125 research outputs found
Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
We have observed the cold collision frequency shift of the 1S-2S transition
in trapped spin-polarized atomic hydrogen. We find , where is the sample density. From this
we derive the 1S-2S s-wave triplet scattering length, nm,
which is in fair agreement with a recent calculation. The shift provides a
valuable probe of the distribution of densities in a trapped sample.Comment: Accepted for publication in PRL, 9 pages, 4 PostScript figures,
ReVTeX. Updated connection of our measurement to theoretical wor
Excitation-assisted inelastic processes in trapped Bose-Einstein condensates
We find that inelastic collisional processes in Bose-Einstein condensates
induce local variations of the mean-field interparticle interaction and are
accompanied by the creation/annihilation of elementary excitation. The physical
picture is demonstrated for the case of three body recombination in a trapped
condensate. For a high trap barrier the production of high energy trapped
single particle excitations results in a strong increase of the loss rate of
atoms from the condensate.Comment: 4 pages, no figure
Electromagnetic response of a static vortex line in a type-II superconductor : a microscopic study
The electromagnetic response of a pinned Abrikosov fluxoid is examined in the
framework of the Bogoliubov-de Gennes formalism. The matrix elements and the
selection rules for both the single photon (emission - absorption) and two
photon (Raman scattering) processes are obtained. The results reveal striking
asymmetries: light absorption by quasiparticle pair creation or single
quasiparticle scattering can occur only if the handedness of the incident
radiation is opposite to that of the vortex core states. We show how these
effects will lead to nonreciprocal circular birefringence, and also predict
structure in the frequency dependence of conductivity and in the differential
cross section of the Raman scattering.Comment: 14 pages (RevTex
Bragg spectroscopy of a Bose-Einstein condensate
Properties of a Bose-Einstein condensate were studied by stimulated,
two-photon Bragg scattering. The high momentum and energy resolution of this
method allowed a spectroscopic measurement of the mean-field energy and of the
intrinsic momentum uncertainty of the condensate. The coherence length of the
condensate was shown to be equal to its size. Bragg spectroscopy can be used to
determine the dynamic structure factor over a wide range of energy and momentum
transfers.Comment: 4 pages, 3 figure
Quantum saturation and condensation of excitons in CuO: a theoretical study
Recent experiments on high density excitons in CuO provide evidence for
degenerate quantum statistics and Bose-Einstein condensation of this nearly
ideal gas. We model the time dependence of this bosonic system including
exciton decay mechanisms, energy exchange with phonons, and interconversion
between ortho (triplet-state) and para (singlet-state) excitons, using
parameters for the excitonic decay, the coupling to acoustic and low-lying
optical phonons, Auger recombination, and ortho-para interconversion derived
from experiment. The single adjustable parameter in our model is the
optical-phonon cooling rate for Auger and laser-produced hot excitons. We show
that the orthoexcitons move along the phase boundary without crossing it (i.e.,
exhibit a ``quantum saturation''), as a consequence of the balance of entropy
changes due to cooling of excitons by phonons and heating by the non-radiative
Auger two-exciton recombination process. The Auger annihilation rate for
para-para collisions is much smaller than that for ortho-para and ortho-ortho
collisions, explaining why, under the given experimental conditions, the
paraexcitons condense while the orthoexcitons fail to do so.Comment: Revised to improve clarity and physical content 18 pages, revtex,
figures available from G. Kavoulakis, Physics Department, University of
Illinois, Urban
Correlating the nanostructure and electronic properties of InAs nanowires
The electronic properties and nanostructure of InAs nanowires are correlated
by creating multiple field effect transistors (FETs) on nanowires grown to have
low and high defect density segments. 4.2 K carrier mobilities are ~4X larger
in the nominally defect-free segments of the wire. We also find that dark field
optical intensity is correlated with the mobility, suggesting a simple route
for selecting wires with a low defect density. At low temperatures, FETs
fabricated on high defect density segments of InAs nanowires showed transport
properties consistent with single electron charging, even on devices with low
resistance ohmic contacts. The charging energies obtained suggest quantum dot
formation at defects in the wires. These results reinforce the importance of
controlling the defect density in order to produce high quality electrical and
optical devices using InAs nanowires.Comment: Related papers at http://pettagroup.princeton.ed
Spinor condensates and light scattering from Bose-Einstein condensates
These notes discuss two aspects of the physics of atomic Bose-Einstein
condensates: optical properties and spinor condensates. The first topic
includes light scattering experiments which probe the excitations of a
condensate in both the free-particle and phonon regime. At higher light
intensity, a new form of superradiance and phase-coherent matter wave
amplification were observed. We also discuss properties of spinor condensates
and describe studies of ground--state spin domain structures and dynamical
studies which revealed metastable excited states and quantum tunneling.Comment: 58 pages, 33 figures, to appear in Proceedings of Les Houches 1999
Summer School, Session LXXI
Condensation of bosons in kinetic regime
We study the kinetic regime of the Bose-condensation of scalar particles with
weak self-interaction. The Boltzmann equation is solved
numerically. We consider two kinetic stages. At the first stage the condensate
is still absent but there is a nonzero inflow of particles towards and the distribution function at grows from finite
values to infinity in a finite time. We observe a profound similarity between
Bose-condensation and Kolmogorov turbulence. At the second stage there are two
components, the condensate and particles, reaching their equilibrium values. We
show that the evolution in both stages proceeds in a self-similar way and find
the time needed for condensation. We do not consider a phase transition from
the first stage to the second. Condensation of self-interacting bosons is
compared to the condensation driven by interaction with a cold gas of fermions;
the latter turns out to be self-similar too. Exploiting the self-similarity we
obtain a number of analytical results in all cases.Comment: 23 pages plus 11 uuencoded figures, LaTeX, REVTEX 3.0 versio
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