13 research outputs found
Thermodynamical Detection of Entanglement by Maxwell's Demons
Quantum correlation, or entanglement, is now believed to be an indispensable
physical resource for certain tasks in quantum information processing, for
which classically correlated states cannot be useful. Besides information
processing, what kind of physical processes can exploit entanglement? In this
paper, we show that there is indeed a more basic relationship between
entanglement and its usefulness in thermodynamics. We derive an inequality
showing that we can extract more work out of a heat bath via entangled systems
than via classically correlated ones. We also analyze the work balance of the
process as a heat engine, in connection with the Second Law of thermodynamics.Comment: 5 pages, 4 figures. v3: a figure added, a few refs added, & typos
correcte
Information-theoretic temporal Bell inequality and quantum computation
An information-theoretic temporal Bell inequality is formulated to contrast
classical and quantum computations. Any classical algorithm satisfies the
inequality, while quantum ones can violate it. Therefore, the violation of the
inequality is an immediate consequence of the quantumness in the computation.
Furthermore, this approach suggests a notion of temporal nonlocality in quantum
computation.Comment: v2: 5 pages, refereces added, discussion slightly revised, main
result unchanged. v3: typos correcte
Recovery of entanglement lost in entanglement manipulation
When an entangled state is transformed into another one with probability one
by local operations and classical communication, the quantity of entanglement
decreases. This letter shows that entanglement lost in the manipulation can be
partially recovered by an auxiliary entangled pair. As an application, a
maximally entangled pair can be obtained from two partially entangled pairs
with probability one. Finally, this recovery scheme reveals a fundamental
property of entanglement relevant to the existence of incomparable states.Comment: 4 pages, 2 figures, REVTeX; minor correction
Entangled states that cannot reproduce original classical games in their quantum version
A model of a quantum version of classical games should reproduce the original
classical games in order to be able to make a comparative analysis of quantum
and classical effects. We analyze a class of symmetric multipartite entangled
states and their effect on the reproducibility of the classical games. We
present the necessary and sufficient condition for the reproducibility of the
original classical games. Satisfying this condition means that complete
orthogonal bases can be constructed from a given multipartite entangled state
provided that each party is restricted to two local unitary operators. We prove
that most of the states belonging to the class of symmetric states with respect
to permutations, including the N-qubit W state, do not satisfy this condition.Comment: 4 page
Accessibility of physical states and non-uniqueness of entanglement measure
Ordering physical states is the key to quantifying some physical property of
the states uniquely. Bipartite pure entangled states are totally ordered under
local operations and classical communication (LOCC) in the asymptotic limit and
uniquely quantified by the well-known entropy of entanglement. However, we show
that mixed entangled states are partially ordered under LOCC even in the
asymptotic limit. Therefore, non-uniqueness of entanglement measure is
understood on the basis of an operational notion of asymptotic convertibility.Comment: 8 pages, 1 figure. v2: main result unchanged but presentation
extensively changed. v3: figure added, minor correction
Error exponents for entanglement concentration
Abstract Asymptotic entanglement concentration with exponentially decreasing error probability is discussed. Distillable entanglement is derived as a function of an error exponent. The formula links the upper bound of distillable entanglement, which is the well-known entropy of entanglement, with the lower bound attained in deterministic concentration. A strong converse of asymptotic entanglement concentration is also presented