19,315 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
Quantum Conference
A notion of quantum conference is introduced in analogy with the usual notion
of a conference that happens frequently in today's world. Quantum conference is
defined as a multiparty secure communication task that allows each party to
communicate their messages simultaneously to all other parties in a secure
manner using quantum resources. Two efficient and secure protocols for quantum
conference have been proposed. The security and efficiency of the proposed
protocols have been analyzed critically. It is shown that the proposed
protocols can be realized using a large number of entangled states and group of
operators. Further, it is shown that the proposed schemes can be easily reduced
to protocol for multiparty quantum key distribution and some earlier proposed
schemes of quantum conference, where the notion of quantum conference was
different.Comment: 12 pages, 1 figur
Orthogonal-state-based protocols of quantum key agreement
Two orthogonal-state-based protocols of quantum key agreement (QKA) are
proposed. The first protocol of QKA proposed here is designed for two-party
QKA, whereas the second protocol is designed for multi-party QKA. Security of
these orthogonal-state-based protocols arise from monogamy of entanglement.
This is in contrast to the existing protocols of QKA where security arises from
the use of non-orthogonal state (non-commutativity principle). Further, it is
shown that all the quantum systems that are useful for implementation of
quantum dialogue and most of the protocols of secure direct quantum
communication can be modified to implement protocols of QKA.Comment: 9 pages, no figur
Quantum e-commerce: A comparative study of possible protocols for online shopping and other tasks related to e-commerce
A set of quantum protocols for online shopping is proposed and analyzed to
establish that it is possible to perform secure online shopping using different
types of quantum resources. Specifically, a single photon based, a Bell state
based and two 3-qubit entangled state based quantum online shopping schemes are
proposed. The Bell state based scheme, being a completely orthogonal state
based protocol, is fundamentally different from the earlier proposed schemes
which were based on conjugate coding. One of the 3-qubit entangled state based
scheme is build on the principle of entanglement swapping which enables us to
accomplish the task without transmission of the message encoded qubits through
the channel. Possible ways of generalizing the entangled state based schemes
proposed here to the schemes which use multiqubit entangled states is also
discussed. Further, all the proposed protocols are shown to be free from the
limitations of the recently proposed protocol of Huang et al. (Quantum Inf.
Process. 14, 2211-2225, 2015) which allows the buyer (Alice) to change her
order at a later time (after initially placing the order and getting it
authenticated by the controller). The proposed schemes are also compared with
the existing schemes using qubit efficiency.Comment: It's shown that quantum e-commerce is not a difficult task, and it
can be done in various way
Asymmetric Quantum Dialogue in Noisy Environment
A notion of asymmetric quantum dialogue (AQD) is introduced. Conventional
protocols of quantum dialogue are essentially symmetric as both the users
(Alice and Bob) can encode the same amount of classical information. In
contrast, the scheme for AQD introduced here provides different amount of
communication powers to Alice and Bob. The proposed scheme, offers an
architecture, where the entangled state and the encoding scheme to be shared
between Alice and Bob depends on the amount of classical information they want
to exchange with each other. The general structure for the AQD scheme has been
obtained using a group theoretic structure of the operators introduced in
(Shukla et al., Phys. Lett. A, 377 (2013) 518). The effect of different types
of noises (e.g., amplitude damping and phase damping noise) on the proposed
scheme is investigated, and it is shown that the proposed AQD is robust and
uses optimized amount of quantum resources.Comment: 11 pages, 2 figure
Cross-verification of independent quantum devices
Quantum computers are on the brink of surpassing the capabilities of even the
most powerful classical computers. This naturally raises the question of how
one can trust the results of a quantum computer when they cannot be compared to
classical simulation. Here we present a verification technique that exploits
the principles of measurement-based quantum computation to link quantum
circuits of different input size, depth, and structure. Our approach enables
consistency checks of quantum computations within a device, as well as between
independent devices. We showcase our protocol by applying it to five
state-of-the-art quantum processors, based on four distinct physical
architectures: nuclear magnetic resonance, superconducting circuits, trapped
ions, and photonics, with up to 6 qubits and 200 distinct circuits
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