57,133 research outputs found
Quantum information with continuous variables
Quantum information is a rapidly advancing area of interdisciplinary
research. It may lead to real-world applications for communication and
computation unavailable without the exploitation of quantum properties such as
nonorthogonality or entanglement. We review the progress in quantum information
based on continuous quantum variables, with emphasis on quantum optical
implementations in terms of the quadrature amplitudes of the electromagnetic
field.Comment: accepted for publication in Reviews of Modern Physic
Experimental demonstration of entanglement assisted coding using a two-mode squeezed vacuum state
We have experimentally realized the scheme initially proposed as quantum
dense coding with continuous variables [Ban, J. Opt. B \textbf{1}, L9 (1999),
and Braunstein and Kimble, \pra\textbf{61}, 042302 (2000)]. In our experiment,
a pair of EPR (Einstein-Podolski-Rosen) beams is generated from two independent
squeezed vacua. After adding two-quadrature signal to one of the EPR beams, two
squeezed beams that contain the signal were recovered. Although our squeezing
level is not sufficient to demonstrate the channel capacity gain over the
Holevo limit of a single-mode channel without entanglement, our channel is
superior to conventional channels such as coherent and squeezing channels. In
addition, optical addition and subtraction processes demonstrated are
elementary operations of universal quantum information processing on continuous
variables.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Channel Detection in Coded Communication
We consider the problem of block-coded communication, where in each block,
the channel law belongs to one of two disjoint sets. The decoder is aimed to
decode only messages that have undergone a channel from one of the sets, and
thus has to detect the set which contains the prevailing channel. We begin with
the simplified case where each of the sets is a singleton. For any given code,
we derive the optimum detection/decoding rule in the sense of the best
trade-off among the probabilities of decoding error, false alarm, and
misdetection, and also introduce sub-optimal detection/decoding rules which are
simpler to implement. Then, various achievable bounds on the error exponents
are derived, including the exact single-letter characterization of the random
coding exponents for the optimal detector/decoder. We then extend the random
coding analysis to general sets of channels, and show that there exists a
universal detector/decoder which performs asymptotically as well as the optimal
detector/decoder, when tuned to detect a channel from a specific pair of
channels. The case of a pair of binary symmetric channels is discussed in
detail.Comment: Submitted to IEEE Transactions on Information Theor
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