4,014 research outputs found
Coulomb crystallization in expanding laser-cooled neutral plasmas
We present long-time simulations of expanding ultracold neutral plasmas,
including a full treatment of the strongly coupled ion dynamics. Thereby, the
relaxation dynamics of the expanding laser-cooled plasma is studied, taking
into account elastic as well as inelastic collisions. It is demonstrated that,
depending on the initial conditions, the ionic component of the plasma may
exhibit short-range order or even a superimposed long-range order resulting in
concentric ion shells. In contrast to ionic plasmas confined in traps, the
shell structures are built up from the center of the plasma cloud rather than
from the periphery
Two-Level Systems in Evaporated Amorphous Silicon
In -beam evaporated amorphous silicon (-Si), the densities of two-level
systems (TLS), and , determined from specific heat
and internal friction measurements, respectively, have been shown to
vary by over three orders of magnitude. Here we show that and
are proportional to each other with a constant of
proportionality that is consistent with the measurement time dependence
proposed by Black and Halperin and does not require the introduction of
additional anomalous TLS. However, and depend strongly
on the atomic density of the film () which depends on both film
thickness and growth temperature suggesting that the -Si structure is
heterogeneous with nanovoids or other lower density regions forming in a dense
amorphous network. A review of literature data shows that this atomic density
dependence is not unique to -Si. These findings suggest that TLS are not
intrinsic to an amorphous network but require a heterogeneous structure to
form
Laser cooling of new atomic and molecular species with ultrafast pulses
We propose a new laser cooling method for atomic species whose level
structure makes traditional laser cooling difficult. For instance, laser
cooling of hydrogen requires single-frequency vacuum-ultraviolet light, while
multielectron atoms need single-frequency light at many widely separated
frequencies. These restrictions can be eased by laser cooling on two-photon
transitions with ultrafast pulse trains. Laser cooling of hydrogen,
antihydrogen, and many other species appears feasible, and extension of the
technique to molecules may be possible.Comment: revision of quant-ph/0306099, submitted to PR
Dispersive Optical Interface Based on Nanofiber-Trapped Atoms
We dispersively interface an ensemble of one thousand atoms trapped in the
evanescent field surrounding a tapered optical nanofiber. This method relies on
the azimuthally-asymmetric coupling of the ensemble with the evanescent field
of an off-resonant probe beam, transmitted through the nanofiber. The resulting
birefringence and dispersion are significant; we observe a phase shift per atom
of \,1\,mrad at a detuning of six times the natural linewidth,
corresponding to an effective resonant optical density per atom of 0.027.
Moreover, we utilize this strong dispersion to non-destructively determine the
number of atoms.Comment: 4 pages, 4 figure
Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber
Trapping and optically interfacing laser-cooled neutral atoms is an essential
requirement for their use in advanced quantum technologies. Here we
simultaneously realize both of these tasks with cesium atoms interacting with a
multi-color evanescent field surrounding an optical nanofiber. The atoms are
localized in a one-dimensional optical lattice about 200 nm above the nanofiber
surface and can be efficiently interrogated with a resonant light field sent
through the nanofiber. Our technique opens the route towards the direct
integration of laser-cooled atomic ensembles within fiber networks, an
important prerequisite for large scale quantum communication schemes. Moreover,
it is ideally suited to the realization of hybrid quantum systems that combine
atoms with, e.g., solid state quantum devices
Strong-coupling effects in the relaxation dynamics of ultracold neutral plasmas
We describe a hybrid molecular dynamics approach for the description of
ultracold neutral plasmas, based on an adiabatic treatment of the electron gas
and a full molecular dynamics simulation of the ions, which allows us to follow
the long-time evolution of the plasma including the effect of the strongly
coupled ion motion. The plasma shows a rather complex relaxation behavior,
connected with temporal as well as spatial oscillations of the ion temperature.
Furthermore, additional laser cooling of the ions during the plasma evolution
drastically modifies the expansion dynamics, so that crystallization of the ion
component can occur in this nonequilibrium system, leading to lattice-like
structures or even long-range order resulting in concentric shells
Narrow Line Cooling and Momentum-Space Crystals
Narrow line laser cooling is advancing the frontier for experiments ranging
from studies of fundamental atomic physics to high precision optical frequency
standards. In this paper, we present an extensive description of the systems
and techniques necessary to realize 689 nm 1S0 - 3P1 narrow line cooling of
atomic 88Sr. Narrow line cooling and trapping dynamics are also studied in
detail. By controlling the relative size of the power broadened transition
linewidth and the single-photon recoil frequency shift, we show that it is
possible to continuously bridge the gap between semiclassical and quantum
mechanical cooling. Novel semiclassical cooling process, some of which are
intimately linked to gravity, are also explored. Moreover, for laser
frequencies tuned above the atomic resonance, we demonstrate momentum-space
crystals containing up to 26 well defined lattice points. Gravitationally
assisted cooling is also achieved with blue-detuned light. Theoretically, we
find the blue detuned dynamics are universal to Doppler limited systems. This
paper offers the most comprehensive study of narrow line laser cooling to date.Comment: 14 pages, 19 figure
Photoemission study of (VM)O (M=Cr, Ti)
We present high-resolution bulk-sensitive photoemission spectra of
(VM)O (M=Cr, Ti). The measurements were made for the
paramagnetic metal (PM), paramagnetic insulator (PI), and antiferromagnetic
insulator (AFI) phases of (VM)O with the samples of =
0, 0.012, and 0.028 for Cr-doping and = 0.01 for Ti-doping. In the PM
phase, we observe a prominent quasiparticle peak in general agreement with
theory, which combines dynamical mean-field theory with the local density
approximation (LDA+DMFT). The quasiparticle peak shows a significantly larger
peak width and weight than in the theory. For both the PI and AFI phases, the
vanadium 3d parts of the valence spectra are not simple one peak structures.
For the PI phase, there is not yet a good theoretical understanding of these
structures. The size of the electron removal gap increases, and spectral weight
accumulates in the energy range closer to the chemical potential, when the PI
to AFI transition occurs. Spectra taken in the same phases with different
compositions show interesting monotonic changes as the dopant concentration
increases, regardless of the dopant species. With increased Cr-doping, the AFI
phase gap decreases and the PI phase gap increases.Comment: 13 pages, 16 figures. accepted for publication in Physical Review
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