3 research outputs found
Critical fluctuations in a confined driven-dissipative quantum condensate
Phase fluctuations determine the low-energy properties of quantum
condensates. However, at the condensation threshold, both density and phase
fluctuations are relevant. While strong emphasis has been given to the
investigation of phase fluctuations, which dominate the physics of the quantum
system away from the critical point -- number fluctuations have been much less
explored, even in thermal equilibrium. In this work, we report experimental
observation and theoretical description of fluctuations in a
circularly-confined non-equilibrium Bose-Einstein condensate of polaritons near
the condensation threshold. We observe critical fluctuations, which combine the
number fluctuations of a single-mode condensate state and competition between
different states. The latter are analogous to mode hopping in photon lasers.
Our theoretical analysis indicates that this phenomenon is of a quantum
character, while classical noise of the pump is not sufficient to explain the
experiments. The manifestation of a critical quantum state competition unlocks
new possibilities for the study of condensate formation while linking to
practical realizations in photonic lasers
Bose condensation of upper-branch exciton-polaritons in a transferrable microcavity
Exciton-polaritons are composite bosonic quasiparticles arising from the
strong coupling of excitonic transitions and optical modes. Exciton-polaritons
have triggered wide exploration in the past decades not only due to their rich
quantum phenomena such as superfluidity, superconductivity and quantized
vortices but also due to their potential applications for unconventional
coherent light sources and all-optical control elements. Here, we report the
observation of Bose-Einstein condensation of the upper polariton branch in a
transferrable WS monolayer microcavity. Near the condensation threshold, we
observe a nonlinear increase in upper polariton intensity. This sharp increase
in intensity is accompanied by a decrease of the linewidth and an increase of
the upper polariton temporal coherence, all of which are hallmarks of
Bose-Einstein condensation. By simulating the quantum Boltzmann equation, we
show that the upper polariton condensation only occurs for a particular range
of particle density. We can attribute the creation of Bose condensation of the
upper polariton to the following requirements: 1) the upper polariton is more
excitonic than the lower one; 2) there is relatively more pumping in the upper
branch; and 3) the conversion time from the upper to the lower polariton branch
is long compared to the lifetime of the upper polaritons
Bose Condensation of Upper-Branch Exciton-Polaritons in a Transferable Microcavity
Exciton-polaritons are composite quasiparticles that
result from
the coupling of excitonic transitions and optical modes. They have
been extensively studied because of their quantum phenomena and potential
applications in unconventional coherent light sources and all-optical
control elements. In this work, we report the observation of Bose–Einstein
condensation of the upper polariton branch in a transferable WS2 monolayer microcavity. Near the condensation threshold, we
observe a nonlinear increase in upper polariton intensity accompanied
by a decrease in line width and an increase in temporal coherence,
all of which are hallmarks of Bose–Einstein condensation. Simulations
show that this condensation occurs within a specific particle density
range, depending on the excitonic properties and pumping conditions.
The manifestation of upper polariton condensation unlocks new possibilities
for studying the condensate competition while linking it to practical
realizations in polaritonic lasers. Our findings contribute to the
understanding of bosonic systems and offer potential for the development
of polaritonic devices