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ABSTRACT: We present a detailed experimental characterization of the spectral and spatial structure of the confined optical modes for oxide-apertured micropillar cavities, showing good-quality Hermite-Gaussian profiles, easily mode-matched to external fields. We further derive a relation between the frequency splitting of the transverse modes and the expected Purcell factor. Finally, we describe a technique to retrieve the profile of the confining refractive index distribution from the spatial profiles of the modes.
Optics Letters 11/2012; 37(22):4678-80. · 3.40 Impact Factor
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ABSTRACT: Hybrid quantum information protocols are based on local qubits, such as
trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling
is achieved through optical cavities. Here we demonstrate far-field optimized
H1 photonic crystal membrane cavities combined with an additional back
reflection mirror below the membrane that meet the optical requirements for
implementing hybrid quantum information protocols. Using numerical optimization
we find that 80% of the light can be radiated within an objective numerical
aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%.
We experimentally prove the unique external mode matching properties by
resonant reflection spectroscopy with a cavity mode visibility above 50%.
10/2012;
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ABSTRACT: Hybrid quantum information protocols are based on local qubits, such as trapped atoms, NV centers, and quantum dots, coupled to photons. The coupling is achieved through optical cavities. Here we demonstrate far-field optimized H1 photonic crystal membrane cavities combined with an additional back reflection mirror below the membrane that meet the optical requirements for implementing hybrid quantum information protocols. Using numerical optimization we find that 80% of the light can be radiated within an objective numerical aperture of 0.8, and the coupling to a single-mode fiber can be as high as 92%. We experimentally prove the unique external mode matching properties by resonant reflection spectroscopy with a cavity mode visibility above 50%.
Optics Express 10/2012; 20(22):24714-26. · 3.59 Impact Factor
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ABSTRACT: We experimentally characterize the spatial far-field emission profiles for
the two lowest confined modes of a photonic crystal cavity of the L3 type,
finding a good agreement with FDTD simulations. We then link the far-field
profiles to relevant features of the cavity mode near-fields, using a simple
Fabry-Perot resonator model. The effect of disorder on far-field cavity
profiles is clarified through comparison between experiments and simulations.
These results can be useful for emission engineering from active centers
embedded in the cavity.
08/2012;
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ABSTRACT: Acousto-electric charge conveyance induced by a surface acoustic wave (SAW) is employed to dissociate photogenerated excitons. Over macroscopic distances, both electrons and holes are injected sequentially into a remotely positioned, isolated and high quality quantum emitter, a self-assembled quantum post. This process is found to be highly efficient and to exhibit improved stability at high acoustic powers when compared to direct optical pumping at the position of the quantum post. These characteristics are attributed to the wide matrix quantum well in which charge conveyance occurs and to the larger number of carriers available for injection in the remote configuration, respectively. The emission of such pumped quantum posts is dominated by recombination of neutral excitons and fully directional when the propagation direction of the SAW and the position of the quantum post are reversed.
Nanotechnology 07/2012; 23(28):285201. · 3.98 Impact Factor
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ABSTRACT: Photonic crystal membranes (PCM) provide a versatile planar platform for
on-chip implementations of photonic quantum circuits. One prominent quantum
element is a coupled system consisting of a nanocavity and a single quantum dot
(QD) which forms a fundamental building block for elaborate quantum information
networks and a cavity quantum electrodynamic (cQED) system controlled by single
photons. So far no fast tuning mechanism is available to achieve control within
the system coherence time. Here we demonstrate dynamic tuning by monochromatic
coherent acoustic phonons formed by a surface acoustic wave (SAW) with
frequencies exceeding 1.7 gigahertz, one order of magnitude faster than
alternative approaches. We resolve a periodic modulation of the optical mode
exceeding eight times its linewidth, preserving both the spatial mode profile
and a high quality factor. Since PCMs confine photonic and phononic
excitations, coupling optical to acoustic frequencies, our technique opens ways
towards coherent acoustic control of optomechanical crystals.
Nature Photonics 05/2012; 5. · 29.28 Impact Factor
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ABSTRACT: We report on recent progress in the acousto-electrical control of
self-assembled quantum dot and quantum post using radio frequency surface
acoustic waves (SAWs). We show that the occupancy state of these optically
active nanostructures can be controlled via the SAW-induced dissociation of
photogenerated excitons and the resulting sequential bipolar carrier injection
which strongly favors the formation of neutral excitons for quantum posts in
contrast to conventional quantum dots. We demonstrate high fidelity preparation
of the neutral biexciton which makes this approach suitable for deterministic
entangled photon pair generation. The SAW driven acoustic charge conveyance is
found to be highly efficient within the wide quantum well surrounding the
quantum posts. Finally we present the direct observation of acoustically
triggered carrier injection into remotely positioned, individual quantum posts
which is required for a low-jitter SAW-triggered single photon source.
10/2011;
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ABSTRACT: Systems of photonic crystal cavities coupled to quantum dots are a promising
architecture for quantum networking and quantum simulators. The ability to
independently tune the frequencies of laterally separated quantum dots is a
crucial component of such a scheme. Here, we demonstrate independent tuning of
laterally separated quantum dots in photonic crystal cavities coupled by
in-plane waveguides by implanting lines of protons which serve to electrically
isolate different sections of a diode structure.
09/2011;
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ABSTRACT: In recent experiments on coupled quantum dot (QD) optical cavity systems, a pronounced interaction between the dot and the cavity has been observed even for detunings of many cavity linewidths. This interaction has been attributed to an incoherent phonon-mediated scattering process and is absent in atomic systems. Here, we demonstrate that despite its incoherent nature, this process preserves the signatures of coherent interaction between a QD and a strong driving laser, which may be observed via the optical emission from the off-resonant cavity. Under bichromatic driving of the QD, the cavity emission exhibits spectral features consistent with optical dressing of the QD transition. These cavity emission measurements are more akin to absorption measurements of a strongly driven QD rather than resonance fluorescence measurements. In addition to revealing new aspects of the off-resonant QD-cavity interaction, this result provides a new, simpler means of coherently probing QDs and opens the possibility of employing off-resonant cavities to optically interface QD nodes in quantum networks.
Phys. Rev. B. 08/2011; 84(8).
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ABSTRACT: We discuss the fine-tuning of the optical properties of self-assembled
quantum dots by the strain perturbation introduced by laser-induced surface
defects. We show experimentally that the quantum dot transition red-shifts,
independently of the actual position of the defect, and that such frequency
shift is about a factor five larger than the corresponding shift of a
micropillar cavity mode resonance. We present a simple model that accounts for
these experimental findings.
07/2011;
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ABSTRACT: "Quantum posts" are roughly cylindrical semiconductor nanostructures that are embedded in an energetically shallower "matrix" quantum well of comparable thickness. We report measurements of voltage-controlled charging and terahertz absorption of 30 nm thick InGaAs quantum wells and posts. Under flat-band (zero-electric field) conditions, the quantum posts each contain approximately six electrons, and an additional ~2.4 × 10(11) cm(-2) electrons populate the quantum well matrix. In this regime, absorption spectra show peaks at 3.5 and 4.8 THz (14 and 19 meV) whose relative amplitude depends strongly on temperature. These peaks are assigned to intersubband transitions of electrons in the quantum well matrix. A third, broader feature has a temperature-independent amplitude and is assigned to an absorption involving quantum posts. Eight-band k·p calculations incorporating the effects of strain and Coulomb repulsion predict that the electrons in the posts strongly repel the electrons in the quantum well matrix, "perforating" the electron gas. The strongest calculated transition, which has a frequency close to the center of the quantum post related absorption at 5 THz (20 meV), is an ionizing transition from a filled state to a quasi-bound state that can easily scatter to empty states in the quantum well matrix.
Nano Letters 04/2011; 12(3):1115-20. · 13.20 Impact Factor
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ABSTRACT: In recent experiments on coupled quantum dot (QD) optical cavity systems a
pronounced interaction between the dot and the cavity has been observed even
for detunings of many cavity linewidths. This interaction has been attributed
to an incoherent phonon-mediated scattering process and is absent in atomic
systems. Here, we demonstrate that despite its incoherent nature, this process
preserves the signatures of coherent interaction between a QD and a strong
driving laser, which may be observed via the optical emission from the
off-resonant cavity. Under bichromatic driving of the QD, the cavity emission
exhibits spectral features consistent with optical dressing of the QD
transition. In addition to revealing new aspects of the off-resonant QD-cavity
interaction, this result provides a new, simpler means of coherently probing
QDs than traditional approaches and opens the possibility of employing
off-resonant cavities to optically interface QD-nodes in quantum networks.
03/2011;
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ABSTRACT: We demonstrate a technique for achieving spectral resonance between a
polarization-degenerate micropillar cavity mode and an embedded quantum dot
transition. Our approach is based on a combination of isotropic and anisotropic
tensile strain effected by laser-induced surface defects, thereby providing
permanent tuning. Such a technique is a prerequisite for the implementation of
scalable quantum information schemes based on solid-state cavity quantum
electrodynamics.
03/2011;
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ABSTRACT: We demonstrate a quantum dot single photon source at 900 nm triggered at 100 MHz by a continuous wave telecommunications wavelength laser followed by an electro-optic modulator. The quantum dot is excited by on-chip-generated second harmonic radiation, resonantly enhanced by a GaAs photonic crystal cavity surrounding the InAs quantum dot. Our result suggests a path toward the realization of telecommunications wavelength-compatible quantum dot single photon sources with speeds exceeding 1 GHz.
Applied Physics Letters 03/2011; · 3.84 Impact Factor
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Stefan Völk,
Florian J. R. Schülein,
Florian Knall,
Achim Wixforth,
Hubert J Krenner,
Arne Laucht,
Jonathan J. Finley,
Juha Riikonen,
Marco Mattila,
Markku Sopanen,
Harri Lipsanen,
Jun He,
Tuan A. Truong, Hyochul Kim,
Pierre M Petroff
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ABSTRACT: We report on recent progress towards single photon sources based on quantum dot and quantum post nanostructures which are manipulated using surface acoustic waves. For this concept acoustic charge conveyance in a quantum well is used to spatially separate electron and hole pairs and transport these in the plane of the quantum well. When conveyed to the location of a quantum dot or quantum post these carriers are sequentially captured into the confined levels. Their radiative decays gives rise to the emission of a train of single photons. Three different approaches using (i) strain- induced and (ii) self-assembled quantum dots, and (iii) self-assembled quantum posts are discussed and their application potential is discussed. First devices and initial experiments towards the realization of such an acoustically driven single photon source are presented and remote acoustically triggered injection into few individual emitters is demonstrated. Comment: 11 pages, 7 figures
11/2010;
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ABSTRACT: Individual self-assembled quantum dots and quantum posts are studied under the influence of a surface acoustic wave. In optical experiments we observe an acoustically induced switching of the occupancy of the nanostructures along with an overall increase of the emission intensity. For quantum posts, switching occurs continuously from predominantly charged excitons (dissimilar number of electrons and holes) to neutral excitons (same number of electrons and holes) and is independent of whether the surface acoustic wave amplitude is increased or decreased. For quantum dots, switching is nonmonotonic and shows a pronounced hysteresis on the amplitude sweep direction. Moreover, emission of positively charged and neutral excitons is observed at high surface acoustic wave amplitudes. These findings are explained by carrier trapping and localization in the thin and disordered two-dimensional wetting layer on top of which quantum dots nucleate. This limitation can be overcome for quantum posts where acoustically induced charge transport is highly efficient in a wide lateral matrix-quantum well.
Nano Letters 09/2010; 10(9):3399-407. · 13.20 Impact Factor
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ABSTRACT: We demonstrate the use of periodically modulated Coulomb shifts in quantum dot (QD) transition energies to obtain differential reflection spectra of a photonic crystal nanocavity containing strongly coupled dots. Measured spectra isolate the change in the empty cavity optical reflectivity spectrum due to the presence of each dot. This technique permits the probing of coupled QD-cavity systems possessing cavity modes of arbitrary polarization, making it attractive for use in both cavity quantum electrodynamics studies and quantum information applications.
Applied Physics Letters 09/2010; · 3.84 Impact Factor
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ABSTRACT: We study the coupling between a photonic crystal cavity and an off-resonant
quantum dot under resonant excitation of the cavity or the quantum dot.
Linewidths of the quantum dot and the cavity as a function of the excitation
laser power are measured. We show that the linewidth of the quantum dot,
measured by observing the cavity emission, is significantly broadened compared
to the theoretical estimate. This indicates additional incoherent coupling
between the quantum dot and the cavity.
03/2010;
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ABSTRACT: The resonance frequency of an InAs quantum dot strongly coupled to a GaAs photonic-crystal cavity was electrically controlled via the quadratic quantum confined Stark effect. Stark shifts up to 0.3 meV were achieved using a lateral Schottky electrode that created a local depletion region at the location of the quantum dot. We report switching of a probe laser coherently coupled to the cavity up to speeds as high as 150 MHz, limited by the RC constant of the transmission line. The coupling strength g and the magnitude of the Stark shift with electric field were investigated while coherently probing the system.
Physical Review Letters 01/2010; 104(4):047402. · 7.37 Impact Factor
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ABSTRACT: One of the main obstacles to coupling two quantum dots (QDs) to a single nanocavity mode in a cavity quantum electrodynamics system is the ability to independently tune the QD frequencies. We demonstrate that in a GaAs photonic crystal membrane structure with two embedded QD layers, the QD emission frequencies of one QD layer can be tuned independently of the other by applying a voltage across only one of the QD layers.
Applied Physics Letters 12/2009; 95(24):243107-243107-3. · 3.84 Impact Factor
