Scientists from the Faculty of Physics of the University of Warsaw have
demonstrated exciton-polariton lasing and parametric scattering of
exciton-polaritons in a system of coupled optical microcavities. The results
have been published in the prestigious journal Nanophotonics.
Exciton-polaritons are quasiparticles formed by a strong coupling between
excitons and photons in a semiconductor. Their bosonic nature and non-linear
interactions allow the observation of fascinating phenomena such as
Bose-Einstein condensation of polaritons and polariton lasing, which, unlike
typical lasering, occurs without occupation inversion.
Coupled microcavity systems, such as those based on two coupled optical
microcavities, offer a promising multi-level platform for basic research and
practical applications. The unique structure consisting of several dozen of
layers with the precisely defined thickness (each with an accuracy of a few
nanometers) was fabricated in the MBE laboratory at the Faculty of Physics,
University of Warsaw.
"In the presented work, we study non-linear effects in a system of two
coupled optical microcavities. Bose-Einstein condensation of polaritons and
polariton lasing occur at the two lowest energy levels of an overall
four-level system. This is a surprising result in the context of what has
previously been observed in single microcavities, where condensation took
place in the system's ground state. Emission dynamics measurements have
shown that in the present case the condensates of different energies share
the same lasing threshold, but do not appear simultaneously, i.e. they form
and disappear subsequently, one by one. Moreover, the transition to the
condensate state is accompanied by an energy-degenerate parametric
scattering of polaritons, i.e. the one in which the state of the crystal is
preserved before and after the scattering process," explains Krzysztof
Sawicki.
In previous studies on coupled microcavities, parametric scattering was
obtained using strictly resonant excitation. The non-resonant excitation
used in the present work enables spectral separation of the signal from the
excitation laser, which is a promising result from the point of view of
implementing sources of entangled photons based on polaritons.
Previously, a coupled microcavity system was used to demonstrate energy
transfer over 2 micrometers, mediated by polariton states. This is a record
distance taking into account the typical nanometer scale of interaction
between excitons in a semiconductor.
"We expect our results to open the way to the research on new types of
non-linear effects in multi-level polariton systems. Our work is essential
for such rapidly developing fields as, for example, all-optical quantum
computing, since the non-linear interactions in a multi-level system may
enable the implementation of logic systems based on polaritons," adds Jan
Suffczynski.
Reference:
Krzysztof Sawicki et al, Polariton lasing and energy-degenerate parametric
scattering in non-resonantly driven coupled planar microcavities,
Nanophotonics (2021). DOI:
10.1515/nanoph-2021-0079
Tags:
Physics