arXiv subjects

Sven Höfling

Publications and source records attributed to Sven Höfling.

At least 73 records · Page 4Linked to original sources

arXiv2024

Optical properties and dynamics of direct and spatially and momentum indirect excitons in AlGaAs/AlAs quantum wells

We present an experimental study on optical properties and dynamics of direct and spatially and momentum indirect excitons in AlGaAs/AlAs quantum wells near the crossover between $\varGamma-$ and $X$-valley confined electron states. The time-integrated photoluminescence experiment at $T=$4.8 K revealed three simultaneously observed optical transitions resulting from (a) a direct exciton recombination, involving an electron and a hole states both located in the $\varGamma$-valley in the quantum well layer, and (b) two spatially and momentum indirect excitons, comprising of the confined electron states in the $X$-valley in the AlAs barrier with different effective masses and quantum well holes in the $\varGamma$-valley. This interpretation has been based on the optical pumping density-dependent, temperature-dependent and spatially-resolved photoluminescence measurements, which provided the characterization of the structure, crucial in potential system's applications. Additionally, the time-resolved photoluminescence experiments unveiled complex carrier relaxation dynamics in the investigated quantum well system, which is strongly governed by a non-radiative carrier recombination - the characteristics further critical in potential system's use. This solid state platform hosting both direct and indirect excitons in a highly tunable monolithic system can benefit and underline the operation principles of novel electronic and photonic devices.

cond-mat.mes-hall↗

arXiv2024

Anomalous dispersion via dissipative coupling in a quantum well exciton-polariton microcavity

Although energy level repulsion is typically observed in interacting quantum systems, non-Hermitian physics predicts the effect of level attraction, which occurs when significant energy dissipation is present. Here, we show a manifestation of dissipative coupling in a high-quality AlGaAs-based polariton microcavity, where two polariton branches attract, resulting in an anomalous, inverted dispersion of the lower branch in momentum dispersion. Using angle-resolved photoluminescence measurements we observe the evolution of the level attraction with exciton-photon detuning, leading to changes in anomalous dispersion shape within a single sample. The dissipative coupling is explained by the interaction with an indirect exciton, acting as a highly dissipative channel in our system, and the observed dispersions are well captured within a phenomenological model. Our results present a new mechanism of dissipative coupling in light-matter systems and offer a tunable and well-controlled AlGaAs-based platform for engineering the non-Hermitian and negative mass effects in polariton systems.

cond-mat.mes-hall↗

arXiv2024

Shot-noise-limited emission from interband and quantum cascade lasers

The intensity noise of a laser source represents one of the key factors limiting the ultimate sensitivity in laser-based systems for sensing and telecommunication. For advanced applications based on interferometry, the availability of a shot-noise-limited local oscillator is even more important for the effective feasibility of high-precision measurements. This is particularly crucial in quantum optics applications based on homodyne detection schemes to measure non-classical light states, such as squeezed states. This work deeply investigates and analyzes the intensity noise features of the most widely used mid-infrared semiconductor heterostructured lasers: quantum cascade and interband cascade lasers. For this purpose, a comprehensive comparison of three different continuous-wave lasers operating at room temperature around 4.5 μm wavelength is presented. First, a thorough electro-optical characterization is given, highlighting the differences and the shared common characteristics of the tested devices. Then, a detailed intensity noise analysis is reported, identifying their different noise operations with a particular reference to shot-noise-limited operations. Finally, some perspectives towards advanced applications are discussed.

physics.optics↗

arXiv2024

Enwrapped Perylene Bisimide Enables Room Temperature Polariton Lasing and Photonic Lattices

Perylene bisimides (PBIs) are organic dyes with photoluminescence quantum yields (PLQY) close to unity in solution and great thermal and photo-chemical stability. These features alongside the tunability of their solid-state packing arrangement via chemical functionalization make this material class an excellent candidate for exciton-polariton lasing at room temperature. Polariton lasing is well understood in III-V semiconductors at cryogenic temperatures, however, the search for emitter materials for robust and versatile room temperature applications is ongoing. While e.g. perovskites and several organic materials have been identified to support polariton lasing, many of these materials lack tunability and long-term stability under ambient conditions. Here, we fabricate optical microcavities using a strongly enwrapped PBI chromophore with prevailing monomer-like absorption and emission properties in the solid state. Voluminous bay-substituents prevent stacking induced PLQY-quenching, thereby enabling polariton lasing at room temperature. Additionally, photonic confinement in single hemispheric resonators is demonstrated leading to localized polaritonic modes with discrete energies, as well as optical lattices revealing distinct polaritonic band-structures. Due to the possibility of tunable properties by the precise control of the solid-state packing arrangement of PBI emitters, our results pave the way for polarization-dependent light-matter coupling, including topological photonic effects within oriented crystalline thin-film microcavity structures.

physics.optics↗

arXiv2024

Wavevector-resolved polarization entanglement from radiative cascades

The generation of entangled photons from radiative cascades has enabled milestone experiments in quantum information science with several applications in photonic quantum technologies. Significant efforts are being devoted to pushing the performances of near-deterministic entangled-photon sources based on single quantum emitters often embedded in photonic cavities, so to boost the flux of photon pairs. The general postulate is that the emitter generates photons in a nearly maximally entangled state of polarization, ready for application purposes. Here, we demonstrate that this assumption is unjustified. We show that in radiative cascades there exists an interplay between photon polarization and emission wavevector, strongly affecting quantum correlations when emitters are embedded in micro-cavities. We discuss how the polarization entanglement of photon pairs from a biexciton-exciton cascade in quantum dots strongly depends on their propagation wavevector, and it can even vanish for large emission angles. Our experimental results, backed by theoretical modelling, yield a brand-new understanding of cascaded emission for various quantum emitters. In addition, our model provides quantitative guidelines for designing optical microcavities that retain both a high degree of entanglement and collection efficiency, moving the community one step further towards an ideal source of entangled photons for quantum technologies.

quant-ph↗

arXiv2024

Losses resistant verification of quantum non-Gaussian photon statistics

Quantum non-Gaussian states of light have fundamental properties that are essential for a multitude of applications in quantum technology. However, many of these features are difficult to detect using standard criteria due to optical losses and detector inefficiency. As the statistics of light are unknown, the loss correction on the data is unreliable, despite the fact that the losses can be precisely measured. To address this issue, we employ a loss-mitigated verification technique utilising quantum non-Gaussian witnesses, which incorporate the known optical losses and detector inefficiency into their derivation. This approach allows us to address the considerable challenge of experimentally demonstrating unheralded quantum non-Gaussian states of single photons and photon pairs.

quant-ph↗

arXiv2024

Coupling Dynamics and Linear Polarization Phenomena in Codirectional Polariton Waveguide Couplers

In this work, we explore the potential of spin-based integrated devices using polariton waveguides that form codirectional couplers. For suitable coupler parameters, a transfer of condensates between the arms of the coupler, occurs leading to the observation of Josephson-like oscillations. The ability to tune the periodicity of these oscillations opens the way to the design of polaritonic circuits in which the directionality of the signal towards the output terminals can be controlled. We also investigate the response of the devices to linearly polarized excitation, delving into the dynamics of linear polarization at the output terminals of long couplers, providing valuable insights into the potential applications of spin-based polariton devices, including polariton switches and logic gates with efficient operation. Our results are supported by numerical simulations based on generalized Gross-Pitaevskii equation describing the dynamics of coherent polaritons in spatially non-uniform system. We show, how the coupling and the controllable spin degree of freedom in polariton couplers opens avenues for innovative optical architectures and functionalities.

cond-mat.mes-hall↗

arXiv2024

Lasing of Moiré Trapped MoSe$_2$/WSe$_2$ Interlayer Excitons Coupled to a Nanocavity

We report lasing of moiré trapped interlayer excitons (IXs) by integrating a pristine hBN-encapsulated MoSe$_2$/WSe$_2$ heterobilayer into a high-$Q$ ($>10^4$) nanophotonic cavity. We control the cavity-IX detuning using a magnetic field and measure their dipolar coupling strength to be $78 \pm 4\ \mathrm{μeV}$, fully consistent with the 82 $\mathrm{μeV}$ predicted by theory. The emission from the cavity mode shows clear threshold-like behavior as the transition is tuned into resonance with the cavity. We observe a superlinear power dependence accompanied by a narrowing of the linewidth as the distinct features of lasing. The onset and prominence of these threshold-like behaviors are pronounced at resonance while weak off-resonance. Our results show that a lasing transition can be induced in interacting moiré IXs with macroscopic coherence extending over the length scale of the cavity mode. Such systems raise interesting perspectives for low-power switching and synaptic nanophotonic devices using two-dimensional materials.

cond-mat.mes-hall↗

arXiv2024

Dirac Cones and Room Temperature Polariton Lasing Evidenced in an Organic Honeycomb Lattice

Artificial one- and two-dimensional lattices have emerged as a powerful platform for the emulation of lattice Hamiltonians, the fundamental study of collective many-body effects, and phenomena arising from non-trivial topology. Exciton-polaritons, bosonic part-light and part-matter quasiparticles, combine pronounced nonlinearities with the possibility of on-chip implementation. In this context, organic semiconductors embedded in microcavities have proven to be versatile candidates to study nonlinear many-body physics and bosonic condensation, and in contrast to most inorganic systems, they allow the use at ambient conditions since they host ultra-stable Frenkel excitons. We implement a well-controlled, high-quality optical lattice that accommodates light-matter quasiparticles. The realized polariton graphene presents with excellent cavity quality factors, showing distinct signatures of Dirac cone and flatband dispersions as well as polariton lasing at room temperature. This is realized by filling coupled dielectric microcavities with the fluorescent protein mCherry. We demonstrate the emergence of a coherent polariton condensate at ambient conditions, taking advantage of coupling conditions as precise and controllable as in state-of-the-art inorganic semiconductor-based systems, without the limitations of e.g. lattice matching in epitaxial growth. This progress allows straightforward extension to more complex systems, such as the study of topological phenomena in two-dimensional lattices including topological lasers and non-Hermitian optics.

physics.optics↗

arXiv2024

A source of entangled photons based on a cavity-enhanced and strain-tuned GaAs quantum dot

A quantum-light source that delivers photons with a high brightness and a high degree of entanglement is fundamental for the development of efficient entanglement-based quantum-key distribution systems. Among all possible candidates, epitaxial quantum dots are currently emerging as one of the brightest sources of highly entangled photons. However, the optimization of both brightness and entanglement currently requires different technologies that are difficult to combine in a scalable manner. In this work, we overcome this challenge by developing a novel device consisting of a quantum dot embedded in a circular Bragg resonator, in turn, integrated onto a micromachined piezoelectric actuator. The resonator engineers the light-matter interaction to empower extraction efficiencies up to 0.69(4). Simultaneously, the actuator manipulates strain fields that tune the quantum dot for the generation of entangled photons with corrected fidelities to a maximally entangled state up to 0.96(1). This hybrid technology has the potential to overcome the limitations of the key rates that plague QD-based entangled sources for entanglement-based quantum key distribution and entanglement-based quantum networks.

quant-ph↗

arXiv2024

Second-order temporal coherence of polariton lasers based on an atomically thin crystal in a microcavity

Bosonic condensation and lasing of exciton-polaritons in microcavities is a fascinating solid-state phenomenon. It provides a versatile platform to study out-of-equilibrium many-body physics and has recently appeared at the forefront of quantum technologies. Here, we study the photon statistics via the second-order temporal correlation function of polariton lasing emerging from an optical microcavity integrated with an atomically thin MoSe2 crystal. Furthermore, we investigate the macroscopic polariton phase transition for varying excitation powers and temperatures. The lower-polariton exhibits photon bunching below the threshold, implying a dominant thermal distribution of the emission, while above the threshold, the second-order correlation transits towards unity, which evidences the formation of a coherent state. Our findings are in agreement with a microscopic numerical model, which explicitly includes scattering with phonons on the quantum level.

cond-mat.mes-hall↗

arXiv2024

Topological Optical Waveguiding of Exciton-Polariton Condensates

One-dimensional models with topological non-trivial band structures are a simple and effective way to study novel and exciting concepts in topological photonics. In this work we are studying the propagation of light-matter quasi-particles, so called exciton-polaritons, in waveguide arrays. Specifically, we are investigating topological states at the interface between dimer chains, characterized by a non-zero winding number. In order to exercise precise control over the polariton propagation, we study non-resonant laser excitation as well as resonant excitation in transmission geometry. The results highlight a new platform for the study of quantum fluids of light and non-linear optical propagation effects in coupled semiconductor waveguides.

physics.optics↗

arXiv2024

Impact of temporal correlations, coherence, and postselection on two-photon interference

Two-photon interference is an indispensable resource in quantum photonics, but it is not straightforward to achieve. The cascaded generation of photon pairs contains intrinsic temporal correlations that negatively affect the ability of such sources to perform two-photon interference, thus hindering applications. We report on how such correlation interplays with decoherence and temporal postselection, and under which conditions temporal postselection could improve two-photon interference visibility. Our study identifies crucial parameters and points the way to a source with optimal performance.

quant-ph↗

arXiv2024

An electrically pumped topological polariton laser

With a seminal work of Raghu and Haldane in 2008, concepts of topology have been successfully introduced in a wide range of optical systems, emulating specific lattice Hamiltonians. Certainly, one of the most promising routes to an application of topological photonics in an actual device are topological lasers, where efficient and highly coherent lasing from a topologically non-trivial mode is achieved. While some attempts have been made to excite such structures electrically, the majority of published fundamental experiments use a form of laser excitation. In this paper, we use a lattice of vertical resonator polariton micropillars to form an exponentially localized topological Su-Schrieffer-Heeger defect. Upon electrical excitation of the p-i-n doped structure, the system unequivocally shows polariton lasing from the topological defect using a carefully placed gold contact. Despite the presence of doping and electrical contacts, the polariton band structure clearly preserves its topological properties. At high excitation power the Mott density is exceeded leading to highly efficient lasing in the weak coupling regime. This work is an important step towards applied topological lasers using vertical resonator microcavity structures.

physics.optics↗

arXiv2024

Coexistence of Topological and Normal Insulating Phases in Electro-Optically Tuned InAs/GaSb Bilayer Quantum Wells

We report on the coexistence of both normal and topological insulating phases in InAs/GaSb bilayer quantum well induced by the built-in electric field tuned optically and electrically. The emergence of topological and normal insulating phases is assessed based on the evolution of the charge carrier densities, the resistivity dependence of the gap via in-plane magnetic fields and the thermal activation of carriers. For the Hall bar device tuned optically, we observe the fingerprints associated with the presence of only the topological insulating phase. For another Hall bar processed identically but with an additional top gate, the coexistence of normal and topological insulating phases is found by electrical tuning. Our finding paves the way for utilizing a new electro-optical tuning scheme to manipulate InAs/GaSb bilayer quantum wells to obtain trivial-topological insulating interfaces in the bulk rather than at the physical edge of the device.

cond-mat.mes-hall↗

arXiv2023

Impact of MBE-grown (In,Ga)As/GaAs metamorphic buffers on excitonic and optical properties of single quantum dots with single-photon emission tuned to the telecom range

Tuning GaAs-based quantum emitters to telecom wavelengths makes it possible to use the existing mature technology for applications in, e.g., long-haul ultra-secure communication in the fiber networks. A promising method re-developed recently is to use a metamorphic InGaAs buffer that redshifts the emission by reducing strain. However, the impact of such a buffer causes also a simultaneous modification of other quantum dot properties. Knowledge of these effects is crucial for actual implementations of QD-based non-classical light sources for quantum communication schemes. Here, we thoroughly study single GaAs-based quantum dots grown by molecular-beam epitaxy on specially designed, digital-alloy InGaAs metamorphic buffers. With a set of structures varying in the buffer indium content and providing quantum dot emission through the telecom spectral range up to 1.6 $μ$m, we analyze the impact of the buffer and its composition on QD structural and optical properties. We identify the mechanisms of quantum dot emission shift with varying buffer composition. We also look into the charge trapping processes and compare excitonic properties for different growth conditions with single-dot emission successfully shifted to both, the second and the third telecom windows.

cond-mat.mes-hall↗

arXiv2023

Purcell-Enhanced Single-Photon Emission in the Telecom C-Band

Purcell-enhanced quantum dot single-photon emission in the telecom C-band from InAs quantum dots inside circular Bragg grating cavities is shown. The InAs quantum dots are grown by means of molecular beam epitaxy on an InP substrate and are embedded into a quaternary $\mathrm{In}_{0.53}\mathrm{Al}_{0.23}\mathrm{Ga}_{0.24}\mathrm{As}$ membrane structure. In a post-growth flip-chip process with subsequent substrate removal and electron beam-lithography, circular Bragg grating ("bullseye") resonators are defined. Micro-photoluminescence studies of the devices at cryogenic temperatures of T = 5 K reveal individual quantum dot emission lines into a pronounced cavity mode. Time-correlated single-photon counting measurements under above-band gap excitation yield Purcell-enhanced excitonic decay times of $τ= (180 \pm 3)$ ps corresponding to a Purcell factor of $F_P = (6.7 \pm 0.6)$. Pronounced photon antibunching with a background limited $g^{(2)}(0) = (0.057 \pm 0.004)$ is observed, which demonstrates that the light originated mostly from one single quantum dot.

cond-mat.mes-hall↗

arXiv2023

Post-fabrication tuning of circular Bragg resonators for enhanced emitter-cavity coupling

Solid-state quantum emitters embedded in circular Bragg resonators are attractive due to their ability to emit quantum states of light with high brightness and low multi-photon probability. As for any emitter-microcavity system, fabrication imperfections limit the spatial and spectral overlap of the emitter with the cavity mode, thus limiting their coupling strength. Here, we show that an initial spectral mismatch can be corrected after device fabrication by repeated wet chemical etching steps. We demonstrate ~16 nm wavelength tuning for optical modes in AlGaAs resonators on oxide, leading to a 4-fold Purcell enhancement of the emission of single embedded GaAs quantum dots. Numerical calculations reproduce the observations and suggest that the achievable performance of the resonator is only marginally affected in the explored tuning range. We expect the method to be applicable also to circular Bragg resonators based on other material platforms, thus increasing the device yield of cavity-enhanced solid-state quantum emitters.

quant-ph↗