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H. A. M. Leymann,
C. Hopfmann,
F. Albert,
A. Foerster,
M. Khanbekyan,
C. Schneider,
S. Höfling, A. Forchel,
M. Kamp,
J. Wiersig,
S. Reitzenstein
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ABSTRACT: We investigate correlations between orthogonally polarized cavity modes of a
bimodal micropillar laser with a single layer of self-assembled quantum dots in
the active region. While one emission mode of the microlaser demonstrates a
characteristic s-shaped input-output curve, the output intensity of the second
mode saturates and even decreases with increasing injection current above
threshold. Measuring the photon auto-correlation function g^{(2)}(\tau) of the
light emission confirms the onset of lasing in the first mode with g^{(2)}(0)
approaching unity above threshold. In contrast, strong photon bunching
associated with super-thermal values of g^{(2)}(0) is detected for the other
mode for currents above threshold. This behavior is attributed to gain
competition of the two modes induced by the common gain material, which is
confirmed by photon crosscorrelation measurements revealing a clear
anti-correlation between emission events of the two modes. The experimental
studies are in excellent qualitative agreement with theoretical studies based
on a microscopic semiconductor theory, which we extend to the case of two modes
interacting with the common gain medium. Moreover, we treat the problem by an
extended birth-death model for two interacting modes, which reveals, that the
photon probability distribution of each mode has a double peak structure,
indicating switching behavior of the modes for the pump rates around threshold.
01/2013;
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Applied Physics Letters 12/2012; 96:042112. · 3.84 Impact Factor
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ABSTRACT: Spin transitions are studied theoretically and experimentally in a resonantly
excited system of cavity polaritons in a magnetic field. Weak pair interactions
in this boson system make possible fast and massive spin flips occurring at
critical amplitudes due to the interplay between amplitude dependent shifts of
eigenstates and the Zeeman splitting. Dominant spin of a condensate can be
toggled forth and back by tuning of the pump intensity only, which opens the
way for ultra-fast spin switchings of polariton condensates on a picosecond
timescale.
12/2012;
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ABSTRACT: Self-assembled Cd(Mn)Se/Zn(Mn)Se quantum dots have been investigated by means of spatially and time-resolved magneto-optical spectroscopy.In such quasi zero-dimensional diluted magnetic semiconductors, the exchange interaction couples the spins of optically generated charge carriers with localized magnetic ion spins.We demonstrate that this can be used on the one hand to monitor nanoscale magnetization with a resolution of o100 mkm by a purely optical technique and on the other hand to optically manipulate the magnetization in a semiconductor quantum dot
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ABSTRACT: The dynamics of the expansion of the first order spatial coherence g(1) for a
polariton system in a high-Q GaAs microcavity was investigated on the basis of
Young's double slit experiment under 3 ps pulse excitation at the conditions of
polariton Bose-Einstein condensation. It was found that in the process of
condensate formation the coherence expands with a constant velocity of about
10^8 cm/s. The measured coherence is smaller than that in thermally equilibrium
system during the growth of condensate density and well exceeds it at the end
of condensate decay. The onset of spatial coherence is governed by polariton
relaxation while condensate amplitude and phase fluctuations are not
suppressed.
Physical Review Letters 10/2012; 110:137402. · 7.37 Impact Factor
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ABSTRACT: A novel concept for on-chip quantum optics using an internal electrically pumped microlaser is presented. The microlaser resonantly excites a quantum dot microcavity system operating in the weak coupling regime of cavity quantum electrodynamics. This work presents the first on-chip application of quantum dot microlasers, and also opens up new avenues for the integration of individual microcavity structures into larger photonic networks.
Advanced Materials 10/2012; · 13.88 Impact Factor
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L. Dusanowski,
A. Golnik,
M. Syperek,
M. Nawrocki,
G. Sek,
J. Misiewicz,
T. W. Schlereth,
C. Schneider,
S. Hofling,
M. Kamp, A. Forchel
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ABSTRACT: Low temperature micro-photoluminecence and second-order single photon correlation experiments were performed on individual self-assembled In0.47Al0.34Ga0.19As/Al0.3Ga0.7As/GaAs quantum dots emitting in the range of 680-780 nm. Emission lines originating from exciton, biexciton, and charge exciton confined in the same dot could be identified. The derived exciton fine structure splitting is similar to 125 mu eV, whereas the biexciton and charge exciton binding energies are similar to 4 and similar to 9meV, respectively. The photon correlation statistics measured for the exciton emission exhibited a clear antibunching with the value of g(X-X)(2)(0) = 0.30 +/- 0.05, confirming unambiguously that such quantum dots act as true single photon quantum emitters. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4750241]
Applied Physics Letters 09/2012; 101:103108. · 3.84 Impact Factor
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ABSTRACT: A technology platform for the epitaxial growth of site-controlled InP quantum dots (QDs) on GaAs substrates is presented. Nanoholes are patterned in a GaInP layer on a GaAs substrate by electron beam lithography and dry chemical etching, serving as QD nucleation centers. The effects of a thermal treatment on the structured surfaces for deoxidation are investigated in detail. By regrowth on these surfaces, accurate QD positioning is obtained for square array arrangements with lattice periods of 1.25 μm along with a high suppression of interstitial island formation. The optical properties of these red-emitting QDs (λ ~ 670 nm) are investigated by means of ensemble- and micro-photoluminescence spectroscopy at cryogenic temperatures.
Nanotechnology 08/2012; 23(37):375301. · 3.98 Impact Factor
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T Heindel,
CA Kessler,
M Rau,
C Schneider,
M Furst,
F Hargart,
WM Schulz,
M Eichfelder,
R Rossbach,
S Nauerth,
M Lermer,
H Weier,
M Jetter,
M Kamp,
S Reitzenstein,
S Hofling,
P Michler,
H Weinfurter, A Forchel
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ABSTRACT: We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s−1 (35.4 kbit s−1) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g(2)(0) value of 0.35 (0.49) at moderate (high) excitation. The red emitting diodes generate sifted keys at a rate of 95.0 kbit s−1 at a QBER of 4.1% and a g(2)(0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios.
New Journal of Physics 08/2012; 14:083001. · 4.18 Impact Factor
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ABSTRACT: The oscillator strength of the fundamental optical transition in GaSb-based type II quantum well structures as one of the crucial parameters for the performance of interband cascade lasers was investigated. Modulation spectroscopy, supported by eight-band k center dot p calculations, has been employed as a sensitive probing technique allowing to determine the transition intensities of samples with various layer structures. The results show that altering the composition of the valence band well in a type II system can efficiently enhance the transition oscillator strength. Especially, the utilization of a quaternary GaInAsSb material for hole confinement turned out to be highly beneficial. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726423]
Applied Physics Letters 06/2012; 100:231908. · 3.84 Impact Factor
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F. Albert,
K. Sivalertporn,
J. Kasprzak,
M Strauß,
C. Schneider,
S. Höfling,
M. Kamp, A. Forchel,
S. Reitzenstein,
E. A. Muljarov,
W. Langbein
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ABSTRACT: Controlled non-local energy and coherence transfer enables light harvesting
in photosynthesis and non-local logical operations in quantum computing. The
most relevant mechanism of coherent coupling of distant qubits is coupling via
the electromagnetic field. Here, we demonstrate the controlled coherent
coupling of spatially separated excitonic qubits via the photon mode of a solid
state microresonator. This is revealed by two-dimensional spectroscopy of the
sample's coherent response, a sensitive and selective probe of the coherent
coupling. The experimental results are quantitatively described by a rigorous
theory of the cavity mediated coupling within a cluster of quantum dots
excitons. Having demonstrated this mechanism, it can be used in extended
coupling channels - sculptured, for instance, in photonic crystal cavities - to
enable a long-range, non-local wiring up of individual emitters in solids.
Nature Communications 06/2012; 4. · 7.40 Impact Factor
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ABSTRACT: The growth of Interband Cascade Laser material to cover the wavelength range from 3–4μm is presented along with the fabrication
and characterization of Broad Area (BA) and Ridge Waveguide (RWG) devices based on this material. Pulsed operation slightly
below room temperature is observed for both device types, and a strong reduction of threshold currents can be observed in
the RWG lasers. Variation of the active Quantum Well width in the epitaxial structures enables laser emission in the 3–4μm
wavelength region.
Applied Physics B 05/2012; 100(2):275-278. · 2.19 Impact Factor
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ABSTRACT: Modulation spectroscopy in its Fourier-transformed mode has been employed to investigate the optical properties of broken
gap ‘W’-shaped GaSb/AlSb/InAs/InGaSb/InAs/AlSb/GaSb quantum well structures designed to emit in the mid infrared range of
3–4 μm for applications in laser-based gas sensing. Besides the optical transitions originating from the confined states in
the type II quantum wells, a number of spectral features at the energy above the GaSb band gap have been detected. They have
been analyzed in a function of InAs and GaSb layer widths and ultimately connected with resonant states in the range of AlSb
tunneling barriers.
KeywordsFourier-transformed photoreflectance–type II quantum well–mid-infrared–resonant states
Opto-Electronics Review 05/2012; 19(2):137-139. · 0.97 Impact Factor
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ABSTRACT: Al0.6Ga0.4As/GaAs/Al0.6Ga0.4As double-barrier resonant-tunneling diodes (RTD) were grown by
molecular beam epitaxy with a nearby, lattice-matched Ga0.89In0.11N0.04As0.96 absorption layer.
RTD mesas with ring contacts and an aperture for optical excitation of charge carriers were
fabricated on the epitaxial layers. Electrical and optical properties of the RTDs were investigated
for different thicknesses of a thin GaAs spacer layer incorporated between the AlGaAs tunnel
barrier adjacent to the GaInNAs absorption layer. Illumination of the RTDs with laser light
of 1.3 lm wavelength leads to a pronounced photo-effect with a sensitivities of around 103 A/W.
Applied Physics Letters 04/2012; 100:172113. · 3.84 Impact Factor
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ABSTRACT: Condensation of exciton polaritons in planar microcavities with GaAs/AlAs quantum wells in the active area has been studied.
It has been found that an increase in the lifetime of polaritons up to ∼10–15 ps when the Q factor of a microcavity exceeds 7000 makes it possible to detect Bose-Einstein condensation of polaritons with a dominant
(>90%) photon component. Condensation occurs under thermodynamically nonequilibrium conditions in lateral traps with diameters
∼10 μm formed due to long-range fluctuations of the polariton potential. The violet shift of the polariton emission line at
the condensation threshold significantly exceeds the energy of the repulsive interaction between polaritons in the condensate.
It has been shown that the shift is mainly due to a decrease in the oscillator strength of bright excitons in lateral traps,
caused by the localization of photoexcited long-living dark excitons.
JETP Letters 04/2012; 92(9):595-599. · 1.35 Impact Factor
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ABSTRACT: In this work we report on the integration of single site-controlled quantum dots (SCQDs) into electrically driven micropillar cavities. The electroluminescence of these devices features emission of single SCQDs with inhomogeneous broadenings down to 170 µeV. The enhancement of electroluminescence by quantum dot-cavity coupling is demonstrated by temperature dependent investigations. Single photon emission from a spatially and spectrally coupled SCQD-resonator system is confirmed by photon autocorrelation measurements under electrical excitation yielding a g (2) (0) value of 0.42.
Applied Physics Letters 02/2012; 100:091108. · 3.84 Impact Factor
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ABSTRACT: We have employed Bloch-wave engineering to realize submicron diameter high quality factor GaAs/AlAs micropillars (MPs). The design features a tapered cavity in which the fundamental Bloch mode is subject to an adiabatic transition to match the Bragg mirror Bloch mode. The resulting reduced scattering loss leads to record-high vacuum Rabi splitting of the strong coupling in MPs with modest oscillator strength quantum dots. A quality factor of 13, 600 and a splitting of 85 μeV with an estimated visibility v of 0.41 are observed for a small mode volume MP with a diameter d{c} of 850 nm.
Physical Review Letters 02/2012; 108(5):057402. · 7.37 Impact Factor
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ABSTRACT: We demonstrate a method to controllably reduce the density of self-assembled InP quantum dots (QDs) by cyclic deposition with growth interruptions. Varying the number of cycles enabled a reduction of the QD density from 7.4 × 10(10) cm(-2) to 1.8 × 10(9) cm(-2) for the same total amount of deposited InP. Simultaneously, a systematic increase of the QD size could be observed. Emission characteristics of different-sized InP QDs were analyzed. Excitation power dependent and time-resolved measurements confirm a transition from type I to type II band alignment for large InP quantum dots. Photon autocorrelation measurements of type I QDs performed under pulsed excitation reveal pronounced antibunching (g((2))(τ = 0) = 0.06 ± 0.03) as expected for a single-photon emitter. The described growth routine has great promise for the exploitation of InP QDs as quantum emitters.
Nanotechnology 01/2012; 23(1):015605. · 3.98 Impact Factor
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ABSTRACT: We report on pump-power-dependent emission features of a nonthermalized and interacting dynamical condensate of exciton polaritons. The system based on a planar AlAs/AlGaAs microcavity sample with twelve GaAs quantum wells in the active region is investigated comprehensively by measuring the energy-momentum dispersion characteristics, the spatial coherence, and the photon statistics under resonant, fs-pulsed optical excitation at high momentum. We observe a significant polariton-population-dependent modification of the emission signatures above the quantum degeneracy. The nonequilibrium polariton condensate is confirmed by its polaritonic energy-momentum dispersion as well as excitation-power-dependent coherence properties and its photon statistics, being different from that of an ideal coherent state. The polaritonic condensate is characterized by a spatial coherence length of up to 4 μm and a super-Poissonian photon statistic of the emitted light well above threshold. Results obtained in second-order photon autocorrelation measurements in momentum-space resolved spectroscopy indicate polariton repulsive interaction throughout the condensate and a spatial coherence length being shorter than the condensate extension of 20–30 μm.
Physical Review B 01/2012; 86:155308. · 3.69 Impact Factor
