31,175 research outputs found
When only two thirds of the entanglement can be distilled
We provide an example of distillable bipartite mixed state such that, even in
the asymptotic limit, more pure-state entanglement is required to create it
than can be distilled from it. Thus, we show that the irreversibility in the
processes of formation and distillation of bipartite states, recently proved in
[G. Vidal, J.I. Cirac, Phys. Rev. Lett. 86, (2001) 5803-5806], is not limited
to bound-entangled states.Comment: 4 pages, revtex, 1 figur
A classical analogue of entanglement
We show that quantum entanglement has a very close classical analogue, namely
secret classical correlations. The fundamental analogy stems from the behavior
of quantum entanglement under local operations and classical communication and
the behavior of secret correlations under local operations and public
communication. A large number of derived analogies follow. In particular
teleportation is analogous to the one-time-pad, the concept of ``pure state''
exists in the classical domain, entanglement concentration and dilution are
essentially classical secrecy protocols, and single copy entanglement
manipulations have such a close classical analog that the majorization results
are reproduced in the classical setting. This analogy allows one to import
questions from the quantum domain into the classical one, and vice-versa,
helping to get a better understanding of both. Also, by identifying classical
aspects of quantum entanglement it allows one to identify those aspects of
entanglement which are uniquely quantum mechanical.Comment: 13 pages, references update
Constructing N-qubit entanglement monotones from anti-linear operators
We present a method to construct entanglement measures for pure states of
multipartite qubit systems. The key element of our approach is an antilinear
operator that we call {\em comb} in reference to the {\em hairy-ball theorem}.
For qubits (or spin 1/2) the combs are automatically invariant under
SL(2,\CC). This implies that the {\em filters} obtained from the combs are
entanglement monotones by construction. We give alternative formulae for the
concurrence and the 3-tangle as expectation values of certain antilinear
operators. As an application we discuss inequivalent types of genuine
four-qubit entanglement.Comment: 5 pages, revtex4; more detailed illustration of the metho
Workshop on Applications of Phase Diagrams in Metallurgy and Ceramics
A workshop was held to assess the current national and international status of phase diagram determinations and evaluations for alloys, ceramics, and semiconductors; to determine the needs and priorities, especially technological, for phase diagram determinations and evaluations; and to estimate the resources being used and potentially available for phase diagram evaluation. Highlights of the workshop, description of a new poster board design used in the poster sessions, lists of attendees and demonstrations, the program, and descriptions of the presentations are included
Unconditionally secure quantum bit commitment is impossible
The claim of quantum cryptography has always been that it can provide
protocols that are unconditionally secure, that is, for which the security does
not depend on any restriction on the time, space or technology available to the
cheaters. We show that this claim does not hold for any quantum bit commitment
protocol. Since many cryptographic tasks use bit commitment as a basic
primitive, this result implies a severe setback for quantum cryptography. The
model used encompasses all reasonable implementations of quantum bit commitment
protocols in which the participants have not met before, including those that
make use of the theory of special relativity.Comment: 4 pages, revtex. Journal version replacing the version published in
the proceedings of PhysComp96. This is a significantly improved version which
emphasis the generality of the resul
Building multiparticle states with teleportation
We describe a protocol which can be used to generate any N-partite pure
quantum state using Einstein-Podolsky-Rosen (EPR) pairs. This protocol employs
only local operations and classical communication between the N parties
(N-LOCC). In particular, we rely on quantum data compression and teleportation
to create the desired state. This protocol can be used to obtain upper bounds
for the bipartite entanglement of formation of an arbitrary N-partite pure
state, in the asymptotic limit of many copies. We apply it to a few
multipartite states of interest, showing that in some cases it is not optimal.
Generalizations of the protocol are developed which are optimal for some of the
examples we consider, but which may still be inefficient for arbitrary states.Comment: 11 pages, 1 figure. Version 2 contains an example for which protocol
P3 is better than protocol P2. Correction to references in version
Irreversibility in asymptotic manipulations of entanglement
We show that the process of entanglement distillation is irreversible by
showing that the entanglement cost of a bound entangled state is finite. Such
irreversibility remains even if extra pure entanglement is loaned to assist the
distillation process.Comment: RevTex, 3 pages, no figures Result on indistillability of PPT states
under pure entanglement catalytic LOCC adde
The Limits of West German Justice in the 1960s: The Post-War Investigation of Walter Gieseke (Oberstleutnant of the Gendarmerie and SS)
This article uses a micro-historical methodology to examine some of the complex problems of bringing to justice Nazi-era war criminals in West Germany in the 1960s. It takes as its focus the failure to bring a case against Walter Gieseke, Oberstleutnant of the Gendarmerie and SS. One of the ‘middle managers’ of the Nazi state Gieseke headed a road building project across the Ukraine which resulted in the murder of substantial numbers of Jewish forced labourers. Under questioning he pursued strategies which maximised the difficulties facing the investigating authorities in West Germany
The 1942 Laconia Order, The Murder of Shipwrecked Survivors and the Allied Pursuit of Justice 1945-46
This article examines the post-war trials of three German naval officers in connection with the Laconia order of 1942. It sets their behaviour, and the order, in the context of maritime custom and the practices of the German submarine arm between 1939 and 1945. It establishes linkages between the three trials and highlights the British Admiralty's faltering pursuit of the German submarine arm over the supposed practice of murdering shipwreck survivors from Allied vessels
Bound on distributed entanglement
Using the convex-roof extended negativity and the negativity of assistance as
quantifications of bipartite entanglement, we consider the possible
remotely-distributed entanglement. For two pure states and
on bipartite systems and , we first show that the
possible amount of entanglement remotely distributed on the system by
joint measurement on the system is not less than the product of two
amounts of entanglement for the states and
in two-qubit and two-qutrit systems. We also provide some sufficient
conditions, for which the result can be generalized into higher-dimensional
quantum systems.Comment: 5 page
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