428 research outputs found
Bloch oscillations in one-dimensional spinor gas
A force applied to a spin-flipped particle in a one-dimensional spinor gas
may lead to Bloch oscillations of particle's position and velocity. The
existence of Bloch oscillations crucially depends on the viscous friction force
exerted by the rest of the gas on the spin excitation. We evaluate the friction
in terms of the quantum fluid parameters. In particular, we show that the
friction is absent for integrable cases, such as SU(2) symmetric gas of bosons
or fermions. For small deviations from the exact integrability the friction is
very weak, opening the possibility to observe Bloch oscillations.Comment: 4 pages, 2 figure
Optical excitation of nonlinear spin waves
We demonstrate a technique for exciting spin waves in an ultracold gas of
Rb-87 atoms based on tunable AC Stark potentials. This technique allows us to
excite normal modes of spin waves with arbitrary amplitudes in the trapped gas,
including dipole, quadrupole, octupole, and hexadecapole modes. These modes
exhibit strong nonlinearities, which manifest as amplitude dependence of the
excitation frequencies and departure from sinusoidal behavior. Our results are
in good agreement with a full treatment of a quantum Boltzmann transport
equation.Comment: 11 pages, 5 figure
Internal state conversion in ultracold gases
We consider an ultracold gas of (non-condensed) bosons or fermions with two
internal states, and study the effect of a gradient of the transition frequency
between these states. When a RF pulse is applied to the sample,
exchange effects during collisions transfer the atoms into internal states
which depend on the direction of their velocity. This results, after a short
time, in a spatial separation between the two states. A kinetic equation is
solved analytically and numerically; the results agree well with the recent
observations of Lewandowski et al.Comment: Accepted version, to appear in PR
Beam-foil spectrum of nitrogen at ultraviolet wavelengths
Spectrum analysis on foil excited nitrogen beam during acceleration at ultraviolet wavelength
The existence of a 2Po excited state for the e+Ca system
The Configuration Interaction method is used to demonstrate that there is an
electronically stable state of positronic calcium with an orbital angular
momentum of L=1. This prediction relies on the use of an asymptotic series to
estimate the variational limit of the energy. The best estimate of the binding
energy is 37 meV. A discussion of the structure of the system is also
presented.Comment: 4 pages, 2 figures, in press PR
Intermediate-mass-fragment Production in the Reaction of 200 MeV 3-He with Ag
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Optical excitations in a non-ideal Bose gas
Optical excitations in a Bose gas are demonstrated to be very sensitive to
many-body effects. At low temperature the momentum relaxation is provided by
momentum exchange collisions, rather than by elastic collisions. A collective
excitation mode forms, which in a Boltzmann gas is manifest in a collision
shift and dramatic narrowing of spectral lines.
In the BEC state, each spectral line splits into two components. The doubling
of the optical excitations results from the physics analogous to that of the
second sound. We present a theory of the line doubling, and calculate the
oscillator strengths and linewidth.Comment: 5 pages, 3 eps figure
Electric field induced strong localization of electrons on solid hydrogen surface: possible applications to quantum computing
Two-dimensional electron system on the liquid helium surface is one of the
leading candidates for constructing large analog quantum computers (P.M.
Platzman and M.I. Dykman, Science 284, 1967 (1999)). Similar electron systems
on the surfaces of solid hydrogen or solid neon may have some important
advantages with respect to electrons on liquid helium in quantum computing
applications, such as larger state separation , absence of
propagating capillary waves (or ripplons), smaller vapor pressure, etc. As a
result, it may operate at higher temperatures. Surface roughness is the main
hurdle to overcome in building a realistic quantum computer using these states.
Electric field induced strong localization of surface electrons is shown to be
a convenient tool to characterize surface roughness.Comment: 4 pages, 3 figure
Однородные и четно-однородные супермногообразия с ретрактом CP(1|4 kk20) при к >= 2
This paper contain the description of non-split even-homogeneous supermanifolds over the complex projective line whose retract corresponds to a holomorphic vector bundle of the signature (k,k, 2,0), where k >= 2. We prove that there are no non-split homogeneous supermanifolds in this case. See [3] and [4] for more information about the complex supermanifolds theory.Описываются чётно-однородные нерасщепимые супермногообразия, связанные с комплексной проективной прямой в случае, когда ретракт определяется векторным расслоением с сигнатурой (к, к, 2, 0) при к >= 2. Показано, что однородных нерасщепимых супермногообразий с требуемым ретрактом нет. Необходимые сведения по теории комплексных супермногообразий можно найти в [3] и [5]
Normal-superfluid interaction dynamics in a spinor Bose gas
Coherent behavior of spinor Bose-Einstein condensates is studied in the
presence of a significant uncondensed (normal) component. Normal-superfluid
exchange scattering leads to a near-perfect local alignment between the spin
fields of the two components. Through this spin locking, spin-domain formation
in the condensate is vastly accelerated as the spin populations in the
condensate are entrained by large-amplitude spin waves in the normal component.
We present data evincing the normal-superfluid spin dynamics in this regime of
complicated interdependent behavior.Comment: 5 pages, 4 fig
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