1,064 research outputs found
Circular quantum secret sharing
A circular quantum secret sharing protocol is proposed, which is useful and
efficient when one of the parties of secret sharing is remote to the others who
are in adjacent, especially the parties are more than three. We describe the
process of this protocol and discuss its security when the quantum information
carrying is polarized single photons running circularly. It will be shown that
entanglement is not necessary for quantum secret sharing. Moreover, the
theoretic efficiency is improved to approach 100% as almost all the instances
can be used for generating the private key, and each photon can carry one bit
of information without quantum storage. It is straightforwardly to utilize this
topological structure to complete quantum secret sharing with multi-level
two-particle entanglement in high capacity securely.Comment: 7 pages, 2 figure
Quantum rebound capacity
Inspired by the power of abstraction in information theory, we consider
quantum rebound protocols as a way of providing a unifying perspective to deal
with several information-processing tasks related to and extending quantum
channel discrimination to the Shannon-theoretic regime. Such protocols, defined
in the most general quantum-physical way possible, have been considered in the
physical context of the DW model of quantum reading [Das and Wilde,
arXiv:1703.03706]. In [Das, arXiv:1901.05895], it was discussed how such
protocols apply in the different physical context of round-trip communication
from one party to another and back. The common point for all quantum rebound
tasks is that the decoder himself has access to both the input and output of a
randomly selected sequence of channels, and the goal is to determine a message
encoded into the channel sequence. As employed in the DW model of quantum
reading, the most general quantum-physical strategy that a decoder can employ
is an adaptive strategy, in which general quantum operations are executed
before and after each call to a channel in the sequence. We determine lower and
upper bounds on the quantum rebound capacities in various scenarios of
interest, and we also discuss cases in which adaptive schemes provide an
advantage over non-adaptive schemes in zero-error quantum rebound protocols.Comment: v2: published version, 7 pages, 2 figures, see companion paper at
arXiv:1703.0370
Multiphoton communication in lossy channels with photon-number entangled states
We address binary and quaternary communication channels based on correlated
multiphoton two-mode states of radiation in the presence of losses. The
protocol are based on photon number correlations and realized upon choosing a
shared set of thresholds to convert the outcome of a joint photon number
measurement into a symbol from a discrete alphabet. In particular, we focus on
channels build using feasible photon-number entangled states (PNES) as two-mode
coherently-correlated (TMC) or twin-beam (TWB) states and compare their
performances with that of channels built using feasible classically correlated
(separable) states. We found that PNES provide larger channel capacity in the
presence of loss, and that TWB-based channels may transmit a larger amount of
information than TMC-based ones at fixed energy and overall loss. Optimized bit
discrimination thresholds, as well as the corresponding maximized mutual
information, are explicitly evaluated as a function of the beam intensity and
the loss parameter. The propagation of TMC and TWB in lossy channels is
analyzed and the joint photon number distribution is evaluated, showing that
the beam statistics, either sub-Poissonian for TMC or super-Poissonian for TWB,
is not altered by losses. Although entanglement is not strictly needed to
establish the channels, which are based on photon-number correlations owned
also by separable mixed states, purity of the support state is relevant to
increase security. The joint requirement of correlation and purity individuates
PNES as a suitable choice to build effective channels. The effects of losses on
channel security are briefly discussed.Comment: 8 pages, 19 figure
Quantum information with continuous variables
Quantum information is a rapidly advancing area of interdisciplinary
research. It may lead to real-world applications for communication and
computation unavailable without the exploitation of quantum properties such as
nonorthogonality or entanglement. We review the progress in quantum information
based on continuous quantum variables, with emphasis on quantum optical
implementations in terms of the quadrature amplitudes of the electromagnetic
field.Comment: accepted for publication in Reviews of Modern Physic
Random Quantum Circuits and Pseudo-Random Operators: Theory and Applications
Pseudo-random operators consist of sets of operators that exhibit many of the
important statistical features of uniformly distributed random operators. Such
pseudo-random sets of operators are most useful whey they may be parameterized
and generated on a quantum processor in a way that requires exponentially fewer
resources than direct implementation of the uniformly random set. Efficient
pseudo-random operators can overcome the exponential cost of random operators
required for quantum communication tasks such as super-dense coding of quantum
states and approximately secure quantum data-hiding, and enable efficient
stochastic methods for noise estimation on prototype quantum processors. This
paper summarizes some recently published work demonstrating a random circuit
method for the implementation of pseudo-random unitary operators on a quantum
processor [Emerson et al., Science 302:2098 (Dec.~19, 2003)], and further
elaborates the theory and applications of pseudo-random states and operators.Comment: This paper is a synopsis of Emerson et al., Science 302: 2098 (Dec
19, 2003) and some related unpublished work; it is based on a talk given at
QCMC04; 4 pages, 1 figure, aipproc.st
Uncertainty Relation for Mutual Information
We postulate the existence of a universal uncertainty relation between the
quantum and classical mutual informations between pairs of quantum systems.
Specifically, we propose that the sum of the classical mutual information,
determined by two mutually unbiased pairs of observables, never exceeds the
quantum mutual information. We call this the complementary-quantum correlation
(CQC) relation and prove its validity for pure states, for states with one
maximally mixed subsystem, and for all states when one measurement is minimally
disturbing. We provide results of a Monte Carlo simulation suggesting the CQC
relation is generally valid. Importantly, we also show that the CQC relation
represents an improvement to an entropic uncertainty principle in the presence
of a quantum memory, and that it can be used to verify an achievable secret key
rate in the quantum one-time pad cryptographic protocol.Comment: 6 pages, 2 figure
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