Semiconductor Microcavities Research Articles

Skew scattering and ratchet effect in photonic graphene

This paper is devoted to a comprehensive theoretical study of asymmetric (skew) scattering in photonic graphene, with the main focus on its realization with semiconductor microcavity exciton-polaritons. As an important consequence of the skew scattering, we prove the appearance of the ratchet effect in this system. Triangular defects in the form of missing micropillars in a regular honeycomb lattice are considered to be ones that break the spatial inversion symmetry, thus providing the possibility of the ratchet effect. By means of the numerical solution of the effective Schrödinger equation, we provide microscopical insight into the process of skew scattering and determine indicatrices, cross sections, and asymmetry parameters. In a system with multiple coherently oriented triangular defects, a macroscopic ratchet effect occurs as a unidirectional flux upon noiselike initial conditions. Our study broadens the concept of ratchet phenomena in the field of photonics and optics of exciton-polaritons. Published by the American Physical Society 2024

Low-threshold limaçon-shaped micro-cavity semiconductor lasers with an approximate ring-shaped top contact

Based on the whispering gallery mode (WGM) characteristics in the limaçon-shaped micro-cavity, we designed a micro-cavity laser with an approximate ring-shaped top electrical contact, which theoretically realized the annular current injection and low temperature rise features in the active gain region. Then we fabricated micro-cavity lasers with approximate ring-shaped top contact at different ring widths and compared them with conventional full disk-shaped top contact lasers, and observed a lower operating injection threshold current as a consequence of this relatively straightforward and feasible technique. The threshold current density of the approximate ring-shaped top contact laser is ∼0.41 kA/cm2, which is 16% lower than that of the conventional laser. Furthermore, we obtain a maximum light output peak power of 133 mW with directional emission at a far-field divergence angle of ∼38° at a full width of half maximum (FWHM).

Manipulation of lasing modes in a deformed octagonal microcavity laser

We have demonstrated a deformed octagonal microcavity semiconductor laser with manipulated lasing modes for bistable operation and direct modulation. There are two sets of degenerated four-bounced modes, S01 and S02, in the octagonal microcavity, and the degeneracy between them is broken by introducing a square hole into the center of the cavity. In the deformed octagonal microcavity laser, mode S01 dominates the lasing process during the current rising process. However, mode S02 also lases when the current decreases and interacts nonlinearly with S01, which is caused by the non-uniform distribution of the refractive index induced by the square-ring-shaped current injection. We observe a counterclockwise bistable hysteresis loop with continuous injection current ranging from 31 to 13 mA at 288 K. We also study the small-signal modulation response of the laser at high and low states with different injection currents. By utilizing the photon-photon resonance effect between modes S01 and S02, we effectively increased the 3-dB bandwidth of the laser from 12 GHz to 16.2 GHz.

Polariton-polariton interaction induced by the hopping effect between two monolayers

Investigating the quantum many-body interaction in microcavity semiconductor systems is a significant objective in current research. Hence, in this study, Green’s function was employed to investigate the hopping effect between two monolayers denoted as L and R. The interaction between excitons in L monolayer and R monolayer, characterized by spin-like properties, leads to the generation of Josephson currents and emergence of two quasiparticle branches, known as LP+ and LP− polaritons (i.e., two low polariton states). And compared with other papers, such as reference 5, the research shows that presence of hopping interaction and many-body interaction between monolayers causes significant enhancement phenomenon of residue Z, which will further reduce the effective mass. This is more conducive to Bose–Einstein condensates (BEC). Furthermore, we investigated the Parity-Time symmetry (PT symmetry) of the system. The PT broken phase transition point will appear when the condition of PT symmetry is satisfied.

Bose–Einstein condensation of light in a semiconductor quantum well microcavity

When particles with integer spin accumulate at low temperature and high density, they undergo Bose–Einstein condensation (BEC). Atoms, magnons, solid-state excitons, surface plasmon polaritons and excitons coupled to light exhibit BEC, which results in high coherence due to massive occupation of the respective system’s ground state. Surprisingly, photons were shown to exhibit BEC recently in organic-dye-filled optical microcavities, which—owing to the photon’s low mass—occurs at room temperature. Here we demonstrate that photons within an inorganic semiconductor microcavity also thermalize and undergo BEC. Although semiconductor lasers are understood to operate out of thermal equilibrium, we identify a region of good thermalization in our system where we can clearly distinguish laser action from BEC. Semiconductor microcavities are a robust system for exploring the physics and applications of quantum statistical photon condensates. In practical terms, photon BECs offer their critical behaviour at lower thresholds than lasers. Our study shows two further advantages: the lack of dark electronic states in inorganic semiconductors allows these BECs to be sustained continuously; and quantum wells offer stronger photon–photon scattering. We measure an unoptimized interaction parameter (g̃\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ilde{{{{{g}}}}}$$\\end{document} ≳ 10–3), which is large enough to access the rich physics of interactions within BECs, such as superfluid light.

The dynamical evolution of exciton-polaritons in asymmetric ring-step potential well

The exciton-polariton, a quasi-particle formed by the coupling of excitons and photons, exhibits a semi-light-semi-matter nature, inheriting the advantages of both constituents and capable of achieving Bose-Einstein condensation at room temperature. This paper investigates the evolution of superposition states of semiconductor microcavity exciton-polariton Bose–Einstein condensate (BEC) within a ring-shaped structure. By employing theoretical modeling, the time-dependent dynamics of the superposition states of exciton-polaritons bound within a unique asymmetric ring-step potential well structure are analyzed, focusing on halide perovskite semiconductor materials. The study reveals correlations between the potential well structure of this step-like configuration and the transition of exciton-polariton BEC superposition states, shedding light on the evolution paths of BEC systems under specific structural influences and the fluctuation patterns of excitonic fields. These findings hold relevance for experimental manipulations of exciton-polariton superposition states within microcavities. This research demonstrates that ring-step potential well structures influence the excitation and evolution of exciton-polariton BEC superposition states, leading to transitions towards higher or lower order states. This transition is reflected macroscopically in alterations in the number and spatial distribution of interference petals in the superposition states. We consider initial states with orbital angular momentum quantum number l = 2, 3, 4, respectively. By exploiting the different structural relationships of ring-step potential wells, we achieve controlled evolutions of macroscopic occupation states, with interference petal numbers ranging from 4 to 6, 4–8, 6–8, 6–10, 8–10, 8–12, and 6–4.

Thermodynamic potential and drag force of the impurity-polariton many-body interaction

Investigating the many-body interaction among polaritons is a fundamental goal in comprehending nonlinear behaviors in microcavity semiconductor systems. Hence, the present study focuses on exploring the many-body interaction between excitons and impurities. It was observed that the energy eigenequation governing this system is of sixth-order, rendering it unsolvable. Consequently, a strategy involving the utilization of impurity weight was employed to partition the initial energy eigenequation into two fourth-order equations, a method deemed suitable for lower order approximations. Subsequently, Green’s function was applied to these two fourth-order equations. The analysis of the computed results, encompassing the energy spectrum, polariton density, and thermodynamic potential of the system, reveals that the many-body interaction between excitons and impurities induces the emergence of novel bound states of quasiparticles. Moreover, the inclusion of impurities leads to a decrease in both energy and density of polaritons. Furthermore, the investigation delves into the drag force exerted by impurities on excitons, demonstrating that the drag force escalates in a second-order fashion with impurity velocity and persists even as impurity velocity increases, surpassing the Landau’s equilibrium theory.

The Intermode Polariton Parametric Scattering Laser in a Strong Coupled Microcavity Via Two-Photon Absorption.

Exciton-polaritons, hybrid quasiparticles from the strong coupling of excitons and cavity photons in semiconductor microcavities, offer a platform for exploring quantum coherence and nonlinear optical properties. The unique polariton parametric scattering (PPS) laser is of interest for its potential in quantum technologies and nonlinear devices. However, direct resonant excitation of polaritons in strong-coupling microcavities is challenging. This study proposes an innovative two-photon absorption (TPA) pump mechanism to address this. We observe TPA-driven PPS lasing in a strongly coupled microcavity at room temperature. High K-value exciton injections promote coherent stimulated emission of polariton scattering through intermode channels. Angle-resolved spectra confirm a TPA process, showing evolution from pump-state to signal-state. Hanbury Brown-Twiss measurement of second-order correlation g2(τ) of signal state indicates a phase transition from a classical thermal state to a quantum coherent state. Theoretical modeling provides insights into the physical mechanisms of PPS. Our work advances nonlinear phenomena exploration in strongly coupled light-matter systems, contributing to quantum polaritonics and nonlinear optics.

Room temperature, cascadable, all-optical polariton universal gates

Today, almost all information processing is performed using electronic logic circuits operating at several gigahertz frequency. All-optical logic holds the promise to allow for up to three orders of magnitude higher speed. Whereas essential all-optical transistor functionalities were demonstrated across a range of platforms, utilising them to implement a complete Boolean logic gate set and in particular negation, i.e. switching off an optical signal with another, weaker, optical signal, poses a major challenge. Here, we realize a cascadable NOT gate by introducing the concept of non-ground-state polariton amplification in organic semiconductor microcavities under non-resonant optical excitation. We unravel the importance of vibron-mediated stimulated scattering in room temperature operation of the inverter. Moreover, we extend the concept to a multi-input universal NOR logic gate, where in the presence of any of the input signals non-ground-state amplification supersedes spontaneous ground-state condensation, resulting in a NOR gate with ~1 ps switching time. The realisation of an ultrafast universal logic gate constitutes an essential step for more complex optical circuitry that could boost information processing applications.

Realization of photonic time crystals via spin bifurcations of exciton-polariton condensates.

We have theoretically realized a photonic time crystal in a homogeneous spinor exciton-polariton condensate subject to a cavity strain induced energy splitting between the x- and y-polarized polaritons with distinct loss rates. Numerical modeling based on the time-dependent open dissipative Gross-Pitaevskii equation results in the phase transition from linearly-polarized spinor condensate at low pump powers into a circularly-polarized one and then a photonic time crystal at higher pump powers. This phenomenon occurs only under the condition that the lower-energy x-polarized condensate has a higher loss rate than the y-polaried condensate, which can exist intrinsically in the semiconductor microcavities.

Topological valley Hall polariton condensation.

A photonic topological insulator features robust directional propagation and immunity to defect perturbations of the edge/surface state. Exciton-polaritons, that is, the hybrid quasiparticles of excitons and photons in semiconductor microcavities, have been proposed as a tunable nonlinear platform for emulating topological phenomena. However, mainly due to excitonic material limitations, experimental observations so far have not been able to enter the nonlinear condensation regime or only show localized condensation in one dimension. Here we show a topological propagating edge state with polariton condensation at room temperature and without any external magnetic field. We overcome material limitations by using excitonic CsPbCl3 halide perovskites with a valley Hall lattice design. The polariton lattice features a large bandgap of 18.8 meV and exhibits strong nonlinear polariton condensation with clear long-range spatial coherence across the critical pumping density. The geometric parameters and material composition of our nonlinear many-body photonic system platform can in principle be tailored to study topological phenomena of other interquasiparticle interactions.

Controllable nonlinear effects in a hybrid magnonical semiconductor microcavity

We investigate the bistability properties of the magnomechanical system driven by an amplitude-modulated pump laser. The bistable behavior exhibits a characteristic magnon switching pattern. This behavior is studied for different values of system parameters. A distinct indication of energy transfer between the mechanical and magnon modes becomes evident while examining the mechanical displacement spectrum within the system. Further, by appropriately adjusting the system parameters, it is observed that the system in its steady state exhibits entanglement dynamics. These findings imply that this system holds potential applications in highly responsive magnon switches, magnon sensors, and quantum communication platforms.

Selective Excitation of Exciton-Polariton Condensate Modes in an Annular Perovskite Microcavity.

Exciton-polariton systems composed of a light-matter quasi-particle with a light effective mass easily realize Bose-Einstein condensation. In this work, we constructed an annular trap in a halide perovskite semiconductor microcavity and observed the spontaneous formation of symmetrical petal-shaped exciton-polariton condensation in the annular trap at room temperature. In our study, we found that the number of petals of the petal-shaped exciton-polariton condensates, which is decided by the orbital angular momentum, is dependent on the light intensity distribution. Therefore, the selective excitation of perovskite microcavity exciton-polariton condensates under all-optical control can be realized by adjusting the light intensity distribution. This could pave the way to room-temperature topological devices, optical cryptographical devices, and new quantum gyroscopes in the exciton-polariton system.

Occupancy-driven Zeeman suppression and inversion in trapped polariton condensates

We study the magnetophotoluminescence of an optically trapped exciton-polariton condensate in a planar semiconductor microcavity with multiple In0.08Ga0.92As quantum wells. Extremely high condensate coherence time and continuous control over the polariton confinement are among the advantages provided by optical trapping. This allows us to resolve magnetically induced ∼µeV fine-energy shifts in the condensate and identify unusual dynamical regions in its parameter space. We observe polariton Zeeman splitting and, in small traps with tight confinement, demonstrate its full parametric screening when the condensate density exceeds a critical value, reminiscent of the spin-Meissner effect. For larger optical traps, we observe a complete inversion in the Zeeman splitting as a function of power, underlining the importance of condensate confinement and interactions with its background reservoir excitons. Published by the American Physical Society 2024

Thermalization rate of polaritons in strongly-coupled molecular systems

Abstract Polariton thermalization is a key process in achieving light–matter Bose–Einstein condensation, spanning from solid-state semiconductor microcavities at cryogenic temperatures to surface plasmon nanocavities with molecules at room temperature. Originated from the matter component of polariton states, the microscopic mechanisms of thermalization are closely tied to specific material properties. In this work, we investigate polariton thermalization in strongly-coupled molecular systems. We develop a microscopic theory addressing polariton thermalization through electron-phonon interactions (known as exciton-vibration coupling) with low-energy molecular vibrations. This theory presents a simple analytical method to calculate the temperature-dependent polariton thermalization rate, utilizing experimentally accessible spectral properties of bare molecules, such as the Stokes shift and temperature-dependent linewidth of photoluminescence, in conjunction with well-known parameters of optical cavities. Our findings demonstrate qualitative agreement with recent experimental reports of nonequilibrium polariton condensation in both ground and excited states, and explain the thermalization bottleneck effect observed at low temperatures. This study showcases the significance of vibrational degrees of freedom in polariton condensation and offers practical guidance for future experiments, including the selection of suitable material systems and cavity designs.

Reservoir computing-based advance warning of extreme events

Physics-based computing exploits nonlinear or disorder-induced complexity, for example, to realize energy-efficient and high-throughput computing tasks. A particularly difficult but useful task is the prediction of extreme events that can occur in a wide range of complex systems. We prepare an experiment based on a microcavity semiconductor laser that produces statistically rare extreme events resulting from the interplay of deterministic nonlinear dynamics and spontaneous emission noise. We then evaluate the performance of three reservoir computing training approaches in predicting the occurrence of extreme events. We show that Dual Training Reservoir Computing (which in turn can be implemented with fast semiconductor laser dynamics) can provide meaningful early warnings up to 15 times the typical linear correlation time of the dynamics.

All-optical triangular and honeycomb lattices of exciton–polaritons

We implement an all-optically reconfigurable triangular lattice of exciton–polariton condensates in a III–V semiconductor microcavity. For this, we utilize a spatial light modulator to structure an incident nonresonant excitation laser beam into a corresponding triangular lattice of Gaussian beams that are focused onto the cavity plane. The optical excitation pattern locally stimulates and blueshifts polaritons due to exciton interactions. At a critical pump power, polaritons condense into a macroscopically coherent Bloch state with sharp Bragg peaks. We reconstruct the full band structure of the system through energy tomography techniques as a function of lattice constant, allowing us to resolve polaritonic Bloch bands from the condensate emission. While for sufficiently large lattice constants, one observes the formation of triangular arrays of condensates, for small lattice constant and pump powers above condensation threshold, one observes the formation of honeycomb, instead of triangular, lattice of condensates, with clear evidence of condensation into the S-band. Our results underpin the quality of all-optically engineered polariton lattices to simulate condensed matter systems in the strong coupling regime.

Quantifying Exciton-Photon Entanglement in Semiconductor Microcavities: A Closed Formula for Strong and Weak Coupling Regimes

Quantifying Exciton-Photon Entanglement in Semiconductor Microcavities: A Closed Formula for Strong and Weak Coupling Regimes

Generation and modulation of shock waves in two-dimensional polariton condensates

Due to the ability of exciton-polariton condensates formed in semiconductor microcavities to be achieved at room temperature and their characteristics such as non-equilibrium and strong interactions, they have become an ideal platform for studying the nonlinear properties of non-equilibrium quantum systems. In 2013, the research group led by L. Dominici observed two-dimensional symmetric shock waves in the polariton condensate driven by coherent pump. However, owing to the characteristics of this system, theoretical researches have lagged behind. In one-dimensional polariton condensates, disregarding cross-interaction of the system, a type of asymmetric shock wave was respectively discovered by A. M. Kamchatnov in 2012 and A. M. Belounis in 2017. In 2023, utilizing the adiabatic approximation, our research team not only uncovered sparse wave, symmetric, and asymmetric shock waves in the system, but also revealed that the symmetric shock waves are triggered by cross-interaction. At present, there is no theoretical research on shock waves in two-dimensional polariton condensate. In this paper, spectral methods and fourth-order Runge-Kutta methods are used to explore the generation and control of shock waves in two-dimensional polariton condensates. It is found that when the cross-interaction between the condensate and the polariton thermal reservoir is quenched at high condensation rates, the initially prepared bright solitons can be modulated into two types of rotationally symmetric shock waves with different velocities, while the initial dark-like solitons can only transform into a single velocity rotationally symmetric shock wave. If quenching the external potential, the dark-like solitons can be transformed into anisotropic supersonic shock waves, and the dependence of shock wave on the width of the external potential is also shown. When the external potential and incoherent pumping are controlled at low condensation rates, multiple anisotropic shock waves can be excited in a uniform condensate, and their amplitudes can be used to control the wave number and amplitude of the shock waves and the range of widths for the external potential or incoherent pumping to excite shock waves is also demonstrated. The proposed methods in this paper not only provide theoretical guidance for the generation and control of shock waves in exciton-polariton condensates, but also find symmetric shock waves similar to experiments (<ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.nature.com/articles/ncomms9993"><i>Nat. Commun.</i> <b>6</b> , 8993</ext-link>) without adopting any approximation, and open up a universal pathway for exciting shock waves in non-equilibrium or non-integrable systems, which may become a paradigm for transforming solitons into shock waves and significantly propel the rapid development of shock wave theory in different domains.

Spatial Imaging and Control of Dark Excitons in Monolayer Transition Metal Dichalcogenides.

Dark excitons play a vital role in exciton condensation and optical properties of monolayer transition metal dichalcogenides (MTMDs). Previous literature mainly focuses on the detection of the energy of the dark exciton, while spatial detection and control are equally important but are less studied. Here we report that for MTMD embedded in a semiconductor microcavity and under a uniform in-plane magnetic field the spatial distribution of the dark exciton can be probed by measuring that of the cavity photon for small exciton-exciton interaction energy. Further, we propose to realize the anomalous exciton Hall effect by exploiting spatially inhomogeneous coupling of the bright and dark excitons under a Gaussian excitation beam. This effect occurs regardless of the exciton-exciton interaction, which will strengthen the diffusion of excitons in the excitation region. These results provide an improved understanding of the excitons in MTMDs, thereby facilitating their potential practical applications.