3,576 research outputs found
The minimum entropy output of a quantum channel is locally additive
We show that the minimum von-Neumann entropy output of a quantum channel is
locally additive. Hasting's counterexample for the additivity conjecture, makes
this result quite surprising. In particular, it indicates that the
non-additivity of the minimum entropy output is a global effect of quantum
channels.Comment: Shorter Version, further simplifications of proof
Equivalence of Additivity Questions in Quantum Information Theory
We reduce the number of open additivity problems in quantum information
theory by showing that four of them are equivalent. We show that the
conjectures of additivity of the minimum output entropy of a quantum channel,
additivity of the Holevo expression for the classical capacity of a quantum
channel, additivity of the entanglement of formation, and strong
superadditivity of the entanglement of formation, are either all true or all
false.Comment: now 20 pages, replaced to add a reference, remove a reference to a
claimed result about locally minimal output entropy states (my proof of this
was incorrect), correct minor typos, and add more explanation for the
background of these conjecture
Covert sensing using floodlight illumination
We propose a scheme for covert active sensing using floodlight illumination
from a THz-bandwidth amplified spontaneous emission (ASE) source and heterodyne
detection. We evaluate the quantum-estimation-theoretic performance limit of
covert sensing, wherein a transmitter's attempt to sense a target phase is kept
undetectable to a quantum-equipped passive adversary, by hiding the signal
photons under the thermal noise floor. Despite the quantum state of each mode
of the ASE source being mixed (thermal), and hence inferior compared to the
pure coherent state of a laser mode, the thousand-times higher optical
bandwidth of the ASE source results in achieving a substantially superior
performance compared to a narrowband laser source by allowing the probe light
to be spread over many more orthogonal temporal modes within a given
integration time. Even though our analysis is restricted to single-mode phase
sensing, this system could be applicable extendible for various practical
optical sensing applications.Comment: We present new results and discuss some results found in
arXiv:1701.06206. Comments are welcom
Entanglement cost and quantum channel simulation
This paper proposes a revised definition for the entanglement cost of a
quantum channel . In particular, it is defined here to be the
smallest rate at which entanglement is required, in addition to free classical
communication, in order to simulate calls to , such that the
most general discriminator cannot distinguish the calls to
from the simulation. The most general discriminator is one who tests the
channels in a sequential manner, one after the other, and this discriminator is
known as a quantum tester [Chiribella et al., Phys. Rev. Lett., 101, 060401
(2008)] or one who is implementing a quantum co-strategy [Gutoski et al., Symp.
Th. Comp., 565 (2007)]. As such, the proposed revised definition of
entanglement cost of a quantum channel leads to a rate that cannot be smaller
than the previous notion of a channel's entanglement cost [Berta et al., IEEE
Trans. Inf. Theory, 59, 6779 (2013)], in which the discriminator is limited to
distinguishing parallel uses of the channel from the simulation. Under this
revised notion, I prove that the entanglement cost of certain
teleportation-simulable channels is equal to the entanglement cost of their
underlying resource states. Then I find single-letter formulas for the
entanglement cost of some fundamental channel models, including dephasing,
erasure, three-dimensional Werner--Holevo channels, epolarizing channels
(complements of depolarizing channels), as well as single-mode pure-loss and
pure-amplifier bosonic Gaussian channels. These examples demonstrate that the
resource theory of entanglement for quantum channels is not reversible.
Finally, I discuss how to generalize the basic notions to arbitrary resource
theories.Comment: 28 pages, 7 figure
The entanglement of purification
We introduce a measure of both quantum as well as classical correlations in a
quantum state, the entanglement of purification. We show that the (regularized)
entanglement of purification is equal to the entanglement cost of creating a
state asymptotically from maximally entangled states, with negligible
communication. We prove that the classical mutual information and the quantum
mutual information divided by two are lower bounds for the regularized
entanglement of purification. We present numerical results of the entanglement
of purification for Werner states in .Comment: 12 pages RevTex, 1 figure, to appear in JMP special issue on quantum
information. v3 contains additional references, motivation, and a small
change in the figur
Local versus non-local information in quantum information theory: formalism and phenomena
In spite of many results in quantum information theory, the complex nature of
compound systems is far from being clear. In general the information is a
mixture of local, and non-local ("quantum") information. To make this point
more clear, we develop and investigate the quantum information processing
paradigm in which parties sharing a multipartite state distill local
information. The amount of information which is lost because the parties must
use a classical communication channel is the deficit. This scheme can be viewed
as complementary to the notion of distilling entanglement. After reviewing the
paradigm, we show that the upper bound for the deficit is given by the relative
entropy distance to so-called psuedo-classically correlated states; the lower
bound is the relative entropy of entanglement. This implies, in particular,
that any entangled state is informationally nonlocal i.e. has nonzero deficit.
We also apply the paradigm to defining the thermodynamical cost of erasing
entanglement. We show the cost is bounded from below by relative entropy of
entanglement. We demonstrate the existence of several other non-local
phenomena. For example,we prove the existence of a form of non-locality without
entanglement and with distinguishability. We analyze the deficit for several
classes of multipartite pure states and obtain that in contrast to the GHZ
state, the Aharonov state is extremely nonlocal (and in fact can be thought of
as quasi-nonlocalisable). We also show that there do not exist states, for
which the deficit is strictly equal to the whole informational content (bound
local information). We then discuss complementary features of information in
distributed quantum systems. Finally we discuss the physical and theoretical
meaning of the results and pose many open questions.Comment: 35 pages in two column, 4 figure
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