19,587 research outputs found
Quantum internet using code division multiple access
A crucial open problem in large-scale quantum networks is how to efficiently
transmit quantum data among many pairs of users via a common data-transmission
medium. We propose a solution by developing a quantum code division multiple
access (q-CDMA) approach in which quantum information is chaotically encoded to
spread its spectral content, and then decoded via chaos synchronization to
separate different sender-receiver pairs. In comparison to other existing
approaches, such as frequency division multiple access (FDMA), the proposed
q-CDMA can greatly increase the information rates per channel used, especially
for very noisy quantum channels.Comment: 29 pages, 6 figure
Polar codes in network quantum information theory
Polar coding is a method for communication over noisy classical channels
which is provably capacity-achieving and has an efficient encoding and
decoding. Recently, this method has been generalized to the realm of quantum
information processing, for tasks such as classical communication, private
classical communication, and quantum communication. In the present work, we
apply the polar coding method to network quantum information theory, by making
use of recent advances for related classical tasks. In particular, we consider
problems such as the compound multiple access channel and the quantum
interference channel. The main result of our work is that it is possible to
achieve the best known inner bounds on the achievable rate regions for these
tasks, without requiring a so-called quantum simultaneous decoder. Thus, our
work paves the way for developing network quantum information theory further
without requiring a quantum simultaneous decoder.Comment: 18 pages, 2 figures, v2: 10 pages, double column, version accepted
for publicatio
Multiple-Access Bosonic Communications
The maximum rates for reliably transmitting classical information over
Bosonic multiple-access channels (MACs) are derived when the transmitters are
restricted to coherent-state encodings. Inner and outer bounds for the ultimate
capacity region of the Bosonic MAC are also presented. It is shown that the
sum-rate upper bound is achievable with a coherent-state encoding and that the
entire region is asymptotically achievable in the limit of large mean input
photon numbers.Comment: 11 pages, 5 figures, corrected two figures, accepted for publication
in Phys. Rev.
Explicit receivers for pure-interference bosonic multiple access channels
The pure-interference bosonic multiple access channel has two senders and one
receiver, such that the senders each communicate with multiple temporal modes
of a single spatial mode of light. The channel mixes the input modes from the
two users pairwise on a lossless beamsplitter, and the receiver has access to
one of the two output ports. In prior work, Yen and Shapiro found the capacity
region of this channel if encodings consist of coherent-state preparations.
Here, we demonstrate how to achieve the coherent-state Yen-Shapiro region (for
a range of parameters) using a sequential decoding strategy, and we show that
our strategy outperforms the rate regions achievable using conventional
receivers. Our receiver performs binary-outcome quantum measurements for every
codeword pair in the senders' codebooks. A crucial component of this scheme is
a non-destructive "vacuum-or-not" measurement that projects an n-symbol
modulated codeword onto the n-fold vacuum state or its orthogonal complement,
such that the post-measurement state is either the n-fold vacuum or has the
vacuum removed from the support of the n symbols' joint quantum state. This
receiver requires the additional ability to perform multimode optical
phase-space displacements which are realizable using a beamsplitter and a
laser.Comment: v1: 9 pages, 2 figures, submission to the 2012 International
Symposium on Information Theory and its Applications (ISITA 2012), Honolulu,
Hawaii, USA; v2: minor change
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