24][25] structures on an ONF. ...
We report a slot waveguide-enhanced asymmetric photonic crystal optical nanofiber (ONF) cavity to realize cavity quantum electrodynamics. We show that the device can strongly enhance the spontaneous emission of a single quantum emitter leading to a Purcell factor as high as 106 and enables single-photon coupling efficiency as high as 86% into fiber-guided modes. The introduction of the slot enhances the Purcell factor by six times as compared to the ONF cavity structure without slot, and the asymmetric cavity design enables unidirectional coupling of single photons. The cavity is designed to minimize the losses leading to a scattering-limited Q-factor and one-pass loss estimated to be 6388 and 1.2%, respectively. This fiber-coupled single-photon device may open advanced possibilities and applications for quantum information processing.
... Various tools and techniques are being used to make fiber Bragg grating (FBG) [20][21][22] and photonic crystal (PhC) cavity [23][24][25] structures on an ONF. ...
We report a slot waveguide-enhanced asymmetric photonic crystal optical nanofiber (ONF) cavity to realize cavity quantum electrodynamics. We show that the device can strongly enhance the spontaneous emission of a single quantum emitter leading to a Purcell factor as high as 106 and enables single-photon coupling efficiency as high as 86% into fiber-guided modes. The introduction of the slot enhances the Purcell factor by six times as compared to the ONF cavity structure without slot, and the asymmetric cavity design enables unidirectional coupling of single photons. The cavity is designed to minimize the losses leading to a scattering-limited Q-factor and one-pass loss estimated to be 6388 and 1.2%, respectively. This fiber-coupled single-photon device may open advanced possibilities and applications for quantum information processing.
... Various tools and techniques are being used to make fiber Bragg grating (FBG) [20][21][22] and photonic crystal (PhC) cavity [23][24][25] structures on an ONF. ...
We report a slot waveguide-enhanced asymmetric photonic crystal optical nanofiber (ONF) cavity to realize cavity quantum electrodynamics. We show that the device can strongly enhance the spontaneous emission of a single quantum emitter leading to a Purcell factor as high as 106 and enables single-photon coupling efficiency as high as 86% into fiber-guided modes. The introduction of the slot enhances the Purcell factor by six times as compared to the ONF cavity structure without slot, and the asymmetric cavity design enables unidirectional coupling of single photons. The cavity is designed to minimize the losses leading to a scattering-limited Q-factor and one-pass loss estimated to be 6388 and 1.2%, respectively. This fiber-coupled single-photon device may open advanced possibilities and applications for quantum information processing.
... Other experimental work has shown that when cold atoms also interact with HOMs, detected signals are stronger than when one uses a SM-ONF only [21]. Introducing a cavity system to the ONF could further increase light-matter interactions due to cavity quantum electrodynamics (cQED) effects [22][23][24]. To date, numerous types of SM-ONF-based cavities have been proposed [25][26][27][28][29][30] and the interactions of their resonance modes with various quantum emitters have been studied [31][32][33]. ...
Optical nanofiber cavity research has mainly focused on the fundamental mode. Here, a Fabry–Pérot fiber cavity with an optical nanofiber supporting the higher-order modes ( TE 01 , TM 01 , HE 21 o , and HE 21 e ) is demonstrated. Using cavity spectroscopy, with mode imaging and analysis, we observed cavity resonances that exhibited complex, inhomogeneous states of polarization with topological features containing Stokes singularities such as C-points, Poincaré vortices, and L-lines. In situ tuning of the intracavity birefringence enabled the desired profile and polarization of the cavity mode to be obtained. We believe these findings open new research possibilities for cold atom manipulation and multimode cavity quantum electrodynamics using the evanescent fields of higher-order mode optical nanofibers.
... From the SP and PL decay times τ 0 , we estimate a coupling efficiency (η = SP τ 0 ) of 3.2 % and 11 % for the coupled and uncoupled QDs, assuming 100 % quantum efficiency. The coupling efficiency of the coupled QD may be further improved by combining it with a moderate finesse ONF cavity [44][45][46]. ...
We demonstrate a bright and polarized fiber in-line single-photon source based on plasmon-enhanced emission of colloidal single quantum dots into an optical nanofiber. We show that emission properties of single quantum dots can be strongly enhanced in the presence of single gold nanorods leading to a bright and strongly polarized single-photon emission. The single photons are efficiently coupled to guided modes of the nanofiber and eventually to a single-mode optical fiber. The brightness (fiber-coupled photon count rate) of the single-photon source is estimated to be 12.2±0.6 MHz, with high single-photon purity [g2(0)=0.20±0.04] and degree of polarization as high as 94–97 %. The polarized and fiber-coupled single photons can be implemented for potential applications in quantum photonics.
... Other experimental work has shown that when cold atoms also interact with HOMs, detected signals are stronger than when one uses a SM-ONF only [21]. Introducing a cavity system to the ONF could further increase light-matter interactions due to cavity quantum electrodynamics (cQED) effects [22][23][24]. To date, numerous types of SM-ONF-based cavities have been proposed [25][26][27][28][29][30] and the interactions of their resonance modes with various quantum emitters have been studied [31][32][33]. ...
Optical nanofiber cavity research has mainly focused on the fundamental mode. Here, a Fabry-P\'erot fiber cavity with an optical nanofiber supporting the higher-order modes, TE01, TM01, HE21o, and HE21e, is demonstrated. Using cavity spectroscopy, with mode imaging and analysis, we observe cavity resonances that exhibit complex, inhomogeneous states of polarization with topological features containing Stokes singularities such as C-points, Poincar\'e vortices, and L-lines. In situ tuning of the intracavity birefringence enables the desired profile and polarization of the cavity mode to be obtained. These findings open new research possibilities for cold atom manipulation and multimode cavity quantum electrodynamics using the evanescent fields of higher-order mode optical nanofibers.
... The coupling efficiency for tapered midsection can be increased from about 30% to up to 80% [111][112][113] by creating a cavity within the nanofiber, e.g., a nanofiber Bragg cavity (NFBC) [114,115] or nanohole cavity [116]. In addition, a cavity can reduce the required excitation power in the nanofiber by more than an order of magnitude [117]. ...
Photonic quantum technology is essentially based on the exchange of individual photons as information carriers. Therefore, the development of practical single-photon sources that emit single photons on-demand is a crucial contribution to advance this emerging technology and to promoting its first real-world applications. In the last two decades, a large number of quantum light sources based on solid state emitters have been developed on a laboratory scale. Corresponding structures today have almost ideal optical and quantum-optical properties. For practical applications, however, one crucial factor is usually missing, namely direct on-chip fiber coupling, which is essential, for example, for the direct integration of such quantum devices into fiber-based quantum networks. In fact, the development of fiber-coupled quantum light sources is still in its infancy, with very promising advances having been made in recent years. Against this background, this review article presents the current status of the de-velopment of fiber-coupled quantum light sources based on solid state quantum emitters and discusses challenges, technological solutions and future prospects. Among other things, the numerical optimiza-tion of the fiber coupling efficiency, coupling methods, and important realizations of such quantum devices are presented and compared. Overall, this article provides an important overview of the state of the art and the performance parameters of fiber-coupled quantum light sources that have been achieved so far. It is aimed equally at experts in the scientific field and at students and newcomers who want to get an overview of the current developments.
... Experimentally, 22% of photons from single quantum dots have been coupled to the ONF guided mode by positioning the QEs on the surface of ONF [4]. In order to increase the spontaneous emission rate and the coupling efficiency, different cavities like photonic crystal (PhC) cavity and fiber Bragg grating (FBG) structures are proposed [13][14][15][16][17][18][19][20]. Various efforts are going on to make PhC and FBG structures on ONFs using femtosecond laser ablation, using an external grating, and by focused ion beam milling method to realize cavity quantum electrodynamics (cQED) [17,[21][22][23][24][25]. ...
We report on a simulation of a nanophotonic cavity constructed by designing periodic holes on an optical nanofiber to realize light-matter interaction. The cavity is designed using finite-difference time-domain simulations to maximize the coupling of spontaneous emission from a quantum emitter into fiber-guided modes. We systematically analyze the dependence of spontaneous emission on the quantum emitter position, polarization, and the grating strength (number of periods). We show that coupling efficiencies as high as 87% and 83% can be realized for a dipole emitter placed at the center of the nanofiber with polarization perpendicular (x-pol) and parallel (y-pol) to the hole-axis, respectively. This system may attract various quantum photonic applications based on single-photon sources.
... From the Γ S P and PL decay times τ 0 , we estimate a coupling efficiency (η = Γ S P τ 0 ) of 3.2% and 11% for the coupled and uncoupled QDs, assuming 100% quantum efficiency. The coupling efficiency of the coupled QD may be further improved by combining it with a moderate finesse ONF cavity [44][45][46]. ...
We demonstrate a bright and polarized fiber in-line single photon source based on plasmon-enhanced emission of colloidal single quantum dots into an optical nanofiber. We show that emission properties of single quantum dots can be strongly enhanced in the presence of single gold nanorods leading to a bright and strongly polarized single photon emission. The single photons are efficiently coupled to guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (fiber-coupled photon count rate) of the single photon source is estimated to be 12.2(0.6) MHz, with high single photon purity (g2(0) = 0.20(0.04)) and degree of polarization as high as 94-97%. The present device can be integrated into fiber networks paving the way for potential applications in quantum networks.
... Although the coupling efficiency of 30% is high, further improvement of the coupling efficiency toward 100% is desirable. For this purpose, nanofibre Bragg cavities (NFBCs), which are optical microcavities embedded in a nanofibre, have recently been proposed and demonstrated [9][10][11][12][13][14] . NFBCs have a single resonant mode with a small mode volume (on the order of the cube of the wavelength), high quality (Q) factors, ultra-wide tunability of the resonant wavelength, and lossless coupling to single-mode fibres 11 . ...
Solid-state quantum emitters coupled with a single mode fibre are of interest for photonic and quantum applications. In this context, nanofibre Bragg cavities (NFBCs), which are microcavities fabricated in an optical nanofibre, are promising devices because they can efficiently couple photons emitted from the quantum emitters to the single mode fibre. Recently, we have realized a hybrid device of an NFBC and a single colloidal CdSe/ZnS quantum dot. However, colloidal quantum dots exhibit inherent photo-bleaching. Thus, it is desired to couple an NFBC with hexagonal boron nitride (hBN) as stable quantum emitters. In this work, we realize a hybrid system of an NFBC and ensemble defect centres in hBN nanoflakes. In this experiment, we fabricate NFBCs with a quality factor of 807 and a resonant wavelength at around 573 nm, which matches well with the fluorescent wavelength of the hBN, using helium-focused ion beam (FIB) system. We also develop a manipulation system to place hBN nanoflakes on a cavity region of the NFBCs and realize a hybrid device with an NFBC. By exciting the nanoflakes via an objective lens and collecting the fluorescence through the NFBC, we observe a sharp emission peak at the resonant wavelength of the NFBC.
... La mise au point de pièges optiques utilisant les modes guidés de la nanofibre a permis d'augmenter la densité optique du milieu atomique entourant la nanofibre et ainsi de réaliser des expériences de stockage de photons par transparence électromagnétiquement induite (EIT) [49,50] et de réflexion de Bragg sur un réseau d'atomes piégés [51,52]. Pour augmenter encore le couplage atome-lumière à l'échelle du photon unique (et atteindre le régime de l'optique quantique non linéaire avec un atome), des cavités ont été réalisées (par gravage) le long de la nanofibre [53,54,55,56,57,58] qui ont permis la démonstration de l'effet Purcell [57] et du régime de couplage fort [59]. ...
Dans ce mémoire, nous avons étudions le comportement d'atomes de rubidium 87 excités dans des états de Rydberg et placés à proximité d'une nanofibre optique. Ce travail est motivé par la perspective d'interfaces atomes-nanofibre utilisant le blocage Rydberg (par exemple pour la manipulation de l'information quantique contenue dans les noeuds atomiques).Nous nous sommes plus précisément attachés à déterminer la part d'émission spontanée d'un atome de Rydberg vers les modes guidés de la nanofibre, à calculer le déplacement énergétique (Lamb shift) engendré par la nanofibre sur cet atome et la force (de Casimir-Polder) qui en dérive. Nous avons ensuite analysé les modifications induites par l'introduction d'une nanofibre optique sur le potentiel d'interaction de van der Waals entre deux atomes de Rydberg. Dans tous les cas, nous avons cherché à caractériser l'influence sur nos résultats de l'état quantique atomique (nombre quantique principal, moment cinétique orbital, etc.) et de la configuration géométrique. Nous avons, en particulier, considéré des états atomiques qui donnent lieu à une interaction chirale avec le champ à proximité de la fibre et engendrent, entre autres, des phénomènes d'émission directionnelle.
... 1,4) Optical nanofiber cavity provides the following unique possibilities for cavity QED approach. 36) i) The transverse confinement in nanofiber (mode radius : 0.4 µm) is much stronger than the typical free-space cavity mode (mode radius : 15 µm). Therefore, strong coupling and high single atom cooperativity can be realized with a moderate finesse (number of photon roundtrips in a cavity) of 50-200 in nanofiber cavity compared to free-space cavity (finesse : 50000-500000). ...
Tapered optical fiber with subwavelength diameter waist, an optical nanofiber, provides a unique and versatile platform for manipulating atoms and photons. In the guided modes of the nanofibers, the optical field can be tightly confined in the transverse direction while enabling strong interaction with the surrounding medium in the evanescent region. Combining laser-cooled atoms with nanofibers has enabled surprising quantum optics experiments, e.g. the efficient channeling of emission from single atoms into the fiber-guided modes, spectroscopy of near-surface atoms, high optical depth with an array of atoms optically trapped around the nanofiber, atomic memories and Bragg reflectors for fiber-guided photons, chiral light-matter interaction etc. In addition, using moderate longitudinal confinement in nanofiber cavities has enabled strong coupling between a single atom and fiber-guided photons. In this article, I review some of the key experimental demonstrations on the “atom＋nanofiber” platform.
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... In particular, using colloidal single QDs on the ONF, it was demonstrated that the channeling efficiency can reach the theoretical limit of 22% [14,24], which is determined by the transverse confinement of the photonic mode in the ONF. Furthermore, it was demonstrated that the channeling efficiency can be enhanced to 65% using a composite photonic crystal ONF cavity [25,26]. However, the experiments were performed in the room temperature resulting in a broadband emission from the QD. ...
We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time ($10.0\pm0.5$ ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimated to be $16\pm2\%$ with a maximum photon count rate of $1.6\pm0.2$ MHz and a high single photon purity ($g^2(0)=0.11\pm0.02$). The device can be easily integrated to the fiber networks paving the way for potential applications in quantum networks.
... It is worth emphasizing that this cavity impact factor is invalid in the weak scattering regime, therefore critical coupling cannot be attributed to the Purcell effect. Compared to the guided modes, the presence of the cavity has a much weaker effect on the distribution of the radiation modes [26], thus we could assume the scattering rates into the radiation modes remains the same with or without the existence of part ii of the resonator. Therefore, in the strong scattering regime, we can define the channeling efficiency, Γ j ðωÞ, which represents the fraction of power coupled from the waveguide into the cavity-modified mode, j [23]: ...
Cavity input-output relations (CIORs) describe a universal formalism relating each of the far-field amplitudes outside the cavity to the internal cavity fields. Conventionally, they are derived based on a weak-scattering approximation. In this context, the amplitude of the off-resonant field remains nearly unaffected by the cavity, with the high coupling efficiency into cavity modes being attributed to destructive interference between the transmitted (or reflected) field and the output field from the cavity. In this Letter, we show that, in a whispering gallery resonator-waveguide coupled system, in the strong-scattering regime, the off-resonant field approaches to zero, but more than 90% coupling efficiency can still be achieved due to the Purcell-enhanced channeling. As a result, the CIORs turn out to be essentially different than in the weak-scattering regime. With this fact, we propose that the CIOR can be tailored by controlling the scattering strength. This is experimentally demonstrated by the transmission spectra exhibiting either bandstop or bandpass-type behavior according to the polarization of the input light field.
... In particular, using colloidal single QDs on the ONF, it was demonstrated that the channeling efficiency can reach the theoretical limit of 22% [14,24], which is determined by the transverse confinement of the photonic mode in the ONF. Furthermore, it was demonstrated that the channeling efficiency can be enhanced to 65% using a composite photonic crystal ONF cavity [25,26]. However, the experiments were performed in the room temperature resulting in a broadband emission from the QD. ...
We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time (\(10.0\pm 0.5\) ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimated to be \(16\pm 2\%\) with a maximum photon count rate of \(1.6\pm \,0.2\) MHz and a high single photon purity (\(g^2(0)=0.11\pm 0.02\)). The device can be easily integrated to the fiber networks paving the way for potential applications in quantum networks.
... Indeed, it was demonstrated that up to 94% (instead of 28%) of spontaneous emission from atoms can be transformed into the guided modes of a nanofiber by using two Bragg-grating mirrors to form a Fabry-Peŕot cavity (F−P in Figure 1b) around the ultrathin waist region where the atoms interact with the optical modes. 25 However, such enhancement occurs due to interference between multiply reflected modes, which have to be quasi-linearly polarized. Consequently, the emission is coupled equally into modes that are guided toward either end of the waveguide and the coupler loses its directionality. ...
Directional coupling of light in nanophotonic circuits has recently attracted increasing interest, with numerous experimental realizations based on broken rotational or mirror symmetries of the light-matter system. The most prominent underlying effect is the spin-orbit interaction of light in subwavelength structures. Unfortunately, coupling of light to such structures is, in general, very inefficient. In this work, we experimentally demonstrate an order of magnitude enhancement of the directional coupling between two nanowaveguides by means of a whispering gallery microcavity. We also show that both transverse magnetic and transverse electric modes can be used for the enhancement.
... Here, the total scattering rate of the emitter γ total = γ guided + γ rad , is the sum of the scattering rate to guided modes of the nanofiber without mirrors and to radiation modes. The channeling efficiency for a nanofiber-based cavity is then given by [31] ...
We demonstrate a cryo-compatible, fully fiber-integrated, alignment-free optical microresonator. The compatibility with low temperatures expands its possible applications to the wide field of solid-state quantum optics, where a cryogenic environment is often a requirement. At a temperature of 4.6 K we obtain a quality factor of (9.9 ± 0.7) × 10⁶. In conjunction with the small mode volume provided by the nanofiber, this cavity can be either used in the coherent dynamics or the fast cavity regime, where it can provide a Purcell factor of up to 15. Our resonator is therefore suitable for significantly enhancing the coupling between light and a large variety of different quantum emitters and due to its proven performance over a wide temperature range, also lends itself for the implementation of quantum hybrid systems.
... Here, the total scattering rate of the emitter γ total = γ guided + γ rad , is the sum of the scattering rate to guided modes of the nanofiber without mirrors and to radiation modes. The channeling efficiency for a nanofiber-based cavity is then given by [31] ...
We demonstrate a cryo-compatible, fully fiber-integrated, alignment-free optical microresonator. The compatibility with low temperatures expands its possible applications to the wide field of solid-state quantum optics, where a cryogenic environment is often a requirement. At a temperature of 4.6 K we obtain a quality factor of $\mathbf{(9.9 \pm 0.7) \times 10^6}$. In conjunction with the small mode volume provided by the nanofiber, this cavity can be either used in the coherent dynamics or the fast cavity regime, where it can provide a Purcell factor of up to 15. Our resonator is therefore suitable for significantly enhancing the coupling between light and a large variety of different quantum emitters and due to its proven performance over a wide temperature range, also lends itself for the implementation of quantum hybrid systems.
... A key point of the technique is that the optical field in the fiber-guided mode can be strongly confined in the transverse dimensions and that it can interact with the surrounding medium in the evanescent region. Fabricating cavity structure on the nanofiber can enable strong atom-photon coupling in an all-fiber platform [8]. The fiber-in-line capability of the nanofiber cavity makes it particularly suitable for quantum photonics applications. ...
We report the photothermal properties of a photonic crystal nanofiber (PhCN) cavity, which is fabricated using a femtosecond laser ablation technique, under ultra-high vacuum conditions. The results show that by launching a non-resonant guided light, the stopband of the PhCN, along with the cavity modes, can be tuned at a rate of 250 GHz ( ∼ 0.5 nm ) / mW . Moreover, due to the thermal self-locking effect of a resonant light, a cavity mode with a finesse of 25 can be tuned over a few free spectral ranges using only a few μW of guided light. As an enabling step, we demonstrate a dual-mode locking scheme to thermally stabilize a cavity mode to the atomic line for single atom–based cavity quantum electrodynamics experiments.
... Targeted toward increasing the coupling efficiency, methods for various nanofiber-based cavities have been demonstrated in recent years. [29][30][31][32][33][34] In this paper, we experimentally demonstrate a nanofiber-based method of optimizing a MOT. Atomic fluorescence is collected very efficiently by a nanofiber with a subwavelength diameter. ...
We experimentally demonstrate a reliable method based on a nanofiber to optimize the number of cold atoms in a magneto-optical trap (MOT) and to monitor the MOT in real time. The atomic fluorescence is collected by a nanofiber with subwavelength diameter of about 400 nm. The MOT parameters are experimentally adjusted in order to match the maximum number of cold atoms provided by the fluorescence collected by the nanofiber. The maximum number of cold atoms is obtained when the intensities of the cooling and re-pumping beams are about 23.5 mW/cm² and 7.1 mW/cm², respectively; the detuning of the cooling beam is-13.0 MHz, and the axial magnetic gradient is about 9.7 Gauss/cm. We observe a maximum photon counting rate of nearly (4.5±0.1)×10⁵ counts/s. The nanofiber-atom system can provide a powerful and flexible tool for sensitive atom detection and for monitoring atom-matter coupling. It can be widely used from quantum optics to quantum precision measurement.
... All-fiber atom-cavity quantum electrodynamics (QED) systems, in which atoms are coupled to the cavity field via evanescent coupling through a tapered optical nanofiber region, are an especially attractive prospect for quantum networking due to the ease of connecting many nodes together in any arbitrary network configuration with minimal loss. A cavity QED system is typically formed by coupling the atoms to an in-fiber cavity formed by either two Fiber Bragg Gratings (FBGs) [10][11][12][13][14][15], or else a ring cavity coupled via a fiber beamsplitter [16][17][18]. This paper is focused on 'coupled-cavities quantum electrodynamics', concerning the interaction of atoms coupled via cavity fields. ...
We report on a combined experimental and theoretical investigation into the normal modes of an all-fiber coupled cavity-quantum-electrodynamics system. The interaction between atomic ensembles and photons in the same cavities, and that between the photons in these cavities and the photons in the fiber connecting these cavities, generates five non-degenerate normal modes. We demonstrate our ability to excite each normal mode individually. We study particularly the `cavity dark mode', in which the two cavities coupled directly to the atoms do not exhibit photonic excitation. Through the observation of this mode, we demonstrate remote excitation and nonlocal saturation of atoms.
... All-fiber atom-cavity quantum electrodynamics (QED) systems, in which atoms are coupled to the cavity field via evanescent coupling through a tapered optical nanofiber region, are an especially attractive prospect for quantum networking due to the ease of connecting many nodes together in any arbitrary network configuration with minimal loss. A cavity QED system is typically formed by coupling the atoms to an in-fiber cavity formed by either two Fiber Bragg Gratings (FBGs) [10][11][12][13][14][15], or else a ring cavity coupled via a fiber beamsplitter [16][17][18]. This paper is focused on 'coupled-cavities quantum electrodynamics', concerning the interaction of atoms coupled via cavity fields. ...
We report on a combined experimental and theoretical investigation into the normal modes of an all-fiber coupled cavity-quantum-electrodynamics system. The interaction between atomic ensembles and photons in the same cavities, and that between the photons in these cavities and the photons in the fiber connecting these cavities, generates five nondegenerate normal modes. We demonstrate our ability to excite each normal mode individually. We study particularly the “cavity dark mode,” in which the two cavities coupled directly to the atoms do not exhibit photonic excitation. Through the observation of this mode, we demonstrate remote excitation and nonlocal saturation of atoms.
... Reaching the strong coupling regime is of interest as it permits single-photon gate operations and allows the observation and exploitation of quantum electrodynamic effects [20][21][22][23][24] . In order to reach this regime an optical cavity would be produced around a quantum system with an appropriate optically-addressable transition, in this case via the use of laser-written Bragg gratings 20,25 on either side of the hole. ...
We discuss the trapping of cold atoms within microscopic voids drilled perpendicularly through the axis of an optical waveguide. The dimensions of the voids considered are between 1 and 40 optical wavelengths. By simulating light transmission across the voids, we find that appropriate shaping of the voids can substantially reduce the associated loss of optical power. Our results demonstrate that the formation of an optical cavity around such a void could produce strong coupling between the atoms and the guided light. By bringing multiple atoms into a single void and exploiting collective enhancement, cooperativities ~400 or more should be achievable. The simulations are carried out using a finite difference time domain method. Methods for the production of such a void and the trapping of cold atoms within it are also discussed.
... When the total grating number was increased to 320 and 640, P was estimated to be at least 6.5 and 15.3, respectively. When there is no propagation loss at the grating of the NFBC, the coupling efficiency η is expressed as a ratio of the cavity-modified emission rate into the nanofiber to the total emission rate as follows [34], ...
Nanofiber Bragg cavities (NFBCs) are solid-state microcavities fabricated in an optical tapered fiber. NFBCs are promising candidates as a platform for photonic quantum information devices due to their small mode volume, ultra-high coupling efficiencies, and ultra-wide tunability. However, the quality (Q) factor has been limited to be approximately 250, which may be due to limitations in the fabrication process. Here we report high Q NFBCs fabricated using a focused helium ion beam. Whenan NFBC with grooves of 640 periods is fabricated, the Q factor is over 4170, which is more than 16 times larger than that previously fabricated using a focused gallium ion beam.
... Reaching the strong coupling regime is of interest as it permits single-photon gate operations and allows the observation and exploitation of quantum electrodynamic effects [20,21,22,23,24]. In order to reach this regime an optical cavity would be produced around a quantum system with an appropriate optically-addressable transition, in this case via the use of laser-written Bragg gratings [20,25] on either side of the hole. ...
We discuss the trapping of cold atoms within microscopic voids drilled perpendicularly through the axis of an optical waveguide. The dimensions of the voids considered are between 1 and 40 optical wavelengths. By simulating light transmission across the voids, we find that appropriate shaping of the voids can substantially reduce the associated loss of optical power. Our results demonstrate that the formation of an optical cavity around such a void could produce strong coupling between the atoms and the guided light. By bringing multiple atoms into a single void and exploiting collective enhancement, cooperativities ~300 or more should be achieveable. The simulations are carried out using a finite difference time domain method. Methods for the production of such a void and the trapping of cold atoms within it are also discussed.
... For spectroscopy, the taper offers a high collection efficiency [286], which can even be doubled by detecting the guided fluorescence light at both ends of the fiber. Further improvement to the efficiency can be achieved, when Bragg mirrors are integrated in the fiber [287]. Tapered fibers used as probes to collect fluorescence from single quantum emitters [270] can be used in quantum information experiments [14,273] or as building blocks in quantum networks [288,289]. ...
Gegenstand der vorliegenden Dissertation ist die Untersuchung von einzelnen nano- und mikrometergroßen Partikeln, zum Verständnis und zur Entwicklung von neuartigen nanooptischen Elementen, wie Lichtquellen und Sensoren, sowie Strukturen zum Aufsammeln und Leiten von Licht. Neben der Charakterisierung stehen dabei verschiedene Methoden zur elektromagnetischen Manipulation im Vordergrund, die auf eine Kontrolle der Position oder der Geometrie der Partikel ausgerichtet sind. Die gezielten Manipulationen werden verwendet, um vorausgewählte Partikel zu isolieren, modifizieren und transferieren. Dadurch können Partikel zu komplexeren photonischen Systemen kombiniert werden, welche die Funktionalität der einzelnen Bestandteile übertreffen. Der Hauptteil der Arbeit behandelt Experimente mit freischwebenden Partikeln in linearen Paul-Fallen. Durch die räumliche Isolation im elektrodynamischen Quadrupolfeld können Partikel mit reduzierter Wechselwirkung untersucht werden. Neben der spektroskopischen Charakterisierung von optisch aktiven Partikeln (farbstoffdotierte Polystyrol-Nanokügelchen, Cluster aus Nanodiamanten mit Stickstoff-Fehlstellen-Zentren, Cluster aus kolloidalen Quantenpunkten) sowie optischen Resonatoren (plasmonische Silber-Nanodrähte, sphärische Siliziumdioxid-Mikroresonatoren) werden neu entwickelte Methoden zur Manipulation vorgestellt, mit denen sich individuelle Partikel freischwebend kombinieren und elektromagnetisch koppeln sowie aus der Falle auf optischen Fasern zur weiteren Untersuchung bzw. zur Funktionalisierung photonischer Strukturen ablegen lassen. In einem weiteren Teil der Arbeit wird eine Methode zur Manipulation der Geometrie von plasmonischen Nanopartikeln vorgestellt. Dabei werden einzelne Goldkugeln auf einem Deckglas mit einem fokussierten Laserstrahl zum Schmelzen gebracht und verformt. Durch die kontrollierte und reversible Veränderung der Symmetrie lassen sich die lokalisierten Oberflächenplasmonen des Partikels gezielt beeinflußen.
... 40,42,43 Coupling of a quantum emitter into guided and radiation modes of an optical fiber has been studied, 35,38,40−42,45−50 being identified as a potential platform for developing devices for quantum information technology. 46,49,50 However, until now the research of such systems has been focused on the study of higher order radiation modes associated with high-Q cavity resonances. ...
We introduce a new platform to achieve a strong magnetic response in optical fibers with nanoscale dimension. We reveal that for a coupled dipole-fiber system, an electric dipole placed near an optical nanofiber can produce strong magnetic response. We show that the magnetic and electric response of such a system depends on the orientation of the dipole source with respect to the fiber. Using the multipole expansion method, we demonstrate that it is possible to suppress the electric response and preferentially enhance the magnetic resonance of a coupled dipole-fiber system, in such a way that the energy in the magnetic mode can be made two orders of magnitude higher than that of the electric mode of the system. This nanophotonic system opens up new possibilities to develop low-dimensional nanodevices with enhanced magnetic response.
A recent experiment [H. S. Han et al., Phys. Rev. Lett. 127, 073604 (2021); see also accompanying online supplemental material] shows that when a three-level V-type atom with two closely lying upper states interacts with the same vacuum radiation field, its excited states enable vacuum-induced coupling (VIC) owing to the quantum interference between the spontaneous emission pathways. Here, we propose a feasible scheme for phase-engineered photon correlations in the presence of the VIC in an optical nanofiber (ONF) cavity quantum electrodynamics (QED) system. Specifically, we show that a phase-dependent strong photon antibunching with high brightness can be generated in the weak-coupling regime of light-atom interactions. This occurs because of the VIC, leading to both the destructive quantum interference between the different pathways for two-photon excitation and the total closed-loop coupling phase. Different types of purely quantum correlations, such as single- and two-photon blockades, can occur by properly tuning the total closed-loop coupling phase adhering on the VIC, and the switch from photon blockade to photon induced tunneling is revealed as well. On the other hand, the strong photon antibunching can be achieved in a broad driving frequency range, which relaxes the requirement for the driving frequency in the ONF cavity QED system. In addition, we compare the analytical and numerical results of the second- and third-order intensity correlation functions, and they are in good agreement. The present study may provide an alternative route to manipulate the few-photon states and have potential applications in single-photon sources and quantum communications.
Vacuum-induced coupling (VIC), arising from the quantum interference between the spontaneous emission pathways from the excited doublet to a common ground state, has attracted significant research interest and has been observed in recent experiments. Here, we present an alternative route to probe the existence of VIC by means of the coherence statistics of photon antibunching and show that, under realistic experimental conditions, the vacuum-induced quantum beat (VIQB) can enable strong photon antibunching with high brightness in an optical nanofiber (ONF) cavity quantum electrodynamics (CQED) system. We find that the occurrence of the photon antibunching corresponds to the existence of the VIC, indicating that the photon antibunching can be an important witness for VIC. In addition, a strong photon antibunching effect appears in the weak-coupling regime of light-atom interactions when the VIQB is present, as a result of the destructive quantum interference between the different paths for two-photon excitation. Furthermore, we find that strong photon antibunching can be generated within a certain driving frequency range in the present system, which can relax the requirement for the driving frequency in the ONF CQED system. Also, we compare the analytical and numerical results of the second-order intensity correlation function, and they are in good agreement. The present study builds a bridge between the photon antibunching and the VIC and VIQB, which is useful for well understanding and researching a tunable single-photon source, as well as enabling potential applications in quantum information processing and quantum communications.
The directional coupling of single photon emission from nitrogen vacancy (NV–) emitters to optical systems for various applications requires a suitable interface between NV– emitters and optical waveguides. Unidirectional coupling of photons may have significant importance in next generation quantum technology such as quantum and complex optical networks, quantum communication, and multi‐scale quantum photonics devices including quantum non‐linearity and quantum metrology. Here, a hybrid asymmetric structure of elliptically faceted (ELFA) diamond nanowire with Bragg grating (BG) containing negatively charged NV– center for efficient and unidirectional optical coupling to optical nanowire (waveguide) is proposed. The calculations indicate that the structure can provide coupling efficiency of ≈90% toward the elliptically facet direction and ≈1% in the opposite direction. Further, Purcell factor is enhanced due to the augmented electric field intensity in the ELFA structure. This structure is significantly robust against imperfect placement and rotational alignment of dipole from its intended position. This article describes photon coupling in hybrid structure containing asymmetric elliptically faceted (ELFA) diamond nanowire with and without Bragg grating (BG) integrated with optical nanowire. Emission from the diamond nanowire with (without) BG leads to unidirectional coupling efficiency of 90% (57%) toward elliptically facet direction. The field intensity profile around dipole in transmission (launched‐light) leads to higher Purcell factor.
A cavity quantum electrodynamics (QED) system, which consists of an atom and photons confined in a cavity, is one of the most basic hybrid systems. In the strong coupling regime of cavity QED, quantum interaction between atoms and photons manifests itself, and it becomes possible to generate, manipulate, and measure quantum states of atom and light. Therefore, a cavity QED system is an ideal testbed for investigating quantum nature of atom and light. Recently, efforts have been made toward realization of a quantum network by connecting multiple cavity QED systems by optical fibers. However, it is technically challenging to connect a large number of conventional Fabry–Perot cavities with high efficiency. Here, we review novel all-fiber cavity QED systems based on optical nanofibers.
Nanofibre-based optical cavities are particularly useful for quantum optics applications, such as the development of integrated single-photon sources, and for studying fundamental light–matter interactions in cavity quantum electrodynamics (cQED). Although several techniques have been used to produce such cavities, focussed ion beam (FIB) milling is becoming popular; it can be used for the fabrication of complex structures directly in the nanofibre. However, it is challenging to mill insulating materials with highly curved geometries and large aspect ratios, such as silica nanofibres, due to charge accumulation in the material. In this article, we highlight the main features of nanofibres and briefly review cQED with nanofibre-based optical cavities. An overview of the milling process is given with a summary of different FIB milled devices and their applications. Finally, we present our technique to produce nanofibre cavities by FIB milling. To overcome the aforementioned challenges, we present a specially designed base plate with an indium tin oxide (ITO)-coated Si substrate and outline our procedure, which improves stability during milling and increases repeatability.
Recent advances in the coherent control of single quanta of light, photons, is a topic of prime interest, and is discussed under the banner of quantum photonics. In the last decade, the subwavelength diameter waist of a tapered optical fiber, referred to as an optical nanofiber, has opened promising new avenues in the field of quantum optics, paving the way toward a versatile platform for quantum photonics applications. The key feature of the technique is that the optical field can be tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This feature has led to surprising possibilities to manipulate single atoms and fiber-guided photons, e.g. the efficient channeling of emission from single atoms and solid-state quantum emitters into the fiber-guided modes, high optical depth with a few atoms around the nanofiber, trapping atoms around a nanofiber, and atomic memories for fiber-guided photons. Furthermore, implementing a moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity quantum electrodynamics to be reached, and the long-range dipole–dipole interaction between quantum emitters mediated by the nanofiber offers a platform for quantum nonlinear optics with an ensemble of atoms. In addition, the presence of a longitudinal component of the guided field has led to unique capabilities for chiral light–matter interactions on nanofibers. In this article, we review the key developments of the nanofiber technology toward a vision for quantum photonics on an all-fiber interface.
Optical nanofiber technologies are discussed for both bare nanofibers and cavity created nanofibers. Emphasis is on the single-photon channeling into the fiber guided modes with a hybrid system of an optical-nanofiber and a single quantum-emitter.
We present a novel approach to enhance the spontaneous emission rate of single quantum emitters in an optical nanofiber-based cavity by introducing a narrow air-filled groove into the cavity. Our results show that the Purcell factor for single quantum emitters located inside the groove of the nanofiber-based cavity can be at least six times greater than that for such an emitter on the fiber surface when using an optimized cavity mode and groove width. Moreover, the coupling efficiency of single quantum emitters into the guided mode of this nanofiber-based cavity can reach up to $\sim$ 80 $\%$ with only 35 cavity-grating periods. This new system has the potential to act as an all-fiber platform to realize efficient coupling of photons from single emitters into an optical fiber for quantum information applications.
Efficient coupling of light to single subwavelength structures is an important theme of many optical researches [1]. The extent to which a nanoscale object and the mode of an optical cavity are strongly coupled is determined by both cavity finesse and mode volume. In this context, a silica fiber tapered down to a few microns or smaller and then sandwiched between two integrated mirrors exhibits attractive features [2]. As a guided mode cavity, such a fiber taper device has merits of allowing strong evanescent field to spread out, thus efficient light-matter interactions, much lower coupling loss to external optical networks, and truly positionable configuration. In order to shorten the effective cavity length to the level of wavelength scale, we explore fiber taper structures with photonic-crystal (PhC) mirrors [3] fabricated by ion beam milling arrays of through holes along microfiber.
Coupling of a single dipole with a nanofiber Bragg cavity (NFBC) approximating an actually fabricated structure was numerically analyzed using three dimensional finite-difference time-domain simulations for different dipole positions. For the given model structure, the Purcell factor and coupling efficiency reached to 19.1 and 82%, respectively, when the dipole is placed outside the surface of the fiber. Interestingly, these values are very close to the highest values of 20.2 and 84% obtained for the case when the dipole was located inside the fiber at the center. The analysis performed in this study will be useful in improving the performance of single-photon emitter-related quantum devices using NFBCs.
Over the past decade, strong interactions of light and matter at the single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science. This work has been performed principally within the setting of cavity quantum electrodynamics with diverse physical systems, including single atoms in Fabry-Perot resonators, quantum dots coupled to micropillars and photonic bandgap cavities and Cooper pairs interacting with superconducting resonators. Experiments with single, localized atoms have been at the forefront of these advances with the use of optical resonators in high-finesse Fabry-Perot configurations. As a result of the extreme technical challenges involved in further improving the multilayer dielectric mirror coatings of these resonators and in scaling to large numbers of devices, there has been increased interest in the development of alternative microcavity systems. Here we show strong coupling between individual caesium atoms and the fields of a high-quality toroidal microresonator. From observations of transit events for single atoms falling through the resonator's evanescent field, we determine the coherent coupling rate for interactions near the surface of the resonator. We develop a theoretical model to quantify our observations, demonstrating that strong coupling is achieved, with the rate of coherent coupling exceeding the dissipative rates of the atom and the cavity. Our work opens the way for investigations of optical processes with single atoms and photons in lithographically fabricated microresonators. Applications include the implementation of quantum networks, scalable quantum logic with photons, and quantum information processing on atom chips.
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The desire to use and control photons in a manner analogous to the control of electrons in solids has inspired great interest in such topics as the localization of light, microcavity quantum electrodynamics and near-field optics. A fundamental constraint in manipulating light is the extremely low transmittivity of apertures smaller than the wavelength of the incident photon. While exploring the optical properties of submicrometre cylindrical cavities in metallic films, we have found that arrays of such holes display highly unusual zero-order transmission spectra (where the incident and detected light are collinear) at wavelengths larger than the array period, beyond which no diffraction occurs. In particular, sharp peaks in transmission are observed at wavelengths as large as ten times the diameter of the cylinders. At these maxima the transmission efficiency can exceed unity (when normalized to the area of the holes), which is orders of magnitude greater than predicted by standard aperture theory. Our experiments provide evidence that these unusual optical properties are due to the coupling of light with plasmons - electronic excitations - on the surface of the periodically patterned metal film. Measurements of transmission as a function of the incident light angle result in a photonic band diagram. These findings may find application in novel photonic devices.
We develop a wideband traveling-wave formalism for analyzing quantum mechanically a degenerate parametric amplifier. The formalism is based on spatial differential equations-spatial Langevin equations-that propagate temporal Fourier components of the field operators through the nonlinear medium. In addition to the parametric nonlinearity, the Langevin equations include absorption and associated fluctuations, dispersion (phase mismatching), and pump quantum fluctuations. We analyze the dominant effects of phase mismatching and pump quantum fluctuations on the squeezing produced by a degenerate parametric amplifier.
We experimentally demonstrate efficient coupling of atomic fluorescence to the guided mode of a subwavelength-diameter silica fiber, an optical nanofiber. We show that fluorescence of a very small number of atoms, around the nanofiber can be readily observed through a single-mode optical fiber. We also show that such a technique enables us to probe the van der Waals interaction between atoms and surface with high precision by observing the fluorescence excitation spectrum through the nanofiber. (C) 2007 Optical Society of America.
We formulate the quantum theory of optical wave propagation without recourse to cavity quantization. This approach avoids the introduction of a box-related mode spacing and enables us to use a continuum frequency space description. We introduce a complete orthonormal set of operators that can describe states of finite energy. The set is countable and the operators have all the usual properties of the single-mode frequency operators. With use of these operators a generalization of the single-mode normal-ordering theorem is proved. We discuss the inclusion of material dispersion and pulse propagation in an optical fiber. Finally, we consider the process of photodetection in free space, concluding with a discussion of homodyne detection with both local oscillator and signal fields pulsed.
An investigation of the spectral response of a small collection of two-state atoms strongly coupled to the field of a high-finesse optical resonator is described for mean number N¯≤10 atoms. For weak excitation, a coupling-induced normal-mode splitting is observed even for one intracavity atom, representing a direct spectroscopic measurement of the so-called vacuum Rabi splitting for the atom-cavity system.
Achieving control of light-material interactions for photonic device applications at nanoscale dimensions will require structures that guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. This cannot be achieved by using conventional waveguides or photonic crystals. It has been suggested that electromagnetic energy can be guided below the diffraction limit along chains of closely spaced metal nanoparticles that convert the optical mode into non-radiating surface plasmons. A variety of methods such as electron beam lithography and self-assembly have been used to construct metal nanoparticle plasmon waveguides. However, all investigations of the optical properties of these waveguides have so far been confined to collective excitations, and direct experimental evidence for energy transport along plasmon waveguides has proved elusive. Here we present observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 microm in plasmon waveguides consisting of closely spaced silver rods. The waveguides are excited by the tip of a near-field scanning optical microscope, and energy transport is probed by using fluorescent nanospheres.
The interaction of matter and light is one of the fundamental processes occurring in nature, and its most elementary form is realized when a single atom interacts with a single photon. Reaching this regime has been a major focus of research in atomic physics and quantum optics for several decades and has generated the field of cavity quantum electrodynamics. Here we perform an experiment in which a superconducting two-level system, playing the role of an artificial atom, is coupled to an on-chip cavity consisting of a superconducting transmission line resonator. We show that the strong coupling regime can be attained in a solid-state system, and we experimentally observe the coherent interaction of a superconducting two-level system with a single microwave photon. The concept of circuit quantum electrodynamics opens many new possibilities for studying the strong interaction of light and matter. This system can also be exploited for quantum information processing and quantum communication and may lead to new approaches for single photon generation and detection.
We create quantized spin gratings by single-photon detection and convert them on demand into photons with retrieval efficiencies exceeding 40% (80%) for single (a few) quanta. We show that the collective conversion process, proceeding via superradiant emission into a moderate-finesse optical resonator, requires phase matching. The storage time of $3\text{ }\text{ }$\mu${}\mathrm{s}$ in the cold-atom sample, as well as the peak retrieval efficiency, are likely limited by Doppler decoherence of the entangled state.
All conventional methods to laser-cool atoms rely on repeated cycles of optical pumping and spontaneous emission of a photon by the atom. Spontaneous emission in a random direction provides the dissipative mechanism required to remove entropy from the atom. However, alternative cooling methods have been proposed for a single atom strongly coupled to a high-finesse cavity; the role of spontaneous emission is replaced by the escape of a photon from the cavity. Application of such cooling schemes would improve the performance of atom-cavity systems for quantum information processing. Furthermore, as cavity cooling does not rely on spontaneous emission, it can be applied to systems that cannot be laser-cooled by conventional methods; these include molecules (which do not have a closed transition) and collective excitations of Bose condensates, which are destroyed by randomly directed recoil kicks. Here we demonstrate cavity cooling of single rubidium atoms stored in an intracavity dipole trap. The cooling mechanism results in extended storage times and improved localization of atoms. We estimate that the observed cooling rate is at least five times larger than that produced by free-space cooling methods, for comparable excitation of the atom.
Cavity-enhanced methods have been extended to fiber optics by use of fiber Bragg gratings (FBGs) as reflectors. High-finesse fiber cavities were fabricated from FBGs made in both germanium/boron-co-doped photosensitive fiber and hydrogen-loaded Corning SMF-28 fiber. Optical losses in these cavities were determined from the measured Fabry-Perot transmission spectra and cavity ring-down spectroscopy. For a 10-m-long single-mode fiber cavity, ring-down times in excess of 2 ms were observed at 1563.6 nm, and individual laser pulses were resolved. An evanescent-wave access block was produced within a fiber cavity, and an enhanced sensitivity to optical loss was observed as the external medium's refractive index was altered.
Cavity-linewidth narrowing in a ring cavity that is due to the high dispersion and reduced absorption produced by electromagnetically induced transparency (EIT) in rubidium-atom vapor has been experimentally observed. The cavity linewidth with rubidium atoms under EIT conditions can be significantly narrowed. Cavity-linewidth narrowing was measured as a function of coupling beam power.
The effect of intracavity electromagnetically induced transparency (EIT) on the properties of optical resonators and active laser devices is discussed theoretically. Pronounced frequency pulling and cavity-linewidth narrowing are predicted. The EIT effect can be used to reduce classical and quantum-phase noise of the beat note of an optical oscillator substantially. Fundamental limits of this stabilization mechanism as well as its potential application to high-resolution spectroscopy are discussed.
This paper discusses a phase-sensitive technique for remote interrogation of passive Bragg grating Fabry-Pe´rot resonators. It is based on Pound-Drever-Hall (PDH) laser frequency locking, using radio-frequency phase modulation sidebands to derive an error signal from the complex optical response, near resonance, of a Fabry-Pe´rot interferometer. We examine how modulation frequency and resonance bandwidth affect this error signal. Experimental results are presented that demonstrate, when the laser is locked, this method detects differential phase shifts in the optical carrier relative to its sidebands, due to minute fiber optical path displacements.
We suggest using a two-color evanescent light field around a subwavelength-diameter fiber to trap and guide atoms. The optical fiber carries a red-detuned light and a blue-detuned light, with both modes far from resonance. When both input light fields are circularly polarized, a set of trapping minima of the total potential in the transverse plane is formed as a ring around the fiber. This design allows confinement of atoms to a cylindrical shell around the fiber. When one or both of the input light fields are linearly polarized, the total potential has two local minimum points in the transverse plane. This design allows confinement of atoms to two straight lines parallel to the fiber axis. Due to the small thickness of the fiber, we can use far-off-resonance fields with substantially differing evanescent decay lengths to produce a net potential with a large depth, a large coherence time, and a large trap lifetime. For example, a 0.2-{mu}m-radius silica fiber carrying 30 mW of 1.06-{mu}m-wavelength light and 29 mW of 700-nm-wavelength light, both fields circularly polarized at the input, gives for cesium atoms a trap depth of 2.9 mK, a coherence time of 32 ms, and a recoil-heating-limited trap lifetime of 541 s.
We study the radiative decay of a cesium atom near a nanofiber in the presence of a weak magnetic field. We show that the direction of the magnetic field relative to the fiber axis plays an important role in deciding the radiative decay from the atom. We find that the decay rates for the different magnetic sublevels of the atom are spread in a wider range in the orthogonal configuration than those in the coaxial configuration. We also show that the cross decay coefficients depend substantially on the orientation of the magnetic field relative to the fiber axis.
The rates of spontaneous emission and stimulated emission and absorption for a two-level atom in a dielectric microsphere are calculated for weak E1 coupling. The A coefficient for spontaneous emission is proportional to the zero-point fluctuation of the electric field εij evaluated in the previous paper [J. Opt. Soc. Am. B 4, 1995 (1987)], which shows sharp resonances in frequency (Q > 104). It is verified that the ratio of the A and B coefficients is determined by the spectral density of thermal radiation. The level shift tends to repel the transition line away from the cavity resonance.
We study the spontaneous emission of a cesium atom in the vicinity of a subwavelength-diameter fiber. We show that the confinement of the guided modes and the degeneracy of the excited and ground states substantially affect the spontaneous emission process. We demonstrate that different magnetic sublevels have different decay rates. When the fiber radius is about 200 nm, a significant fraction (up to 28%) of spontaneous emission by the atom can be channeled into guided modes. Our results may find applications for developing nanoprobes for atoms and efficient couplers for subwavelength-diameter fibers.
A three-dimensional quantum nonperturbative theory of spontaneous emission in a planar microcavity is developed on the basis of a complete set of orthogonal standing-wave mode functions. Earlier results on the spontaneous decay rate and far-field emission pattern which have been obtained in a perturbative fashion are shown to be contained in our theory. Time evolution of the initially excited atomic state is considered and comparison with perturbative results is given. It is found that though the Fabry-Perot cavity is of an open type, vacuum-field Rabi oscillations are still possible. Conditions that are favorable for this strong coupling regime are discussed. The near-field spontaneous-emission pattern and the transition from the near field to the far field are investigated. For moderate mirror reflectivities, the spread in the near-field emission pattern is found to be in good agreement with the effective mode radius concept. When the mirror reflectivity increases, however, one has a strong coupling regime and together with it, multiple reabsorptions and reemissions of the photon may occur, leading to a better localization of the photon around the atomic position. These considerations may be useful in designing microlasers of the planar type.
We study intracavity electromagnetically induced transparency in atoms around a nanofiber with a pair of Bragg grating mirrors. We calculate the transmission of the composite cavity-fiber-atom system and the time development of the guided probe light field. We derive analytical approximate expressions for the output probe field and its group delay. We show that the group delay of the guided light substantially depends on the input pulse length, the mirror reflectivity, the atomic number density, and the coupling field intensity. We demonstrate that the group delay of the guided light can be significantly enhanced by the presence of the fiber-Bragg-grating cavity even when the finesse of the cavity is moderate.
We calculate the atomic energy-level shift and the modified dipolar radiation rate inside a hollow dielectric cylinder and outside a solid cylinder using a quantum-mechanical linear-response formalism in the dipole approximation. We first derive the electromagnetic fields scattered by the cylindrical surface for an oscillating dipole inside and outside the cylinder. When an atom is located on the axis of the cylindrical hollow, we obtain analytic expressions of the atomic level shifts in two limiting cases: when b (radius of hollow) is very small, the level shift is proportional to b-2 which is associated with the kinetic-energy change of the atomic electron, whereas when b is very large, the shift is proportional to b-4 which is identified as the retarded (Casimir-Polder) interaction energy. Moreover, we calculate the atomic potentials as a function of the position of atoms in the hollow region, which is important for the atom-guiding experiment. We also calculate the decay rates and find enhanced rates inside and outside the cylinder. In particular, we compare the radiative properties of an atom inside the hollow cylinder with those between two plates, and those near a cylinder with near a single surface.
A model for spontaneous emission in active dielectric microstructures is given in terms of the classical electric field Green’s tensor and the quantum-mechanical operators for the generating currents. A formalism is given for calculating the Green’s tensor, which does not rely on the existence of a complete power orthogonal set of electromagnetic modes, and the formalism may therefore be applied to microstructures with gain and/or absorption. The Green’s tensor is calculated for an optical fiber amplifier, and the spontaneous emission in fiber amplifiers is studied with respect to the position, transition frequency, and vector orientation of a spatially localized current source. Radiation patterns are studied using a Poynting vector approach taking into account amplification or absorption from an active medium in the fiber.
We present an optical resonator with modified properties due to a nonabsorbing highly dispersive medium. The steep nonabsorbing dispersion is created with an additional pump field in an atomic beam using the effect of coherent population trapping. The linewidth of such a resonator depends on the slope of the dispersion line, which in turn depends on the atomic density and the intensity of pump and probe field. In the experiments presented here, the cavity linewidth is reduced by a factor of more than 50 relative to the linewidth of the empty resonator. We have studied the influence of the relative intensities of pump and probe field on the line profile. Due to the dispersion of the medium, the resonance frequency is nearly independent of the geometrical length of the resonator.
The properties of fiber Bragg gratings are investigated theoretically and experimentally. The effects of experimental parameters on grating characteristics are modeled for both uniform and non-uniform gratings. Particular emphasis is placed on the formation of fiber Bragg gratings tilted at 45 degrees with respect to the fiber axis in single mode fibers. In this case, light is coupled out of the fiber in a surface normal manner. Several fabrication methods for producing tilted fiber gratings are explored and characterized. The most efficient gratings are obtained with a prism coupling technique. Experimental tilted grating performance is shown to be in good agreement with the predictions of a two-dimensional coupled mode theory. Fiber gratings are also used to demonstrate an Er/Nd co-doped fiber laser. This dual wavelength laser is formed with a common cavity and common gain medium.
Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques interferometric, phase mask, and point by point are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed. © 1997 American Institute of Physics. S0034-67489701312-9
A quantum mechanical treatment for the spontaneous emission from a two-level atom inside a dielectric sphere with a continuum of electric field modes is presented. The analytical expressions for the spontaneous emission rates obtained by Chew [J. Chem. Phys. 87 (1987) 1355] in a classical treatment for an oscillating dipole are shown to be contained in our theory. A delay-differential equation, which shows how multiple reflections off the dielectric sphere surface alter the emission of the atom in a multimode lossy cavity, is derived in a nonperturbative fashion. The numerical solution to this equation shows that vacuum-field Rabi oscillations in the case of a spherical cavity are rather strong as compared to the case of a planar Fabry–Pérot cavity. The conditions for vacuum-Rabi oscillations and the enhancement of the spontaneous emission rate in the single-mode regime of a spherical cavity are discussed.
We study spontaneous emission from a pair of two-level atoms near a nanofiber. We demonstrate a substan-tial radiative exchange between distant atoms mediated by the guided modes of the nanofiber. The exchange is shown to lead to increased and decreased lifetimes of the subradiant and superradiant states, respectively. Our analysis is based on the full quantization of both the radiation and guided modes of the fiber in the framework of the Heisenberg-Langevin theory and the master equation formalism.
Although mainstream grating writing, more often than not using single photon excitation of germanosilicate based defects with CW 244 nm light, remains the key technology for complex devices it is now being complemented by a whole host of processes which can enhance and tailor the properties of both conventional and not-so-conventional fibre Bragg gratings. Further, processes for writing of gratings in non-germanosilicate fibres have also continued to develop and include multi-photon excitation directly into the band edge of the glass. It is now possible to custom tailor a gratings property based on the application and the nature of production as well as custom tailor the grating writing process to suit the type of fibre and application. Examples and suggestions where these can benefit sensors and lasers are outlined.
The transmission spectrum of three-level atoms in a vapor cell inside an optical cavity shows distinct peaks associated with atom-cavity polaritons in the system. We develop the theory of these resonances in a Doppler-broadened medium and present the results of experimental observations of these spectra in three-level Lambda-type rubidium atoms inside an optical ring cavity.
An important development in modern physics is the emerging capability for investigations of dynamical processes for open quantum systems in a regime of strong coupling for which individual quanta play a decisive role. Of particular significance in this context is research in cavity quantum electrodynamics which explores quantum dynamical processes for individual atoms strongly coupled to the electromagnetic field of a resonator. An overview of the research activities in the Quantum Optics Group at Caltech is presented with an emphasis on strong coupling in cavity QED which enables exploration of a new regime of nonlinear optics with single atoms and photons.
We investigate the suitability of toroidal microcavities for strong-coupling cavity quantum electrodynamics (QED). Numerical modeling of the optical modes demonstrate a significant reduction of the modal volume with respect to the whispering gallery modes of dielectric spheres, while retaining the high-quality factors representative of spherical cavities. The extra degree of freedom of toroid microcavities can be used to achieve improved cavity QED characteristics. Numerical results for atom-cavity coupling strength g, critical atom number No, and critical photon number no for cesium are calculated and shown to exceed values currently possible using Fabry-Perot cavities. Modeling predicts coupling rates g/2π exceeding 700 MHz and critical atom numbers approaching 10^(-7) in optimized structures. Furthermore, preliminary experimental measurements of toroidal cavities at a wavelength of 852 nm indicate that quality factors in excess of 108 can be obtained in a 50-µm principal diameter cavity, which would result in strong-coupling values of (g/(2π),n(0),N-0) = (86 MHz, 4.6 x 10^(-4), 1.0 x 10^(-3)).
The combination of cold atoms and large coherent coupling enables investigations in a new regime in cavity QED with single-atom trajectories monitored in real time with high signal-to-noise ratio. The underlying “vacuum-Rabi” splitting is clearly reflected in the frequency dependence of atomic transit signals recorded atom by atom, with evidence for mechanical light forces for intracavity photon number <1. The nonlinear optical response of one atom in a cavity is observed to be in accord with the one-atom quantum theory but at variance with semiclassical predictions.
The manner in which the reflection coefficient follows from the Schroedinger equation decribing the coupling of the atoms to the dielectric mirror and to the field is examined. A dielectric medium of identical two-state atoms coupled by the radiation field to an intially excited atom outside the dielectric is considered. A delay-differential equation in which a Fresnel reflection coefficient appears is derived. These data are applied to an atom in a Fabry-Perot resonator, and a general delay-differential equation for the probability amplitude of the initially excited state is obtained. The Ewald-Oseen extinction theorm is discussed in terms of quantum mechanics.
A quantum theory of spontaneous emission from an initially excited two-level atom in a one-dimensional optical cavity with output coupling from both sides is developed. Orthonormal mode functions with a continuous spectrum are employed, which are derived by imposing a periodic boundary condition on the whole space with a period much larger than the cavity length. The delay differential equation of the atomic state of Cook and Milonni [Phys. Rev. A 35, 5081 (1987)] is re-derived in a strict manner, where the reflectivity of the cavity mirrors is included naturally in the mode functions. An approximate solution at a single-resonant-mode limit shows the results of ``vacuum'' Rabi oscillation in an underdamped cavity and enhanced spontaneous emission rate in an overdamped cavity. For the latter case, it is found that in the optical range the spontaneous emission rate is enhanced by a factor F (finesse of the cavity).
The quantum theory of the spontaneous emission (SpE) from an active microscopic cavity (microcavity) is given with emphasis on mirror separations of the order of the optical wavelength. The theory is based on a complete set of orthonormal-mode functions that include both transverse polarizations and span the infinite three dimensional space that pervades and surrounds the microcavity. SpE rates for different active-dipole orientations and cavity configurations are calculated. The SpE pulse shape detected outside the cavity is shown to be generally nonexponential. A detailed computer simulation of the process is presented on the basis of the given theory in the perspective of our experiment, for a cavity terminated by mirrors bearing either metal- or semiconductor-multilayered coatings. We then report an extensive experimental verification of the theory by adopting an Eu-dibenzoylmethane complex as active medium with SpE from the 5D70-F2 line at lambda=6111 Å, under coherent uv excitation at lambdap=3547 Å. The results show evidence of ``SpE inhibition'' and ``enhancement,'' of nonexponential decay of SpE signals, and of competition with superradiance and stimulated emission. Finally we report the results of an experimental test of the algorithm adopted in all computer calculations of the optical parameters of the multilayered structures used for cavity confinement.
The lifetime of an excited atom near an absorbing dielectric surface is calculated from an exact solution of a microscopic Hamiltonian model, which includes the effects of dispersion, local-field correction, and near-field Coulomb interaction. Results for the total decay rate are shown to be in excellent agreement with those based on classical electromagnetic theory and to yield the well-known result for the rate of nonradiative energy transfer in the limit of very small distance from the surface. © 1996 The American Physical Society.
The motion of individual cesium atoms trapped inside an optical resonator is revealed with the atom-cavity microscope (ACM).
A single atom moving within the resonator generates large variations in the transmission of a weak probe laser, which are
recorded in real time. An inversion algorithm then allows individual atom trajectories to be reconstructed from the record
of cavity transmission and reveals single atoms bound in orbit by the mechanical forces associated with single photons. In
these initial experiments, the ACM yields 2-micrometer spatial resolution in a 10-microsecond time interval. Over the duration
of the observation, the sensitivity is near the standard quantum limit for sensing the motion of a cesium atom.
The creation of a photon-atom bound state was first envisaged for the case of an atom in a long-lived excited state inside a high-quality microwave cavity. In practice, however, light forces in the microwave domain are insufficient to support an atom against gravity. Although optical photons can provide forces of the required magnitude, atomic decay rates and cavity losses are larger too, and so the atom-cavity system must be continually excited by an external laser. Such an approach also permits continuous observation of the atom's position, by monitoring the light transmitted through the cavity. The dual role of photons in this system distinguishes it from other single-atom experiments such as those using magneto-optical traps, ion traps or a far-off-resonance optical trap. Here we report high-finesse optical cavity experiments in which the change in transmission induced by a single slow atom approaching the cavity triggers an external feedback switch which traps the atom in a light field containing about one photon on average. The oscillatory motion of the trapped atom induces oscillations in the transmitted light intensity; we attribute periodic structure in intensity-correlation-function data to 'long-distance' flights of the atom between different anti-nodes of the standing-wave in the cavity. The system should facilitate investigations of the dynamics of single quantum objects and may find future applications in quantum information processing.
Modern cavity quantum electrodynamics (cavity QED) illuminates the most fundamental aspects of coherence and decoherence in
quantum mechanics. Experiments on atoms in cavities can be described by elementary models but reveal intriguing subtleties
of the interplay of coherent dynamics with external couplings. Recent activity in this area has pioneered powerful new approaches
to the study of quantum coherence and has fueled the growth of quantum information science. In years to come, the purview
of cavity QED will continue to grow as researchers build on a rich infrastructure to attack some of the most pressing open
questions in micro- and mesoscopic physics.
Propagation of a light pulse through a high-Q optical microcavity containing a few cold atoms (N<10) in its cavity mode is investigated experimentally. With less than ten cold rubidium atoms launched into an optical microcavity, up to 170 ns propagation lead time ("superluminal"), and 440 ns propagation delay time (subluminal) are observed. Comparison of the experimental data with numerical simulations as well as future experiments are discussed.
Single cesium atoms are cooled and trapped inside a small optical cavity by way of a novel far-off-resonance dipole-force trap, with observed lifetimes of 2-3 s. Trapped atoms are observed continuously via transmission of a strongly coupled probe beam, with individual events lasting approximately 1 s. The loss of successive atoms from the trap N>/=3-->2-->1-->0 is thereby monitored in real time. Trapping, cooling, and interactions with strong coupling are enabled by the trap potential, for which the center-of-mass motion is only weakly dependent on the atom's internal state.
We describe a technique that enables strong, coherent coupling between individual optical emitters and guided plasmon excitations in conducting nanostructures at optical frequencies. We show that under realistic conditions optical emission can be almost entirely directed into the plasmon modes. As an example, we describe an application of this technique involving efficient generation of single photons on demand, in which the plasmon is efficiently outcoupled to a dielectric waveguide.
A fiber Fabry-Perot interferometer (FFPI) sensor is formed with broadband (~3 nm, 3-dB bandwidth) fiber Bragg grating (FBG) mirrors. Repetitively modulating a distributed-feedback laser produces chirping that modulates the reflectance of the FFPI. Because the reflectance of the FBG mirrors varies with optical frequency, the fringes in the sensor reflectance modulation are distinguishable, making it possible to extend the sensor dynamic range versus that of a FFPI sensor with conventional wavelength-dependent mirrors. An ambient temperature is determined in the range from 25 to 170 degrees C with a resolution of 0.005 degrees C.
We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.
We study the properties of the field in the fundamental mode HE$_{11}$ of a vacuum-clad \textit{subwavelength-diameter} optical fiber using the exact solutions of Maxwell's equations. We obtain simple analytical expressions for the total intensity of the electric field. We discuss the origin of the deviations of the exact fundamental mode HE$_{11}$ from the approximate mode LP$_{01}$. We show that the thin thickness of the fiber and the high contrast between the refractive indices of the silica core and the vacuum clad substantially modify the intensity distributions and the polarization properties of the field and its components, especially in the vicinity of the fiber surface. One of the promising applications of the field around the subwavelength-diameter fiber is trapping and guiding of atoms by the optical force of the evanescent field.