4,094 research outputs found
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
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
A very brief introduction to quantum computing and quantum information theory for mathematicians
This is a very brief introduction to quantum computing and quantum
information theory, primarily aimed at geometers. Beyond basic definitions and
examples, I emphasize aspects of interest to geometers, especially connections
with asymptotic representation theory. Proofs of most statements can be found
in standard references
Inapproximability of the Standard Pebble Game and Hard to Pebble Graphs
Pebble games are single-player games on DAGs involving placing and moving
pebbles on nodes of the graph according to a certain set of rules. The goal is
to pebble a set of target nodes using a minimum number of pebbles. In this
paper, we present a possibly simpler proof of the result in [CLNV15] and
strengthen the result to show that it is PSPACE-hard to determine the minimum
number of pebbles to an additive term for all , which improves upon the currently known additive constant hardness of
approximation [CLNV15] in the standard pebble game. We also introduce a family
of explicit, constant indegree graphs with nodes where there exists a graph
in the family such that using constant pebbles requires moves
to pebble in both the standard and black-white pebble games. This independently
answers an open question summarized in [Nor15] of whether a family of DAGs
exists that meets the upper bound of moves using constant pebbles
with a different construction than that presented in [AdRNV17].Comment: Preliminary version in WADS 201
Lived experiences of informal caregivers of people with chronic musculoskeletal pain: a systematic review and meta-ethnography
BACKGROUND: People with chronic pain often seek support from friends and family for everyday tasks. These individuals are termed informal caregivers. There remains uncertainty regarding the lived experiences of these people who care for individuals with chronic musculoskeletal pain. The aim of this paper is to synthase the evidence on the lived experiences of informal caregivers providing care to people with chronic musculoskeletal pain. METHODS: A systematic literature review was undertaken of published and unpublished literature databases including: EMBASE, MEDLINE, CINAHL, PubMed, the WHO International Clinical Trial Registry and ClinicalTrials.gov registry (to September 2019). Qualitative studies exploring the lived experiences of informal caregivers of people with chronic musculoskeletal pain were included. Data were synthesised using a meta-ethnography approach. Evidence was evaluated using the Critical Appraisal Skills Programme (CASP) qualitative appraisal tool. RESULTS: From 534 citations, 10 studies were eligible (360 participants: 171 informal caregivers of 189 care recipients). The evidence was moderate quality. Seven themes arose: the relationship of caregivers to healthcare professionals, role reversal with care recipients; acting the confidant to the care recipient; a constant burden in caregiving; legitimising care recipient’s condition; knowledge and skills to provide caregiving; and the perception of other family members and wider-society to the caregiver/care recipient dyad. CONCLUSIONS: The lived experiences of caregivers of people with chronic musculoskeletal pain is complex and dynamic. There is an inter-connected relationship between caregivers, care recipients and healthcare professionals. Exploring how these experiences can be modified to improve a caregiving dyad’s lived experience is now warranted
Complete quantum teleportation using nuclear magnetic resonance
Quantum mechanics provides spectacular new information processing abilities
(Bennett 1995, Preskill 1998). One of the most unexpected is a procedure called
quantum teleportation (Bennett et al 1993) that allows the quantum state of a
system to be transported from one location to another, without moving through
the intervening space. Partial implementations of teleportation (Bouwmeester et
al 1997, Boschi et al 1998) over macroscopic distances have been achieved using
optical systems, but omit the final stage of the teleportation procedure. Here
we report an experimental implementation of the full quantum teleportation
operation over inter-atomic distances using liquid state nuclear magnetic
resonance (NMR). The inclusion of the final stage enables for the first time a
teleportation implementation which may be used as a subroutine in larger
quantum computations, or for quantum communication. Our experiment also
demonstrates the use of quantum process tomography, a procedure to completely
characterize the dynamics of a quantum system. Finally, we demonstrate a
controlled exploitation of decoherence as a tool to assist in the performance
of an experiment.Comment: 15 pages, 2 figures. Minor differences between this and the published
versio
A Factorization Law for Entanglement Decay
We present a simple and general factorization law for quantum systems shared
by two parties, which describes the time evolution of entanglement upon passage
of either component through an arbitrary noisy channel. The robustness of
entanglement-based quantum information processing protocols is thus easily and
fully characterized by a single quantity.Comment: 4 pages, 5 figure
Quantum Lightning Never Strikes the Same State Twice
Public key quantum money can be seen as a version of the quantum no-cloning
theorem that holds even when the quantum states can be verified by the
adversary. In this work, investigate quantum lightning, a formalization of
"collision-free quantum money" defined by Lutomirski et al. [ICS'10], where
no-cloning holds even when the adversary herself generates the quantum state to
be cloned. We then study quantum money and quantum lightning, showing the
following results:
- We demonstrate the usefulness of quantum lightning by showing several
potential applications, such as generating random strings with a proof of
entropy, to completely decentralized cryptocurrency without a block-chain,
where transactions is instant and local.
- We give win-win results for quantum money/lightning, showing that either
signatures/hash functions/commitment schemes meet very strong recently proposed
notions of security, or they yield quantum money or lightning.
- We construct quantum lightning under the assumed multi-collision resistance
of random degree-2 systems of polynomials.
- We show that instantiating the quantum money scheme of Aaronson and
Christiano [STOC'12] with indistinguishability obfuscation that is secure
against quantum computers yields a secure quantum money schem
The thermodynamic meaning of negative entropy
Landauer's erasure principle exposes an intrinsic relation between
thermodynamics and information theory: the erasure of information stored in a
system, S, requires an amount of work proportional to the entropy of that
system. This entropy, H(S|O), depends on the information that a given observer,
O, has about S, and the work necessary to erase a system may therefore vary for
different observers. Here, we consider a general setting where the information
held by the observer may be quantum-mechanical, and show that an amount of work
proportional to H(S|O) is still sufficient to erase S. Since the entropy H(S|O)
can now become negative, erasing a system can result in a net gain of work (and
a corresponding cooling of the environment).Comment: Added clarification on non-cyclic erasure and reversible computation
(Appendix E). For a new version of all technical proofs see the Supplementary
Information of the journal version (free access
Application of Permutation Group Theory in Reversible Logic Synthesis
The paper discusses various applications of permutation group theory in the
synthesis of reversible logic circuits consisting of Toffoli gates with
negative control lines. An asymptotically optimal synthesis algorithm for
circuits consisting of gates from the NCT library is described. An algorithm
for gate complexity reduction, based on equivalent replacements of gates
compositions, is introduced. A new approach for combining a group-theory-based
synthesis algorithm with a Reed-Muller-spectra-based synthesis algorithm is
described. Experimental results are presented to show that the proposed
synthesis techniques allow a reduction in input lines count, gate complexity or
quantum cost of reversible circuits for various benchmark functions.Comment: In English, 15 pages, 2 figures, 7 tables. Proceeding of the RC 2016
conferenc
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