1,243 research outputs found
Some Remarks on Quantum Coherence
There are many striking phenomena which are attributed to
``quantum coherence''. It is natural to wonder if there are new quantum
coherence effects waiting to be discovered which could lead to interesting
results and perhaps even practical applications. A useful starting point for
such discussions is a definition of ``quantum coherence''. In this article I
give a definition of quantum coherence and use a number of illustrations to
explore the implications of this definition. I point to topics of current
interest in the fields of cosmology and quantum computation where questions of
quantum coherence arise, and I emphasize the impact that interactions with the
environment can have on quantum coherence.Comment: 25 pages plain LaTeX, no figures. More references have been added and
typos have been corrected. Journal of Modern Optics, in press.
Imperial/TP/93-94/1
Precise numerical results for limit cycles in the quantum three-body problem
The study of the three-body problem with short-range attractive two-body
forces has a rich history going back to the 1930's. Recent applications of
effective field theory methods to atomic and nuclear physics have produced a
much improved understanding of this problem, and we elucidate some of the
issues using renormalization group ideas applied to precise nonperturbative
calculations. These calculations provide 11-12 digits of precision for the
binding energies in the infinite cutoff limit. The method starts with this
limit as an approximation to an effective theory and allows cutoff dependence
to be systematically computed as an expansion in powers of inverse cutoffs and
logarithms of the cutoff. Renormalization of three-body bound states requires a
short range three-body interaction, with a coupling that is governed by a
precisely mapped limit cycle of the renormalization group. Additional
three-body irrelevant interactions must be determined to control subleading
dependence on the cutoff and this control is essential for an effective field
theory since the continuum limit is not likely to match physical systems ({\it
e.g.}, few-nucleon bound and scattering states at low energy). Leading order
calculations precise to 11-12 digits allow clear identification of subleading
corrections, but these corrections have not been computed.Comment: 37 pages, 8 figures, LaTeX, uses graphic
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