15,611 research outputs found
Quantum Reverse Shannon Theorem
Dual to the usual noisy channel coding problem, where a noisy (classical or
quantum) channel is used to simulate a noiseless one, reverse Shannon theorems
concern the use of noiseless channels to simulate noisy ones, and more
generally the use of one noisy channel to simulate another. For channels of
nonzero capacity, this simulation is always possible, but for it to be
efficient, auxiliary resources of the proper kind and amount are generally
required. In the classical case, shared randomness between sender and receiver
is a sufficient auxiliary resource, regardless of the nature of the source, but
in the quantum case the requisite auxiliary resources for efficient simulation
depend on both the channel being simulated, and the source from which the
channel inputs are coming. For tensor power sources (the quantum generalization
of classical IID sources), entanglement in the form of standard ebits
(maximally entangled pairs of qubits) is sufficient, but for general sources,
which may be arbitrarily correlated or entangled across channel inputs,
additional resources, such as entanglement-embezzling states or backward
communication, are generally needed. Combining existing and new results, we
establish the amounts of communication and auxiliary resources needed in both
the classical and quantum cases, the tradeoffs among them, and the loss of
simulation efficiency when auxiliary resources are absent or insufficient. In
particular we find a new single-letter expression for the excess forward
communication cost of coherent feedback simulations of quantum channels (i.e.
simulations in which the sender retains what would escape into the environment
in an ordinary simulation), on non-tensor-power sources in the presence of
unlimited ebits but no other auxiliary resource. Our results on tensor power
sources establish a strong converse to the entanglement-assisted capacity
theorem.Comment: 35 pages, to appear in IEEE-IT. v2 has a fixed proof of the Clueless
Eve result, a new single-letter formula for the "spread deficit", better
error scaling, and an improved strong converse. v3 and v4 each make small
improvements to the presentation and add references. v5 fixes broken
reference
Remote preparation of quantum states
Remote state preparation is the variant of quantum state teleportation in
which the sender knows the quantum state to be communicated. The original paper
introducing teleportation established minimal requirements for classical
communication and entanglement but the corresponding limits for remote state
preparation have remained unknown until now: previous work has shown, however,
that it not only requires less classical communication but also gives rise to a
trade-off between these two resources in the appropriate setting. We discuss
this problem from first principles, including the various choices one may
follow in the definitions of the actual resources. Our main result is a general
method of remote state preparation for arbitrary states of many qubits, at a
cost of 1 bit of classical communication and 1 bit of entanglement per qubit
sent. In this "universal" formulation, these ebit and cbit requirements are
shown to be simultaneously optimal by exhibiting a dichotomy. Our protocol then
yields the exact trade-off curve for arbitrary ensembles of pure states and
pure entangled states (including the case of incomplete knowledge of the
ensemble probabilities), based on the recently established quantum-classical
trade-off for quantum data compression. The paper includes an extensive
discussion of our results, including the impact of the choice of model on the
resources, the topic of obliviousness, and an application to private quantum
channels and quantum data hiding.Comment: 21 pages plus 2 figures (eps), revtex4. v2 corrects some errors and
adds obliviousness discussion. v3 has section VI C deleted and various minor
oversights correcte
A novel method for unambiguous ion identification in mixed ion beams extracted from an EBIT
A novel technique to identify small fluxes of mixed highly charged ion beams
extracted from an Electron Beam Ion Trap (EBIT) is presented and practically
demonstrated. The method exploits projectile charge state dependent potential
emission of electrons as induced by ion impact on a metal surface to separate
ions with identical or very similar mass-to-charge ratio.Comment: 8 pages, 5 figure
Development of Safeguards Procedures for Heavy Water Moderated, Cooled, and Reflected Pressurised Water Type Reactors
On the fidelity of two pure states
The fidelity of two pure states (also known as transition probability) is a
symmetric function of two operators, and well-founded operationally as an event
probability in a certain preparation-test pair. Motivated by the idea that the
fidelity is the continuous quantum extension of the combinatorial equality
function, we enquire whether there exists a symmetric operational way of
obtaining the fidelity. It is shown that this is impossible. Finally, we
discuss the optimal universal approximation by a quantum operation.Comment: LaTeX2e, 8 pages, submitted to J. Phys. A: Math. and Ge
Emission of light through thin silver films via near-field coupling to surface plasmon polaritons
Copyright © 2006 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 88 (2006) and may be found at http://link.aip.org/link/?APPLAB/88/051109/1We show that the emission of light from a dye layer through an adjacent thin silver film is maximal for a silver thickness of approximately 50 nm. This effect is explained as the result of competition between enhancement of the electric field at the metal surface due to the excitation of a surface plasmon-polariton mode, the amount of power coupled to the surface plasmon-polariton mode, and the attenuation of the field transmitted through the silver, all three of which vary with metal thickness. We indicate how these findings may be of relevance in the design of some surface plasmon-polariton-based fluorescence biosensing schemes
EarthN: A new Earth System Nitrogen Model
The amount of nitrogen in the atmosphere, oceans, crust, and mantle have
important ramifications for Earth's biologic and geologic history. Despite this
importance, the history and cycling of nitrogen in the Earth system is poorly
constrained over time. For example, various models and proxies contrastingly
support atmospheric mass stasis, net outgassing, or net ingassing over time. In
addition, the amount available to and processing of nitrogen by organisms is
intricately linked with and provides feedbacks on oxygen and nutrient cycles.
To investigate the Earth system nitrogen cycle over geologic history, we have
constructed a new nitrogen cycle model: EarthN. This model is driven by mantle
cooling, links biologic nitrogen cycling to phosphate and oxygen, and
incorporates geologic and biologic fluxes. Model output is consistent with
large (2-4x) changes in atmospheric mass over time, typically indicating
atmospheric drawdown and nitrogen sequestration into the mantle and continental
crust. Critical controls on nitrogen distribution include mantle cooling
history, weathering, and the total Bulk Silicate Earth+atmosphere nitrogen
budget. Linking the nitrogen cycle to phosphorous and oxygen levels, instead of
carbon as has been previously done, provides new and more dynamic insight into
the history of nitrogen on the planet.Comment: 36 pages, 12 figure
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