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Abstract
Parametric scattering dynamics are general and of crucial importance for cavity exciton polaritons. Here, parametric scattering process driven by exciton polariton condensates has been revealed in a 1D ZnO microcavity between the whispering-gallery mode and quasiwhispering-gallery mode. When the occupation of the produced polariton condensate is dense enough, polariton condensates formed on quasiwhispering-gallery mode can be scattered towards the ground state of the adjacent whispering-gallery modes at higher and lower energies. By using the femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of this intermode polariton parametric scattering have been explicitly observed. The scattering towards a higher mode occurs faster than that to a lower-energy mode by less than a picosecond. The revealed dynamics can not only expand the present investigations on polariton parametric scattering, but also promote the potential applications in, e.g., quantum information processing.
... Indeed, nonlinearities of polaritons governed by polaritonic interactions have become one of the most studied topics in the field of polariton physics. A variety of nonlinear phenomena, such as inter-and intra-band parametric scattering, 2,[8][9][10][11] polariton blockade, [12][13][14] topological edge mode, [15][16][17] and evaporative cooling 18) have been reported in recent years. Understanding and controlling the nonlinearities of polaritons is critical for both fundamental polariton physics and their potential optoelectronic applications. ...
In this work, we report the experimental observation of the ballistic transport of condensed exciton-polaritons at room temperature in a one-dimensional whispering-gallery microcavity. Such coherent transport, initiated by the pronounced inter-particle interactions of polaritons, leads to the generation of two symmetric emission beams in the momentum (angular) space. By means of spatially filtered angle-resolved photoluminescence imaging spectroscopy, we were able to identify their origin and successfully rationalize these observations using the potential energy-to-kinetic energy conversion picture. The energy-dependent emission linewidth, as well as TM to TE inter-mode scattering, have also been discussed.
A supersolid is a counter-intuitive phase of matter in which its constituent particles are arranged into a crystalline structure, yet they are free to flow without friction. This requires the particles to share a global macroscopic phase while being able to reduce their total energy by spontaneous, spatial self-organization. The existence of the supersolid phase of matter was speculated more than 50 years ago1, 2, 3–4. However, only recently has there been convincing experimental evidence, mainly using ultracold atomic Bose–Einstein condensates (BECs) coupled to electromagnetic fields. There, various guises of the supersolid were created using atoms coupled to high-finesse cavities5,6, with large magnetic dipole moments7, 8, 9, 10, 11, 12–13, and spin–orbit-coupled, two-component systems showing stripe phases14, 15–16. Here we provide experimental evidence of a new implementation of the supersolid phase in a driven-dissipative, non-equilibrium context based on exciton–polaritons condensed in a topologically non-trivial, bound state in the continuum (BiC) with exceptionally low losses, realized in a photonic-crystal waveguide. We measure the density modulation of the polaritonic state indicating the breaking of translational symmetry with a precision of several parts in a thousand. Direct access to the phase of the wavefunction allows us to also measure the local coherence of the supersolid. We demonstrate the potential of our synthetic photonic material to host phonon dynamics and a multimode excitation spectrum.
An electrically driven low-threshold exciton-polariton microlaser diode based on an n-ZnO:Ga microribbon/p-GaN heterojunction was realized.
Due to the ability of exciton-polariton condensates formed in semiconductor microcavities to be achieved at room temperature and their characteristics such as non-equilibrium and strong interactions,they have become an ideal platform for studying the nonlinear properties of non-equilibrium quantum systems.In 2013,the research group led by L.Dominici observed two-dimensional symmetric shock waves in the polariton condensate driven by coherent pump.However,owing to the characteristics of this system,theoretical researches have lagged behind.In one-dimensional polariton condensates,disregarding cross-interaction of the system,a type of asymmetric shock wave was respectively discovered by A.M.Kamchatnov in 2012 and A.M.Belounis in 2017.In 2023,utilizing the adiabatic approximation,our research team not only uncovered sparse wave,symmetric,and asymmetric shock waves in the system,but also revealed that the symmetric shock waves are triggered by cross-interaction.At present,there is no theoretical research on shock waves in two-dimensional polariton condensate.In this paper,spectral methods and fourth-order RungeKutta methods are used to explore the generation and control of shock waves in two-dimensional polariton condensates.It is found that when the cross-interaction between the condensate and the polariton thermal reservoir is quenched at high condensation rates,the initially prepared bright solitons can be modulated into two types of rotationally symmetric shock waves with different velocities,while the initial dark-like solitons can only transform into a single velocity rotationally symmetric shock wave.If quenching the external potential,the dark-like solitons can be transformed into anisotropic supersonic shock waves,and the dependence of shock wave on the width of the external potential is also shown.When the external potential and incoherent pumping are controlled at low condensation rates,multiple anisotropic shock waves can be excited in a uniform condensate,and their amplitudes can be used to control the wave number and amplitude of the shock waves and the range of widths for the external potential or incoherent pumping to excite shock waves is also demonstrated.The proposed methods in this paper not only provide theoretical guidance for the generation and control of shock waves in exciton-polariton condensates,but also find symmetric shock waves similar to experiments (Nat.Commun. 6 ,8993) without adopting any approximation,and open up a universal pathway for exciting shock waves in non-equilibrium or non-integrable systems,which may become a paradigm for transforming solitons into shock waves and significantly propel the rapid development of shock wave theory in different domains.
Exciton polaritons have shown great potential for applications such as low-threshold lasing, quantum simulation, and dissipation-free circuits. In this paper, we realize a room temperature ultrafast polaritonic switch where the Bose-Einstein condensate population can be depleted at the hundred femtosecond timescale with high extinction ratios. This is achieved by applying an ultrashort optical control pulse, inducing parametric scattering within the photon part of the polariton condensate via a four-wave mixing process. Using a femtosecond angle-resolved spectroscopic imaging technique, the erasure and revival of the polariton condensates can be visualized. The condensate depletion and revival are well modeled by an open-dissipative Gross-Pitaevskii equation including parametric scattering process. This pushes the speed frontier of all-optical controlled polaritonic switches at room temperature towards the THz regime.
Based on ZnO microcavities with high quality factors, where the gain medium exhibits confinement of wave packets due to the intrinsically formed whispering gallery microcavity, strong coupling between excitons and cavity photons can be obtained at room temperature resulting in hybrid quasiparticles, e.g. exciton polaritons. In this work, polariton condensation is induced under the non-resonant excitation by linearly polarized femtosecond pulses with different polarization directions. The dynamical angle-resolved k-space spectra of the photoluminescence emission of polariton condensates are measured with sub-picosecond resolution by the self-developed femtosecond angle-resolved spectroscopic imaging technique. Our results show that the ultrafast dynamics of polariton condensation is sensitive to the polarization direction of the excitation pulses which can be explained qualitatively by the combined effect of selective excitation of distinct exciton modes in the sample and the effective coupling strength of the excitation pulses in the ZnO microcavity for various polarization directions. This work strengthened the understanding of the underlying physics of the condensation process for cavity exciton polaritons at room temperature.room temperature.
In this work, by using femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of confined exciton-polaritons in an optical induced potential well based on a ZnO whispering-gallery microcavity is explicitly visualized. The sub-picosecond transition between succeeding quantum harmonic oscillator states can be experimentally distinguished. The landscape of the potential well can be modified by the pump power, the spatial distance and the time delay of the two input laser pulses. Clarifying the underlying mechanism of the polariton harmonic oscillator is interesting for the applications of polariton-based optoelectronic devices and quantum information processing.
Polaritons are quasi-particles that originate from the coupling of light with matter and that demonstrate quantum phenomena at the many-particle mesoscopic level, such as Bose-Einstein condensation and superfluidity. A highly sought and long-time missing feature of polaritons is a genuine quantum manifestation of their dynamics at the single-particle level. Although they are conceptually perceived as entangled states and theoretical proposals abound for an explicit manifestation of their single-particle properties, so far their behavior has remained fully accounted for by classical and mean-field theories. We report the first experimental demonstration of a genuinely quantum state of the microcavity polariton field, by swapping a photon for a polariton in a two-photon entangled state generated by parametric downconversion. When bringing this single-polariton quantum state in contact with a polariton condensate, we observe a disentangling with the external photon. This manifestation of a polariton quantum state involving a single quantum unlocks new possibilities for quantum information processing with interacting bosons.
Polariton lasing is the coherent emission arising from a macroscopic polariton condensate first proposed in 1996. Over the past two decades, polariton lasing has been demonstrated in a few inorganic and organic semiconductors in both low and room temperatures. Polariton lasing in inorganic materials significantly relies on sophisticated epitaxial growth of crystalline gain medium layers sandwiched by two distributed Bragg reflectors in which combating the built-in strain and mismatched thermal properties is nontrivial. On the other hand, organic active media usually suffer from large threshold density and weak nonlinearity due to the Frenkel exciton nature. Further development of polariton lasing towards technologically significant applications demand more accessible materials, ease of device fabrication and broadly tunable emission at room temperature. Herein, we report the experimental realization of room-temperature polariton lasing based on an epitaxy-free all-inorganic cesium lead chloride perovskite microcavity. Polariton lasing is unambiguously evidenced by a superlinear power dependence, macroscopic ground state occupation, blueshift of ground state emission, narrowing of the linewidth and the build-up of long-range spatial coherence. Our work suggests considerable promise of lead halide perovskites towards large-area, low-cost, high performance room temperature polariton devices and coherent light sources extending from the ultraviolet to near infrared range.
We report on pure-quantum-state polariton condensates in optical annular
traps. The study of the underlying mechanism reveals that the polariton
wavefunction always coalesces in a single pure-quantum-state that,
counter-intuitively, is always the uppermost confined state with the highest
overlap to the exciton reservoir. The tunability of such states combined with
the short polariton lifetime allows for ultrafast transitions between coherent
mesoscopic wavefunctions of distinctly different symmetries rendering optically
confined polariton condensates a promising platform for applications such as
many-body quantum circuitry and continuous-variable quantum processing.
Significance
Bose–Einstein condensation of polaritons in periodically modulated cavities is a very interesting fundamental effect of the physics of many-body systems. It is also promising for application in solid-state lighting and information communication technologies. By a simple microassembling method, we created periodically modulated polariton condensates at room temperature, and observed the stabilization of the coherent condensate due to the spontaneous symmetry-breaking transition. This manifests a previously unidentified type of phase transition, leading to a novel state of matter: the weak lasing state. The optical imaging in both direct and reciprocal space provides clear evidence for the weak lasing in the specific range of the pumping intensities.
Recently a new type of system exhibiting spontaneous coherence has emerged --
the exciton-polariton condensate. Exciton-polaritons (or polaritons for short)
are bosonic quasiparticles that exist inside semiconductor microcavities,
consisting of a superposition of an exciton and a cavity photon. Above a
threshold density the polaritons macroscopically occupy the same quantum state,
forming a condensate. The lifetime of the polaritons are typically comparable
to or shorter than thermalization times, making them possess an inherently
non-equilibrium nature. Nevertheless, they display many of the features that
would be expected of equilibrium Bose-Einstein condensates (BECs). The
non-equilibrium nature of the system raises fundamental questions of what it
means for a system to be a BEC, and introduces new physics beyond that seen in
other macroscopically coherent systems. In this review we focus upon several
physical phenomena exhibited by exciton-polariton condensates. In particular we
examine topics such as the difference between a polariton BEC, a polariton
laser, and a photon laser, as well as physical phenomena such as superfluidity,
vortex formation, BKT (Berezinskii-Kosterlitz-Thouless) and BCS
(Bardeen-Cooper-Schrieffer) physics. We also discuss the physics and
applications of engineered polariton structures.
We report observation of oscillations in the dynamics of a microcavity
polariton condensate formed under pulsed non resonant excitation. While
oscillations in a condensate have always been attributed to Josephson
mechanisms due to a chemical potential unbalance, here we show that under some
localisation conditions of the condensate, they may arise from relaxation
oscillations, a pervasive classical dynamics that repeatedly provokes the
sudden decay of a reservoir, shutting off relaxation as the reservoir is
replenished. Using non-resonant excitation, it is thus possible to obtain
condensate injection pulses with a record frequency of 0:1 THz.
Under the right conditions, cavity polaritons form a macroscopic condensate in the ground state. The fascinating nonlinear behaviour of this condensate is largely dictated by the strength of polariton-polariton interactions. In inorganic semiconductors, these result principally from the Coulomb interaction between Wannier-Mott excitons. Such interactions are considerably weaker for the tightly bound Frenkel excitons characteristic of organic semiconductors and were notably absent in the first reported demonstration of organic polariton lasing. In this work, we demonstrate the realization of an organic polariton condensate, at room temperature, in a microcavity containing a thin film of 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene. On reaching threshold, we observe the spontaneous formation of a linearly polarized condensate, which exhibits a superlinear power dependence, long-range order and a power-dependent blueshift: a clear signature of Frenkel polariton interactions.
We experimentally demonstrate resonant coupling between photons and excitons in microcavities which can efficiently generate enormous single-pass optical gains approaching 100. This new parametric phenomenon appears as a sharp angular resonance of the incoming pump beam, at which the moving excitonic polaritons undergo very large changes in momentum. Ultrafast stimulated scattering is clearly identified from the exponential dependence on pump intensity. This device utilizes boson amplification
induced by stimulated energy relaxation.
We report the experimental observation of the quasi-whispering-gallery mode (quasi-WGM) polariton lasing in a one dimensional ZnO microrod cavity at room temperature. Under nonresonant optical pulsed excitation, we measure the pumping power dependence of the emission intensity and the blueshift of the polariton modes, and a fairly low lasing threshold for the quasi-WG mode is determined. We also measure the lasing threshold versus the photon-exciton detuning by dispersion simulations. These experiment results show that both of the WGMs with higher Q factors and the quasi-WGMs with lower Q factors can lase when the detuning between the optical modes and the exciton energies is optimum.
In the past decade, a two-dimensional matter-light system called the microcavity exciton-polariton has emerged as a new promising candidate of Bose-Einstein condensation (BEC) in solids. Many pieces of important evidence of polariton BEC have been established recently in GaAs and CdTe microcavities at the liquid helium temperature, opening a door to rich many-body physics inaccessible in experiments before. Technological progress also made polariton BEC at room temperatures promising. In parallel with experimental progresses, theoretical frameworks and numerical simulations are developed, and our understanding of the system has greatly advanced. In this article, recent experiments and corresponding theoretical pictures based on the Gross-Pitaevskii equations and the Boltzmann kinetic simulations for a finite-size BEC of polaritons are reviewed.
Although optical technology provides the best solution for the transmission of information, all-optical devices must satisfy several qualitative criteria to be used as logic elements. In particular, cascadability is difficult to obtain in optical systems, and it is assured only if the output of one stage is in the correct form to drive the input of the next stage. Exciton-polaritons, which are composite particles resulting from the strong coupling between excitons and photons, have recently demonstrated huge non-linearities and unique propagation properties. Here we show that polariton fluids moving in the plane of the microcavity can operate as input and output of an all-optical transistor, obtaining up to 19 times amplification and demonstrating the cascadability of the system. Moreover, the operation as an AND/OR gate is shown, validating the connectivity of multiple transistors in the microcavity plane and opening the way to the implementation of polariton integrated circuits.
A polariton condensate transistor switch is realized through optical
excitation of a microcavity ridge with two beams. The ballistically ejected
polaritons from a condensate formed at the source are gated using the 20 times
weaker second beam to switch on and off the flux of polaritons. In the absence
of the gate beam the small built-in detuning creates potential landscape in
which ejected polaritons are channelled toward the end of the ridge where they
condense. The low loss photon-like propagation combined with strong
nonlinearities associated with their excitonic component makes polariton based
transistors particularly attractive for the implementation of all-optical
integrated circuits.
We report direct observation of the strong exciton-photon coupling in a ZnO tapered whispering gallery (WG) microcavity at room temperature. By scanning excitations along the tapered arm of the ZnO tetrapod using a micro-photoluminescence spectrometer with different polarizations, we observed a transition from the pure WG optical modes in the weak interaction regime to the excitonic polariton in the strong coupling regime. The experimental observations are well described by using the plane wave model including the excitonic polariton dispersion relation. This provides a direct mapping of the polariton dispersion, and thus a comprehensive picture for coupling of different excitons with differently polarized WG modes.
We report the photoluminescence (PL) investigations of quasi-whispering gallery mode (quasi-WGM) polaritons in a ZnO microrod at room temperature. By using the confocal micro-PL spectroscopic technique, we observe the clear optical quasi-WGMs. These quasi-WGMs appeared in the ultraviolet (UV) emission region where the cavity modes strongly couple with excitons and form polaritons. The quasi-WGMs polaritons can be well described by the plane wave interference and the coupling oscillator model.
The optical properties of organic semiconductors are almost exclusively described using the Frenkel exciton picture. In this description, the strong Coulombic interaction between an excited electron and the charged vacancy it leaves behind (a hole) is automatically taken into account. If, in an optical microcavity, the exciton-photon interaction is strong compared to the excitonic and photonic decay rates, a second quasiparticle, the microcavity polariton, must be introduced to properly account for this coupling. Coherent, laser-like emission from polaritons has been predicted to occur when the ground-state occupancy of polaritons , reaches 1 (ref. 3). This process, known as polariton lasing, can occur at thresholds much lower than required for conventional lasing. Polaritons in organic semiconductors are highly stable at room temperature, but to our knowledge, there has as yet been no report of nonlinear emission from these structures. Here, we demonstrate polariton lasing at room temperature in an organic microcavity composed of a melt-grown anthracene single crystal sandwiched between two dielectric mirrors.
A microscopic theory is presented for the giant amplification from microcavities in the strong exciton-photon coupling regime, providing excellent agreement with recent angle-resolved pump-probe experiments. The analytical and numerical solutions give insight into the physics of the polariton parametric amplifier. The coherent gain, due to polariton four-wave-mixing, has a threshold dependence on the pump power and is spectrally blueshifted from the lower polariton energy. The gain shift does not depend on the power, but on the unperturbed polariton linewidth.
The spectral response of a monolithic semiconductor quantum microcavity with quantum wells as the active medium displays mode splittings when the quantum wells and the optical cavity are in resonance. This effect can be seen as the Rabi vacuum-field splitting of the quantum-well excitons, or more classically as the normal-mode splitting of coupled oscillators, the excitons and the electromagnetic field of the microcavity. An exciton oscillator strength of 4 x 10 exp 12/sq cm is deduced for 76-A quantum wells.
Optical parametric oscillation is a nonlinear process that enables coherent generation of 'signal' and 'idler' waves, shifted in frequency from the pump wave. Efficient parametric conversion is the paradigm for the generation of twin or entangled photons for quantum optics applications such as quantum cryptography, or for the generation of new frequencies in spectral domains not accessible by existing devices. Rapid development in the field of quantum information requires monolithic, alignment-free sources that enable efficient coupling into optical fibres and possibly electrical injection. During the past decade, much effort has been devoted to the development of integrated devices for quantum information and to the realization of all-semiconductor parametric oscillators. Nevertheless, at present optical parametric oscillators typically rely on nonlinear crystals placed into complex external cavities, and pumped by powerful external lasers. Long interaction lengths are typically required and the phase mismatch between the parametric waves propagating at different velocities results in poor parametric conversion efficiencies. Here we report the demonstration of parametric oscillation in a monolithic semiconductor triple microcavity with signal, pump and idler waves propagating along the vertical direction of the nanostructure. Alternatively, signal and idler beams can also be collected at finite angles, allowing the generation of entangled photon pairs. The pump threshold intensity is low enough to envisage the realization of an all-semiconductor electrically pumped micro-parametric oscillator.
Phase transitions to quantum condensed phases--such as Bose-Einstein condensation (BEC), superfluidity, and superconductivity--have long fascinated scientists, as they bring pure quantum effects to a macroscopic scale. BEC has, for example, famously been demonstrated in dilute atom gas of rubidium atoms at temperatures below 200 nanokelvin. Much effort has been devoted to finding a solid-state system in which BEC can take place. Promising candidate systems are semiconductor microcavities, in which photons are confined and strongly coupled to electronic excitations, leading to the creation of exciton polaritons. These bosonic quasi-particles are 10(9) times lighter than rubidium atoms, thus theoretically permitting BEC to occur at standard cryogenic temperatures. Here we detail a comprehensive set of experiments giving compelling evidence for BEC of polaritons. Above a critical density, we observe massive occupation of the ground state developing from a polariton gas at thermal equilibrium at 19 K, an increase of temporal coherence, and the build-up of long-range spatial coherence and linear polarization, all of which indicate the spontaneous onset of a macroscopic quantum phase.
We observe a room-temperature low-threshold transition to a coherent polariton state in bulk GaN microcavities in the strong-coupling regime. Nonresonant pulsed optical pumping produces rapid thermalization and yields a clear emission threshold of 1 mW, corresponding to an absorbed energy density of 29 microJ cm-2, 1 order of magnitude smaller than the best optically pumped (In,Ga)N quantum-well surface-emitting lasers (VCSELs). Angular and spectrally resolved luminescence show that the polariton emission is beamed in the normal direction with an angular width of +/-5 degrees and spatial size around 5 microm.
We have created polaritons in a harmonic potential trap analogous to atoms in optical traps. The trap can be loaded by creating polaritons 50 micrometers from its center that are allowed to drift into the trap. When the density of polaritons exceeds a critical threshold, we observe a number of signatures of Bose-Einstein condensation: spectral and spatial narrowing, a peak at zero momentum in the momentum distribution, first-order coherence, and spontaneous linear polarization of the light emission. The polaritons, which are eigenstates of the light-matter system in a microcavity, remain in the strong coupling regime while going through this dynamical phase transition.
By using the femtosecond angle-resolved spectroscopic imaging technique, the ultrafast buildup dynamics of room-temperature polariton condensation is explicitly visualized in a ZnO whispering gallery mode microcavity. The buildup time of polariton condensation with respect to the arrival of the femtosecond pump pulse decreases with the increasing pump power and reaches a lower limit of about 4 ps. Simulation results by numerically solving the open-dissipative Gross-Pitaevskii equation coupled to an incoherent reservoir are in quantitative agreement with the experimental observations, showing that the scattering from exciton reservoir to the lower polariton branches and the decay from these branches dominate the buildup process.
Comparing with pure photons, higher nonlinearity in polariton systems has been exploited in various proof-of-principle demonstrations of efficient optical devices based on the parametric scattering effect. However, most of them demand cryogenic temperatures limited by the small exciton binding energy of traditional semiconductors or exhibit weak nonlinearity resulting from Frenkel excitons. Lead halide perovskites, possessing both a large binding energy and a strong polariton interaction, emerge as ideal platforms to explore nonlinear polariton physics toward room temperature operation. Here, we report the first observation of nonlinear parametric scattering in a lead halide perovskite microcavity with multiple polariton branches at room temperature. Driven by the scattering source from condensation in one polariton branch, correlated polariton pairs are obtained at high k states in an adjacent branch. Our results strongly advocate the ability to reach the nonlinear regime essential for perovskite polaritonics working at room temperature.
In a ZnO microcavity, the exciton-polariton effect with ultralarge Rabi splitting (can be as large as several hundreds of millielectron volts) may dominate the optical properties at the energies near the band edge. Due to the light-matter coupling, the renormalized energy states, i.e., the exciton-polariton states are expected to show very different dynamical behavior compared to the free exciton state. In this work, we used a femtosecond laser to pump a high-quality ZnO whispering gallery microcavity at room temperature. In the time-resolved photoluminescence measurements, we observed that both the fast and slow decay rates of the exciton-polaritons are faster than that of the free exciton due to the strong coupling between excitons and photons in a microcavity. The decay time constants are found to depend on the exciton-photon energy detuning (δ=Ephoton−Eexciton).
Polariton condensation of one-dimensional multimode whispering gallery mode exciton polaritons is investigated in hexagonal ZnO microwires at cryogenic temperatures. At threshold, stimulated scattering is fed by the resonant emission from highly populated defect-bound excitons. With further increasing excitation power, condensates relax within the multimode whispering gallery mode polariton ladder, leading to their effective evaporative cooling. The relaxation is a parametric polariton-polariton scattering process evidenced by its intensity, energy, and momentum evolution. The experimental observations are in good agreement with numerical simulations based on a model for polariton-polariton scattering extended to the multimodal whispering gallery mode system.
The implementation of a large-scale quantum network is a key challenge for
quantum science. Such network consists of stationary quantum nodes that can
store and process quantum information locally. The nodes are connected by
quantum channels for flying information carriers, i.e. photons. These channels
serve both to directly exchange quantum information between nodes as well as to
distribute entanglement over the whole network. In order to scale such network
to many particles and long distances, an efficient interface between the nodes
and the channels is required. This article describes the cavity-based approach
to this goal, with an emphasis on experimental systems in which single atoms
are trapped in and coupled to optical resonators. Besides being conceptually
appealing, this approach is promising for quantum networks on larger scales, as
it gives access to long qubit coherence times and high light-matter coupling
efficiencies. Thus, it allows one to generate entangled photons on the push of
a button, to reversibly map the quantum state of a photon onto an atom, to
transfer and teleport quantum states between remote atoms, to entangle distant
atoms, to detect optical photons nondestructively, to perform entangling
quantum gates between an atom and one or several photons, and even provides a
route towards efficient heralded quantum memories for future repeaters. The
presented general protocols and the identification of key parameters are
applicable to other experimental systems.
Exciton-polariton lasing in a one-dimensional ZnO microcavity is demonstrated at high temperature of 455 K. The massive occupation of the polariton ground state above a distinct pump power threshold is clearly demonstrated by using the angular resolved spectroscopy under non-resonant excitation. The temperature dependence of the polariton lasing threshold is well interpreted by two competing mechanisms, i.e., the thermodynamic and kinetic mechanisms. Michelson interference measurements are performed to investigate the temporal and spatial coherence of polariton laser, with the coherence time and coherence length being τc∼0.97 ps and rc∼0.72μm at 440 K and 400 K, respectively.
We report a study of refractive index of a wurtzite ZnO single crystal microwire at a temperature range from room temperature to about 400 K using optical cavity modes. The photoluminescence (PL) spectra of the ZnO microwire at different temperatures were performed using a confocal micro-photoluminescence setup. The whispering gallery modes observed in the PL spectra show a redshift both in the ultraviolet and the visible range as the temperature rises. The redshift is used to extract the refractive index of the ZnO microwire. The dispersion relations are deduced at different temperatures, and the results show that the refractive index increases with raising temperature for both transverse electric and transverse magnetic modes. The refractive index increases faster at a shorter wavelength, which is due to the fact that the shorter wavelength is closer to the resonance frequencies of ZnO microwire according to the Lorentz oscillator model.
Optical resonances in polygonal resonators are due to whispering gallery modes (WGM). We investigate WGM in regular and deformed hexagonal ZnO microwire resonators. Four types of geometries are investigated: regular hexagonal and dodecagonal cross sections, hexagonal cross section elongated for one pair of facets and hexagonal cross section deformed by bending (uniaxial stress). Experimental data on mode energies and angular dispersion are correlated with model calculations and Poincaré surfaces of section. Hexagonal (ϕ = 60°), square (ϕ = 45°), triangular (ϕ = 30°), and Fabry–Pérot modes (ϕ = 0°) are observed in the various investigated geometries, ϕ being the angle of incidence at the facets with respect to the normal direction.
Hexagonal WGMs (green, 6-WGM), triangular (red, 3-WGM), and double-triangular (blue, D3-WGM) rays in regular hexagons, elongated hexagons and hexagons deformed by bending. Triangular WGMs are stable modes in all three resonators. Hexagonal modes are not stable in the bent hexagon.
Wurtzite structural ZnO microneedles with hexagonal cross section were fabricated by vapor-phase transport method and an individual microneedle was employed as a lasing microcavity. Under excitation of a femtosecond pulse laser with 800 nm wavelength, the ultraviolet (UV) laser emission was obtained, which presented narrow linewidth and high Q value. The UV emission, resonant mechanism, and laser mode characteristics were discussed in detail. The results demonstrated that the UV laser originated from the whispering-gallery mode induced by two-photon absorption assisted by Rabi oscillation.
Angle-resolved spectroscopy of wire-shaped microcavities in the strong coupling regime is used to demonstrate elastic polariton pair scattering. Due to the lateral confinement of the light field each of the polariton modes of a planar cavity splits into a multiplet of subbranches. The polariton mode fan gives access to a variety of channels for polariton pair scattering. Parametric scattering among branches of the lower polariton multiplet is realized as well as processes involving the upper polariton modes. In the scattering events signal and idler state have to be located in subbranches with identical symmetry to conserve parity. This constraint adds to the requirements of energy and momentum conservation.
Parametric polariton scattering is studied in quasi-one-dimensional microcavities. A polarization splitting of the polariton modes is observed and its origin is discussed. In contrast to planar cavities, here, the large splitting leads to a comprehensive analysis of the polarization dynamics. We demonstrate phase matched intersubbranch parametric polariton scattering at k=0 with an inversion of the linear polarization of signal and idler with respect to the pump beam.
We demonstrate a novel way to realize room-temperature polariton parametric scattering in a one-dimensional ZnO microcavity. The polariton parametric scattering is driven by a polariton condensate, with a balanced polariton pair generated at the adjacent polariton mode. This parametric scattering is experimentally investigated by the angle-resolved photoluminescence spectroscopy technique under different pump powers and it is well described by the rate equation of interacting bosons. The direct relation between the intensity of the scattered polariton signal and that of the polariton reservoir is acquired under nonresonant excitation, exhibiting the explicit nonlinear characteristic of this room-temperature polariton parametric process.
The size dependence of whispering gallery modes in dielectric resonators with hexagonal cross section has been observed within the visible spectral range for cavity diameters comparable to the light wavelength. As a model system single, tapered, high aspect ratio zinc oxide nanoneedles were analyzed. They enable systematic investigations as a function of the resonator diameter down to the nanometer regime. A simple plane wave interference model without free parameter describes the spectral positions and the linewidths of the modes in good agreement with the experiment.