Showing papers by "Sven Höfling published in 2018"
TL;DR: In this paper, an exciton-polariton topological insulator was shown to be possible without a magnetic field in an array of semiconductor microcavities, where an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array.
Abstract: Topological insulators—materials that are insulating in the bulk but allow electrons to flow on their surface—are striking examples of materials in which topological invariants are manifested in robustness against perturbations such as defects and disorder1. Their most prominent feature is the emergence of edge states at the boundary between areas with different topological properties. The observable physical effect is unidirectional robust transport of these edge states. Topological insulators were originally observed in the integer quantum Hall effect2 (in which conductance is quantized in a strong magnetic field) and subsequently suggested3–5 and observed6 to exist without a magnetic field, by virtue of other effects such as strong spin–orbit interaction. These were systems of correlated electrons. During the past decade, the concepts of topological physics have been introduced into other fields, including microwaves7,8, photonic systems9,10, cold atoms11,12, acoustics13,14 and even mechanics15. Recently, topological insulators were suggested to be possible in exciton-polariton systems16–18 organized as honeycomb (graphene-like) lattices, under the influence of a magnetic field. Exciton-polaritons are part-light, part-matter quasiparticles that emerge from strong coupling of quantum-well excitons and cavity photons19. Accordingly, the predicted topological effects differ from all those demonstrated thus far. Here we demonstrate experimentally an exciton-polariton topological insulator. Our lattice of coupled semiconductor microcavities is excited non-resonantly by a laser, and an applied magnetic field leads to the unidirectional flow of a polariton wavepacket around the edge of the array. This chiral edge mode is populated by a polariton condensation mechanism. We use scanning imaging techniques in real space and Fourier space to measure photoluminescence and thus visualize the mode as it propagates. We demonstrate that the topological edge mode goes around defects, and that its propagation direction can be reversed by inverting the applied magnetic field. Our exciton-polariton topological insulator paves the way for topological phenomena that involve light–matter interaction, amplification and the interaction of exciton-polaritons as a nonlinear many-body system. A part-light, part-matter exciton-polariton topological insulator is created in an array of semiconductor microcavities.
363 citations
TL;DR: Strong light-matter coupling in two-dimensional semiconductors arising from confined excitons interacting with trapped photons or localized plasmons is reviewed.
Abstract: The optical properties of transition metal dichalcogenide monolayers are widely dominated by excitons, Coulomb-bound electron–hole pairs. These quasi-particles exhibit giant oscillator strength and give rise to narrow-band, well-pronounced optical transitions, which can be brought into resonance with electromagnetic fields in microcavities and plasmonic nanostructures. Due to the atomic thinness and robustness of the monolayers, their integration in van der Waals heterostructures provides unique opportunities for engineering strong light-matter coupling. We review first results in this emerging field and outline future opportunities and challenges.
259 citations
TL;DR: The optical properties of transition metal dichalcogenide monolayers are widely dominated by excitons, Coulomb-bound electron-hole pairs as mentioned in this paper, which give rise to narrow-band, well-pronounced optical transitions, which can be brought into resonance with electromagnetic fields in microcavities and plasmonic nanostructures.
Abstract: The optical properties of transition metal dichalcogenide monolayers are widely dominated by excitons, Coulomb-bound electron-hole pairs. These quasi-particles exhibit giant oscillator strength and give rise to narrow-band, well-pronounced optical transitions, which can be brought into resonance with electromagnetic fields in microcavities and plasmonic nanostructures. Due to the atomic thinness and robustness of the monolayers, their integration in van der Waals heterostructures provides unique opportunities for engineering strong light-matter coupling. We review first results in this emerging field and outline future opportunities and challenges.
185 citations
TL;DR: In this article, it was shown that careful tuning of the coupled system allows for a modest photon blockade effect as evidenced by a reduction of simultaneous two-polariton generation probability by 5 %.
Abstract: Cavity-polaritons in semiconductor microstructures have emerged as a promising system for exploring nonequilibrium dynamics of many-body systems. Key advances in this field, including the observation of polariton condensation, superfluidity, realization of topological photonic bands, and dissipative phase transitions, generically allow for a description based on a mean-field Gross-Pitaevskii formalism. While observation of polariton intensity squeezing and decoherence of a polarization entangled photon pair by a polariton condensate provide counter-examples, quantum effects in these experiments show up at high polariton occupancy. Going beyond into the regime of strongly correlated polaritons requires the observation of a photon blockade effect where interactions are strong enough to suppress double occupancy of a photonic lattice site. Here, we report the observation of quantum correlations between polaritons in a fiber cavity which spatially confines polaritons into an area of 3 $\mu$m$^2$. Photon correlation measurements show that careful tuning of the coupled system allows for a modest photon blockade effect as evidenced by a reduction of simultaneous two-polariton generation probability by 5 %. Concurrently, our experiments provide an unequivocal measurement of the polariton interaction strength, thereby resolving the controversy stemming from recent experimental reports. Our findings constitute a first essential step towards the realization of strongly interacting photonic systems.
124 citations
TL;DR: This experiment uses a quantum-dot-micropillar single-photon source demultiplexed into up to seven input ports of a 16×16 mode ultralow-loss photonic circuit, and detects three-, four- and fivefold coincidence counts, and demonstrates that boson sampling with a few photons lost can increase the sampling rate.
Abstract: Boson sampling is a well-defined task that is strongly believed to be intractable for classical computers, but can be efficiently solved by a specific quantum simulator. However, an outstanding problem for large-scale experimental boson sampling is the scalability. Here we report an experiment on boson sampling with photon loss, and demonstrate that boson sampling with a few photons lost can increase the sampling rate. Our experiment uses a quantum-dot-micropillar single-photon source demultiplexed into up to seven input ports of a 16×16 mode ultralow-loss photonic circuit, and we detect three-, four- and fivefold coincidence counts. We implement and validate lossy boson sampling with one and two photons lost, and obtain sampling rates of 187, 13.6, and 0.78 kHz for five-, six-, and seven-photon boson sampling with two photons lost, which is 9.4, 13.9, and 18.0 times faster than the standard boson sampling, respectively. Our experiment shows an approach to significantly enhance the sampling rate of multiphoton boson sampling.
119 citations
TL;DR: In this paper, a strain induced single photon source using a WSe2 monolayer on a silver substrate, coated with a very thin dielectric layer, is described.
Abstract: Atomic monolayers of transition metal dichalcogenides represent an emerging material platform for the implementation of ultracompact quantum light emitters via strain engineering. In this framework, we discuss experimental results on creation of strain induced single photon sources using a WSe2 monolayer on a silver substrate, coated with a very thin dielectric layer. We identify quantum emitters that are formed at various locations in the sample. Their emission is highly linearly polarized, stable in linewidth, and decay times down to 100 ps are observed. We provide numerical calculations of our monolayer-metal device platform to assess the strength of the radiative decay rate enhancement by the presence of the plasmonic structure. We believe that our results represent a crucial step toward the ultracompact integration of high performance single photon sources in nanoplasmonic devices and circuits.
85 citations
TL;DR: In this paper, the authors demonstrate bosonic condensation driven by excitons hosted in an atomically thin layer of MoSe2, strongly coupled to light in a solid-state resonator.
Abstract: Bosonic condensation belongs to the most intriguing phenomena in physics, and was mostly reserved for experiments with ultra-cold quantum gases. More recently, it became accessible in exciton-based solid-state systems at elevated temperatures. Here, we demonstrate bosonic condensation driven by excitons hosted in an atomically thin layer of MoSe2, strongly coupled to light in a solid-state resonator. The structure is operated in the regime of collective strong coupling between a Tamm-plasmon resonance, GaAs quantum well excitons, and two-dimensional excitons confined in the monolayer crystal. Polariton condensation in a monolayer crystal manifests by a superlinear increase of emission intensity from the hybrid polariton mode, its density-dependent blueshift, and a dramatic collapse of the emission linewidth, a hallmark of temporal coherence. Importantly, we observe a significant spin-polarization in the injected polariton condensate, a fingerprint for spin-valley locking in monolayer excitons. Our results pave the way towards highly nonlinear, coherent valleytronic devices and light sources.
55 citations
TL;DR: This work introduces an electronically driven square and honeycomb lattice of exciton polaritons, paving the way towards real world devices based on polariton lattices for on-chip applications.
Abstract: Two-dimensional electronic materials such as graphene and transition metal dichalgenides feature unique electrical and optical properties due to the conspirative effect of band structure, orbital coupling, and crystal symmetry. Synthetic matter, as accomplished by artificial lattice arrangements of cold atoms, molecules, electron patterning, and optical cavities, has emerged to provide manifold intriguing frameworks to likewise realize such scenarios. Exciton polaritons have recently been added to the list of promising candidates for the emulation of system Hamiltonians on a semiconductor platform, offering versatile tools to engineer the potential landscape and to access the nonlinear electro-optical regime. In this work, we introduce an electronically driven square and honeycomb lattice of exciton polaritons, paving the way towards real world devices based on polariton lattices for on-chip applications. Our platform exhibits laserlike emission from high-symmetry points under direct current injection, hinting at the prospect of electrically driven polariton lasers with possibly topologically nontrivial properties.
43 citations
TL;DR: In this paper, transition edge sensors (TESs) are used to resolve the number of photons in an ultraweak optical pulse, allowing the determination of the full photon statistics, which is not possible using standard commercial detectors.
Abstract: Transition edge sensors (TESs) are remarkable detectors that resolve the number of photons in an ultraweak optical pulse, allowing the determination of the full photon statistics, which is not possible using standard commercial detectors. In demonstrating the potential of these TESs for nanophotonics, the authors uncover subtle differences in the optical properties of two bimodal quantum-dot micropillar lasers with nominally similar characteristics, yet different photon-number distributions, whether in standard single-mode lasing or polarization-mode switching.
36 citations
TL;DR: In this article, the impact of a free carrier reservoir on the optical properties of excitonic and trionic complexes in a MoSe2 monolayer at cryogenic temperatures was investigated.
Abstract: The luminescence and absorption properties of transition metal dichalcogenide monolayers are widely determined by neutral and charged excitonic complexes. Here, we focus on the impact of a free carrier reservoir on the optical properties of excitonic and trionic complexes in a MoSe2 monolayer at cryogenic temperatures. By applying photodoping via a non-resonant pump laser, the electron density can be controlled in our sample, which is directly reflected in the contribution of excitons and trions to the luminescence signal. We find significant shifts of both the exciton and trion energies in the presence of an induced electron gas both in power- and in time evolution (on the second to minute scale) in our photoluminescence spectra. In particular, in the presence of the photo-doped carrier reservoir, we observe that the splitting between excitons and trions can be enhanced by up to 4 meV. This behaviour is phenomenologically explained by an interplay between an increased screening of excitons via electrons ...
36 citations
TL;DR: The full photon-number distribution emitted from a Bose condensate of microcavity exciton polaritons confined in a micropillar cavity is measured, paving the way for a full understanding of the contribution of interactions in light-matter condensates in the coherence buildup at threshold.
Abstract: We measure the full photon-number distribution emitted from a Bose condensate of microcavity exciton polaritons confined in a micropillar cavity. The statistics are acquired by means of a photon-number-resolving transition edge sensor. We directly observe that the photon-number distribution evolves with the nonresonant optical excitation power from geometric to quasi-Poissonian statistics, which is canonical for a transition from a thermal to a coherent state. Moreover, the photon-number distribution allows one to evaluate the higher-order photon correlations, shedding further light on the coherence formation and phase transition of the polariton condensate. The experimental data are analyzed in terms of thermal-coherent states, which gives direct access to the thermal and coherent fraction from the measured distributions. These results pave the way for a full understanding of the contribution of interactions in light-matter condensates in the coherence buildup at threshold.
TL;DR: In this article, the authors demonstrate the controlled loading of an exciton-polariton vortex chain into a 1D array of trapping potentials by appropriately shaping an off-resonant pump beam that drives the system to the regime of bosonic condensation.
Abstract: We demonstrate, experimentally and theoretically, controlled loading of an exciton-polariton vortex chain into a 1D array of trapping potentials Switching between two types of vortex chains, with topological charges of the same or alternating signs, is achieved by appropriately shaping an off-resonant pump beam that drives the system to the regime of bosonic condensation In analogy to spin chains, these vortex sequences realize either a "ferromagnetic" or an "antiferromagnetic" order, whereby the role of spin is played by the orbital angular momentum The ferromagnetic ordering of vortices is associated with the formation of a persistent chiral current Our results pave the way for the controlled creation of nontrivial distributions of orbital angular momentum and topological order in a periodic exciton-polariton system
TL;DR: Coupling of site-selectively induced quantum emitters in exfoliated monolayers of WSe2 to plasmonic nanostructures represents a significant step towards the scalable implementation of coupled quantum emitter-resonator systems for highly integrated quantum photonic and plAsmonic applications.
Abstract: We discuss coupling of site-selectively induced quantum emitters in exfoliated monolayers of WSe2 to plasmonic nanostructures. Gold nanorods of 20 nm-240 nm size, which are arranged in pitches of a few micrometers on a dielectric surface, act as seeds for the formation of quantum emitters in the atomically thin materials. We observe characteristic narrow-band emission signals from the monolayers, which correspond well with the positions of the metallic nanopillars with and without thin dielectric coating. Single photon emission from the emitters is confirmed by autocorrelation measurements, yielding g2(τ = 0) values as low as 0.17. Moreover, we observe a strong co-polarization of our single photon emitters with the frequency matched plasmonic resonances, as a consequence of light-matter coupling. Our work represents a significant step towards the scalable implementation of coupled quantum emitter-resonator systems for highly integrated quantum photonic and plasmonic applications.
TL;DR: In this article, a two-level system based on a semiconductor quantum dot (QD), which is excited resonantly by a fiber-coupled electrically driven micropillar laser, is presented.
Abstract: Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state. Most interesting is the strict resonant excitation of such emitters to control their occupation coherently and to generate close to ideal quantum light, which is of utmost importance for applications in photonic quantum technology. To date, the approaches and experiments in this field have been performed exclusively using bulky lasers, which hinders the application of resonantly driven two-level emitters in compact photonic quantum systems. Here we address this issue and present a concept for a compact resonantly driven single-photon source by performing quantum-optical spectroscopy of a two-level system using a compact high-β microlaser as the excitation source. The two-level system is based on a semiconductor quantum dot (QD), which is excited resonantly by a fiber-coupled electrically driven micropillar laser. We dress the excitonic state of the QD under continuous wave excitation, and trigger the emission of single photons with strong multi-photon suppression (
$$\, g^{(2)}(0) = 0.02$$
) and high photon indistinguishability (V = 57±9%) via pulsed resonant excitation at 156 MHz. These results clearly demonstrate the high potential of our resonant excitation scheme, which can pave the way for compact electrically driven quantum light sources with excellent quantum properties to enable the implementation of advanced quantum communication protocols. Sending encrypted quantum data over long distances is set to become more feasible using a low-cost system for generating photons one at a time. Repeating signals in a quantum network requires techniques for emitting single photons that preserve information such as polarization states. Stephan Reitzenstein from the Technische Universitat Berlin, Germany, and co-workers report that bulky lasers used in typical quantum repeaters can be downsized using low-dimensional semiconductor nanostructures known as quantum dots. They fabricated micropillar structures, each containing aluminum–gallium–arsenic-based quantum dots as active medium, which produce coherent laser pulses when electrically stimulated. By directing the micropillar-driven pulses onto another quantum dot that resonates after absorbing laser light, the team triggered emission of high-quality, individual photons that may be beneficial for the implementation of long-distance quantum communication protocols.
TL;DR: By increasing the pump power beyond the condensation threshold, temporal coherence significantly improves in devices with increased spatial confinement, as revealed in the transition from thermal to coherent statistics of the emitted light.
Abstract: We study the influence of spatial confinement on the second-order temporal coherence of the emission from a semiconductor microcavity in the strong coupling regime. The confinement, provided by etched micropillars, has a favorable impact on the temporal coherence of solid state quasicondensates that evolve in our device above threshold. By fitting the experimental data with a microscopic quantum theory based on a quantum jump approach, we scrutinize the influence of pump power and confinement and find that phonon-mediated transitions are enhanced in the case of a confined structure, in which the modes split into a discrete set. By increasing the pump power beyond the condensation threshold, temporal coherence significantly improves in devices with increased spatial confinement, as revealed in the transition from thermal to coherent statistics of the emitted light.
TL;DR: In this article, a site-selectively induced quantum emitters in exfoliated monolayers of WSe$_2$ to plasmonic nanostructures are discussed.
Abstract: We discuss coupling of site-selectively induced quantum emitters in exfoliated monolayers of WSe$_2$ to plasmonic nanostructures. Squared and rectangular gold nanopillars, which are arranged in pitches of \SI{4}{\micro\meter} on the surface, have sizes of tens of nanometers, and act as seeds for the formation of quantum emitters in the atomically thin materials. We observe chraracteristic narrow-band emission signals from the monolayers, which correspond well with the positions of the metallic nanopillars with and without thin dielectric coating. Single photon emission from the emitters is confirmed by autocorrelation measurements, yielding $g^{2}(\tau=0)$ values as low as 0.17. Moreover, we observe a strong co-polarization of our single photon emitters with the frequency matched plasmonic resonances, indicating deterministic light-matter coupling. Our work represents a significant step towards the scalable implementation of coupled quantum emitter-resonator systems for highly integrated quantum photonic and plasmonics applications.
20 Nov 2018
TL;DR: In this article, the authors measured the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique.
Abstract: While the advanced coherent control of qubits is now routinely carried out in low-frequency (gigahertz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the terahertz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing microspectroscopy, we here measure the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain, this oscillation generates the Autler–Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the four-wave mixing dynamics on the picosecond time scale, because it leads to transitions between the dressed states.
TL;DR: In this paper, the interference properties of a single-photon source based on a In(Ga)As quantum dot embedded in a quasiplanar GaAs microcavity were investigated.
Abstract: We report a joint experimental and theoretical study of the interference properties of a single-photon source based on a In(Ga)As quantum dot embedded in a quasiplanar GaAs microcavity. Using resonant laser excitation with a pulse separation of 2 ns, we find near-perfect interference of the emitted photons, and a corresponding indistinguishability of $\mathcal{I}=(99.6{\phantom{\rule{0.16em}{0ex}}}_{\ensuremath{-}\phantom{\rule{0.16em}{0ex}}1.4}^{+\phantom{\rule{0.16em}{0ex}}0.4})%$. For larger pulse separations, quasiresonant excitation conditions, increasing pump power, or with increasing temperature, the interference contrast is progressively and notably reduced. We present a systematic study of the relevant dephasing mechanisms and explain our results in the framework of a microscopic model of our system. For strictly resonant excitation, we show that photon indistinguishability is independent of pump power, but strongly influenced by virtual phonon-assisted processes which are not evident in excitonic Rabi oscillations.
TL;DR: In this article, a resonant tunneling diode-photodetectors (RTD-PDs) with GaAs0.64In0.36As 0.33Sb0.67 absorption layer covering the fingerprint absorption lines of various gases in the mid-infrared wavelength spectral region is presented.
Abstract: We present resonant tunneling diode-photodetectors (RTD-PDs) with GaAs0.15Sb0.85/AlAs0.1Sb0.9 double barrier structures combined with an additional quaternary Ga0.64In0.36As0.33Sb0.67 absorption layer covering the fingerprint absorption lines of various gases in the mid-infrared wavelength spectral region. The absorption layer cut-off wavelength is determined to be 3.5 μm, and the RTD-PDs show peak-to-valley current ratios up to 4.3 with a peak current density of 12 A/cm−2. The incorporation of the quaternary absorption layer enables the RTD-PDs to be sensitive to illumination with light up to the absorption lines of HCl at 3395 nm. At this wavelength, the detector shows a responsivity of 6.3 mA/W. At the absorption lines of CO2 and CO at 2004 nm and 2330 nm, respectively, the RTD-PDs reach responsivities up to 0.97 A/W. Thus, RTD-PDs pave the way towards high sensitive mid-infrared detectors that can be utilized in tunable laser absorption spectroscopy.
TL;DR: In this paper, the authors measured the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot and revealed the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence.
Abstract: While the advanced coherent control of qubits is now routinely carried out in low frequency (GHz) systems like single spins, it is far more challenging to achieve for two-level systems in the optical domain. This is because the latter evolve typically in the THz range, calling for tools of ultrafast, coherent, nonlinear optics. Using four-wave mixing micro-spectroscopy, we here measure the optically driven dynamics of a single exciton quantum state confined in a semiconductor quantum dot. In a combined experimental and theoretical approach, we reveal the intrinsic Rabi oscillation dynamics by monitoring both central exciton quantities, i.e., its occupation and the microscopic coherence, as resolved by the four-wave mixing technique. In the frequency domain this oscillation generates the Autler-Townes splitting of the light-exciton dressed states, directly seen in the four-wave mixing spectra. We further demonstrate that the coupling to acoustic phonons strongly influences the FWM dynamics on the picosecond timescale, because it leads to transitions between the dressed states.
TL;DR: In this article, the authors demonstrate the tunability of an open microcavity with an embedded active organic layer providing parallel alignment of molecular transition dipole moments as well as strong self-absorption inside the cavity.
Abstract: Open microcavities represent a versatile cavity design that allows the external control of internal properties such as cavity thickness and mode detuning without changing the key parameters of the cavity itself, rendering them particularly interesting for light–matter interaction experiments. Here, we demonstrate the tunability of an open microcavity with an embedded active organic layer providing parallel alignment of molecular transition dipole moments as well as strong self-absorption inside the cavity. By decreasing the cavity thickness, we observe a transition from the weak coupling regime into the strong coupling regime evidenced by the onset of avoided crossing behavior between involved modes. This change of coupling mechanism is shown for 2D (planar) as well as 0D (hemispherical) cavities.
TL;DR: This work experimentally and theoretically investigates the effects of delayed optical feedback on the mode-switching dynamics of an electrically driven bimodal quantum-dot micropillar laser, characterizing its impact on the micropills' output power, optical spectrum and photon statistics.
Abstract: Microlasers are ideal candidates to bring the fascinating variety of nonlinear complex dynamics found in delay-coupled systems to the realm of quantum optics. Particularly attractive is the possibility of tailoring the devices' emission properties via non-invasive delayed optical coupling. However, until now scarce research has been done in this direction. Here, we experimentally and theoretically investigate the effects of delayed optical feedback on the mode-switching dynamics of an electrically driven bimodal quantum-dot micropillar laser, characterizing its impact on the micropillar's output power, optical spectrum and photon statistics. Feedback is found to influence the switching dynamics and its characteristics time scales. In addition, stochastic switching is reduced with the subsequent impact on the microlaser photon statistics. Our results contribute to the comprehension of feedback-induced phenomena in micropillar lasers and pave the way towards the external control and tailoring of the properties of these key systems for the nanophotonics community.
01 Aug 2018
TL;DR: In this article, a source with optimized nonlinearity for preparing time-bin entangled photons in the telecommunication wavelength range was used for constructing entangled photon pairs in a single photon detector.
Abstract: Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state’s density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of 88.9(1.8)% and a fidelity of 94.2(9)% with respect to a Bell state.
TL;DR: In this paper, a source with optimized nonlinearity for preparing time-bin entangled photons in the telecommunication wavelength range was used for building up integrated quantum optics devices, and the tomographic reconstruction of the state's density matrix reveals that the source exhibits a high degree of entanglement.
Abstract: Semiconductor Bragg-reflection waveguides are well-established sources of correlated photon pairs as well as promising candidates for building up integrated quantum optics devices. Here, we use such a source with optimized non-linearity for preparing time-bin entangled photons in the telecommunication wavelength range. By taking advantage of pulsed state preparation and efficient free-running single-photon detection, we drive our source at low pump powers, which results in a strong photon-pair correlation. The tomographic reconstruction of the state's density matrix reveals that our source exhibits a high degree of entanglement. We extract a concurrence of $88.9\pm 1.8\%$ and a fidelity of $94.2 \pm 0.9\%$ with respect to a Bell state.
TL;DR: The authors demonstrate the formation of a bosonic condensate driven by excitons in two-dimensional MoSe2 strongly coupled to light in a solid-state resonator, paving the way towards highly nonlinear, coherent valleytronic devices and light sources.
Abstract: Condensation of bosons into a macroscopic quantum state belongs to the most intriguing phenomena in nature. It was first realized in quantum gases of ultra-cold atoms, but more recently became accessible in open-dissipative, exciton-based solid-state systems at elevated temperatures. Semiconducting monolayer crystals have emerged as a new platform for studies of strongly bound excitons in ultimately thin materials. Here, we demonstrate the formation of a bosonic condensate driven by excitons hosted in an atomically thin layer of MoSe2, strongly coupled to light in a solid-state resonator. The structure is operated in the regime of collective strong coupling, giving rise to hybrid exciton-polariton modes composed of a Tamm-plasmon resonance, GaAs quantum well excitons and two-dimensional excitons confined in a monolayer of MoSe2. Polariton condensation in a monolayer crystal manifests by a superlinear increase of emission intensity from the hybrid polariton mode at injection powers as low as 4.8 pJ/pulse, as well as its density-dependent blueshift and a dramatic collapse of the emission linewidth as a hallmark of temporal coherence. Importantly, we observe a significant spin-polarization in the injected polariton condensate, a fingerprint of the core property of monolayer excitons subject to spin-valley locking. The observed effects clearly underpin the perspective of building novel highly non-linear valleytronic devices based on light-matter fluids, coherent bosonic light sources based on atomically thin materials, and paves the way towards studying materials with unconventional topological properties in the framework of bosonic condensation.
Posted Content•
TL;DR: In this article, a new approach to integrate single layer MoSeR2R and WSeR 2R flakes into a monolithic all-dielectric planar high-quality micro-cavities is presented.
Abstract: We demonstrate a new approach to integrate single layer MoSeR2R and WSeR2R flakes into monolithic all-dielectric planar high-quality micro-cavities. These distributed-Bragg-reflector (DBR) cavities may e.g. be tuned to match the exciton resonance of the 2D-materials. They are highly robust and compatible with cryogenic and room-temperature operation. The integration is achieved by a customized ion-assisted physical vapor deposition technique, which does not degrade the optical properties of the 2D-materials. The monolithic 2D resonator is shown to have a high Q-factor in excess of 4500. We use photoluminescence (PL) experiments to demonstrate that the coating procedure with an SiO2 coating on a prepared surface does not significantly alter the electrooptical properties of the 2D-materials. Moreover, we observe a resonance induced modification of the PL-spectrum for the DBR embedded flake. Our system thus represents a versatile platform to resonantly enhance and tailor light-matter-interaction in 2D-materials. The gentle processing conditions would also allow the integration of other sensitive materials into these highly resonant structures.
25 Jan 2018
TL;DR: In this paper, the authors proposed a method to use the European Research Council (ERC) (EnSeNa 257531); State of Bavaria; China Scholarship Council (201503170272); and German Research Foundation (DFG) (SCHN1376/2.2.1);
Abstract: Austrian Science Fund (FWF) (I-2065, J-4125); German Research Foundation (DFG) (SCHN1376/2-1); European Research Council (ERC) (EnSeNa 257531); State of Bavaria; China Scholarship Council (201503170272)
TL;DR: In this article, a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths, is discussed.
Abstract: In this work, we discuss a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths. The nanostructures are embedded inside lithographically defined, in-plane asymmetric photonic mesa structures, which generate polarization-dependent photonic confinement. First, we study the influence of the photonic confinement on the polarization anisotropy of the emission by photoluminescence spectroscopy, and we find evidence of different contributions to a degree of linear polarization (DOLP), i.e., from the quantum dash and the photonic mesa, in total giving rise to $\mathrm{DOLP}=0.85$. Then, we perform finite-difference time-domain simulations of photonic confinement, and we calculate the DOLP in a dipole approximation showing well-matched results for the established model. Furthermore, by using numerical calculations, we demonstrate several types of photonic confinements where highly linearly polarized emission with DOLP of about 0.9 is possible by controlling the position of a quantum emitter inside the photonic structure. Then, we elaborate on anisotropic quantum emitters allowing for exceeding $\mathrm{DOLP}=0.95$ in an optimized case, and we discuss the ways towards efficient linearly polarized single photon source at telecom bands.
TL;DR: In this article, the authors are grateful for financial support from the State of Bavaria, the German Ministry of Education and Research (BMBF), via the national project HIRT (Grant No. FKZ 13XP5003B).
Abstract: The authors are grateful for financial support from the State of Bavaria, the German Ministry of Education and Research (BMBF) via the national project HIRT (Grant No. FKZ 13XP5003B).
TL;DR: It is demonstrated that a higher photon yield at a lower background on biocompatible metal-dielectric nanocoatings substantially improves SMLM performance and increases the localization precision by up to a factor of two.
Abstract: Single-molecule localization microscopy (SMLM) aims for maximized precision and a high signal-to-noise ratio1. Both features can be provided by placing the emitter in front of a metal-dielectric nanocoating that acts as a tuned mirror2-4. Here, we demonstrate that a higher photon yield at a lower background on biocompatible metal-dielectric nanocoatings substantially improves SMLM performance and increases the localization precision by up to a factor of two. The resolution improvement relies solely on easy-to-fabricate nanocoatings on standard glass coverslips and is spectrally and spatially tunable by the layer design and wavelength, as experimentally demonstrated for dual-color SMLM in cells.