87 research outputs found
Path Integrals for (Complex) Classical and Quantum Mechanics
An analysis of classical mechanics in a complex extension of phase space
shows that a particle in such a space can behave in a way redolant of quantum
mechanics; additional degrees of freedom permit 'tunnelling' without recourse
to instantons and lead to time/energy uncertainty. In practice, 'classical'
particle trajectories with additional degrees of freedom have arisen in several
different formulations of quantum mechanics. In this talk we compare the
extended phase space of the closed time-path formalism with that of complex
classical mechanics, to suggest that has a role in our understanding of
the latter. However, differences in the way that trajectories are used make a
deeper comparison problematical. We conclude with some thoughts on quantisation
as dimensional reduction.Comment: 13 pages: Published in the Proceedings of AAMP 7, (Prague) 2011. This
file differs from the published version by the inclusion of extra references,
with minor changes of text (which leave conclusions unaltered
Spontaneous Fluxon Formation in Annular Josephson Tunnel Junctions
It has been argued by Zurek and Kibble that the likelihood of producing
defects in a continuous phase transition depends in a characteristic way on the
quench rate. In this paper we discuss our experiment for measuring the
Zurek-Kibble scaling exponent sigma for the production of fluxons in annular
symmetric Josephson Tunnel Junctions. The predicted exponent is sigma = 0.25,
and we find sigma = 0.27 +/- 0.05. Further, there is agreement with the ZK
prediction for the overall normalisation
The Non-universal behaviour of Cold Fermi Condensates with Narrow Feshbach Resonances
In this paper we construct an effective field theory for a condensate of cold
Fermi atoms whose scattering is controlled by a narrow Feshbach resonance. We
show how, from first principles, it permits a hydrodynamic description of the
BEC-BCS crossover from which the equation of state, intimately related to the
speed of sound, can be derived. Specifically, we stress the non-universal
behaviour of the equation of state at the unitary limit of infinite scattering
length that arises when either, or both, of the range of the inter-atomic force
and the scale of the molecular field become large.Comment: 7 pages, there is no differences in results between this (v2) and the
older version (v1), but v2 makes the nature of the non-canonical behavior of
the EOS cleare
Fluxoid formation: size effects and non-equilibrium universality
Simple causal arguments put forward by Kibble and Zurek suggest that the
scaling behaviour of condensed matter at continuous transitions is related to
the familiar universality classes of the systems at quasi-equilibrium. Although
proposed 25 years ago or more, it is only in the last few years that it has
been possible to devise experiments from which scaling exponents can be
determined and in which this scenario can be tested. In previous work, an
unusually high Kibble-Zurek scaling exponent was reported for spontaneous
fluxoid production in a single isolated superconducting Nb loop, albeit with
low density. Using analytic approximations backed up by Langevin simulations,
we argue that densities as small as these are too low to be attributable to
scaling, and are conditioned by the small size of the loop. We also reflect on
the physical differences between slow quenches and small rings, and derive some
criteria for these differences, noting that recent work on slow quenches does
not adequately explain the anomalous behaviour seen here.Comment: 7 pages, 4 figures, presentation given at CMMP 201
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