We review the practical conditions required to achieve a non-equilibrium BEC driven by quantum dynamics in a system comprising a microcavity field mode and a distribution of localised two-level systems driven to a step-like population inversion profile. A candidate system based on eight 3.8nm layers of In(0.23)Ga(0.77)As in GaAs shows promising characteristics with regard to the total dipole strength which can be coupled to the field mode.
The first realization of a polariton condensate was recently achieved in a CdTe microcavity [Kasprzak et al., Nature 443, 409 (2006)]. We compare the experimental phase boundaries, for various detunings and cryostat temperatures, with those found theoretically from a model which accounts for features of microcavity polaritons such as reduced dimensionality, internal composite structure, disorder in the quantum wells, polariton-polariton interactions, and finite lifetime.
We investigate the statistics of microcavity polariton Bose-Einstein condensation by measuring photoluminescence dynamics from a GaAs microcavity excited by single laser excitation pulses. We directly observe fluctuations (jitter) of the polariton condensation onset time and model them using a master equation for the occupancy probabilities. The jitter of the condensation onset time is an inherent property of the condensate formation and its magnitude is approximately equal to the rise time of the condensate density. We investigate temporal correlations between the emission of condensate in op…
Condensation of microcavity polaritons and the substantial influence of pair-breaking disorder and decoherence leading to a laser regime has been recently considered using two different models: a model for direct two band excitons in a disordered quantum well coupled to light and a model where the cavity mode couples instead to a medium of localised excitons, represented by two-level oscillators in the presence of dephasing processes. Even if complementary from the point of view of assumptions, the models share most of the main conclusions and show similar phase diagrams. The issue whether exc…
We present a microcavity structure with a shifted photonic stop-band to enable efficient non-resonant injection of a polariton condensate with spectrally broad femtosecond pulses. The concept is demonstrated theoretically and confirmed experimentally for a planar GaAs/AlGaAs multilayer heterostructure pumped with ultrashort near-infrared pulses while photoluminescence is collected to monitor the optically injected polariton density. As the excitation wavelength is scanned, a regime of polariton condensation can be reached in our structure at a consistently lower fluence threshold than in a sta…
We calculate the absorption spectra of a semiconductor microcavity into which a non-equilibrium exciton population has been pumped. We predict strong peaks in the spectrum corresponding to collective modes analogous to the Cooper modes in superconductors and fermionic atomic gases. These modes can become unstable, leading to the formation of off-equilibrium quantum condensates. We calculate a phase diagram for condensation, and show that the dominant instabilities can be at a finite momentum. Thus we predict the formation of inhomogeneous condensates, similar to Fulde-Ferrel-Larkin-Ovchinnikov…
We develop a kinetic theory of microcavity polaritons in presence of both Coulomb and polariton-phonon interaction, obeying particle number conservation. We study the growth of a macroscopic population of condensed particles in the lowest polariton state, under steady-state incoherent excitation of higher energy states. The collective excitation spectrum, resulting from the Coulomb Hamiltonian treated within the Hartree-Fock-Bogolubov framework, strongly influences the polariton condensation kinetics. In particular, for values of the excitation intensity above the condensation threshold, scatt…
Polariton lattice condensates provide a platform for on chip quantum emulations. Interactions in extended polariton lattices are currently limited by the intrinsic photonic disorder of microcavities. Here, we fabricate a strain compensated planar GaAs/AlAs microcavity with embedded InGaAs quantum wells and report on polariton condensation under non-resonant optical excitation. Evidence of polariton condensation is supported spectroscopically both in reflection and transmission geometry, whilst the observation of a second threshold to photon lasing allows us to conclusively distinguish between …
The Hartree-Fock-Popov theory of interacting Bose particles is developed, for modeling exciton-polaritons in semiconductor microcavities undergoing Bose-Einstein condensation. A self-consistent treatment of the linear exciton-photon coupling and of the exciton non-linearity provides a thermal equilibrium description of the collective excitation spectrum, of the polariton energy shifts and of the phase diagram. Quantitative predictions support recent experimental findings.
We create exciton-polaritons in a zero-dimensional (0D) microcavity filled with organic ladder-type conjugated polymer in the strong light-matter interaction regime. Photonic confinement at wavelength scale is realized in the longitudinal direction by two dielectric Bragg mirrors and laterally by a sub-micron Gaussian-shaped defect. The cavity is separated into two parts allowing nanometer position control and enabling tuning of exciton and photon fractions of the polariton wavefunction. Polariton condensation is achieved with non-resonant, picosecond optical excitation at ambient conditions a…
Exciton-polariton modes arising from interaction between bound excitons in monolayer thin semiconductor sheets and photons in a Fabry-Perot microcavity are considered theoretically. We calculate the dispersion curves, mode lifetimes, Rabi splitting, and Hopfield coefficients of these structures for two nearly 2D semiconductor materials, MoS2 and WS2, and suggest that they are interesting for studying the rich physics associated with the Bose-Einstein condensation of exciton-polaritons. The large exciton binding energy and dipole allowed exciton transitions, in addition to the relatively easily…
In this work we derive a theory of polariton condensation based on the theory of interacting Bose particles. In particular, we describe self-consistently the linear exciton-photon coupling and the exciton-nonlinearities, by generalizing the Hartree-Fock-Popov description of BEC to the case of two coupled Bose fields at thermal equilibrium. In this way, we compute the density-dependent one-particle spectrum, the energy occupations and the phase diagram. The results quantitatively agree with the existing experimental findings. We then present the equations for the linear response of a polariton …
We consider polariton condensation in a generalized Dicke model, describing a single-mode cavity containing quantum dots, and extend our previous mean-field theory to allow for finite-size fluctuations. Within the fluctuation-dominated regime the correlation functions differ from their (trivial) mean-field values. We argue that the low-energy physics of the model, which determines the photon statistics in this fluctuation-dominated crossover regime, is that of the (quantum) anharmonic oscillator. The photon statistics at the crossover are different in the high- and low- temperature limits. Whe…
The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation are investigated in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses. It is shown that the onset of the condensate first order sparial coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct mea…
In this work we perform a numerical study of a rotating, harmonically trapped, Bose-Einstein condensate of microcavity polaritons. An efficient numerical method (toolbox) to solve the complex Gross-Pitaevskii equation is developed. Using this method, we investigate how the behavior of the number of vortices formed inside the condensate changes as the various system parameters are varied. In contrast to the atomic condensates, we show, there exists an (experimentally realizable) range of parameter values in which all the vortices can be made to vanish even when there is a high rotation. We furt…
A spatial potential trap is formed in a 6.0 μm Al(Ga)N nanowire by varying the Al composition along its length during epitaxial growth. The polariton emission characteristics of a dielectric microcavity with the single nanowire embedded in-plane has been studied at room temperature. Excitation is provided at the Al(Ga)N end of the nanowire and polariton emission is observed from the lowest bandgap GaN region of the nanowire. Comparison of the results with those measured in an identical microcavity with an uniform GaN nanowire and having an identical exciton-photon detuning suggests evaporative…
The Bose-Einstein condensation (BEC) of the two-dimensional (2D) magnetoexciton-polaritons in microcavity, when the Landau quantization of the electron and hole states accompanied by the Rashba spin-orbit coupling plays the main role, were investigated. The Landau quantization levels of the 2D heavy holes with nonparabolic dispersion law and third order chirality terms both induced by the external electric field perpendicular to the semiconductor quantum well as the strong magnetic field B gives rise to the nonmonotous dependence on B of the magnetoexciton energy levels and of the polariton en…
We study the time dependent polariton condensation as well as the parametric scattering process of polaritons in a semiconductor microcavity. Based upon a new stochastic scheme the dynamics for both cases is fully analyzed. We show how the evolution of the system is described by a set of stochastic differential Schrodinger equations which in average reproduces the exact dynamics. Furthermore, we underline the role that Coulomb correlations plays in the polariton dynamics. Threshold behaviors are well captured by the present approach. The results are in complete agreement with recent experiment…
Two-photon absorption (TPA) allows accessing dark states of matter otherwise inaccessible to light, which serve as important building blocks for quantum information processing. In a semiconductor microcavity, TPA driven condensation of strongly-coupled light-matter exciton-polaritons can enable new solid-state quantum simulations of dark state-condensate interactions, and was predicted to stimulate THz emission. Here, we report the first observation of two-photon pumped polariton condensation, demonstrated by angle-resolved photoluminescence in a GaAs-based microcavity. TPA is evidenced in the…
The comment to article "Coexistence of Diamagnetism and Vanishingly Small Electrical Resistance at Ambient Temperature and Pressure in Nanostructures" shows the role of local electron pairing and Bose-Einstein-Condensation of pairs for superconductivity at Tc = 286 K in nanostructures.
The Bose-Einstein condensation (BEC) of magnetoexcitonic polaritons in a graphene layer embedded in a optical microcavity in a high magnetic field $B$ is predicted. The essential property of this system (in contrast, e.g., to a quantum well embedded in a cavity) is stronger influence of magnetic field and weaker influence of disorder. A two-dimensional (2D) magnetoexcitonic polaritons gas is considered in a planar harmonic electric field potential applied to excitons or a parabolic shape of the optical cavity causing the trapping of microcavity photons. It is shown that the effective polariton…
We studied optical response of microcavity non-equilibrium exciton-polariton Bose-Einstein condensate with saturable nonlinearity under simultaneous resonant and non-resonant pumping. We demonstrated the emergence of multistabile behavior due to the satutration of the excitonic absorbtion. Stable periodic Rabi- type oscillations of the excitonic and photonic condensate components in the regime of the stationary pump and their transition to the chaotic dynamics through the cascade of Hopf bifurcations by tuning of the electrical pump are revealed.
Microcavity polaritons are composite half-light half-matter quasi-particles, which have recently been demonstrated to exhibit rich physical properties, such as non-equilibrium Bose-Einstein condensation, parametric scattering and superfluidity. At the same time, polaritons have some important advantages over photons for information processing applications, since their excitonic component leads to weaker diffraction and stronger inter-particle interactions, implying, respectively, tighter localization and lower powers for nonlinear functionality. Here we present the first experimental observati…
We clarify the condition for the occurrence of magnon Bose-Einstein condensation (BEC) in spin pumping systems without using external pumping magnetic fields. The Goldstone model is generalized and the stability of the vacuum is closely investigated. By applying the generalized Goldstone model to spin pumping systems, the condition for the experimental realization of the stable magnon BEC in spin pumping systems is theoretically proposed.
