3,163 research outputs found
-algebras and quantum dynamics: some existence results
We discuss the possibility of defining an algebraic dynamics within the
settings of -algebras. Compared with our previous results on this
subject, the main improvement here is that we are not assuming the existence of
some hamiltonian for the {\em full} physical system. We will show that, under
suitable conditions, the dynamics can still be defined via some limiting
procedure starting from a given {\em regularized sequence}
Note on the Relativistic Thermodynamics of Moving Bodies
We employ a novel thermodynamical argument to show that, at the macroscopic
level,there is no intrinsic law of temperature transformation under Lorentz
boosts. This result extends the corresponding microstatistical one of earlier
works to the purely macroscopic regime and signifies that the concept of
temperature as an objective entity is restricted to the description of bodies
in their rest frames. The argument on which this result is based is centred on
the thermal transactions between a body that moves with uniform velocity
relative to a certain inertial frame and a thermometer, designed to measure its
temperature, that is held at rest in that frame.Comment: To be published in J. Phys. A. A few minor corrections have been made
to the earlier version of this articl
Variational approach to transport in quantum dots
We have derived a variational principle that defines the nonequilibrium
steady-state transport across a correlated impurity mimicking, e.g., a quantum
dot coupled to biased leads. This variational principle has been specialized to
a Gutzwiller's variational space, and applied to the study of the simple
single-orbital Anderson impurity model at half filling, finding a good
qualitative accord with the observed behavior in quantum dots for the expected
regime of values of the bias. Beyond the purely theoretical interest in the
formal definition of a variational principle in a nonequilibrium problem, the
particular methods proposed have the important advantage to be simple and
flexible enough to deal with more complicated systems and variational spaces.Comment: 15 pages, 4 figure
Manufacturing time operators: covariance, selection criteria, and examples
We provide the most general forms of covariant and normalized time operators
and their probability densities, with applications to quantum clocks, the time
of arrival, and Lyapunov quantum operators. Examples are discussed of the
profusion of possible operators and their physical meaning. Criteria to define
unique, optimal operators for specific cases are given
Quantum control of spin-correlations in ultracold lattice gases
We demonstrate that it is possible to prepare a lattice gas of ultracold
atoms with a desired non-classical spin-correlation function using atom-light
interaction of the kind routinely employed in quantum spin polarization
spectroscopy. Our method is based on quantum non-demolition (QND) measurement
and feedback, and allows in particular to create on demand exponentially or
algebraically decaying correlations, as well as a certain degree of
multi-partite entanglement.Comment: 2 figure
KMS, etc
A general form of the ``Wick rotation'', starting from imaginary-time Green
functions of quantum-mechanical systems in thermal equilibrium at positive
temperature, is established. Extending work of H. Araki, the role of the KMS
condition and of an associated anti-unitary symmetry operation, the ``modular
conjugation'', in constructing analytic continuations of Green functions from
real- to imaginary times, and back, is clarified.
The relationship between the KMS condition for the vacuum with respect to
Lorentz boosts, on one hand, and the spin-statistics connection and the PCT
theorem, on the other hand, in local, relativistic quantum field theory is
recalled.
General results on the reconstruction of local quantum theories in various
non-trivial gravitational backgrounds from ``Euclidian amplitudes'' are
presented. In particular, a general form of the KMS condition is proposed and
applied, e.g., to the Unruh- and the Hawking effects.
This paper is dedicated to Huzihiro Araki on the occasion of his seventieth
birthday, with admiration, affection and best wishes.Comment: 56 pages, submitted to J. Math. Phy
Quantum macrostatistical picture of nonequilibrium steady states
We employ a quantum macrostatistical treatment of irreversible processes to
prove that, in nonequilibrium steady states, (a) the hydrodynamical observables
execute a generalised Onsager-Machlup process and (b) the spatial correlations
of these observables are generically of long range. The key assumptions behind
these results are a nonequilibrium version of Onsager's regression hypothesis,
together with certain hypotheses of chaoticity and local equilibrium for
hydrodynamical fluctuations.Comment: TeX, 13 page
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