3,783 research outputs found
Mode-locking and mode-competition in a non-equilibrium solid-state condensate
A trapped polariton condensate with continuous pumping and decay is analyzed
using a generalized Gross-Pitaevskii model. Whereas an equilibrium condensate
is characterized by a macroscopic occupation of a ground state, here the
steady-states take more general forms. Some are characterized by a large
population in an excited state, and others by large populations in several
states. In the latter case, the highly-populated states synchronize to a common
frequency above a critical density. Estimates for the critical density of this
synchronization transition are consistent with experiments.Comment: 5 pages, 2 figure
Condensation and Lasing of Microcavity Polaritons: Comparison between two Models
Condensation of microcavity polaritons and the substantial influence of
pair-breaking disorder and decoherence leading to a laser regime has been
recently considered using two different models: a model for direct two band
excitons in a disordered quantum well coupled to light and a model where the
cavity mode couples instead to a medium of localised excitons, represented by
two-level oscillators in the presence of dephasing processes. Even if
complementary from the point of view of assumptions, the models share most of
the main conclusions and show similar phase diagrams. The issue whether
excitons are propagating or localised seems secondary for the polariton
condensation and the way in which pair-breaking disorder and decoherence
processes influence the condensation and drive the microcavity into a lasing
regime is, within the approximations used in each model, generic. The reasons
for the similarities between the two physical situations are analysed and
explained.Comment: Proceeding of the First International Conference on Spontaneous
Coherence in Excitonic Systems (ICSCE'04); 7 pages, 2 eps figure
The crossover between lasing and polariton condensation in optical microcavities
We study a model of a photon mode dipole-coupled to a medium of two-level
oscillators in a microcavity in the presence of dephasing processes introduced
by coupling to external baths. Decoherence processes can be classified as
pair-breaking or non-pair-breaking in analogy with magnetic or non-magnetic
impurities in superconductors. In the absence of dephasing, the ground state of
the model is a polariton condensate with a gap in the excitation spectrum.
Increase of the pair-breaking parameter reduces the gap, which becomes
zero at a critical value ; for large , the conventional
laser regime is obtained in a way that demonstrates its close analogy to a
gapless superconductor. In contrast, weak non-pair-breaking processes have no
qualitative effect on the condensate or the existence of a gap, although they
lead to inhomogeneous broadening of the excitations
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