High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Abstract

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons. Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures. Here we demonstrate polariton parametric amplification up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-based microcavities. We show that the cut-off temperature for the amplification is ultimately determined by the binding energy of the exciton. A 5-micrometer-thick planar microcavity can amplify a weak light pulse more than 5,000 times. The effective gain coefficient of an equivalent homogeneous medium would be 107 cm-1. The subpicosecond duration and high efficiency of the amplification could be exploited for high-repetition all-optical microscopic switches and amplifiers. 105 polaritons occupy the same quantum state during the amplification, realizing a dynamical condensate of strongly interacting bosons which can be studied at high temperature.

Coherence and correlation in semiconductor microcavities

“…Fig. 1 (lower panel) shows that an increase of less then a factor 1/3 in the polariton splitting produces an increase of the maximum achievable gain at T = 77 K of six time in agreement with experimental results [3]. This result shows how the increase of the exciton-photon coupling favours high-temperature operation.…”

Polariton lasing in high-quality selenide-based micropillars in the strong coupling regime

“…16 With this idea in mind, ZnSe or CdTe based microstructures in the strong coupling regime have a great potential: On the one hand, they have an excitonic binding energy, in principle, large enough to be able to maintain the strong coupling regime at room temperature. 17 On the other hand, keeping in mind that the excitonic nonlinearity scales like the Bohr radius 18 a B , the latter is still large enough in these materials to provide a sizeable nonlinearity. 17 Finally, ZnSe has the advantage over CdTe to exhibit a polaritonic optical transition in the blue region of the spectrum (440 nm versus 740 nm, respectively), thus allowing to squeeze the polaritonic wavefunction into smaller diameter as we will see further on.…”

“…17 On the other hand, keeping in mind that the excitonic nonlinearity scales like the Bohr radius 18 a B , the latter is still large enough in these materials to provide a sizeable nonlinearity. 17 Finally, ZnSe has the advantage over CdTe to exhibit a polaritonic optical transition in the blue region of the spectrum (440 nm versus 740 nm, respectively), thus allowing to squeeze the polaritonic wavefunction into smaller diameter as we will see further on.…”

Polaritronics in view

“…Second, they might be stable at room temperature, with obvious advantages. Finally, they are good bosons, meaning that they can be parametrically amplified 4 (that is, split up or joined together in units of different energy, a useful technique for signal amplification), and that many of them can pile up in a given quantum state, eventually leading to the formation of the state of matter known as a Bose-Einstein condensate 5 .…”

“…The nigh-on simultaneous advances in the field 2,6-8 , on the back of the parametric amplification 4 and Bose-Einstein condensation 5 To survive, organisms must adapt to their everchanging environment. Animals rely mainly on behavioural adaptive responses such as fighting or fleeing.…”