14 research outputs found
The quantum cryptographic switch
We illustrate using a quantum system the principle of a cryptographic switch,
in which a third party (Charlie) can control to a continuously varying degree
the amount of information the receiver (Bob) receives, after the sender (Alice)
has sent her information. Suppose Charlie transmits a Bell state to Alice and
Bob. Alice uses dense coding to transmit two bits to Bob. Only if the 2-bit
information corresponding to choice of Bell state is made available by Charlie
to Bob can the latter recover Alice's information. By varying the information
he gives, Charlie can continuously vary the information recovered by Bob. The
performance of the protocol subjected to the squeezed generalized amplitude
damping channel is considered. We also present a number of practical situations
where a cryptographic switch would be of use.Comment: 7 pages, 4 Figure
A General Method for Selecting Quantum Channel for Bidirectional Controlled State Teleportation and Other Schemes of Controlled Quantum Communication
Recently, a large number of protocols for bidirectional controlled state
teleportation (BCST) have been proposed using -qubit entangled states
() as quantum channel. Here, we propose a general method of
selecting multi-qubit quantum channels suitable for BCST and show that
all the channels used in the existing protocols of BCST can be obtained using
the proposed method. Further, it is shown that the quantum channels used in the
existing protocols of BCST forms only a negligibly small subset of the set of
all the quantum channels that can be constructed using the proposed method to
implement BCST. It is also noted that all these quantum channels are also
suitable for controlled bidirectional remote state preparation (CBRSP).
Following the same logic, methods for selecting quantum channels for other
controlled quantum communication tasks, such as controlled bidirectional joint
remote state preparation (CJBRSP) and controlled quantum dialogue, are also
provided.Comment: 8 pages, no figur
Beyond Gisin's Theorem and its Applications: Violation of Local Realism by Two-Party Einstein-Podolsky-Rosen Steering
We demonstrate here that for a given mixed multi-qubit state if there are at
least two observers for whom mutual Einstein-Podolsky-Rosen steering is
possible, i.e. each observer is able to steer the other qubits into two
different pure states by spontaneous collapses due to von Neumann type
measurements on his/her qubit, then nonexistence of local realistic models is
fully equivalent to quantum entanglement (this is not so without this
condition). This result leads to an enhanced version of Gisin's theorem
(originally: all pure entangled states violate local realism). Local realism is
violated by all mixed states with the above steering property. The new class of
states allows one e.g. to perform three party secret sharing with just pairs of
entangled qubits, instead of three qubit entanglements (which are currently
available with low fidelity). This significantly increases the feasibility of
having high performance versions of such protocols. Finally, we discuss some
possible applications.Comment: 9 pages, 1 figur
Continuous variable controlled quantum dialogue and secure multiparty quantum computation
A continuous variable controlled quantum dialogue scheme is proposed. The
scheme is further modified to obtain two other protocols of continuous variable
secure multiparty computation. The first one of these protocols provides a
solution of two party socialist millionaire problem, while the second protocol
provides a solution for a special type of multi-party socialist millionaire
problem which can be viewed as a protocol for multiparty quantum private
comparison. It is shown that the proposed scheme of continuous variable
controlled quantum dialogue can be performed using bipartite entanglement and
can be reduced to obtain several other two and three party cryptographic
schemes in the limiting cases. The security of the proposed scheme and its
advantage over corresponding discrete variable counterpart are also discussed.
Specifically, the ignorance of an eavesdropper in the proposed scheme is shown
to be very high compared with corresponding discrete variable scheme and thus
the present scheme is less prone to information leakage inherent with the
discrete variable quantum dialogue based schemes.It is further established that
the proposed scheme can be viewed as a continuous variable counterpart of
quantum cryptographic switch which allows a supervisor to control the
information transferred between the two legitimate parties to a continuously
varying degree.Comment: Quantum dialogue and its application in the continuous variable
scenario is studied in detai
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
Applications of quantum cryptographic switch: Various tasks related to controlled quantum communication can be performed using Bell states and permutation of particles
Recently, several aspects of controlled quantum communication (e.g.,
bidirectional controlled state teleportation, controlled quantum secure direct
communication, controlled quantum dialogue, etc.) have been studied using
-qubit () entanglement. Specially, a large number of schemes for
bidirectional controlled state teleportation are proposed using -qubit
entanglement (). Here, we propose a set of protocols to
illustrate that it is possible to realize all these tasks related to controlled
quantum communication using only Bell states and permutation of particles
(PoP). As the generation and maintenance of a Bell state is much easier than a
multi-partite entanglement, the proposed strategy has a clear advantage over
the existing proposals. Further, it is shown that all the schemes proposed here
may be viewed as applications of the concept of quantum cryptographic switch
which was recently introduced by some of us. The performances of the proposed
protocols as subjected to the amplitude damping and phase damping noise on the
channels are also discussed.Comment: 12 pages, 3 figure
Semi-quantum communication: Protocols for key agreement, controlled secure direct communication and dialogue
Semi-quantum protocols that allow some of the users to remain classical are
proposed for a large class of problems associated with secure communication and
secure multiparty computation. Specifically, first time semi-quantum protocols
are proposed for key agreement, controlled deterministic secure communication
and dialogue, and it is shown that the semi-quantum protocols for controlled
deterministic secure communication and dialogue can be reduced to semi-quantum
protocols for e-commerce and private comparison (socialist millionaire
problem), respectively. Complementing with the earlier proposed semi-quantum
schemes for key distribution, secret sharing and deterministic secure
communication, set of schemes proposed here and subsequent discussions have
established that almost every secure communication and computation tasks that
can be performed using fully quantum protocols can also be performed in
semi-quantum manner. Further, it addresses a fundamental question in context of
a large number problems- how much quantumness is (how many quantum parties are)
required to perform a specific secure communication task? Some of the proposed
schemes are completely orthogonal-state-based, and thus, fundamentally
different from the existing semi-quantum schemes that are
conjugate-coding-based. Security, efficiency and applicability of the proposed
schemes have been discussed with appropriate importance.Comment: 19 pages 1 figur
A comparative study of protocols for secure quantum communication under noisy environment: single-qubit-based protocols versus entangled-state-based protocols
The effect of noise on various protocols of secure quantum communication has
been studied. Specifically, we have investigated the effect of amplitude
damping, phase damping, squeezed generalized amplitude damping, Pauli type as
well as various collective noise models on the protocols of quantum key
distribution, quantum key agreement,quantum secure direct quantum communication
and quantum dialogue. From each type of protocol of secure quantum
communication, we have chosen two protocols for our comparative study; one
based on single qubit states and the other one on entangled states. The
comparative study reported here has revealed that single-qubit-based schemes
are generally found to perform better in the presence of amplitude damping,
phase damping, squeezed generalized amplitude damping noises, while
entanglement-based protocols turn out to be preferable in the presence of
collective noises. It is also observed that the effect of noise entirely
depends upon the number of rounds of quantum communication involved in a scheme
of quantum communication. Further, it is observed that squeezing, a completely
quantum mechanical resource present in the squeezed generalized amplitude
channel, can be used in a beneficial way as it may yield higher fidelity
compared to the corresponding zero squeezing case.Comment: 23 pages 7 figure