544 research outputs found
Experimental demonstration of painting arbitrary and dynamic potentials for Bose-Einstein condensates
There is a pressing need for robust and straightforward methods to create
potentials for trapping Bose-Einstein condensates which are simultaneously
dynamic, fully arbitrary, and sufficiently stable to not heat the ultracold
gas. We show here how to accomplish these goals, using a rapidly-moving laser
beam that "paints" a time-averaged optical dipole potential in which we create
BECs in a variety of geometries, including toroids, ring lattices, and square
lattices. Matter wave interference patterns confirm that the trapped gas is a
condensate. As a simple illustration of dynamics, we show that the technique
can transform a toroidal condensate into a ring lattice and back into a toroid.
The technique is general and should work with any sufficiently polarizable
low-energy particles.Comment: Minor text changes and three references added. This is the final
version published in New Journal of Physic
RF spectroscopy in a resonant RF-dressed trap
We study the spectroscopy of atoms dressed by a resonant radiofrequency (RF)
field inside an inhomogeneous magnetic field and confined in the resulting
adiabatic potential. The spectroscopic probe is a second, weak, RF field. The
observed line shape is related to the temperature of the trapped cloud. We
demonstrate evaporative cooling of the RF-dressed atoms by sweeping the
frequency of the second RF field around the Rabi frequency of the dressing
field.Comment: 7 figures, 8 pages; to appear in J. Phys.
High-resolution imaging of ultracold fermions in microscopically tailored optical potentials
We report on the local probing and preparation of an ultracold Fermi gas on
the length scale of one micrometer, i.e. of the order of the Fermi wavelength.
The essential tool of our experimental setup is a pair of identical,
high-resolution microscope objectives. One of the microscope objectives allows
local imaging of the trapped Fermi gas of 6Li atoms with a maximum resolution
of 660 nm, while the other enables the generation of arbitrary optical dipole
potentials on the same length scale. Employing a 2D acousto-optical deflector,
we demonstrate the formation of several trapping geometries including a tightly
focussed single optical dipole trap, a 4x4-site two-dimensional optical lattice
and a 8-site ring lattice configuration. Furthermore, we show the ability to
load and detect a small number of atoms in these trapping potentials. A site
separation of down to one micrometer in combination with the low mass of 6Li
results in tunneling rates which are sufficiently large for the implementation
of Hubbard-models with the designed geometries.Comment: 15 pages, 6 figure
Rolling friction of a viscous sphere on a hard plane
A first-principle continuum-mechanics expression for the rolling friction
coefficient is obtained for the rolling motion of a viscoelastic sphere on a
hard plane. It relates the friction coefficient to the viscous and elastic
constants of the sphere material. The relation obtained refers to the case when
the deformation of the sphere is small, the velocity of the sphere is
much less than the speed of sound in the material and when the characteristic
time is much larger than the dissipative relaxation times of the
viscoelastic material. To our knowledge this is the first ``first-principle''
expression of the rolling friction coefficient which does not contain empirical
parameters.Comment: 6 pages, 2 figure
Matter-wave interferometers using TAAP rings
We present two novel matter-wave Sagnac interferometers based on ring-shaped time-averaged adiabatic potentials (TAAP). For both the atoms are put into a superposition of two different spin states and manipulated independently using elliptically polarized rf-fields. In the first interferometer the atoms are accelerated by spin-state-dependent forces and then travel around the ring in a matter-wave guide. In the second one the atoms are fully trapped during the entire interferometric sequence and are moved around the ring in two spin-state-dependent `buckets'. Corrections to the ideal Sagnac phase are investigated for both cases. We experimentally demonstrate the key atom-optical elements of the interferometer such as the independent manipulation of two different spin states in the ring-shaped potentials under identical experimental conditions
Bias in exponential and power function fits due to noise: Comment on Myung, Kim, and Pitt
Phonon-induced artificial magnetic fields
We investigate the effect of a rotating Bose-Einstein condensate on a system
of immersed impurity atoms trapped by an optical lattice. We analytically show
that for a one-dimensional, ring-shaped setup the coupling of the impurities to
the Bogoliubov phonons of the condensate leads to a non-trivial phase in the
impurity hopping. The presence of this phase can be tested by observing a drift
in the transport properties of the impurities. These results are quantitatively
confirmed by a numerically exact simulation of a two-mode Bose-Hubbard model.
We also give analytical expressions for the occurring phase terms for a
two-dimensional setup. The phase realises an artificial magnetic field and can
for instance be used for the simulation of the quantum Hall effect using atoms
in an optical lattice.Comment: 6 pages, 4 figure
Photofragmentation dynamics of <i>N,N</i>-dimethylformamide following excitation at 193 nm
N,N-dimethylformamide, HCON(CH3)2, is a useful model compound for
investigating peptide bond photofragmentation dynamics. We report data
from a comprehensive experimental and theoretical study into the photofragmentation
dynamics of N,N-dimethylformamide in the gas phase at 193 nm.
Through a combination of velocity-map imaging and hydrogen atom Rydberg
tagging photofragment translational spectroscopy, we have identified
two primary fragmentation channels, namely fission of the NCO `peptide'
bond, and NCH3 bond fission leading to loss of CH3. The possible fragmentation
channels leading to the observed products are rationalised with
recourse to CASPT2 calculations of the ground and first few excited-state
potential energy curves along the relevant dissociation coordinates, and the
results are compared with data from previous experimental and theoretical studies on the same system
QMLE: Fast, robust, and efficient estimation of distribution functions based on quantiles
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