954 research outputs found
Quantum Zeno and anti-Zeno effects in an asymmetric nonlinear optical coupler
Quantum Zeno and anti-Zeno effects in an asymmetric nonlinear optical coupler
are studied. The asymmetric nonlinear optical coupler is composed of a linear
waveguide () and a nonlinear waveguide
() interacting with each other through the evanescent
waves. The nonlinear waveguide has quadratic nonlinearity and it operates under
second harmonic generation. A completely quantum mechanical description is used
to describe the system. The closed form analytic solutions of Heisenberg's
equations of motion for the different field modes are obtained using Sen-Mandal
perturbative approach. In the coupler, the linear waveguide acts as a probe on
the system (nonlinear waveguide). The effect of the presence of the probe
(linear waveguide) on the photon statistics of the second harmonic mode of the
system is considered as quantum Zeno and anti-Zeno effects. Further,it is also
shown that in the stimulated case, it is easy to switch between quantum Zeno
and anti-Zeno effects just by controlling the phase of the second harmonic mode
of the asymmetric couplerComment: 7 pages. This work was presented in the International Conference on
Optics and Photonics 2015,Kolkata, Indi
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
Kak's three-stage protocol of secure quantum communication revisited: Hitherto unknown strengths and weaknesses of the protocol
Kak's three-stage protocol for quantum key distribution is revisited with
special focus on its hitherto unknown strengths and weaknesses. It is shown
that this protocol can be used for secure direct quantum communication.
Further, the implementability of this protocol in the realistic situation is
analyzed by considering various Markovian noise models. It is found that the
Kak's protocol and its variants in their original form can be implemented only
in a restricted class of noisy channels, where the protocols can be transformed
to corresponding protocols based on logical qubits in decoherence free
subspace. Specifically, it is observed that Kak's protocol can be implemented
in the presence of collective rotation and collective dephasing noise, but
cannot be implemented in its original form in the presence of other types of
noise, like amplitude damping and phase damping noise. Further, the performance
of the protocol in the noisy environment is quantified by computing average
fidelity under various noise models, and subsequently a set of preferred states
for secure communication in noisy environment have also been identified.Comment: Kak's protocol is not suitable for quantum cryptography in presence
of nois
Design of Quantum Circuits for Galois Field Squaring and Exponentiation
This work presents an algorithm to generate depth, quantum gate and qubit
optimized circuits for squaring in the polynomial basis. Further, to
the best of our knowledge the proposed quantum squaring circuit algorithm is
the only work that considers depth as a metric to be optimized. We compared
circuits generated by our proposed algorithm against the state of the art and
determine that they require fewer qubits and offer gates savings that
range from to . Further, existing quantum exponentiation are
based on either modular or integer arithmetic. However, Galois arithmetic is a
useful tool to design resource efficient quantum exponentiation circuit
applicable in quantum cryptanalysis. Therefore, we present the quantum circuit
implementation of Galois field exponentiation based on the proposed quantum
Galois field squaring circuit. We calculated a qubit savings ranging between
to and quantum gate savings ranging between to
compared to identical quantum exponentiation circuit based on existing squaring
circuits.Comment: To appear in conference proceedings of the 2017 IEEE Computer Society
Annual Symposium on VLSI (ISVLSI 2017
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