Semiconductor Microcavities Research Articles

Optical feedback-induced dynamics and nonclassical photon statistics of semiconductor microcavity laser

We study a coherently driven semiconductor laser cavity containing a single quantum dot(QD) (as gain medium) with optical feedback under Markovian approximation. We have obtained coupled operator equations for the model Hamiltonian using standard input-output formalism of cavity-QED and have found that these equations do not have any finite steady state solutions. We have also used an exact numerical framework based on Matlab platform qotoolbox, to compute the temporal dynamics of the mean excitation number of laser cavity mode under high feedback coupling regime. We have further studied the photon correlations of both the cavity mode as well as external feedback mode to feedback identify the laser parameters and coupling strength that give the nonclassical sub-Poissonian photon statistics. This work is useful for coherent control of photon statistics and photon correlations in the semiconductor laser with optical feedback.

Polarization conversion in a polariton three-waveguide coupler

We propose an approach to control of polarization of propagating light in a waveguide geometry. We suggest using a three-waveguide coupler etched in a planar semiconductor microcavity with embedded quantum wells. The structure allows converting a linear polarization of polaritons, photons hybridized with quantum well excitons, excited by a resonant optical pump, to circular polarization, herewith opposite circularly-polarized components are spaced apart from each other in different waveguides. The mutual effect of the evanescent coupling of waveguides and the TE-TM splitting of guided modes are in the basis of the predicted effect.

Theory of polariton-electron interactions in semiconductor microcavities

We develop a microscopic description of an electron-doped two-dimensional semiconductor embedded in a microcavity. Specifically, we investigate the interactions between exciton-polaritons and electrons for the case where the interactions between charges are strongly screened and the system is spin polarized. As a starting point, we obtain an analytic expression for the exciton-polariton wave function, and we relate the microscopic parameters of the light-matter system to experimentally measurable quantities, such as the Rabi coupling and the cavity photon frequency. We then derive the polariton-electron interaction within the standard Born approximation and compare it with the exact polariton-electron scattering $T$ matrix that we obtain from a diagrammatic approach that has proven highly successful in the context of nuclear physics and ultracold atomic gases. In particular, we show that the Born approximation provides an upper bound on the polariton-electron coupling strength at vanishing momentum. Using our exact microscopic calculation, we demonstrate that polariton-electron scattering can be strongly enhanced compared to the exciton-electron case, which is the opposite of that expected from the Born approximation. We furthermore expose a resonance-like peak at scattering momenta near the polariton inflection point, whose size is set by the strength of the light-matter coupling. Our results arise from the non-Galilean nature of the polariton system and should thus be applicable to a range of semiconductor microcavities such as GaAs quantum wells and atomically thin materials.

Periodic exciton–polariton solitons in semiconductor nanowires

Exciton–polariton solitons are nonlinear quasiparticles composed of exciton–photon bound states due to the interaction of light with matter. In semiconductor micro-cavity systems, such as semiconductor micro and nanowires, polaritons are characterized by a negative mass which, combined with the repulsive nonlinear exciton–exciton interaction, leads to the generation of bright polariton solitons. In this work, we investigate the dynamics of bright exciton–polariton solitons in a finite-sized microcavity waveguide, assuming radiative losses to be balanced by the external pumping. Bright-soliton solutions to the model equations of motion, which consist of a periodic train of polariton pulses, are obtained in terms of Jacobi elliptic functions. Analytical expressions of the energies of both photonic and excitonic components of the pulse train are found. Results suggest that the size of a nanowire waveguide plays a relevant role in the quantitative estimate of the energy conveyed by polariton solitons propagating in the medium.

Polariton spin jets through optical control

We demonstrate spin polarized jets in extended systems of ballistic exciton-polariton condensates in semiconductor microcavities using optical non-resonant excitation geometries. The structure of the spin jets is determined by the digitally reprogrammable, spatially non-uniform, degree of circular polarization of the excitation laser. The presence of the laser excitation, strong particle interactions, and spin-relaxation leads to a tunable spin-dependent potential landscape for polaritons, with the appearance of intricate polarization patterns due to coherent matter-wave interference. Our work realizes polarization-structured coherent light sources in the absence of gauge fields.

Suppression of Surface-Related Loss in a Gated Semiconductor Microcavity

We present a surface passivation method that reduces surface-related losses by almost two orders of magnitude in a highly miniaturized GaAs open microcavity. The microcavity consists of a curved dielectric distributed Bragg reflector (DBR) with radius $\sim 10$ $\mu$m paired with a GaAs-based heterostructure. The heterostructure consists of a semiconductor DBR followed by an n-i-p diode with a layer of quantum dots in the intrinsic region. Free-carrier absorption in the highly doped n- and p-layers is minimized by positioning them close to a node of the vacuum electromagnetic-field. The surface, however, resides at an anti-node of the vacuum field and results in significant loss. These losses are much reduced by surface passivation. The strong dependence on wavelength implies that the main effect of the surface passivation is to eliminate the surface electric field, thereby quenching below-bandgap absorption via a Franz-Keldysh-like effect. An additional benefit is that the surface passivation reduces scattering at the GaAs surface. These results are important in other nano-photonic devices which rely on a GaAs-vacuum interface to confine the electromagnetic field.

Measuring Topological Invariants in a Polaritonic Analog of Graphene.

Topological materials rely on engineering global properties of their bulk energy bands called topological invariants. These invariants, usually defined over the entire Brillouin zone, are related to the existence of protected edge states. However, for an important class of Hamiltonians corresponding to 2D lattices with time-reversal and chiral symmetry (e.g., graphene), the existence of edge states is linked to invariants that are not defined over the full 2D Brillouin zone, but on reduced 1D subspaces. Here, we demonstrate a novel scheme based on a combined real- and momentum-space measurement to directly access these 1D topological invariants in lattices of semiconductor microcavities confining exciton polaritons. We extract these invariants in arrays emulating the physics of regular and critically compressed graphene where Dirac cones have merged. Our scheme provides a direct evidence of the bulk-edge correspondence in these systems and opens the door to the exploration of more complex topological effects, e.g., involving disorder and interactions.

Observation of photon-mode decoupling in a strongly coupled multimode microcavity.

We have fabricated organic semiconductor microcavities having an extended optical path-length (up to 2 µm) that contain J-aggregates of a cyanine dye. These structures are studied using optical-reflectivity and are found to be characterized by a series of polaritonic modes. By changing the effective oscillator strength of the dye within the cavity, we evidence a transition from "normal" strong coupling in which the photon modes are coupled to one another via the excitonic transition of the molecular dye to a state in which photon-modes become decoupled. We use an eight-level modified Hamiltonian to describe the optical properties of the system and compare the distribution of the confined optical field in coupled and decoupled structures.

Microcavity polaritons for topological photonics [Invited

Microcavity polaritons are light-matter quasiparticles that arise from the strong coupling between excitons and photons confined in a semiconductor microcavity. They are typically studied at visible or near visible wavelengths. They combine the properties of confined electromagnetic fields, including a sizeable spin-orbit coupling, and the sensitivity to external magnetic fields and particle interactions inherited from their partly matter nature. These features make polaritons an excellent platform to study topological phases in photonics in one and two-dimensional lattices, whose band properties can be directly accessed using standard optical tools. In this review, we describe the main properties of microcavity polaritons and the main observations in the field of topological photonics, which include, among others, lasing in topological edge states, the implementation of a polariton Chern insulator under an external magnetic field, and the direct measurement of fundamental quantities, such as the quantum geometric tensor and winding numbers in one- and two-dimensional lattices. Polariton interactions open exciting perspectives for the study of nonlinear topological phases.

Spontaneously coherent orbital coupling of counterrotating exciton polaritons in annular perovskite microcavities

Exciton-polariton condensation is regarded as a spontaneous macroscopic quantum phenomenon with phase ordering and collective coherence. By engineering artificial annular potential landscapes in halide perovskite semiconductor microcavities, we experimentally and theoretically demonstrate the room-temperature spontaneous formation of a coherent superposition of exciton-polariton orbital states with symmetric petal-shaped patterns in real space, resulting from symmetry breaking due to the anisotropic effective potential of the birefringent perovskite crystals. The lobe numbers of such petal-shaped polariton condensates can be precisely controlled by tuning the annular potential geometry. These petal-shaped condensates form in multiple orbital states, carrying locked alternating π phase shifts and vortex–antivortex superposition cores, arising from the coupling of counterrotating exciton-polaritons in the confined circular waveguide. Our geometrically patterned microcavity exhibits promise for realizing room-temperature topological polaritonic devices and optical polaritonic switches based on periodic annular potentials.

Neuromorphic Binarized Polariton Networks.

The rapid development of artificial neural networks and applied artificial intelligence has led to many applications. However, current software implementation of neural networks is severely limited in terms of performance and energy efficiency. It is believed that further progress requires the development of neuromorphic systems, in which hardware directly mimics the neuronal network structure of a human brain. Here, we propose theoretically and realize experimentally an optical network of nodes performing binary operations. The nonlinearity required for efficient computation is provided by semiconductor microcavities in the strong quantum light-matter coupling regime, which exhibit exciton–polariton interactions. We demonstrate the system performance against a pattern recognition task, obtaining accuracy on a par with state-of-the-art hardware implementations. Our work opens the way to ultrafast and energy-efficient neuromorphic systems taking advantage of ultrastrong optical nonlinearity of polaritons.

Nonlinear optical response properties of a quantum dot embedded in a semiconductor microcavity: possible applications in quantum communication platforms

We theoretically investigate optical bistability, mechanically induced absorption (MIA) and Fano resonance of a hybrid system comprising of a single quantum dot (QD) embedded in a solid-state microcavity interacting with the quantized cavity mode and the deformation potential associated with the lattice vibration. We find that the bistability can be tuned by the QD-cavity mode coupling. We further show that the normalized power transmission displays anomalous dispersion indicating that the system can be used to generate slow light. We also demonstrate the possibility of using the system as all optomechanical Kerr switch.

Polariton Laser in the Bardeen-Cooper-Schrieffer Regime

Experiments show signatures of a long-sought-after condensed quantum phase---the so-called Bardeen-Cooper-Schrieffer state---in a semiconductor microcavity, laying the foundation for future efficient semiconductor lasers.

Limit cycle phase and Goldstone mode in driven dissipative systems

In this article, we theoretically investigate the first- and second-order quantum dissipative phase transitions of a three-mode cavity with a Hubbard interaction. In both types, there is a mean-field (MF) limit cycle phase where the local U(1) symmetry and the time-translational symmetry of the Liouvillian superoperator are spontaneously broken. In MF, this spontaneous symmetry breaking manifests itself through the appearance of an unconditionally and fully squeezed state at the cavity output, connected to the well-known Goldstone mode. By employing the Wigner function formalism, hence, properly including the quantum noise, we show that away from the thermodynamic limit and within the quantum regime, fluctuations notably limit the coherence time of the Goldstone mode due to the phase diffusion. Our theoretical predictions suggest that interacting multimode photonic systems are rich, versatile test beds for investigating the crossovers between the mean-field picture and quantum phase transitions, a problem that can be investigated in various platforms including superconducting circuits, semiconductor microcavities, atomic Rydberg polaritons, and cuprite excitons.

Drag force of an exciton-polariton condensate under nonresonant pumping

Exciton-polariton condensate in semiconductor microcavities constitute a novel kind of non-equilibrium superfluid. In a recent experiment [P. Stepanov, {\it et. al.,} Nat. Commun. {\bf 10}, 1038 (2019)], the dispersion relation of collective excitations in a polariton condensate under the resonant pumping has been investigated with the emphasis on the role of reservoir of long-lived excitons in determining the superfluidity. Inspired by such an experimental advance, we study the superfluidity of a exciton-polaritonn condensate under non-resonant pumping by calculating the drag force exerted on a classical impurity moving in a polariton condensate. For a non-resonant pumped polariton condensate prepared in the gapped phase, due to the reservoir's modes, the drag force can be large when the velocity of the impurity is small. Besides, as the velocity increases, the drag force can decrease. For not very large velocity, the drag force is enhanced if the condensate is tuned to be more dissipative. When the condensate is close to the transition point between the gapped phase and the gapless one, the drag force is similar to that of the equilibrium superfluid. Our present work reveals the effects of the reservoir's modes on the superfluidity properties of a polariton condensate with the non-resonant pumping.

Mediated Interactions and Photon Bound States in an Exciton-Polariton Mixture.

The quest to realize strongly interacting photons remains an outstanding challenge both for fundamental science and for applications. Here, we explore mediated photon-photon interactions in a highly imbalanced two-component mixture of exciton polaritons in a semiconductor microcavity. Using a theory that takes into account nonperturbative correlations between the excitons as well as strong light-matter coupling, we demonstrate the high tunability of an effective interaction between quasiparticles formed by minority component polaritons interacting with a Bose-Einstein condensate (BEC) of a majority component polaritons. In particular, the interaction, which is mediated by sound modes in the BEC can be made strong enough to support a bound state of two quasiparticles. Since these quasiparticles consist partly of photons, this in turn corresponds to a dimer state of photons propagating through the BEC. This gives rise to a new light transmission line where the dimer wave function is directly mapped onto correlations between the photons. Our findings open new routes for highly nonlinear optical materials and novel hybrid light-matter quantum systems.

Genetic Algorithm Applied to the Optimized Design of Semiconductor Microcavity Lasers

Semiconductor microcavities have been used in important studies of several areas for technological or purely scientific purposes. However, the definition of the optimal parameters for the fabrication of microcavities is a difficult task. Moreover, some uncertainties related to the growth process can change the device features. These problems cannot be experimentally controlled, hindering the development of theoretical models. In this work we present a theoretical model to simulate the microcavities and also propose an evolutionary approach to optimize the device under uncertainty in order to ensure the growth with the desired features. Thus, based on the reflectance spectra of a AlxGa1-xAs semiconductor microcavity, the aluminum concentrations, x, and the number of layers that compose the heterostructure were optimized. This set of parameters may offer increased robustness in the growth process, while providing a considerable quality factor and the desired position of the cavity resonance, achieving the device’s operation limits. The device was optimized considering the cavity resonance between 700nm and 2000nm, where the results indicate that the proposed algorithm is able to find satisfactory solutions, minimizing the problems caused by inaccuracy in the growth process.

Phonon-induced interactions and entanglement formation between two microcavity modes mediated by two semiconductor quantum dots

Using a polaron master equation approach, we investigate the cooperative two-photon resonance behavior between two modes of a field inside a semiconductor microcavity containing two quantum dots. The cooperative two-mode two-photon resonance occurs when two off-resonant quantum dots, initially prepared in exciton states, emit one photon in each cavity mode and deexcite simultaneously. Using this two-photon two-mode interaction, we demonstrate how to generate an entangled state of two qutrits (tripartite unit of quantum information). The bases for the qutrits are formed by the states of the cavity modes containing zero, one, and two photons. We also study the effect of exciton-phonon coupling on the entanglement and the probability of generating two-qutrit states, and explore the role of the phonon bath temperature.

Quantum correlation and statistical properties in semiconductor microcavities with time-varying coupling effect

In this manuscript, we show how the photon-exciton entanglement and distribution of photons depend on the main parameters of the physical model in the semiconductor microcavities without and with of the time-dependent coupling effect (TDCE). We examine the dynamics of the quantum entanglement and photon statistics by considering the time variation of the coupling between the excitons and photons in weak excitation regime of quantum well confined in a semiconductor microcavity. We show that the manipulation and control of the degree of the entanglement and statistical distribution of photons in the presence of the TDCE can be benefited by a convenient choice of the strength field and the rate of the excitonic spontaneous emission.

Direct Generation of Radially Polarized Vector Vortex Beam with an Exciton-Polariton Laser

Vector vortex beams are a class of optical beams with singularities in their space-variant polarization. Vector vortex beam lasers have applications in many areas including imaging and communication, where vertical-cavity lasers emitting Gaussian beams have been most widely used so far. Generation of vector vortex beams from vertical-cavity lasers has required external control or modulation. Here, by utilizing a polarization-selective subwavelength grating as one of the reflectors in a vertical semiconductor microcavity, we design the spin textures of the polariton mode and demonstrate polariton lasing in a single-mode, radially polarized vector vortex beam. Polarization and phase distributions of the emission are characterized by polarization-resolved imaging and interferometry. This method of vector vortex laser beam generation allows low threshold power, stable single-mode operation, scalability, and on-chip integration, all of which are important for applications in imaging and communication.