11,765 research outputs found
Which verification qubits perform best for secure communication in noisy channel?
In secure quantum communication protocols, a set of single qubits prepared
using 2 or more mutually unbiased bases or a set of -qubit ()
entangled states of a particular form are usually used to form a verification
string which is subsequently used to detect traces of eavesdropping. The qubits
that form a verification string are referred to as decoy qubits, and there
exists a large set of different quantum states that can be used as decoy
qubits. In the absence of noise, any choice of decoy qubits provides equivalent
security. In this paper, we examine such equivalence for noisy environment
(e.g., in amplitude damping, phase damping, collective dephasing and collective
rotation noise channels) by comparing the decoy-qubit assisted schemes of
secure quantum communication that use single qubit states as decoy qubits with
the schemes that use entangled states as decoy qubits. Our study reveals that
the single qubit assisted scheme perform better in some noisy environments,
while some entangled qubits assisted schemes perform better in other noisy
environments. Specifically, single qubits assisted schemes perform better in
amplitude damping and phase damping noisy channels, whereas a few
Bell-state-based decoy schemes are found to perform better in the presence of
the collective noise. Thus, if the kind of noise present in a communication
channel (i.e., the characteristics of the channel) is known or measured, then
the present study can provide the best choice of decoy qubits required for
implementation of schemes of secure quantum communication through that channel.Comment: 11 pages, 4 figure
Some Directions beyond Traditional Quantum Secret Sharing
We investigate two directions beyond the traditional quantum secret sharing
(QSS). First, a restriction on QSS that comes from the no-cloning theorem is
that any pair of authorized sets in an access structure should overlap. From
the viewpoint of application, this places an unnatural constraint on secret
sharing. We present a generalization, called assisted QSS (AQSS), where access
structures without pairwise overlap of authorized sets is permissible, provided
some shares are withheld by the share dealer. We show that no more than
withheld shares are required, where is the minimum number
of {\em partially linked classes} among the authorized sets for the QSS. Our
result means that such applications of QSS need not be thwarted by the
no-cloning theorem. Secondly, we point out a way of combining the features of
QSS and quantum key distribution (QKD) for applications where a classical
information is shared by quantum means. We observe that in such case, it is
often possible to reduce the security proof of QSS to that of QKD.Comment: To appear in Physica Scripta, 7 pages, 1 figure, subsumes
arXiv:quant-ph/040720
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
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