2,291 research outputs found
Nonlinear backreaction in a quantum mechanical SQUID
In this paper we discuss the coupling between a quantum mechanical
superconducting quantum interference device (SQUID) and an applied static
magnetic field. We demonstrate that the backreaction of a SQUID on the applied
field can interfere with the ability to bias the SQUID at values of the static
(DC) magnetic flux at, or near to, transitions in the quantum mechanical SQUID.Comment: 9 pages, to be published in Phys. Rev.
Cool for Cats
The iconic Schr\"odinger's cat state describes a system that may be in a
superposition of two macroscopically distinct states, for example two clearly
separated oscillator coherent states. Quite apart from their role in
understanding the quantum classical boundary, such states have been suggested
as offering a quantum advantage for quantum metrology, quantum communication
and quantum computation. As is well known these applications have to face the
difficulty that the irreversible interaction with an environment causes the
superposition to rapidly evolve to a mixture of the component states in the
case that the environment is not monitored. Here we show that by engineering
the interaction with the environment there exists a large class of systems that
can evolve irreversibly to a cat state. To be precise we show that it is
possible to engineer an irreversible process so that the steady state is close
to a pure Schr\"odinger's cat state by using double well systems and an
environment comprising two-photon (or phonon) absorbers. We also show that it
should be possible to prolong the lifetime of a Schr\"odinger's cat state
exposed to the destructive effects of a conventional single-photon decohering
environment. Our protocol should make it easier to prepare and maintain
Schr\"odinger cat states which would be useful in applications of quantum
metrology and information processing as well as being of interest to those
probing the quantum to classical transition.Comment: 10 pages, 7 figures. Significantly updated version with supplementary
informatio
Fast algorithm for detecting community structure in networks
It has been found that many networks display community structure -- groups of
vertices within which connections are dense but between which they are sparser
-- and highly sensitive computer algorithms have in recent years been developed
for detecting such structure. These algorithms however are computationally
demanding, which limits their application to small networks. Here we describe a
new algorithm which gives excellent results when tested on both
computer-generated and real-world networks and is much faster, typically
thousands of times faster than previous algorithms. We give several example
applications, including one to a collaboration network of more than 50000
physicists.Comment: 5 pages, 4 figure
Non-linear dynamics, entanglement and the quantum-classical crossover of two coupled SQUID rings
We explore the quantum-classical crossover of two coupled, identical,
superconducting quantum interference device (SQUID) rings. We note that the
motivation for this work is based on a study of a similar system comprising two
coupled Duffing oscillators. In that work we showed that the entanglement
characteristics of chaotic and periodic (entrained) solutions differed
significantly and that in the classical limit entanglement was preserved only
in the chaotic-like solutions. However, Duffing oscillators are a highly
idealised toy model. Motivated by a wish to explore more experimentally
realisable systems we now extend our work to an analysis of two coupled SQUID
rings. We observe some differences in behaviour between the system that is
based on SQUID rings rather than on Duffing oscillators. However, we show that
the two systems share a common feature. That is, even when the SQUID ring's
trajectories appear to follow (semi) classical orbits entanglement persists.Comment: 9 pages, 4 figures. Published as part of the proceedings of the 32nd
International Workshop on Condensed Matter Theories (CMT32) Loughborough
University, 2008 (invited paper
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