EPHQUAMHalbleiteroptik
Cascaded Single-Photon Emission from the Mollow Triplet Sidebands of a Quantum Dot
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Emission from a resonantly excited quantum emitter is a fascinating research topic within quantum optics and a useful source for different types of quantum light fields. The resonance spectrum consists of a single spectral line which develops into a triplet above saturation of the quantum emitter. The three closely-spaced photon channels from the resonance fluorescence (RF) have different photon statistical signatures. We present a detailed photon-statistics analysis of the RF emission triplet from a solid state-based artificial atom, i.e. a semiconductor quantum dot. The photon correlation measurements demonstrate both 'single' and 'cascaded' photon emission from the Mollow triplet sidebands. The bright and narrow sideband emission (5.9 million photons/second into the first lens) can be conveniently frequency-tuned by laser detuning over 15 times its linewidth (~ 1.0 GHz). These unique properties make the Mollow triplet sideband emission a valuable light source for, e.g. quantum light spectroscopy and quantum information applications.
Publication:
Cascaded Single-Photon Emission from the Mollow Triplet Sidebands of a Quantum Dot
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Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single InxGa1-xAs/GaAs Quantum Dots on the Applied Uniaxial Stress
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We apply external uniaxial stress to tailor the optical properties of In xGa 1-xAs/GaAs quantum dots. Unexpectedly, the emission energy of single quantum dots controllably shifts to both higher and lower energies under tensile strain. Theoretical calculations using a million atom empirical pseudopotential many-body method indicate that the shifting direction and magnitude depend on the lateral extension and more interestingly on the gallium content of the quantum dots. Our experimental results are in good agreement with the underlying theory.
Publication:
Dependence of the Redshifted and Blueshifted Photoluminescence Spectra of Single
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Triggered single-photon emission in the red spectral range from optically excited InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K
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Systematic excitation power and temperature-dependent measurements on the emission lines of single self-assembled InP/(Al 0.20Ga 0.80) 0.51In 0.49P quantum dots embedded in micropillars have been performed. The quantum dots were excited optically via a pulsed laser and their luminescence was collected using a micro-photoluminescence setup. The exciton and biexciton intensity, linewidth, and spectral position was investigated in a temperature range from 4 K up to 130 K. Single-photon emission from the quantum dots is presented up to a temperature of 100 K, confirmed by photon-statistics measurements.
Publication:
Triggered single-photon emission in the red spectral range from optically excited
InP/(Al,Ga)InP quantum dots embedded in micropillars up to 100 K
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Dephasing of Triplet-Sideband Optical Emission of a Resonantly Driven InAs/GaAs Quantum Dot inside a Microcavity
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Detailed properties of resonance fluorescence from a single quantum dot in a micropillar cavity are investigated, with particular focus on emission coherence in the dependence on optical driving field power and detuning. A power-dependent series over a wide range reveals characteristic Mollow triplet spectra with large Rabi splittings of |Ω|≤15GHz. In particular, the effect of dephasing in terms of systematic spectral broadening ~Ω 2 of the Mollow sidebands is observed as a strong fingerprint of excitation-induced dephasing. Our results are in excellent agreement with predictions of a recently presented model on phonon-dressed quantum dot Mollow triplet emission in the cavity-QED regime.
Publication:
Dephasing of Triplet-Sideband Optical Emission of a Resonantly Driven InAs/GaAs Quantum Dot
inside a Microcavity
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Lasing properties of InP/(Ga_0.51In_0.49)P quantum dots in microdisk cavities
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We investigated the photoluminescence from InP quantum dots incorporated in (Ga0.51In0.49)P microdisk structures. With increasing pump power we observe a transition to stimulated emission indicated by the S shape of the input-output curve. This transition is accompanied with a concentration of the emission to one or a few modes exhibiting quality factors on the order of 10 4 at transparency. Time-resolved measurements show that at the same time the photoluminescence decay time considerably decreases. Furthermore, in the transition regime the linewidth of the lasing mode is reduced and the second-order photon correlation function exhibits a reduction of fluctuations as previously reported for lasers with InAs quantum dots in photonic crystal, microdisk and micropillar cavities as the gain medium. The experimental findings are compared with the predictions of a microscopic theory.
Publication:
Lasing properties of InP/(Ga_0.51In_0.49)P quantum dots in microdisk cavities
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Emission characteristics of a highly correlated system of a quantum dot coupled to two distinct micropillar cavity modes
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Nonresonant coupling is a recently discovered phenomenon that allows deeper insight into the interaction of a quantum dot with the surrounding solid state medium. In this work investigations on a quantum dot coupled to two distinct modes of a micro pillar cavity are shown where we focus on the emission characteristics of the quantum dot compared to the two mode emission channels. In cross-correlation measurements, the anti-correlation between all three emission channels is unambiguously demonstrated. While the emission dynamics of the quantum dot is transferred to the spectrally closest mode as proven by temperature-dependent lifetime measurements, the coherence of the mode emission stays at a low constant level unperturbed by the detuning of the emitter to the modes. This effect can be attributed to the additional pure dephasing that the photons undergo while being transferred to either of the modes. Additionally, power-dependent measurements under purely resonant excitation have revealed strong emitter-mode coupling with spectral detunings up to 3.7 meV.
Publication:
Emission characteristics of a highly correlated system of a quantum dot coupled to two distinct
micropillar cavity modes
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Triggered single-photon emission from electrically excited quantum dots
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Pulsed electrical excitation of single InP/GaInP quantum dots was used to achieve triggered single-photon emission in the red spectral range with an excitation repetition rate of up to 200 MHz. ncreased repetition rates were prevented by the finite decay-time of the quantum dots, and autocorrelation measurements with excitation rates above 1 GHz look similar to what is expected for dc injection. However, negative voltage pulses can increase the decay-rate considerably such that 1 GHz excitation rates should be possible.
Publication:
Triggered single-photon emission from electrically excited quantum dots
Contact person: Christian Kessler |
Non-resonant dot-cavity coupling and its potential for resonant single-quantum-dot spectroscopy
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Non-resonant emitter–cavity coupling is a fascinating effect recently observed as unexpected pronounced cavity resonance emission even in strongly detuned single quantum dot–microcavity systems. This phenomenon indicates strong, complex light–matter interactions in these solid-state systems, and has major implications for single-photon sources and quantum information applications.We study non-resonant dot–cavity coupling of individual quantum dots in micropillars under resonant excitation, revealing a pronounced effect over positive and negative quantum dot mode detunings. Our results suggest a dominant role of phonon-mediated dephasing in dot–cavity coupling, giving a new perspective to the controversial discussions ongoing in the literature. Such enhanced insight is essential for various cavity-based quantum electrodynamic systems using emitters that experience phonon coupling, such as colour centres in diamond and colloidal nanocrystals. Non-resonant coupling is demonstrated to be a versatile "monitoring" tool for observing relevant quantum dot s-shell emission properties and background-free photon statistics. In particular, the line broadening of the QD s-shell is “monitored” by the mode signal with high conformity to the directly measured QD linewidth. The mode signal also monitors the saturation behavior of a near Fourier transform-limited photon emission from a resonantly excited QD. We have also investigated the temperature dependence of the coupling mechanism between an off-resonant QD and a cavity mode under pure resonant excitation of the quantum emitter.
Publication:
Non-resonant dot-cavity coupling and its potential for resonant single-quantum-dot
spectroscopy
Publication:
Linewidth broadening and emission saturation of a resonantly excited quantum dot monitored via
an off-resonant cavity mode
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Post-Selected Indistinguishable Photons from the Resonance Fluorescence of a Single Quantum Dot in a Microcavity
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Applying continuous-wave pure resonant s-shell optical excitation of individual quantum dots in a high-quality micropillar cavity, we demonstrate the generation of post-selected indistinguishable photons in resonance fluorescence. Close to ideal visibility contrast of 90% is verified by polarization-dependent Hong-Ou-Mandel two-photon interference measurements. Furthermore, a strictly resonant continuous wave excitation together with controlling the spontaneous emission lifetime of the single quantum dots via tunable emitter-mode coupling (Purcell) is proven as a versatile scheme to generate close to Fourier transform-limited (T 2/(2T 1) = 0.91) single photons even at 80% of the emission saturation level.
Publication:
Post-Selected Indistinguishable Photons from the Resonance Fluorescence of a Single Quantum Dot
in a Microcavity
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Single Semiconductor Quantum Dots Single Semiconductor Quantum Dots
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This book reviews recent advances in the exciting and rapidly growing field of semiconductor quantum dots via contributions from some of the most prominent researchers in the scientific community. Special focus is given to optical, quantum optical, and spin properties of single quantum dots due to their potential applications in devices operating with single electron spins and/or single photons. This includes single and coupled quantum dots in external fields, cavity-quantum electrodynamics, and single and entangled photon pair generation. Single Semiconductor Quantum Dots also addresses growth techniques to allow for a positioned nucleation of dots as well as applications of quantum dots in quantum information technologies.
Publication:
Single Semiconductor Quantum Dots
Contact person: Prof. Dr. P. Michler |
The Dark Exciton State in Quantum Dots
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The influence of the dark exciton state on single InP QDs was investigated. The exciton intensity drops sharply compared to the biexciton with rising pulsed laser excitation power while the opposite is true with temperature. Also, the decay rate is faster for the exciton than the biexciton and the dark-to-bright state spin flip is enhanced with temperature. Furthermore, long-lived dark state related memory effects are observed in second-order cross-correlation measurements between the exciton and biexciton. Therefore, future QD devices based on the exciton decay, such as single-photon sources, or on the biexciton-exciton cascade, such as entangled-photon sources, must take the dark state into account.
Publication:
Influence of the Dark Exciton State on the Optical and Quantum Optical Properties of Single
Quantum Dots
Contact person:
Christian Kessler
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Semiconductor-based Entangled Photon Pair Source Influence of the SE coupling factor beta on the coherence length of microcavity lasers
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A systematic experimental and theoretical study of first-order coherence properties of high beta quantum-dot micropillar lasers is presented. A nonlinear increase in the coherence length is found in the transition regime from spontaneous to dominantly stimulated emission. This increase is accompanied by a qualitative change in the first-order field-correlation function from a Gaussian-type profile to an exponential behavior, which is in excellent agreement with a microscopic semiconductor laser theory. Our results also demonstrate a decreasing coherence length with increasing spontaneous emission coupling beta, thus raising questions about the practicability of high beta lasers for device applications.
Publication:
Influence of the spontaneous optical emission factor beta on the first-order coherence of a
semiconductor microcavity laser
Contact person: Dr. Sven M. Ulrich |
Electrically pumped single-photon emission
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An electrically pumped single-photon emitter in the visible spectral range, working up to 80 K
has been realized using a self-assembled single InP quantum dot embedded in AlGaInP. Aluminum was
added to the barrier material in order to provide a higher QD confinement potential.
Publication:
Electrically pumped single-photon emission in the visible spectral range up to 80 K
Contact person: Christian Kessler |
Semiconductor-based Entangled Photon Pair Source
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Self-assembled InGaAs quantum dots can emit two photons that are in a polarization superposition state, a so called EPR or entangled state. In general, this quantum correlation is reduced by a spin coupling of the charge carriers that create these photons after their recombination. A high-resolution photoluminescence measuring technique allows us to determine the size of the resulting fine structure splitting. We were able to verify the conditions of entangled or classically correlated photon pairs in full consistence with observed fine structure properties. Furthermore, we demonstrate reliable polarization entanglement at elevated sample temperatures up to 30 K.
Publication:
Triggered polarization-entangled photon pairs from a single quantum dot up to 30 K
Contact person: Robert Hafenbrak |
Micropillar Laser Photon Emission Statistics
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Detailed measurements of the first- and second-order coherence properties of quantum dot-based micropillar lasers have been performed and interpreted on the basis of a refined semiconductor laser theory. Under increasing optical excitation the transition into lasing is accompanied by both pronounced photon intensity fluctuations and strong coherence length changes. Our investigations clearly visualize a smooth transition from the regime of spontaneous into predominantly stimulated emission, which becomes harder to determine with high beta values. In our theory, a microscopic approach is used to incorporate the semiconductor nature of QDs. The results are in agreement with the experimental intensity traces and the photon statistics measurements.
Publication:
Photon Statistics of Semiconductor Microcavity Lasers
Contact person: Dr. Sven M. Ulrich |
Micropillar Laser Mode Coherence Properties
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This project addresses the coherence properties of spontaneous and stimulated emission processes from QD-based high quality semiconductor micropillar cavities with elliptical cross-section. Due to the reduced symmetry, a clear polarization splitting of the fundamental emission mode is revealed, in full conformity with an oscillatory behavior found from corresponding g(1)(t) first-order field correlation measurements. In addition, power-dependent g(1)(t) series on a single polarization component of the lasing mode systematically revealed a strong coherence time increase, thus reflecting the change of emission characteristics from thermal to coherent light.
Publication:
Coherence properties of high-ß elliptical semiconductor micropillar lasers
Contact person: Dr. Sven M. Ulrich |
High Aspect Ratio InP Single Quantum Dots
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These InP dots have a very high aspect ratio (ratio of width to height) of approximately 27:1. In general, even at high excitation power densities, the dots with ground-state transition energies above 1.82 eV exhibit only s-shell emission, while the larger dots emitting below 1.82 eV tend to exhibit emission from several (in some cases up to eight) shells. Calculations indicate that this change is due to the smaller dots having only one confined election level while the larger dots have two or more. Time-resolved investigations indicate the presence of fast carrier relaxation and recombination processes for both dot types, however, only the larger dots display clear inter-level relaxation effects as expected. Such QDs are interesting as they allow for a large tuning of the electronic interlevel spacing within the dots without significantly shifting the related ground-state emission energy.
Publication:
Electronic shell structure and carrier dynamics of high aspect ratio InP single quantum dots
Related work:
Single-photon emission from a type-B InP/GaInP quantum dot
Contact person: Christian Kessler |
Semipolar GaInN/GaN Multi-quantum Well Structures
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The carrier lifetime and photoluminescence intensity of semi-polar GaInN/GaN multi-quantum wells (MQWs) has been investigated. The MQWs of both samples are overgrown by a Mg-doped GaN layer in order to form a light emitting diode (LED) structure. The stripes have a triangular shape. The PL decay time is reduced in the case of the semi-polar sample by almost two orders of magnitude to 650 ps at 4 K as a result of the much reduced piezoelectric field. The PL intensity of the semi-polar sample is subsequently more than double that of the polar sample as a result of the improved recombination probability.
Publication:
Time- and locally resolved photoluminescence of semipolar GaInN/GaN facet light emitting
diodes
Contact person: Dr. Michael Jetter |
InP Asymmetric Quantum Dot Pairs InP Asymmetric Quantum Dot Pairs
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Single pairs of vertically stacked asymmetric InP quantum dots embedded in GaInP barriers have been investigated as a function of the inter-dot spacer thickness. Time-integrated and time-resolved photoluminescence measurements have been performed with the former showing a change of the intensity ratio between the two dots and the latter an increasing difference in the photoluminescence decay-time of the two dots with decreasing spacer thickness. Hence, we suggest transitions from vanishing tunnel-coupling to electron tunneling and finally to electron and hole tunneling for successively smaller barrier widths. The results clearly show the nonresonant character of the tunneling process which is due to the different ground state energies (different by approx. 40 meV) of the unequally sized dots.
Publication:
Nonresonant tunneling in single asymmetric pairs of vertically stacked InP quantum dots
Contact person: Christian Kessler |
QD Emission Control and Fine Structure Tuning by Lateral Electric Fields
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The quantum-confined Stark effect (QCSE) of excitonic states in self-assembled (In,Ga)As/GaAs
quantum dots was studied by microphotoluminescence spectroscopy. A similar Stark-shift behavior for
excitons, biexcitons, and a charged state has been observed. Our investigations suggest the absence
of a permanent dipole moment in the lateral quantum dot plane. Values of the polarizability could
be derived for all the investigated states.
Publication:
Influence of lateral electric fields on multiexcitonic transitions and fine structure of single
quantum dots
Contact person: Dr. Sven M. Ulrich |
Lateral Quantum Dot Molecules
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Self-assembled lateral quantum dot molecules that are fabricated by a unique combination of quantum dot growth and atomic layer precise in-situ etching are studied using micro-photoluminescence experiments. The electronic coupling of charge carriers confined in quantum dot molecules is observed using photon correlation experiments. By applying a lateral electric field an electron can be reversibly transferred from one dot to the other. This control potentially allows for the use of such artificial molecules as the basic building block of a quantum computer, that is, as a quantum gate or as a tunable single-photon source. A recent progress could be achieved in embedding the dot molecules in a planar cavity structure which led to a 30 times enhancement of the single-photon emission rate up to almost 1 MHz.
Publication:
2.
Polarization fine-structure and enhanced single-photon emission of self-assembled lateral InGaAs
quantum dot molecules embedded in a planar micro-cavity
Contact person: Matthias Heldmaier |