536 research outputs found
Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition
The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with
coupled magnetic and structural (martensitic) phase transitions were studied
experimentally and theoretically. The magnetocaloric effect was measured by a
direct method in magnetic fields 0-26 kOe at temperatures close to the
magnetostructural transition temperature. For theoretical description of the
alloy properties near the magnetostructural transition a statistical model is
suggested, that takes into account the coexistence of martensite and austenite
domains in the vicinity of martensite transformation point.Comment: presented at ICM-2003, to appear in JMM
Isospectral domains with mixed boundary conditions
We construct a series of examples of planar isospectral domains with mixed
Dirichlet-Neumann boundary conditions. This is a modification of a classical
problem proposed by M. Kac.Comment: 9 figures. Statement of Theorem 5.1 correcte
Locally Accessible Information of Multisite Quantum Ensembles Violates Monogamy
Locally accessible information is a useful information-theoretic physical
quantity of an ensemble of multiparty quantum states. We find it has properties
akin to quantum as well as classical correlations of single multiparty quantum
states. It satisfies monotonicity under local quantum operations and classical
communication. However we show that it does not follow monogamy, an important
property usually satisfied by quantum correlations, and actually violates any
such relation to the maximal extent. Violation is obtained even for locally
indistinguishable, but globally orthogonal, multisite ensembles. The results
assert that while single multiparty quantum states are monogamous with respect
to their shared quantum correlations, ensembles of multiparty quantum states
may not be so. The results have potential implications for quantum
communication systems.Comment: 6 pages, RevTeX
Genuine Multiparty Quantum Entanglement Suppresses Multiport Classical Information Transmission
We establish a universal complementarity relation between the capacity of
classical information transmission by employing a multiparty quantum state as a
multiport quantum channel, and the genuine multipartite entanglement of the
quantum state. The classical information transfer is from a sender to several
receivers by using the quantum dense coding protocol with the multiparty
quantum state shared between the sender and the receivers. The relation holds
for arbitrary pure or mixed quantum states of an arbitrary number of parties in
arbitrary dimensions.Comment: 5 (+ epsilon) pages, 2 figures, Revtex4-1; v2: Theorem 3 extended to
all states, other results unchange
A Thermodynamical Approach to Quantifying Quantum Correlations
We consider the amount of work which can be extracted from a heat bath using
a bipartite state shared by two parties. In general it is less then the amount
of work extractable when one party is in possession of the entire state. We
derive bounds for this "work deficit" and calculate it explicitly for a number
of different cases. For pure states the work deficit is exactly equal to the
distillable entanglement of the state, and this is also achievable for
maximally correlated states. In these cases a form of complementarity exists
between physical work which can be extracted and distillable entanglement. The
work deficit is a good measure of the quantum correlations in a state and
provides a new paradigm for understanding quantum non-locality.Comment: 4 pages, Revtex4, title changed, caveat added to theore
Thermodynamical Cost of Accessing Quantum Information
Thermodynamics is a macroscopic physical theory whose two very general laws
are independent of any underlying dynamical laws and structures. Nevertheless,
its generality enables us to understand a broad spectrum of phenomena in
physics, information science and biology. Recently, it has been realised that
information storage and processing based on quantum mechanics can be much more
efficient than their classical counterpart. What general bound on storage of
quantum information does thermodynamics imply? We show that thermodynamics
implies a weaker bound than the quantum mechanical one (the Holevo bound). In
other words, if any post-quantum physics should allow more information storage
it could still be under the umbrella of thermodynamics.Comment: 3 figure
Hawking Radiation and Unitary evolution
We find a family of exact solutions to the semi-classical equations
(including back-reaction) of two-dimensional dilaton gravity, describing
infalling null matter that becomes outgoing and returns to infinity without
forming a black hole. When a black hole almost forms, the radiation reaching
infinity in advance of the original outgoing null matter has the properties of
Hawking radiation. The radiation reaching infinity after the null matter
consists of a brief burst of negative energy that preserves unitarity and
transfers information faster than the theoretical bound for positive energy.Comment: LaTex file + uuencoded ps version including 4 figure
Capacities of noiseless quantum channels for massive indistinguishable particles: Bosons vs. fermions
We consider information transmission through a noiseless quantum channel,
where the information is encoded into massive indistinguishable particles:
bosons or fermions. We study the situation in which the particles are
noninteracting. The encoding input states obey a set of physically motivated
constraints on the mean values of the energy and particle number. In such a
case, the determination of both classical and quantum capacity reduces to a
constrained maximization of entropy. In the case of noninteracting bosons,
signatures of Bose Einstein condensation can be observed in the behavior of the
capacity. A major motivation for these considerations is to compare the
information carrying capacities of channels that carry bosons with those that
carry fermions. We show analytically that fermions generally provide higher
channel capacity, i.e., they are better suited for transferring bits as well as
qubits, in comparison to bosons. This holds for a large range of power law
potentials, and for moderate to high temperatures. Numerical simulations seem
to indicate that the result holds for all temperatures. Also, we consider the
low temperature behavior for the three-dimensional box and harmonic trap, and
again we show that the fermionic capacity is higher than the bosonic one for
sufficiently low temperatures.Comment: 16 pages, 8 eps figures, RevTeX4; v2: small change in a figure; v3:
significant new additions about quantum capacity, previous results unchanged,
title changed, published versio
Implementation of generalized quantum measurements: superadditive quantum coding, accessible information extraction, and classical capacity limit
Quantum information theory predicts that when the transmission resource is
doubled in quantum channels, the amount of information transmitted can be
increased more than twice by quantum channel coding technique, whereas the
increase is at most twice in classical information theory. This remarkable
feature, the superadditive quantum coding gain, can be implemented by
appropriate choices of code words and corresponding quantum decoding which
requires a collective quantum measurement. Recently, the first experimental
demonstration was reported [Phys. Rev. Lett. 90, 167906 (2003)]. The purpose of
this paper is to describe our experiment in detail. Particularly, a design
strategy of quantum collective decoding in physical quantum circuits is
emphasized. We also address the practical implication of the gain on
communication performance by introducing the quantum-classical hybrid coding
scheme. We show how the superadditive quantum coding gain, even in a small code
length, can boost the communication performance of conventional coding
technique.Comment: 15 pages, 14 figure
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