Coherent Control of Polariton Parametric Scattering in Semiconductor Microcavities

Abstract

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k 0, even for delays much longer than the pulse width. The control of a large population at k 0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity. In the past few years, microcavities working in the strong coupling regime have attracted quite a lot of attention [1][2][3]. The excitonic transition of the embedded quantum well is strongly coupled to the cavity photon mode. In the radiative region near k 0 the resonant exciton and photon modes split and give rise to composite bosons, the so-called microcavity polaritons [4]. The dispersion of the lower polariton (LP) strongly deviates from the unperturbed exciton dispersion. The particular shape of the lower polariton dispersion allows for a parametric polariton scattering process conserving energy and in-plane momentum [2,5,6]. Two polaritons with an in-plane momentum k p scatter into a signal-idler pair with zero and 2k p momenta. The microcavity can thus be understood as an optical parametric oscillator.It is well-known that the parametric oscillation in a classical optical parametric oscillator (OPO) is a fully coherent process. The crystal is pumped in the transparency region and the coherence time of the process is given by the duration of the pump pulses. The pump intensity required to achieve parametric oscillation is very high because the involved electronic states are virtual [7,8]. The semiconductor microcavity system exhibits three major differences to the classical OPO. First, the signal, pump, and idler states are real and thus very efficiently coupled to external laser light. Second, the excitations are interacting via a real Coulomb interaction which results in high parametric scattering rates. These two features illustrate the high efficiency of the process [2,5,6]. The third difference is that for our system the coherence time should not be given by the external laser pulses but by the properties of the excitations and the scattering themselves. The coherent control technique allows one to sense these coherence properties and to manipulate the scattering within its coherence time [9][10][11].In this Letter we report the coherent control of the parametric polariton scattering. The dynamics of the parametric scattering are governed by the lifetime of the real polariton states and the applied pump power [12]. Especially just above threshold the dynamics of the polariton scattering are ...

Vortices in Polariton OPO Superfluids

“…OPA was first observed in an InGaAs/GaAs/AlGaAs microcavity [49], where a substantial signal gain of up to 70 was measured. Much experimental work has followed this first result [50,51,52,53,54,55,56,57,58,59]. Pump-probe parametric amplification of polaritons with an extraordinary gain up to 5000 and at temperatures up to 120K has been reached in GaAlAs-based microcavities and up to 220K in CdTe-based microcavities [55].…”

Non‐linear dynamical effects in semiconductor microcavities

“…Phase controlled pulse pairs can be created using a Michelson interferometer; while the delay can be varied by moving one of the mirrors with a micrometre screw, the phase is changed and actively stabilised using a piezoelectric element controlled by an optoelectronic feedback loop [30,31]. The first probe pulse creates some polarisation near k ≈ 0 in the µC, stimulating parametric scattering.…”

Resonant nonlinear studies of trapped 0D‐microcavity polaritons

“…This process is similar to the optical parametric oscillator (OPO). It has lead to the observation of several phenomena of interest as giant parametric amplification [5] or coherent control of polaritons [6] along with a varied phenomenology. For one given pump state, the allowed couples of signals and idlers are described by 8-shaped lines in the 2D reciprocal space, as was observed by [7].…”