We consider theoretically nonlinear effects in a semiconductor quantum well embedded inside a photonic microcavity. Two-photon absorption by a 2p exciton state is considered and investigated; the matrix element of two-photon absorption is calculated. We compute the emission spectrum of the sample and demonstrate that under coherent pumping the nonlinearity of the two photon absorption process gives rise to bistability.
We consider theoretically nonlinear effects in a semiconductor quantum well embedded inside a photonic microcavity. Two-photon absorption by a 2p exciton state is considered and investigated; the matrix element of two-photon absorption is calculated. We compute the emission spectrum of the sample and demonstrate that under coherent pumping the nonlinearity of the two photon absorption process gives rise to bistability.
The exciton–photon effects on a microcavity are reported. In particular, the emission spectrum of a semiconductor quantum well embedded in a microcavity is obtained, including nonlinear effects such as exciton–exciton correlation. By solving the Heisenberg equations for the excitons and photons the polariton dispersion energy and the emission spectrum is calculated. It is shown the presence of collapses and revivals when the nonlinear interaction parameter is less than the exciton–photon coupling. For nonlinear exciton–exciton coupling values similar to exciton–photon coupling the results show that the time line shape is independent of the nonlinear term but the polariton peak position is blueshifted. Reasonable agreement is found with the experimental situation.
The main scope of this thesis is the investigation of quantum properties of nonlinear, dissipative, optical and condensed matter systems. Compared with previous studies on this subjects, we reached several milestone of general interests for the theoretical and experimental community. \nThe main experimental platform we refer to in this thesis is microcavity polaritons: polaritons arise from the coupling of light with excitons in a quantum well, i.e., a 2D semiconductor material embedded in the microcavity. They have attracted the interest of the scientific community for their rich physics. Polaritons can form out-of-equilibrium Bose-Einstein condensates, they can experience superfluid phase transition and, due to their interaction via the excitonic component, they show a variety of phenomena which are typical of nonlinear physics, such as bistability and parametric scattering. \nIn particular, motivated by recent proposals about the generation of single photons from weakly nonlinear system, like the unconventional photon blockade, and by the production of squeezed states in polariton systems, we studied the possibility of obtaining antibunched light and other quantum states (like squeezed states and entangled states), when the nonlinear system shows some peculiar features: in particular we consider polariton soliton and cascade systems. \nFinally, when considering nonlinear incoherent processes, we investigate the effect of the PT-symmetry and the PT-symmetry breaking on the quantum state of the emitted light. \nHence, this research work has two main objectives: first, from the fundamental physics point of view, to understand the interplay between nonlinear phenomena and quantum optics, second to provide useful tools for future technological applications. Specifically, for the latter case, we demonstrate a theorem that links the measurement of intensity correlations with the occurrence of certain phase transitions, and we propose a setup to maximize the non-classicality of the light emitted by weakly non-linear systems via a cascade configuration. \n \n \n
Abstract A quantum behavior of the light emitted by exciton polaritons excited in a pillar semiconductor microcavity with embedded quantum well is investigated. Considering the bare excitons and photon modes as coupled quantum oscillators allows for an accurate accounting of the nonlinear and dissipative effects. In particular, using the method of quantum states presentation in a quantum phase space via quasiprobability functions (namely, a P-function and a Wigner function), we study the effect of the laser and the exciton-photon detuning on the second order correlation function of the emitted photons. We determine the conditions for the phenomena of bunching, giant bunching, and antibunching of the emitted light. In particular, we predict the effect of a giant bunching for the case of a large exciton to photon population ratio. Within the domain of parameters supporting a bistability regime we demonstrate the effect of bunching of photons.
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 quadratic emission dependence on pump power below and above the condensation threshold, and second-harmonic generation is ruled out by both this threshold behaviour and by the emission peak energy showing no dependence on pump photon energy. Our results pave the way towards novel polariton-based sources and solid-state coherent control of collective quantum states with individual two-level systems.
Optical bistability and bright and dark resonator solitons exist in semiconductor resonator at room temperature [C.O. Weis and Ye. Larionova, Rep. Prog. Phys. 70 (2007) 255-335], with the usual semiconductor nonlinearity. At low temperature in the strong coupling regime between quantum well excitons and the optical field in a semiconductor microcavity the nonlinearities are strong and based on “polariton nonlinearity”. The strong coupling results in a quasi-particle “exciton-polariton” which gives access to positive and negative reactive and dissipative optical nonlinearities, as opposed to the usual room temperature semiconductor nonlinearities possessing essentially only one sign. The type of nonlinearity and the properties of solitons can be varied widely by the detuning between the photon- and exciton resonances. We show for the first time experimentally the existence of patterns, bright and dark solitons based on polariton nonlinearity. 1. INTRODUCTION Bright and dark spatial solitons were shown to exist in such microresonators with and without population inversion [1-3]. At room temperature the nonlinearity which is at the origin of the soliton existence is the usual mixed absorptive/refractive semiconductor nonlinearity which can have transverse effects (e.g. self-focusing) and longitudinal effects such as nonlinear resonance, both ingredients for soliton stability. At low temperature (or at large exciton binding energies) the exciton, which merges with the absorption band at room temperature, is well separated spectrally from the absorption band so that the nonlinearity becomes that of a 2-level system. If the exciton resonance is strongly coupled with the field inside a resonator the exciton- and the photon resonances mix. At coincidence of the two resonance frequencies, the photon- and the exciton resonances hybridize in an avoided crossing and the two hybrid resonances are ascribed to a quasi-particle, the excitonpolariton. This quasi-particle has unusual optical properties. E.g. is the photon nonlinearity determined by exciton collisions. That the exciton-polariton system has interesting nonlinearities (e.g. induced absorption as opposed to the usual saturable absorption) has been shown previously [4]. It was realized that semiconductor microresonators in the strong field-exciton coupling regime might show optical bistability and first experimental proofs for bistability were given recently [5]. As optical bistability of a resonator is a precondition for the existence of spatial resonator solitons, the question arises whether semiconductor microresonators with polariton nonlinearity can support spatial resonator solitons, which, as a consequence of the large nonlinearity of the polaritons, could be expected to exist at rather small light intensities, as it is of importance for all applications. 2. EXPERIMENTAL ARRANGEMENT AND RESULTS The cooled resonator sample (4 K) is illuminated by light at the polariton resonance wavelengths, and the light reflected from the resonator is observed. The light source is a Ar
We present an overview of our results concerning the influence of two-pair continuum coherences on the transient nonlinear optical response of semiconductor microcavities. We show that the interplay between these 4-particle coherences and the nonperturbative light-matter interaction produces highly desirable almost decoherence-free exciton-exciton collisions on the lower polariton branch. This effect gives rise to the very different nonlinear absorption rates on the two polariton branches observed in many experiments and make possible to reach a very high degree of amplification in samples with large Rabi splitting. Moreover, we show that the availability of almost decoherence free exciton-exciton collisions can be used for the realization of coherent trapping of polariton emission and amplification. This coherent manipulation and trapping of many-particle polariton states can be performed employing both ultrafast and continuous wave operation.