The strong coupling of photons and quantum well excitons in semiconductor microcavities leads to the formation of new eigenstates called polaritons. Due to their peculiar dispersion curve and the convenient experimental accessibility, microcavity polaritons have gained considerable interest in the recent years. Polariton states can be selectively populated by choosing the excitation angle and the wavelength of the excitation laser. After a lifetime of a few picoseconds the polariton decays and a photon is emitted from the cavity. This photon carries the whole information on the underlying polariton state.
The strong coupling of photons and quantum well excitons in semiconductor microcavities leads to the formation of new eigenstates called polaritons. Due to their peculiar dispersion curve and the convenient experimental accessibility, microcavity polaritons have gained considerable interest in the recent years. Polariton states can be selectively populated by choosing the excitation angle and the wavelength of the excitation laser. After a lifetime of a few picoseconds the polariton decays and a photon is emitted from the cavity. This photon carries the whole information on the underlying polariton state.
Summary form only given. Semiconductor microcavities can be engineered to produce strong coupling between photons and quantum well excitons leading to the formation of new eigenstates called polaritons. Due to their peculiar dispersion, enabling non-equilibrium Bose-Einstein condensation [1], and their straightforward experimental accessibility, microcavity polaritons have gained considerable interest in recent years. Polariton states can be selectively populated by choosing the excitation angle and the wavelength of the excitation laser. After a lifetime of a few picoseconds the polariton decays and a photon is emitted from the cavity, carrying the complete information on the underlying polariton state. Several theoretical works [2-3] suggest that polariton-polariton interactions can be a source of non-classical photon correlations, producing photon pairs that are entangled in either the energy, the polarization, or the momentum degree of freedom. One appeal of such a system is that many parameters such as the polariton-polariton interaction strength are tunable [4] and multipartite entangled states can be created in a single device [5]. However, due to the lack of high-quality samples, experimental realisations of these schemes have been elusive so far. In this contribution, we will discuss some of our experimental work on the statistics of polariton-polariton parametric scattering. Excited polaritons can scatter in a four-wave mixing process into signal and idler states lying on a figure-eight shaped curve in k-space, where phase-matching is fulfilled. We make use of a sample with ultra narrow exciton resonances, which allows for the generation and detection of correlated light. We present our measurements of the second order correlation functions using time-correlated photon counting. We discuss in detail, how polariton quantum correlations depend on a number of experimental parameters, such as phase space location and excitation density and find that the results can be understood in the framework of the well known Bogoliubov theory for 2D Bose gases utilised for microcavity polaritons [6]. We find bunching below the parametric threshold and a slow buildup of coherence above the threshold similar to the quantum statistics of a non-degenerate optical parametric oscillator, which is well known for its nonclassical properties [7]. We discuss in particular the influence of strong background processes on the observed photon statistics.
Recent theoretical studies of quantum nonlinear dynamics of laser-driven semiconductor microcavities in presence of a lateral photonic potential are reviewed. The following effects are discussed: (i) polariton parametric interactions can be tailored in photonic microstructures (e.g., photonic wires) to generate peculiar entangled states, which are efficiently coupled to the extra-cavity field and which are conveniently protected from the excitonic reservoir, (ii) the peculiar polariton superfluid behavior can be probed through the angle-resolved resonant Rayleigh scattering produced by point defects, (iii) polaritonic "circuits" can be designed to produce efficiently non-classical states of light as output.
Semiconductor microcavities are widely used to study collective interactions of cavity exciton-polaritons leading to their condensation phenomenon. Exciton-light interaction is highly enhanced in such structures due to the resonance enhancement of the electromagnetic field inside the high quality cavity. Considerably lower interest is concerned to exciton states non-resonant with the cavity mode for which the exciton-photon interaction is strongly reduced due to the existence of the cavity. We point out here that these states are responsible for non-classical light generation in semiconductor microcavities.
Entanglement generation by means of microcavity exciton-polaritons is an interesting application of the peculiar properties of these half-light/half-matter quasiparticles. In this paper, we theoretically investigate their luminescence dynamics and entanglement formation in single, and double cavities. We discuss the selection rules for polariton–polariton scattering in double cavities, and evaluate a number of possible parametric scattering schemes in terms of entanglement in the polarization degree of freedom, and identify the ones that are experimentally most promising.
We review, aiming at an audience of final year undergraduates, the phenomena observed in, and properties of, microcavity exciton–polariton condensates. These are condensates of mixed light and matter, consisting of superpositions of photons in semiconductor microcavities and excitons in quantum wells. Because of the imperfect confinement of the photon component, exciton–polaritons have a finite lifetime, and have to be continuously re-populated. Therefore, exciton–polariton condensates lie somewhere between equilibrium Bose–Einstein condensates and lasers. We review in particular the evidence for condensation, the coherence properties studied experimentally, and the wide variety of spatial structures either observed or predicted to exist in exciton–polariton condensates, including quantised vortices and other coherent structures. We also discuss the question of superfluidity in a non-equilibrium system, reviewing both the experimental attempts to investigate superfluidity to date, and the theoretical suggestions of how it may be further elucidated.
The quantum correlations between the beams generated by polariton pair scattering in a semiconductor microcavity above the parametric oscillation threshold are computed analytically. The influence of various parameters, including the cavity-exciton detuning, the intensity mismatch between the signal and idler beams, and the amount of spurious noise, is analyzed. We show that very strong quantum correlations between the signal and idler polaritons can be achieved. However, the quantum effects in the outgoing light fields are strongly reduced due to the large mismatch in the coupling of the signal and idler polaritons to the external photons.