1,640 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
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
On the Question of Temperature Transformations under Lorentz and Galilei Boosts
We provide a quantum statistical thermodynamical solution of the long
standing problem of temperature transformations of uniformly moving bodies. Our
treatment of this question is based on the well established quantum statistical
result that the thermal equilibrium conditions demanded by both the Zeroth and
Second Laws of Thermodynamics are precisely those of Kubo, Martin and Schwinger
(KMS). We prove that, in both the special relativistic and nonrelativistic
settings, a state of a body cannot satisfy these conditions for different
inertial frames with non-zero relative velocity. Hence a body that serves as a
thermal reservoir, in the sense of the Zeroth Law, in an inertial rest frame
cannot do so in a laboratory frame relative to which it moves with non-zero
uniform velocity. Consequently, there is no law of temperature transformation
under either Lorentz or Galilei boosts, and so the concept of temperature
stemming from the Zeroth Law is restricted to states of bodies in their rest
frames.Comment: A few minor corrections have been made. The article will be published
in J. Phys.
Thermal behavior induced by vacuum polarization on causal horizons in comparison with the standard heat bath formalism
Modular theory of operator algebras and the associated KMS property are used
to obtain a unified description for the thermal aspects of the standard heat
bath situation and those caused by quantum vacuum fluctuations from
localization. An algebraic variant of lightfront holography reveals that the
vacuum polarization on wedge horizons is compressed into the lightray
direction. Their absence in the transverse direction is the prerequisite to an
area (generalized Bekenstein-) behavior of entropy-like measures which reveal
the loss of purity of the vacuum due to restrictions to wedges and their
horizons. Besides the well-known fact that localization-induced (generalized
Hawking-) temperature is fixed by the geometric aspects, this area behavior
(versus the standard volume dependence) constitutes the main difference between
localization-caused and standard thermal behavior.Comment: 15 page Latex, dedicated to A. A. Belavin on the occasion of his 60th
birthda
Certified quantum non-demolition measurement of material systems
An extensive debate on quantum non-demolition (QND) measurement, reviewed in
Grangier et al. [Nature, {\bf 396}, 537 (1998)], finds that true QND
measurements must have both non-classical state-preparation capability and
non-classical information-damage tradeoff. Existing figures of merit for these
non-classicality criteria require direct measurement of the signal variable and
are thus difficult to apply to optically-probed material systems. Here we
describe a method to demonstrate both criteria without need for to direct
signal measurements. Using a covariance matrix formalism and a general noise
model, we compute meter observables for QND measurement triples, which suffice
to compute all QND figures of merit. The result will allow certified QND
measurement of atomic spin ensembles using existing techniques.Comment: 11 pages, zero figure
The Fulling-Unruh effect in general stationary accelerated frames
We study the generalized Unruh effect for accelerated reference frames that
include rotation in addition to acceleration. We focus particularly on the case
where the motion is planar, with presence of a static limit in addition to the
event horizon. Possible definitions of an accelerated vacuum state are examined
and the interpretation of the Minkowski vacuum state as a thermodynamic state
is discussed. Such athermodynamic state is shown to depend on two parameters,
the acceleration temperature and a drift velocity, which are determined by the
acceleration and angular velocity of the accelerated frame. We relate the
properties of Minkowski vacuum in the accelerated frame to the excitation
spectrum of a detector that is stationary in this frame. The detector can be
excited both by absorbing positive energy quanta in the "hot" vacuum state and
by emitting negative energy quanta into the "ergosphere" between the horizon
and the static limit. The effects are related to similar effects in the
gravitational field of a rotating black hole.Comment: Latex, 39 pages, 5 figure
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