340 research outputs found
The general structure of quantum resource theories
In recent years it was recognized that properties of physical systems such as
entanglement, athermality, and asymmetry, can be viewed as resources for
important tasks in quantum information, thermodynamics, and other areas of
physics. This recognition followed by the development of specific quantum
resource theories (QRTs), such as entanglement theory, determining how quantum
states that cannot be prepared under certain restrictions may be manipulated
and used to circumvent the restrictions. Here we discuss the general structure
of QRTs, and show that under a few assumptions (such as convexity of the set of
free states), a QRT is asymptotically reversible if its set of allowed
operations is maximal; that is, if the allowed operations are the set of all
operations that do not generate (asymptotically) a resource. In this case, the
asymptotic conversion rate is given in terms of the regularized relative
entropy of a resource which is the unique measure/quantifier of the resource in
the asymptotic limit of many copies of the state. This measure also equals the
smoothed version of the logarithmic robustness of the resource.Comment: 5 pages, no figures, few references added, published versio
SMUGGLING AS ANOTHER CAUSE OF FAILURE OF THE PPP
In theoretical literature, smuggling is considered as a factor contributing to the deviation of the PPP-based exchange rates from the equilibrium exchange rates with little empirical support. In this paper, we used panel data for 33 developing countries over the period 1982-1995 and used panel unit root and panel cointegration technique along with pooled OLS, fixed effects, random effects, and Parks estimator in an augmented Balassa-Samuelson framework. Using two different proxies for smuggling it is found that smuggling into a country leads to an appreciation of domestic currency that can be considered as another cause of loosing competitiveness by many developing countries.Smuggling, PPP, Real Exchange Rate, Panel Data, Panel Unit Root, Panel Cointegration, LDCs
Mixed State Entanglement of Assistance and the Generalized Concurrence
We consider the maximum bipartite entanglement that can be distilled from a
single copy of a multipartite mixed entangled state, where we focus mostly on
-dimensional tripartite mixed states. We show that this {\em
assisted entanglement}, when measured in terms of the generalized concurrence
(named G-concurrence) is (tightly) bounded by an entanglement monotone, which
we call the G-concurrence of assistance. The G-concurrence is one of the
possible generalizations of the concurrence to higher dimensions, and for pure
bipartite states it measures the {\em geometric mean} of the Schmidt numbers.
For a large (non-trivial) class of -dimensional mixed states, we are
able to generalize Wootters formula for the concurrence into lower and upper
bounds on the G-concurrence. Moreover, we have found an explicit formula for
the G-concurrence of assistance that generalizes the expression for the
concurrence of assistance for a large class of dimensional
tripartite pure states.Comment: 7 page
Comparison of area spectra in loop quantum gravity
We compare two area spectra proposed in loop quantum gravity in different
approaches to compute the entropy of the Schwarzschild black hole. We describe
the black hole in general microcanonical and canonical area ensembles for these
spectra. We show that in the canonical ensemble, the results for all
statistical quantities for any spectrum can be reproduced by a heuristic
picture of Bekenstein up to second order. For one of these spectra - the
equally-spaced spectrum - in light of a proposed connection of the black hole
area spectrum to the quasinormal mode spectrum and following hep-th/0304135, we
present explicit calculations to argue that this spectrum is completely
consistent with this connection. This follows without requiring a change in the
gauge group of the spin degrees of freedom in this formalism from SU(2) to
SO(3). We also show that independent of the area spectrum, the degeneracy of
the area observable is bounded by , where is measured in
Planck units and is a constant of order unity.Comment: 8 pages, Revtex 4, version to appear in Classical and Quantum Gravit
(Quantumness in the context of) Resource Theories
We review the basic idea behind resource theories, where we quantify quantum
resources by specifying a restricted class of operations. This divides the
state space into various sets, including states which are free (because they
can be created under the class of operations), and those which are a resource
(because they cannot be). One can quantify the worth of the resource by the
relative entropy distance to the set of free states, and under certain
conditions, this is a unique measure which quantifies the rate of state to
state transitions. The framework includes entanglement, asymmetry and purity
theory. It also includes thermodynamics, which is a hybrid resource theory
combining purity theory and asymmetry. Another hybrid resource theory which
merges purity theory and entanglement can be used to study quantumness of
correlations and discord, and we present quantumness in this more general
framework of resource theories.Comment: review articl
Entanglement of Assistance is not a bipartite measure nor a tripartite monotone
The entanglement of assistance quantifies the entanglement that can be
generated between two parties, Alice and Bob, given assistance from a third
party, Charlie, when the three share a tripartite state and where the
assistance consists of Charlie initially performing a measurement on his share
and communicating the result to Alice and Bob through a one-way classical
channel. We argue that if this quantity is to be considered an operational
measure of entanglement, then it must be understood to be a tripartite rather
than a bipartite measure. We compare it with a distinct tripartite measure that
quantifies the entanglement that can be generated between Alice and Bob when
they are allowed to make use of a two-way classical channel with Charlie. We
show that the latter quantity, which we call the entanglement of collaboration,
can be greater than the entanglement of assistance. This demonstrates that the
entanglement of assistance (considered as a tripartite measure of
entanglement), and its multipartite generalizations such as the localizable
entanglement, are not entanglement monotones, thereby undermining their
operational significance.Comment: 5 pages, revised, title changed, added a discussion explaining why
entanglement of assistance can not be considered as a bipartite measure, to
appear in Phys. Rev.
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