3,541 research outputs found
Equilibrium temperature anisotropy and black-hole analogues
When long-range interactions are present the usual definition of temperature implies that two systems in thermal equilibrium can be at different temperatures. This local temperature has physical significance, if the sub-systems cease to interact, each system will be at their different local temperatures. This is formally related to redshifting of temperature in general relativity. We propose experiments to test this effect which are feasible using current microfabrication techniques. It is also possible to display thermodynamical analogues to black-hole space-time
Public Quantum Communication and Superactivation
Is there a meaningful quantum counterpart to public communication? We argue
that the symmetric-side channel -- which distributes quantum information
symmetrically between the receiver and the environment -- is a good candidate
for a notion of public quantum communication in entanglement distillation and
quantum error correction.
This connection is partially motivated by [Brand\~ao and Oppenheim,
arXiv:1004.3328], where it was found that if a sender would like to communicate
a secret message to a receiver through an insecure quantum channel using a
shared quantum state as a key, then the insecure quantum channel is only ever
used to simulate a symmetric-side channel, and can always be replaced by it
without altering the optimal rate. Here we further show, in complete analogy to
the role of public classical communication, that assistance by a symmetric-side
channel makes equal the distillable entanglement, the recently-introduced
mutual independence, and a generalization of the latter, which quantifies the
extent to which one of the parties can perform quantum privacy amplification.
Symmetric-side channels, and the closely related erasure channel, have been
recently harnessed to provide examples of superactivation of the quantum
channel capacity. Our findings give new insight into this non-additivity of the
channel capacity and its relation to quantum privacy. In particular, we show
that single-copy superactivation protocols with the erasure channel, which
encompasses all examples of non-additivity of the quantum capacity found to
date, can be understood as a conversion of mutual independence into distillable
entanglement.Comment: 10 page
Study of nonequilibrium two-phase flow of a gas-particle mixture Technical note no. 2
Two-phase nonequilibrium flow of particle suspensions in gaseous mediu
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Death after closed adolescent knee injury and popliteal artery occlusion: a case report and clinical review.
A healthy adolescent male soccer player sustained a radiograph-negative, effusion-negative physeal injury of the proximal tibia from a ground-level fall with traumatic occlusion of the popliteal artery. Orthopaedic evaluation and arteriography were delayed for 72 hours after the injury. He arrived at a tertiary referral center in multisystem organ failure secondary to lower extremity ischemic necrosis, septic pulmonary thromboembolism, and systemic shock. Emergent medical evaluation, a high index of suspicion, and a careful neurovascular examination are imperative after every closed knee injury in the young athlete
When does noise increase the quantum capacity?
Superactivation is the property that two channels with zero quantum capacity
can be used together to yield positive capacity. Here we demonstrate that this
effect exists for a wide class of inequivalent channels, none of which can
simulate each other. We also consider the case where one of two zero capacity
channels are applied, but the sender is ignorant of which one is applied. We
find examples where the greater the entropy of mixing of the channels, the
greater the lower bound for the capacity. Finally, we show that the effect of
superactivation is rather generic by providing example of superactivation using
the depolarizing channel.Comment: Corrected minor typo
Measurement of opaque film thickness
The theoretical and experimental framework for thickness measurements of thin metal films by low frequency thermal waves is described. Although it is assumed that the films are opaque and the substrates are comparatively poor thermal conductors, the theory is easily extended to other cases of technological interest. A brief description is given of the thermal waves and the experimental arrangement and parameters. The usefulness of the technique is illustrated for making absolute measurements of the thermal diffusivities of isotropic substrate materials. This measurement on pure elemental solids provides a check on the three dimensional theory in the limiting case of zero film thickness. The theoretical framework is then presented, along with numerical calculations and corresponding experimental results for the case of copper films on a glass substrate
Are there phase transitions in information space?
The interplay between two basic quantities -- quantum communication and
information -- is investigated. Quantum communication is an important resource
for quantum states shared by two parties and is directly related to
entanglement. Recently, the amount of local information that can be drawn from
a state has been shown to be closely related to the non-local properties of the
state. Here we consider both formation and extraction processes, and analyze
informational resources as a function of quantum communication. The resulting
diagrams in information space allow us to observe phase-like transitions when
correlations become classical.Comment: 4 pages, 3 epsi figures, to appear in Phys. Rev. Let
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