35,798 research outputs found
The Unruh Quantum Otto Engine
We introduce a quantum heat engine performing an Otto cycle by using the
thermal properties of the quantum vacuum. Since Hawking and Unruh, it has been
established that the vacuum space, either near a black hole or for an
accelerated observer, behaves as a bath of thermal radiation. In this work, we
present a fully quantum Otto cycle, which relies on the Unruh effect for a
single quantum bit (qubit) in contact with quantum vacuum fluctuations. By
using the notions of quantum thermodynamics and perturbation theory we obtain
that the quantum vacuum can exchange heat and produce work on the qubit.
Moreover, we obtain the efficiency and derive the conditions to have both a
thermodynamic and a kinematic cycle in terms of the initial populations of the
excited state, which define a range of allowed accelerations for the Unruh
engine.Comment: 31 pages, 11 figure
Nonviolation of Bell's Inequality in Translation Invariant Systems
The nature of quantum correlations in strongly correlated systems has been a
subject of intense research. In particular, it has been realized that
entanglement and quantum discord are present at quantum phase transitions and
able to characterize it. Surprisingly, it has been shown for a number of
different systems that qubit pairwise states, even when highly entangled, do
not violate Bell's inequalities, being in this sense local. Here we show that
such a local character of quantum correlations is in fact general for
translation invariant systems and has its origins in the monogamy trade-off
obeyed by tripartite Bell correlations. We illustrate this result in a quantum
spin chain with a soft breaking of translation symmetry. In addition, we extend
the monogamy inequality to the -qubit scenario, showing that the bound
increases with and providing examples of its saturation through uniformly
generated random pure states.Comment: Published erratum added at the en
Fourier Eigenfunctions, Uncertainty Gabor Principle and Isoresolution Wavelets
Shape-invariant signals under Fourier transform are investigated leading to a
class of eigenfunctions for the Fourier operator. The classical uncertainty
Gabor-Heisenberg principle is revisited and the concept of isoresolution in
joint time-frequency analysis is introduced. It is shown that any Fourier
eigenfunction achieve isoresolution. It is shown that an isoresolution wavelet
can be derived from each known wavelet family by a suitable scaling.Comment: 6 pages, XX Simp\'osio Bras. de Telecomunica\c{c}\~oes, Rio de
Janeiro, Brazil, 2003. Fixed typo
Overcoming ambiguities in classical and quantum correlation measures
We identify ambiguities in the available frameworks for defining quantum,
classical, and total correlations as measured by discordlike quantifiers. More
specifically, we determine situations for which either classical or quantum
correlations are not uniquely defined due to degeneracies arising from the
optimization procedure over the state space. In order to remove such
degeneracies, we introduce a general approach where correlations are
independently defined, escaping therefore from a degenerate subspace. As an
illustration, we analyze the trace-norm geometric quantum discord for two-qubit
Bell-diagonal states.Comment: 5 pages, 2 figures. v2: Minor corrections. Published versio
The fluctuation-dissipation theorem and the linear Glauber model
We obtain exact expressions for the two-time autocorrelation and response
functions of the -dimensional linear Glauber model. Although this linear
model does not obey detailed balance in dimensions , we show that the
usual form of the fluctuation-dissipation ratio still holds in the stationary
regime. In the transient regime, we show the occurence of aging, with a special
limit of the fluctuation-dissipation ratio, , for a quench at
the critical point.Comment: Accepted for publication (Physical Review E
Compactly Supported Wavelets Derived From Legendre Polynomials: Spherical Harmonic Wavelets
A new family of wavelets is introduced, which is associated with Legendre
polynomials. These wavelets, termed spherical harmonic or Legendre wavelets,
possess compact support. The method for the wavelet construction is derived
from the association of ordinary second order differential equations with
multiresolution filters. The low-pass filter associated with Legendre
multiresolution analysis is a linear phase finite impulse response filter
(FIR).Comment: 6 pages, 6 figures, 1 table In: Computational Methods in Circuits and
Systems Applications, WSEAS press, pp.211-215, 2003. ISBN: 960-8052-88-
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