7 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
Pulse Shape Analysis and Identification of Multipoint Events in a Large-Volume Proportional Counter in an Experimental Search for 2K Capture Kr-78
A pulse shape analysis algorithm and a method for suppressing the noise
component of signals from a large copper proportional counter in the experiment
aimed at searching for 2K capture of Kr-78 are described. These signals
correspond to a compound event with different numbers of charge clusters due to
from primary ionization is formed by these signals. A technique for separating
single- and multipoint events and determining the charge in individual clusters
is presented. Using the Daubechies wavelets in multiresolutional signal
analysis, it is possible to increase the sensitivity and the resolution in
extraction of multipoint events in the detector by a factor of 3-4.Comment: 10 pages, 8 figures. submitted to Instruments and Experimental
Techniques; ISSN 0020/441
Improved protocols of secure quantum communication using W states
Recently, Hwang et al. [Eur. Phys. J. D. 61, 785 (2011)] and Yuan et al.
[Int. J. Theo. Phys. 50, 2403 (2011)] have proposed two efficient protocols of
secure quantum communication using 3-qubit and 4-qubit symmetric W state
respectively. These two dense coding based protocols are generalized and their
efficiencies are considerably improved. Simple bounds on the qubit efficiency
of deterministic secure quantum communication (DSQC) and quantum secure direct
communication (QSDC) protocols are obtained and it is shown that dense coding
is not essential for designing of maximally efficient DSQC and QSDC protocols.
This fact is used to design maximally efficient protocols of DSQC and QSDC
using 3-qubit and 4-qubit W states.Comment: 8 page
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
Linear optical scheme for entanglement concentration of two partially entangled three-photon states
Photonic spatial Bell-state analysis for robust quantum secure direct communication using quantum dot-cavity systems
Recently, experiments showed that the spatial-mode states of entangled
photons are more robust than their polarization-mode states in quantum
communications. Here we construct a complete and deterministic protocol for
analyzing the spatial Bell states using the interaction between a photon and an
electron spin in a charged quantum dot inside a one-side micropillar
microcavity. A quantum nondemolition detector (QND) for checking the parity of
a two-photon system can be constructed with the giant optical Faraday rotation
in this solid state system. With this parity-check QND, we present a complete
and deterministic proposal for the analysis of the four spatial-mode Bell
states. Moreover, we present a robust two-step quantum secure direct
communication protocol based on the spatial-mode Bell states and the photonic
spatial Bell-state analysis. Our analysis shows that our BSA proposal works in
both the strong and the weak coupling regimes if the side leakage and cavity
loss rate is small.Comment: 8 pages, 4 figure