Showing papers by "Stephan Reitzenstein published in 2013"
09 Jun 2013
TL;DR: Polariton lasing under electrical pumping is observed in a multi-quantum well microcavity as mentioned in this paper, and the system's hybrid nature of part light and part matter is probed by measuring the Zeeman-splitting of the microcave mode in the regime of polariton Lasing.
Abstract: Polariton lasing under electrical pumping is observed in a multi quantum well microcavity. The system’s hybrid nature of part light and part matter is probed by measuring the Zeeman-splitting of the microcavity mode in the regime of polariton lasing.
158 citations
TL;DR: In this paper, a deterministic fabrication of sub-μm mesa-structures containing single quantum dots (QDs) by in situ electron-beam lithography was reported.
Abstract: We report on the deterministic fabrication of sub-μm mesa-structures containing single quantum dots (QDs) by in situ electron-beam lithography. The fabrication method is based on a two-step lithography process: After detecting the position and spectral features of single InGaAs QDs by cathodoluminescence (CL) spectroscopy, circular sub-μm mesa-structures are defined by high-resolution electron-beam lithography and subsequent etching. Micro-photoluminescence spectroscopy demonstrates the high optical quality of the single-QD mesa-structures with emission linewidths below 15 μeV and g(2)(0) = 0.04. Our lithography method has an alignment precision better than 100 nm which paves the way for a fully deterministic device technology using in situ CL lithography.
102 citations
TL;DR: In this paper, a deterministic fabrication of sub-um mesa structures containing single quantum dots by in-situ electron-beam lithography was reported. But the fabrication method is based on a two-step lithography process using a low-temperature cathodoluminescence (CL) spectroscopy setup.
Abstract: We report on the deterministic fabrication of sub-um mesa structures containing single quantum dots by in-situ electron-beam lithography. The fabrication method is based on a two-step lithography process using a low-temperature cathodoluminescence (CL) spectroscopy setup. In the first step the position and spectral features of single InGaAs quantum dots (QDs) are detected by CL. Then circular sub-um mesa-structures are exactly defined by high-resolution electron-beam lithography and subsequent etching in the second step. CL spectroscopy and micro-photoluminscence spectroscopy demonstrate the high optical quality of the single-QD mesa-structures with emission linewidths below 15 ueV and g(2)(0) = 0.04. Our lithography method allows for an alignment precision better than 100 nm which paves the way for a fully-deterministic device technology using in-situ CL lithography.
78 citations
TL;DR: A scheme to control cavity quantum electrodynamics in the single photon limit by delayed feedback by treating the quantum correlation of external and internal light modes dynamically and demonstrating a possible way to implement a fully quantum mechanical time-delayed feedback.
Abstract: We propose a scheme to control cavity quantum electrodynamics in the single photon limit by delayed feedback. In our approach a single emitter-cavity system, operating in the weak coupling limit, can be driven into the strong coupling-type regime by an external mirror: The external loop produces Rabi oscillations directly connected to the electron-photon coupling strength. As an expansion of typical cavity quantum electrodynamics, we treat the quantum correlation of external and internal light modes dynamically and demonstrate a possible way to implement a fully quantum mechanical time-delayed feedback. Our theoretical approach proposes a way to experimentally feedback control quantum correlations in the single photon limit.
72 citations
TL;DR: 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.
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.
62 citations
TL;DR: In this paper, the authors investigated correlations between orthogonally polarized cavity modes of a bimodal micropillar laser with a single layer of self-assembled quantum dots in the active region.
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 autocorrelation function ${g}^{(2)}(\ensuremath{\tau})$ 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 superthermal 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 cross-correlation measurements revealing a clear anticorrelation between emission events of the two modes The experimental studies are in 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 a phenomenological birth-death model extended to 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 pump rates around threshold
59 citations
TL;DR: The controlled coherent coupling of spatially separated quantum dots via the photon mode of a solid state microresonator using the strong exciton–photon coupling regime is demonstrated by two-dimensional spectroscopy of the sample's coherent response, a sensitive probe of the coherent coupling.
Abstract: Controlled non-local energy and coherence transfer enables light harvesting in photosynthesis and non-local logical operations in quantum computing. This process is intuitively pictured by a pair of mechanical oscillators, coupled by a spring, allowing for a reversible exchange of excitation. On a microscopic level, the most relevant mechanism of coherent coupling of distant quantum bits—like trapped ions, superconducting qubits or excitons confined in semiconductor quantum dots—is coupling via the electromagnetic field. Here we demonstrate the controlled coherent coupling of spatially separated quantum dots via the photon mode of a solid state microresonator using the strong exciton–photon coupling regime. This is enabled by two-dimensional spectroscopy of the sample’s coherent response, a sensitive probe of the coherent coupling. The results are quantitatively understood in a rigorous description of the cavity-mediated coupling of the quantum dot excitons. This mechanism can be used, for instance in photonic crystal cavity networks, to enable a long-range, non-local coherent coupling.
59 citations
TL;DR: In this article, a combined experimental and theoretical study of two-photon emission from the biexciton cascade in single GaN quantum dots is presented, which highlights how photon statistics can be steered between one-and twophoton decay processes towards an increased, bunched two photon emission probability up to 50 K with the perspective for efficient photon pair generation in the UV spectral range.
Abstract: We present a combined experimental and theoretical study of two-photon emission from the biexciton cascade in single GaN quantum dots. By changing the biexciton binding energy, pump power, and temperature, the balance between the one- and two-photon decay processes is controlled in this four-level system, which drastically affects the photon statistics of the resulting emission. As the most pronounced feature of this interplay we observe a bunching phenomenon and a transition from sub- to super-Poissonian photon statistics, originating from the complex nature of the biexciton cascade. This work highlights how photon statistics can be steered between one- and two-photon processes towards an increased, bunched two-photon emission probability up to 50 K with the perspective for efficient photon pair generation in the UV spectral range.
46 citations
TL;DR: A novel method for selecting certain lasing modes from a whispering gallery mode (WGM) spectrum of electrically pumped microrings is presented and it is shown that the notches act as scattering centers, suppressing modes that have maxima in intensity at the notch position.
Abstract: Within this paper a novel method for selecting certain lasing modes from a whispering gallery mode (WGM) spectrum of electrically pumped microrings is presented. Selection is achieved by introducing sub-wavelength sized notches of about 50nm width and 500nm depth to the sidewalls of ring shaped quantum dot micro cavities with 80µm diameter and ridge widths below 2µm. It is shown that the notches act as scattering centers, suppressing modes that have maxima in intensity at the notch position. By a variation of the angle between the notches, different repetitive patterns of lasing modes and suppressed modes are conceivable.
28 citations
TL;DR: In this article, a detailed study of the threshold pump power and the spontaneous emission β factor in the lasing regime for different diameters dc is presented, demonstrating a reduction in power by over 2 orders of magnitude from dc 2.25 µm down to 0.95 µm.
Abstract: We report on lasing in optically pumped adiabatic micropillar cavities, based on the AlAs/GaAs material system. A detailed study of the threshold pump power and the spontaneous emission β factor in the lasing regime for different diameters dc is presented. We demonstrate a reduction of the threshold pump power by over 2 orders of magnitude from dc = 2.25 μm down to 0.95 μm. Lasing with β factors exceeding 0.5 shows that adiabatic micropillars are operating deeply in the cavity quantum electrodynamics regime.
27 citations
TL;DR: In this article, an external mirror was used to control the laser characteristics of high-β microlaser emission modes in terms of output power, coherence time and photon statistics.
Abstract: We report on electrically pumped quantum dot–microlasers in the presence of polarized self-feedback. The high-β microlasers show two orthogonal, linearly polarized emission modes which are coupled via the common gain medium. This coupling is explained in terms of gain competition between the two lasing modes and leads to distinct differences in their input–output characteristics. By applying polarized self-feedback via an external mirror, we are able to control the laser characteristics of the emission modes in terms of the output power, the coherence time and the photon statistics. We find that linearly polarized self-feedback stabilizes the lasing of a given mode, while cross-polarized feedback between the two modes reduces strongly the intensity of the other emission mode showing particular high-intensity fluctuations and even super-thermal values of the photon autocorrelation function g(2)(τ) at zero delay. Measurements of g(2)(τ) under external feedback also allow us to detect revival peaks associated with the round trip time of the external cavity. Analyzing the damping and shape of the g(2)(τ) revival peaks by a phenomenological model provides us insight into the underlying physics such as the effective exciton lifetime and gain characteristics of the quantum dots in the active region of these microlasers.
TL;DR: In this paper, a thermal hopping model was proposed to transfer electron-hole pairs within two separate sets of zero-dimensional states of considerably different densities connected by a two-dimensional mobility channel.
Abstract: Carrier relaxation processes have been studied in low indium content self-assembled (In,Ga)As/GaAs quantum dots (QDs). Temperature-dependent photoluminescence of the wetting layer (WL) and QDs, and QD photoluminescence rise time elongation from $\ensuremath{\sim}$100 to $\ensuremath{\sim}$200 ps in the range of 10--45 K, indicated a complex carrier relaxation scheme. It involves localization of carriers/excitons in the WL, their temperature-mediated release, and subsequent transfer between the states of the WL and QD ensemble. These observations are explained by a thermal hopping model, in which electron-hole pairs are redistributed within two separate sets of zero-dimensional states of considerably different densities connected by a two-dimensional mobility channel.
TL;DR: In this paper, the authors measured and modeled coherent anharmonic response of a strongly coupled exciton-cavity system at resonance and demonstrated a larger polariton splitting with respect to the vacuum Rabi splitting.
Abstract: Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes–Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton–cavity system at resonance. Injecting two photons into the cavity, we demonstrate a $\sqrt {2}$ larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime.
TL;DR: In this paper, the formation of spatially confined exciton-polaritons under electrical injection in a textured microcavity was reported, and the polaritonic resonances of traps with diameters of 10 and 2μm were studied by angular-resolved electroluminescence spectroscopy.
Abstract: We report on the formation of spatially confined exciton-polaritons under electrical injection in a textured microcavity. The trapping of polaritons in the diode sample is achieved through a locally elongated GaAs microcavity with a quality factor exceeding 6000. The polaritonic resonances of traps with diameters of 10 μm and 2 μm are studied by angular-resolved electroluminescence spectroscopy, revealing their hybrid light-matter nature.
TL;DR: A diode incorporating a large number of GaAs quantum wells that emits light from exciton-polariton states at room temperature is presented and electroluminescence studies reveal two polariton branches which are spectrally separated.
Abstract: We present a diode incorporating a large number (12) of GaAs quantum wells that emits light from exciton-polariton states at room temperature. A reversely biased tunnel junction is placed in the cavity region to improve current injection into the device. Electroluminescence studies reveal two polariton branches which are spectrally separated by a Rabi splitting of 6.5 meV. We observe an anticrossing of the two branches when the temperature is lowered below room temperature as well as a Stark shift of both branches in a bias dependent photoluminescence measurement.
TL;DR: In this paper, the optical characterization of site-controlled InP/GaInP quantum dots (QDs) is presented, revealing a yield of ∼90% of optically active, positioned QDs and a strong suppression of emitters on interstitial positions.
Abstract: We report on the optical characterization of site-controlled InP/GaInP quantum dots (QDs). Spatially resolved low temperature cathodoluminescence proves the long-range ordering of the buried emitters, revealing a yield of ∼90% of optically active, positioned QDs and a strong suppression of emitters on interstitial positions. The emission of single QDs shows a pronounced degree of linear polarization along the [0,−1,1] crystal axis with an average degree of polarization of 94%. Photon correlation measurements of the emission from a single QD indicate the single-photon character of the exciton and biexciton emission lines as well as the cascaded nature of the photon pair.
05 Aug 2013
TL;DR: In this article, the magnetic properties of trapped polariton modes were investigated in a single InGaAs quantum well microresonator with a lithographically defined modulation of the cavity length.
Abstract: We report on pronounced magneto-optical effects of trapped polariton modes in a single InGaAs quantum well microresonator with a lithographically defined modulation of the cavity length. In our optical polariton traps with diameters ranging from 1 to 10 μm, a confinement potential of 7.5 meV is achieved. In magnetic-field dependent experiments, a diamagnetic shift and a Zeeman splitting of the trap-modes are observed which confirms that the polaritonic nature of the quantized emission modes are preserved even for traps as small as 1 μm. Furthermore, focusing on theoretical estimates using a simple model, we have identified a clear correlation between the polaritons' magnetic response and their excitonic fraction, corresponding to the Hopfield coefficients of the composite particles.
TL;DR: In this article, the first successful realization of an electrically pumped polariton laser based on a GaAs/AlAs distributed Bragg reflector cavity was presented, and the system's response to an applied magnetic field was identified as a sensitive tool to distinguish a polariton LAS from a standard VCSEL device in the weak light-matter coupling regime.
Abstract: Polariton Lasers do not rely on stimulated emission of photons, a criterion that sets stringent conditions on the threshold current in a conventional laser. Therefore, they have the capability to outperform photon lasers in the weak coupling regime in terms of the threshold power consumption. We present the first successful realization of an electrically pumped polariton laser based on a GaAs/AlAs distributed Bragg reflector cavity. We have furthermore identified the system’s response to an applied magnetic field as a sensitive tool to distinguish a polariton laser from a standard VCSEL device in the weak light-matter coupling regime
12 Nov 2013
TL;DR: A new type of electrically pumped semiconductor laser has been demonstrated which promises an energy efficient laser operation: Recent achievements in the field of polariton-laser development are presented and an outlook is given as mentioned in this paper.
Abstract: A new type of electrically pumped semiconductor laser has been demonstrated which promises an energy efficient laser operation: Recent achievements in the field of ‘polariton-laser’ development are presented and an outlook is given.
19 May 2013
TL;DR: In this paper, the buried oxide current-aperture in a pin diode-structure was used to create a strain field for the self-aligned nucleation of site-controlled single quantum dots.
Abstract: The buried oxide current-aperture in a pin diode-structure is used to create a strain field for the self-aligned nucleation of site-controlled single quantum dots. A single-photon source fabricated applying this approach shows spectrally very narrow emission lines (FWHM ≤ 25 μeV) and spectrally pure single-photon emission with a second-order autocorrelation g(2)(0) = 0.05.
12 May 2013
TL;DR: In this article, a novel concept for on-chip quantum optics and fully integrated quantum light sources is presented, which combines so far independent routes in the emerging field of cQED in solid state within an integrated nanophotonics device concept with unprecedented features.
Abstract: In this contribution, a novel concept for on-chip quantum optics and fully integrated quantum light sources is presented. The concept combines so far independent routes in the emerging field of cQED in solid state within an integrated nanophotonics device concept with unprecedented features. The proposed concept utilizes the fact that micropillar cavities allow for the localization of vertically emitting modes and laterally emitting whispering gallery modes (WGMs). This approach takes advantage of this unique opportunity provided by the micropillar geometry and comprises an electrically pumped WGM micropillar acting as in-plane laser source and radially displaced QD-micropillars which are optically pumped by the integrated microlaser. This specific configuration allows for the first time on-chip quantum optics in the cQED regime using an integrated coherent light source.
TL;DR: In this article, a novel adiabatic design where Bloch-wave engineering is employed to improve the mode matching is presented, allowing the demonstration of a record-high vacuum Rabi splitting of 85 μe V and a Q of 13600 for a 850 nm diameter micropillar.
Abstract: The semiconductor micropillar is attractive for cavity QED experiments. For strong coupling, the figure of merit is proportional to Q/√V , and a design combining a high Q and a low mode volume V is thus desired. However, for the standard submicron diameter design, poor mode matching between the cavity and the DBR Bloch mode limits the Q . We present a novel adiabatic design where Bloch-wave engineering is employed to improve the mode matching, allowing the demonstration of a record-high vacuum Rabi splitting of 85 μe V and a Q of 13600 for a 850 nm diameter micropillar.
12 May 2013
TL;DR: The field of quantum key distribution has made rapid advances in the past years and commercial QKD systems are available and research systems have reached GHz repetition rates and distances beyond 200 km as discussed by the authors.
Abstract: Summary form only given. The field of quantum key distribution has made rapid advances in the past years. Networks of QKD links were implemented, commercial QKD systems are available and research systems have reached GHz repetition rates and distances beyond 200 km. Usually decoy protocols with attenuated laser light pulses are used, where the asymptotic key rate of a QKD system is proportional to the fraction of single photon pulses sent [1]. Single photon sources (SPSs) intrinsically have a higher single photon fraction and thus reach higher key rates.
28 Oct 2013
TL;DR: In this paper, the non-linear polariton emission caused by stimulated scattering in micropillar cavities under electrical pumping is discussed. But the authors distinguish their polariton laser from a conventional cavity mediated laser by probing it in a magnetic field.
Abstract: Exciton-polaritons are hybrid light-matter quasiparticles. They are composite and interacting bosons which can condense dynamically in a single-particle ground state via stimulated scattering. The formation of exciton-polaritons under electrical pumping has been demonstrated in quasi two dimensional systems [1-3]. In this work, we discuss the non-linear polariton emission caused by stimulated scattering in micropillar cavities under electrical pumping [4]. We distinguish our polariton laser from a conventional cavity mediated laser by probing it in a magnetic field. While a characteristic Zeeman-splitting is present in the regime of polariton lasing [4,5], it is fully absent when the device enters the weak coupling regime.