48,372 research outputs found
Dietary factors affecting exogenous and endogenous sources of fat and carbohydrate for energy production and synthesis Annual progress report, 1 Oct. 1967 - 30 Jun. 1968
Dietary effects on total fatty acid content in rats, and changes in liver, adipose tissue, and carbohydrate metabolis
Mixedness and teleportation
We show that on exceeding a certain degree of mixedness (as quantified by the
von Neumann entropy), entangled states become useless for teleporatation. By
increasing the dimension of the entangled systems, this entropy threshold can
be made arbitrarily close to maximal. This entropy is found to exceed the
entropy threshold sufficient to ensure the failure of dense coding.Comment: 6 pages, no figure
Entanglement of pure states for a single copy
An optimal local conversion strategy between any two pure states of a
bipartite system is presented. It is optimal in that the probability of success
is the largest achievable if the parties which share the system, and which can
communicate classically, are only allowed to act locally on it. The study of
optimal local conversions sheds some light on the entanglement of a single copy
of a pure state. We propose a quantification of such an entanglement by means
of a finite minimal set of new measures from which the optimal probability of
conversion follows.Comment: Revtex, 4 pages, no figures. Minor changes. Appendix remove
Quantum Energy Teleportation in Spin Chain Systems
We propose a protocol for quantum energy teleportation which transports
energy in spin chains to distant sites only by local operations and classical
communication. By utilizing ground-state entanglement and notion of negative
energy density region, energy is teleported without breaking any physical laws
including causality and local energy conservation. Because not excited physical
entity but classical information is transported in the protocol, the
dissipation rate of energy in transport is expected to be strongly suppressed.Comment: 22 pages, 4 figure, to be published in JPS
Research investigation directed toward extending the useful range of the electromagnetic spectrum Progress report, 1 May - 31 Oct. 1968
Microwave frequency probes of ionized helium, rubidium lasers, cesium spectrum, and ruby crystal
Classical communication and non-classical fidelity of quantum teleportation
In quantum teleportation, the role of entanglement has been much discussed.
It is known that entanglement is necessary for achieving non-classical
teleportation fidelity. Here we focus on the amount of classical communication
that is necessary to obtain non-classical fidelity in teleportation. We
quantify the amount of classical communication that is sufficient for achieving
non-classical fidelity for two independent 1-bit and single 2-bits noisy
classical channels. It is shown that on average 0.208 bits of classical
communication is sufficient to get non-classical fidelity. We also find the
necessary amount of classical communication in case of isotropic
transformation. Finally we study how the amount of sufficient classical
communication increases with weakening of entanglement used in the
teleportation process.Comment: Accepted in Quantum Info. Proces
Laser-like Instabilities in Quantum Nano-electromechanical Systems
We discuss negative damping regimes in quantum nano-electromechanical systems
formed by coupling a mechanical oscillator to a single-electron transistor
(normal or superconducting). Using an analogy to a laser with a tunable
atom-field coupling, we demonstrate how these effects scale with system
parameters. We also discuss the fluctuation physics of both the oscillator and
the single-electron transistor in this regime, and the degree to which the
oscillator motion is coherent.Comment: 4+ pages, 1 figure; reference to the work of Dykman and Krivoglaz
adde
Difficulty of distinguishing product states locally
Non-locality without entanglement is a rather counter-intuitive phenomenon in
which information may be encoded entirely in product (unentangled) states of
composite quantum systems in such a way that local measurement of the
subsystems is not enough for optimal decoding. For simple examples of pure
product states, the gap in performance is known to be rather small when
arbitrary local strategies are allowed. Here we restrict to local strategies
readily achievable with current technology; those requiring neither a quantum
memory nor joint operations. We show that, even for measurements on pure
product states there can be a large gap between such strategies and
theoretically optimal performance. Thus even in the absence of entanglement
physically realizable local strategies can be far from optimal for extracting
quantum information.Comment: 5 pages, 1 figur
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
New classes of n-copy undistillable quantum states with negative partial transposition
The discovery of entangled quantum states from which one cannot distill pure
entanglement constitutes a fundamental recent advance in the field of quantum
information. Such bipartite bound-entangled (BE) quantum states \emph{could}
fall into two distinct categories: (1) Inseparable states with positive partial
transposition (PPT), and (2) States with negative partial transposition (NPT).
While the existence of PPT BE states has been confirmed, \emph{only one} class
of \emph{conjectured} NPT BE states has been discovered so far. We provide
explicit constructions of a variety of multi-copy undistillable NPT states, and
conjecture that they constitute families of NPT BE states. For example, we show
that for every pure state of Schmidt rank greater than or equal to three, one
can construct n-copy undistillable NPT states, for any . The abundance
of such conjectured NPT BE states, we believe, considerably strengthens the
notion that being NPT is only a necessary condition for a state to be
distillable.Comment: Latex, 10 page
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