2,409 research outputs found
Crossover from Diffusive to Ballistic Transport in Periodic Quantum Maps
We derive an expression for the mean square displacement of a particle whose
motion is governed by a uniform, periodic, quantum multi-baker map. The
expression is a function of both time, , and Planck's constant, , and
allows a study of both the long time, , and semi-classical,
, limits taken in either order. We evaluate the expression using
random matrix theory as well as numerically, and observe good agreement between
both sets of results. The long time limit shows that particle transport is
generically ballistic, for any fixed value of Planck's constant. However, for
fixed times, the semi-classical limit leads to diffusion. The mean square
displacement for non-zero Planck's constant, and finite time, exhibits a
crossover from diffusive to ballistic motion, with crossover time on the order
of the inverse of Planck's constant. We argue, that these results are generic
for a large class of 1D quantum random walks, similar to the quantum
multi-baker, and that a sufficient condition for diffusion in the
semi-classical limit is classically chaotic dynamics in each cell. Some
connections between our work and the other literature on quantum random walks
are discussed. These walks are of some interest in the theory of quantum
computation.Comment: Final version to appear in Physica D, Proceedings of the
International Workshop and Seminar on Microscopic Chaos and Transport in
Many-Particle Systems, Dresden, 2002; corrected a minor error in section 3.1,
new section 4.
One-parameter scaling theory for DNA extension in a nanochannel
Experiments measuring DNA extension in nanochannels are at odds with even the
most basic predictions of current scaling arguments for the conformations of
confined semiflexible polymers such as DNA. We show that a theory based on a
weakly self-avoiding, one-dimensional "telegraph" process collapses
experimental data and simulation results onto a single master curve throughout
the experimentally relevant region of parameter space and explains the
mechanisms at play.Comment: Revised version. 5 pages, 4 figures, revised version, supplementary
informatio
Distribution of label spacings for genome mapping in nanochannels
In genome mapping experiments, long DNA molecules are stretched by confining
them to very narrow channels, so that the locations of sequence-specific
fluorescent labels along the channel axis provide large-scale genomic
information. It is difficult, however, to make the channels narrow enough so
that the DNA molecule is fully stretched. In practice its conformations may
form hairpins that change the spacings between internal segments of the DNA
molecule, and thus the label locations along the channel axis. Here we describe
a theory for the distribution of label spacings that explains the heavy tails
observed in distributions of label spacings in genome mapping experiments.Comment: 18 pages, 4 figures, 1 tabl
The gauging of two-dimensional bosonic sigma models on world-sheets with defects
We extend our analysis of the gauging of rigid symmetries in bosonic
two-dimensional sigma models with Wess-Zumino terms in the action to the case
of world-sheets with defects. A structure that permits a non-anomalous coupling
of such sigma models to world-sheet gauge fields of arbitrary topology is
analysed, together with obstructions to its existence, and the classification
of its inequivalent choices.Comment: 94 pages, 1 figur
Fictions, Fault, and Forgiveness: Jury Nullification in a New Context
Recently, critics of the Anglo-American jury system have complained that juries in criminal trials have been ignoring the law, in favor of defendants who claim that they lack criminal responsibility because they are afflicted by the various victimization syndromes now popularized in the mass media. In this Article, Professors Dorfman and Iijima counter this characterization of the runaway jury and argue that juries are not ignoring the law, but rather, are exercising a primary power of the jury, to nullify the application of the law when such application to a particular defendant is unjust. The Authors trace the development of the jury nullification power from its beginnings in the late seventeenth century to the present. The Authors then counter the standard arguments against jury nullification. Finally, the Authors propose an explicit jury nullification instruction and accommodating adjustments to other trial procedures that would solve the deficiencies of the current manner in which juries exercise their nullification power
Detection of photon statistics and multimode field correlations by Raman processes
Glauber’s g^(2)-function provides a common measure of quantum field statistics through two-photon coincidence counting in Hanbury Brown–Twiss measurements. Here, we propose to use nonlinear optical signals as a tool for the characterization of quantum light. In particular, we show that Raman measurements provide an alternative direct probe for a different component of the four-point correlation function underlying the g^(2)-function. We illustrate this capacity for a specific quantum state obtained from a frequency conversion process. Our work points out how the analysis of controlled optical nonlinear processes can provide an alternative window toward the analysis of quantum light sources
Quantum-Coherence-Enhanced Surface Plasmon Amplification by Stimulated Emission of Radiation
We investigate surface plasmon amplification in a silver nanoparticle coupled
to an externally driven three-level gain medium, and show that quantum
coherence significantly enhances the generation of surface plasmons. Surface
plasmon amplification by stimulated emission of radiation is achieved in the
absence of population inversion on the spasing transition, which reduces the
pump requirements. The coherent drive allows us to control the dynamics, and
holds promise for quantum control of nanoplasmonic devices.Comment: 5 pages, 4 figure
Hairpins in the conformations of a confined polymer
If a semiflexible polymer confined to a narrow channel bends around by 180
degrees, the polymer is said to exhibit a hairpin. The equilibrium extension
statistics of the confined polymer are well understood when hairpins are
vanishingly rare or when they are plentiful. Here we analyze the extension
statistics in the intermediate situation via experiments with DNA coated by the
protein RecA, which enhances the stiffness of the DNA molecule by approximately
one order of magnitude. We find that the extension distribution is highly
non-Gaussian, in good agreement with Monte Carlo simulations of confined
discrete wormlike chains. We develop a simple model that qualitatively explains
the form of the extension distribution. The model shows that the tail of the
distribution at short extensions is determined by conformations with one
hairpin.Comment: Revised version. 22 pages, 7 figures, 2 tables, supplementary
materia
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