329,747 research outputs found
Chiral Quantum Walks
Given its importance to many other areas of physics, from condensed matter
physics to thermodynamics, time-reversal symmetry has had relatively little
influence on quantum information science. Here we develop a network-based
picture of time-reversal theory, classifying Hamiltonians and quantum circuits
as time-symmetric or not in terms of the elements and geometries of their
underlying networks. Many of the typical circuits of quantum information
science are found to exhibit time-asymmetry. Moreover, we show that
time-asymmetry in circuits can be controlled using local gates only, and can
simulate time-asymmetry in Hamiltonian evolution. We experimentally implement a
fundamental example in which controlled time-reversal asymmetry in a
palindromic quantum circuit leads to near-perfect transport. Our results pave
the way for using time-symmetry breaking to control coherent transport, and
imply that time-asymmetry represents an omnipresent yet poorly understood
effect in quantum information science.Comment: 9 pages, 4 figures, REVTeX 4.1 - published versio
A Unified Approach for Network Information Theory
In this paper, we take a unified approach for network information theory and
prove a coding theorem, which can recover most of the achievability results in
network information theory that are based on random coding. The final
single-letter expression has a very simple form, which was made possible by
many novel elements such as a unified framework that represents various network
problems in a simple and unified way, a unified coding strategy that consists
of a few basic ingredients but can emulate many known coding techniques if
needed, and new proof techniques beyond the use of standard covering and
packing lemmas. For example, in our framework, sources, channels, states and
side information are treated in a unified way and various constraints such as
cost and distortion constraints are unified as a single joint-typicality
constraint.
Our theorem can be useful in proving many new achievability results easily
and in some cases gives simpler rate expressions than those obtained using
conventional approaches. Furthermore, our unified coding can strictly
outperform existing schemes. For example, we obtain a generalized
decode-compress-amplify-and-forward bound as a simple corollary of our main
theorem and show it strictly outperforms previously known coding schemes. Using
our unified framework, we formally define and characterize three types of
network duality based on channel input-output reversal and network flow
reversal combined with packing-covering duality.Comment: 52 pages, 7 figures, submitted to IEEE Transactions on Information
theory, a shorter version will appear in Proc. IEEE ISIT 201
Surface Aided Polarization Reversal In Small Ferroelectric Particles.
Polarization reversal in ferroelectric particles driven by a pulsed electric field is examined theoretically using Landau-Devonshire-Khalatnikov theory. A significant reduction in reversal times is shown to be possible if certain surface properties and size criteria are met. The surface properties are also shown to control the magnitude of the applied field needed for irreversible switching. An interesting signature of surface effects is found in the switching current. The theory predicts that the switching current for small ferroelectric particles can exhibit double peaks as a function of time. The size and relative times of the peaks provide specific information on the
magnitude and rate of surface reversal dynamics
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