11,680 research outputs found
On the Structure of the Bose-Einstein Condensate Ground State
We construct a macroscopic wave function that describes the Bose-Einstein
condensate and weakly excited states, using the su(1,1) structure of the
mean-field hamiltonian, and compare this state with the experimental values of
second and third order correlation functions.Comment: 10 pages, 2 figure
Criteria for reachability of quantum states
We address the question of which quantum states can be inter-converted under
the action of a time-dependent Hamiltonian. In particular, we consider the
problem applied to mixed states, and investigate the difference between pure
and mixed-state controllability introduced in previous work. We provide a
complete characterization of the eigenvalue spectrum for which the state is
controllable under the action of the symplectic group. We also address the
problem of which states can be prepared if the dynamical Lie group is not
sufficiently large to allow the system to be controllable.Comment: 14 pages, IoP LaTeX, first author has moved to Cambridge university
([email protected]
Thermalization of Squeezed States
Starting with a thermal squeezed state defined as a conventional thermal
state based on an appropriate hamiltonian, we show how an important physical
property, the signal-to-noise ratio, is degraded, and propose a simple model of
thermalization (Kraus thermalization).Comment: 7 pages, 1 table, 1 figure. Presented at ICSSUR 2005, Besancon,
Franc
MEVTV Workshop on Nature and Composition of Surface Units on Mars
Topics addressed include: SNC meteorites and their potential for providing information about the geochemical evolution of Mars; remote sensing; photogeological inferences of Martian surface compositions; and interactions of the surface with volatiles in either the surface or the atmosphere
(Re-)Inventing the Relativistic Wheel: Gravity, Cosets, and Spinning Objects
Space-time symmetries are a crucial ingredient of any theoretical model in
physics. Unlike internal symmetries, which may or may not be gauged and/or
spontaneously broken, space-time symmetries do not admit any ambiguity: they
are gauged by gravity, and any conceivable physical system (other than the
vacuum) is bound to break at least some of them. Motivated by this observation,
we study how to couple gravity with the Goldstone fields that non-linearly
realize spontaneously broken space-time symmetries. This can be done in
complete generality by weakly gauging the Poincare symmetry group in the
context of the coset construction. To illustrate the power of this method, we
consider three kinds of physical systems coupled to gravity: superfluids,
relativistic membranes embedded in a higher dimensional space, and rotating
point-like objects. This last system is of particular importance as it can be
used to model spinning astrophysical objects like neutron stars and black
holes. Our approach provides a systematic and unambiguous parametrization of
the degrees of freedom of these systems.Comment: 30 page
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