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[资源] Dynamic Condensation of Semiconductor Microcavity Polaritons

DYNAMIC CONDENSATION OF SEMICONDUCTOR MICROCAVITY POLARITONS
a dissertation submitted to the department of applied physics and the committee on graduate studies of stanford university
in partial fulfillment of the requirements for the degree of doctor of philosophy
Hui Deng
June 2006

Abstract
There are a countable number of experimental systems where a macroscopic quantum
order is established, such as lasers, superfluids, superconductors and Bose-Einstein
condensates of atomic vapors. Each of these systems has deepened our fundamental
understanding of many-body physics, and has led to novel research tools as well as
applications. A newcomer to the family is the unique half-light half-matter quasi-
particles in solids { the semiconductor microcavity polaritons. In this thesis, we use
microcavities with multiple GaAs-quantum wells and search for a macroscopic phase
of the polaritons at a temperature of 4 K.

We demonstrated a quantum degeneracy threshold of polaritons stemming from
the Bose-final state stimulation of polaritons. The threshold density is two orders of
magnitude less than that of a photon laser and well below the electronic population
inversion condition. This result is a proof of principle that microcavity polaritons
hold promise for a new source of coherent light with high energy efficiency.
Further, many of the quantum statistical properties of polariton can be directly
measured by well-developed optical techniques. We study for the first time the time-
domain second order coherence function of the polaritons, and demonstrate that
macroscopic coherence gradually builds up in the polariton ground state above the
quantum degeneracy threshold. We measure the momentum distributions of the
polaritons, and observe a quantum degenerate Bose-Einstein distribution at the lattice
temperature, with a chemical potential close to zero. This is the first observation of
simultaneous quantum degeneracy and thermal equilibrium in a gas of quasi-particles
in solids. Polarization properties and spatial distributions of the polariton condensate
also show distinct features associated with the phase transition.

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