146 research outputs found
Generalized Log-Majorization and Multivariate Trace Inequalities
© 2017, Springer International Publishing. We show that recent multivariate generalizations of the Araki–Lieb–Thirring inequality and the Golden–Thompson inequality (Sutter et al. in Commun Math Phys, 2016. doi:10.1007/s00220-016-2778-5) for Schatten norms hold more generally for all unitarily invariant norms and certain variations thereof. The main technical contribution is a generalization of the concept of log-majorization which allows us to treat majorization with regard to logarithmic integral averages of vectors of singular values
Chain rules for smooth min-and max-entropies
The chain rule for the Shannon and von Neumann entropy, which relates the total entropy of a system to the entropies of its parts, is of central importance to information theory. Here, we consider the chain rule for the more general smooth min-and max-entropies, used in one-shot information theory. For these entropy measures, the chain rule no longer holds as an equality. However, the standard chain rule for the von Neumann entropy is retrieved asymptotically when evaluating the smooth entropies for many identical and independently distributed states. © 1963-2012 IEEE
Tight Finite-Key Analysis for Quantum Cryptography
Despite enormous progress both in theoretical and experimental quantum
cryptography, the security of most current implementations of quantum key
distribution is still not established rigorously. One of the main problems is
that the security of the final key is highly dependent on the number, M, of
signals exchanged between the legitimate parties. While, in any practical
implementation, M is limited by the available resources, existing security
proofs are often only valid asymptotically for unrealistically large values of
M. Here, we demonstrate that this gap between theory and practice can be
overcome using a recently developed proof technique based on the uncertainty
relation for smooth entropies. Specifically, we consider a family of
Bennett-Brassard 1984 quantum key distribution protocols and show that security
against general attacks can be guaranteed already for moderate values of M.Comment: 11 pages, 2 figure
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
The Quantum Reverse Shannon Theorem based on One-Shot Information Theory
The Quantum Reverse Shannon Theorem states that any quantum channel can be
simulated by an unlimited amount of shared entanglement and an amount of
classical communication equal to the channel's entanglement assisted classical
capacity. In this paper, we provide a new proof of this theorem, which has
previously been proved by Bennett, Devetak, Harrow, Shor, and Winter. Our proof
has a clear structure being based on two recent information-theoretic results:
one-shot Quantum State Merging and the Post-Selection Technique for quantum
channels.Comment: 30 pages, 4 figures, published versio
Stress in nursing staff: a comparative analysis between intensive care units and general medicine units
It's a current belief that stress is an outstanding feature of intensive care units, in particular within nursing staff. The aim of this study was to compare some variables belonging to stress (i.e. anxiety, depression and `Burnout' syndrome) between nurses working in intensive care units (ICUs) and general medicine units (GMUs).
Materials and methods
We studied a population of 883 nurses working in ICUs, distributed in 79 Italian hospitals (70.1 % female) and 509 nurses working in GMUs, distributed in 35 Italian hospitals (80.2 % female). We asked them to fill in a form including: 1) general data and his/her work environment; 2) different evaluation standardized scales - the Hospital Anxiety and Depression Scale, divided into anxiety (HAD A) and depression (HAD D) status 0-7 `non cases', 8-10 `doubtful cases', 11-21 `cases'; the S.T.A.I. scale, divided into acute anxiety (Y-1) and chronic anxiety (Y-2) status; the Maslach Burnout Inventory-Human Services Survey (MBI.) divided into Emotional Exhaustion (EE), 64 18 `low', 19-26 `average', 65 27 `high', Depersonalization (DP) and Personal Accomplishment (PA). We also evaluated the different reasons of anxiety through individual questions (higher value, more anxiety): A1, a critically ill patient; A2, a young patient; A3, an old patient; A4, a suicidal patient; A5, a terminal patient; A6, presence of mechanical supports; A7, relationship with patients' relatives. The comparison between the two groups was performed by the Mann-Whitney Rank Sum test and z-test; statistical significance was accepted as P<0.05.
Results
The results, expressed as median value, with 25th and 75th percentile in brackets, are shown in Tables 1 and 2.
Table 1 also shows the proportions of nurses that had a highest value of HAD A and M.B.I. EE.
Conclusions
Pathologic anxiety and emotional exhaustion are more prevalent in nurses working in GMUs. Thus, contrary to a common belief, `stress' is a more distinctive peculiarity of general medicine units than intensive care units
A Quantum-Proof Non-Malleable Extractor, With Application to Privacy Amplification against Active Quantum Adversaries
In privacy amplification, two mutually trusted parties aim to amplify the
secrecy of an initial shared secret in order to establish a shared private
key by exchanging messages over an insecure communication channel. If the
channel is authenticated the task can be solved in a single round of
communication using a strong randomness extractor; choosing a quantum-proof
extractor allows one to establish security against quantum adversaries.
In the case that the channel is not authenticated, Dodis and Wichs (STOC'09)
showed that the problem can be solved in two rounds of communication using a
non-malleable extractor, a stronger pseudo-random construction than a strong
extractor.
We give the first construction of a non-malleable extractor that is secure
against quantum adversaries. The extractor is based on a construction by Li
(FOCS'12), and is able to extract from source of min-entropy rates larger than
. Combining this construction with a quantum-proof variant of the
reduction of Dodis and Wichs, shown by Cohen and Vidick (unpublished), we
obtain the first privacy amplification protocol secure against active quantum
adversaries
Quantum encryption with certified deletion
Given a ciphertext, is it possible to prove the deletion of the underlying
plaintext? Since classical ciphertexts can be copied, clearly such a feat is
impossible using classical information alone. In stark contrast to this, we
show that quantum encodings enable certified deletion. More precisely, we show
that it is possible to encrypt classical data into a quantum ciphertext such
that the recipient of the ciphertext can produce a classical string which
proves to the originator that the recipient has relinquished any chance of
recovering the plaintext should the decryption key be revealed. Our scheme is
feasible with current quantum technology: the honest parties only require
quantum devices for single-qubit preparation and measurements; the scheme is
also robust against noise in these devices. Furthermore, we provide an analysis
that is suitable in the finite-key regime.Comment: 28 pages, 1 figure. Some technical details modifie
Unification of different views of decoherence and discord
Macroscopic behavior such as the lack of interference patterns has been
attributed to "decoherence", a word with several possible definitions such as
(1) the loss of off-diagonal density matrix elements, (2) the flow of
information to the environment, (3) the loss of complementary information, and
(4) the loss of the ability to create entanglement in a measurement. In this
article, we attempt to unify these distinct definitions by providing general
quantitative connections between them, valid for all finite-dimensional quantum
systems or quantum processes. The most important application of our results is
to the understanding of quantum discord, a measure of the non-classicality of
the correlations between quantum systems. We show that some popular measures of
discord measure the information missing from the purifying system and hence
quantify security, which can be stated operationally in terms of distillable
secure bits. The results also give some strategies for constructing discord
measures.Comment: 15 pages, 2 figures. Final version, to appear in Phys. Rev. A.
Notation has been improved to make the paper more readabl
Decoupling with unitary approximate two-designs
Consider a bipartite system, of which one subsystem, A, undergoes a physical
evolution separated from the other subsystem, R. One may ask under which
conditions this evolution destroys all initial correlations between the
subsystems A and R, i.e. decouples the subsystems. A quantitative answer to
this question is provided by decoupling theorems, which have been developed
recently in the area of quantum information theory. This paper builds on
preceding work, which shows that decoupling is achieved if the evolution on A
consists of a typical unitary, chosen with respect to the Haar measure,
followed by a process that adds sufficient decoherence. Here, we prove a
generalized decoupling theorem for the case where the unitary is chosen from an
approximate two-design. A main implication of this result is that decoupling is
physical, in the sense that it occurs already for short sequences of random
two-body interactions, which can be modeled as efficient circuits. Our
decoupling result is independent of the dimension of the R system, which shows
that approximate 2-designs are appropriate for decoupling even if the dimension
of this system is large.Comment: Published versio
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