Sources of single photons are key elements in the study of basic quantum optical concepts and applications in quantum information science. Among the different sources available, semiconductor quantum dots excel with their straight forward integrabili
ty in semiconductor based on-chip solutions and the potential that photon emission can be triggered on demand. Usually, the photon emission event is part of a cascaded biexciton-exciton emission scheme. Important properties of the emitted photon such as polarization and time of emission are either probabilistic in nature or pre-determined by electronic properties of the system. In this work, we study the direct two-photon emission from the biexciton. We show that emission through this higher-order transition provides a much more versatile approach to generate a single photon. In the scheme we propose, the two-photon emission from the biexciton is enabled by a laser field (or laser pulse) driving the system into a virtual state inside the band gap. From this intermediate virtual state, the single photon of interest is then spontaneously emitted. Its properties are determined by the driving laser pulse, enabling all-optical on-the-fly control of polarization state, frequency, and time of emission of the photon.
Based on a microscopic many-particle theory, we predict large optical gain in the probe and background-free four-wave mixing directions caused by excitonic instabilities in semiconductor quantum wells. For a single quantum well with radiative-decay l
imited dephasing in a typical pump-probe setup we discuss the microscopic driving mechanisms and polarization and frequency dependence of these instabilities.
Using a microscopic many-particle theory, we propose all-optical switching in planar semiconductor microcavities where a weak beam switches a stronger signal. Based on four-wave-mixing instabilities, the general scheme is a semiconductor adaptation o
f a recently demonstrated switch in an atomic vapor [Dawes et al., Science 308, 672 (2005)].
Based on a microscopic many-particle theory we study the amplification of polaritons in a multiple-quantum-well resonant photonic crystal. For the Bragg-spaced multiple quantum wells under investigation we predict that in a typical pump-probe setup f
our-wave mixing processes can lead to an unstable energy transfer from the pump into the probe and the background-free four-wave mixing directions. We find that under certain excitation conditions this phase-conjugate oscillation induced instability can lead to a large amplification of the weak probe pulse.
Based on a microscopic many-particle theory we investigate the influence of excitonic correlations on the vectorial polarization state characteristics of the parametric amplification of polaritons in semiconductor microcavities. We study a microcavit
y with perfect in-plane isotropy. A linear stability analysis of the cavity polariton dynamics shows that in the co-linear (TE-TE or TM-TM) pump-probe polarization state configuration, excitonic correlations diminish the parametric scattering process whereas it is enhanced by excitonic correlations in the cross-linear (TE-TM or TM-TE) configuration. Without any free parameters, our microscopic theory gives a quantitative understanding how many-particle effects can lead to a rotation or change of the outgoing (amplified) probe signals vectorial polarization state relative to the incoming ones.
