304 research outputs found
Conductance Distribution of a Quantum Dot with Non-Ideal Single-Channel Leads
We have computed the probability distribution of the conductance of a
ballistic and chaotic cavity which is connected to two electron reservoirs by
leads with a single propagating mode, for arbitrary values of the transmission
probability Gamma of the mode, and for all three values of the symmetry index
beta. The theory bridges the gap between previous work on ballistic leads
(Gamma = 1) and on tunneling point contacts (Gamma << 1). We find that the
beta-dependence of the distribution changes drastically in the crossover from
the tunneling to the ballistic regime. This is relevant for experiments, which
are usually in this crossover regime. ***Submitted to Physical Review B.***Comment: 7 pages, REVTeX-3.0, 4 postscript figures appended as self-extracting
archive, INLO-PUB-940607
Diagnostic criterion for crystallized beams
Small ion crystals in a Paul trap are stable even in the absence of laser
cooling. Based on this theoretically and experimentally well-established fact
we propose the following diagnostic criterion for establishing the presence of
a crystallized beam: Absence of heating following the shut-down of all cooling
devices. The validity of the criterion is checked with the help of detailed
numerical simulations.Comment: REVTeX, 11 pages, 4 figures; submitted to PR
Correlations and pair emission in the escape dynamics of ions from one-dimensional traps
We explore the non-equilibrium escape dynamics of long-range interacting ions
in one-dimensional traps. The phase space of the few ion setup and its impact
on the escape properties are studied. As a main result we show that an
instantaneous reduction of the trap's potential depth leads to the synchronized
emission of a sequence of ion pairs if the initial configurations are close to
the crystalline ionic configuration. The corresponding time-intervals of the
consecutive pair emission as well as the number of emitted pairs can be tuned
by changing the final trap depth. Correlations between the escape times and
kinetic energies of the ions are observed and analyzed.Comment: 17 pages, 9 figure
Mesoscopic Transport Through Ballistic Cavities: A Random S-Matrix Theory Approach
We deduce the effects of quantum interference on the conductance of chaotic
cavities by using a statistical ansatz for the S matrix. Assuming that the
circular ensembles describe the S matrix of a chaotic cavity, we find that the
conductance fluctuation and weak-localization magnitudes are universal: they
are independent of the size and shape of the cavity if the number of incoming
modes, N, is large. The limit of small N is more relevant experimentally; here
we calculate the full distribution of the conductance and find striking
differences as N changes or a magnetic field is applied.Comment: 4 pages revtex 3.0 (2-column) plus 2 postscript figures (appended),
hub.pam.94.
How Phase-Breaking Affects Quantum Transport Through Chaotic Cavities
We investigate the effects of phase-breaking events on electronic transport
through ballistic chaotic cavities. We simulate phase-breaking by a fictitious
lead connecting the cavity to a phase-randomizing reservoir and introduce a
statistical description for the total scattering matrix, including the
additional lead. For strong phase-breaking, the average and variance of the
conductance are calculated analytically. Combining these results with those in
the absence of phase-breaking, we propose an interpolation formula, show that
it is an excellent description of random-matrix numerical calculations, and
obtain good agreement with several recent experiments.Comment: 4 pages, revtex, 3 figures: uuencoded tar-compressed postscrip
Failure of Effective Potential Approach: Nucleus-Electron Entanglement in the He-Ion
Entanglement may be considered a resource for quantum-information processing,
as the origin of robust and universal equilibrium behaviour, but also as a
limit to the validity of an effective potential approach, in which the
influence of certain interacting subsystems is treated as a potential. Here we
show that a closed three particle (two protons, one electron) model of a He-ion
featuring realistic size, interactions and energy scales of electron and
nucleus, respectively, exhibits different types of dynamics depending on the
initial state: For some cases the traditional approach, in which the nucleus
only appears as the center of a Coulomb potential, is valid, in others this
approach fails due to entanglement arising on a short time-scale. Eventually
the system can even show signatures of thermodynamical behaviour, i.e. the
electron may relax to a maximum local entropy state which is, to some extent,
independent of the details of the initial state.Comment: Submitted to Europhysics Letter
Doppler cooling of a Coulomb crystal
We study theoretically Doppler laser-cooling of a cluster of 2-level atoms
confined in a linear ion trap. Using several consecutive steps of averaging we
derive, from the full quantum mechanical master equation, an equation for the
total mechanical energy of the one dimensional crystal, defined on a
coarse-grained energy scale whose grid size is smaller than the linewidth of
the electronic transition. This equation describes the cooling dynamics for an
arbitrary number of ions and in the quantum regime. We discuss the validity of
the ergodic assumption (i.e. that the phase space distribution is only a
function of energy). From our equation we derive the semiclassical limit (i.e.
when the mechanical motion can be treated classically) and the Lamb-Dicke limit
(i.e. when the size of the mechanical wave function is much smaller than the
laser wavelength). We find a Fokker-Planck equation for the total mechanical
energy of the system, whose solution is in agreement with previous analytical
calculations which were based on different assumptions and valid only in their
specific regimes. Finally, in the classical limit we derive an analytic
expression for the average coupling, by light scattering, between motional
states at different energies.Comment: 19 pages, 3 figure
LIFE-SHARE Project: Developing a Digitisation Strategy Toolkit
This poster will outline the Digitisation Strategy Toolkit created as part of the LIFE-SHARE project. The toolkit is based on the lifecycle model created by the LIFE project and explores the creation, acquisition, ingest, preservation (bit-stream and content) and access requirements for a digitisation strategy. This covers the policies and infrastructure required in libraries to establish successful practices. The toolkit also provides both internal and external resources to support the service. This poster will illustrate how the toolkit works effectively to support digitisation with examples from three case studies at the Universities of Leeds, Sheffield and York
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