35 research outputs found
Polariton Condensation and Lasing
The similarities and differences between polariton condensation in
microcavities and standard lasing in a semiconductor cavity structure are
reviewed. The recent experiments on "photon condensation" are also reviewed.Comment: 23 pages, 6 figures; Based on the book chapter in Exciton Polaritons
in Microcavities, (Springer Series in Solid State Sciences vol. 172), V.
Timofeev and D. Sanvitto, eds., (Springer, 2012
Physical Response Functions of Strongly Coupled Massive Quantum Liquids
We study physical properties of strongly coupled massive quantum liquids from
their spectral functions using the AdS/CFT correspondence. The generic model
that we consider is dense, heavy fundamental matter coupled to SU(N_c) super
Yang-Mills theory at finite temperature above the deconfinement phase
transition but below the scale set by the baryon number density. In this setup,
we study the current-current correlators of the baryon number density using new
techniques that employ a scaling behavior in the dual geometry. Our results,
the AC conductivity, the quasi-particle spectrum and the Drude-limit parameters
like the relaxation time are simple temperature-independent expressions that
depend only on the mass-squared to density ratio and display a crossover
between a baryon- and meson-dominated regime. We concentrated on the
(2+1)-dimensional defect case, but in principle our results can also be
generalized straightforwardly to other cases.Comment: 21 pages, 10 figures, extra paragraph and figure are added in
response to referee's comment
Dynamics of spin polarization in tilted polariton rings
This is an accepted manuscript of an article published by the American Physical Society in Physical Review B on 22/04/2021, available online: https://doi.org/10.1103/PhysRevB.103.165306
The accepted version of the publication may differ from the final published version.We have observed the effect of pseudomagnetic field originating from the polaritonic analog of spin-orbit coupling [transverse electric and transverse magnetic (TE-TM) splitting] on a polariton condensate in a ring-shaped microcavity. The effect gives rise to a stable four-leaf pattern around the ring as seen from the linear polarization measurements of the condensate photoluminescence. This pattern is found to originate from the interplay of the cavity potential, energy relaxation, and TE-TM splitting in the ring. Our observations are compared to the dissipative one-dimensional spinor Gross-Pitaevskii equation with the TE-TM splitting energy, which shows good qualitative agreement.Published versio
Beyond Gross-Pitaevskii Mean Field Theory
A large number of effects related to the phenomenon of Bose-Einstein
Condensation (BEC) can be understood in terms of lowest order mean field
theory, whereby the entire system is assumed to be condensed, with thermal and
quantum fluctuations completely ignored. Such a treatment leads to the
Gross-Pitaevskii Equation (GPE) used extensively throughout this book. Although
this theory works remarkably well for a broad range of experimental parameters,
a more complete treatment is required for understanding various experiments,
including experiments with solitons and vortices. Such treatments should
include the dynamical coupling of the condensate to the thermal cloud, the
effect of dimensionality, the role of quantum fluctuations, and should also
describe the critical regime, including the process of condensate formation.
The aim of this Chapter is to give a brief but insightful overview of various
recent theories, which extend beyond the GPE. To keep the discussion brief,
only the main notions and conclusions will be presented. This Chapter
generalizes the presentation of Chapter 1, by explicitly maintaining
fluctuations around the condensate order parameter. While the theoretical
arguments outlined here are generic, the emphasis is on approaches suitable for
describing single weakly-interacting atomic Bose gases in harmonic traps.
Interesting effects arising when condensates are trapped in double-well
potentials and optical lattices, as well as the cases of spinor condensates,
and atomic-molecular coupling, along with the modified or alternative theories
needed to describe them, will not be covered here.Comment: Review Article (19 Pages) - To appear in 'Emergent Nonlinear
Phenomena in Bose-Einstein Condensates: Theory and Experiment', Edited by
P.G. Kevrekidis, D.J. Frantzeskakis and R. Carretero-Gonzalez (Springer
Verlag
Transition to a Bose-Einstein condensate of excitons at sub-Kelvin temperatures
Bose-Einstein condensation (BEC) is a quantum mechanical phenomenon directly
linked to the quantum statistics of bosons. While cold atomic gases provide a
new arena for exploring the nature of BEC, a long-term quest to confirm BEC of
excitons, quasi-Bose particles formed as a bound state of an electron-hole
pair, has been underway since its theoretical prediction in the 1960s.
Ensembles of electrons and holes are complex quantum systems with strong
Coulomb correlations; thus, it is non-trivial whether nature chooses a form of
exciton BEC. Various systems have been examined in bulk and two-dimensional
semiconductors and also exciton-photon hybrid systems. Among them, the 1s
paraexciton state in a single crystal of Cu2O has been a prime candidate for
realizing three-dimensional BEC. The large binding energy and long lifetime
enable preparation of cold excitons in thermal equilibrium with the lattice and
decoupled from the radiation field. However, collisional loss severely limits
the conditions for reaching BEC. Such a system with a large inelastic cross
section is excluded in atomic BEC experiments, where a small inelastic
scattering rate and efficient elastic scattering are necessary for evaporative
cooling. Here we demonstrate that it is nevertheless possible to achieve BEC by
cooling paraexcitons to sub-Kelvin temperatures in a cold phonon bath. Emission
spectra from paraexcitons in a three-dimensional trap show an anomalous
distribution in a threshold-like manner at the critical number of BEC expected
for ideal bosons. Bosonic stimulated scattering into the condensate and
collisional loss compete and limit the condensate to a fraction of about 1%.
This observation adds a new class of experimentally accessible BEC for
exploring a rich variety of matter phases of electron-hole ensembles.Comment: 19 pages, 3 figures, Supplementary Information (12 pages, 4 figures)
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