1,501 research outputs found
Properties of quasi two-dimensional condensates in highly anisotropic traps
We theoretically investigate some of the observable properties of quasi
two-dimensional condensates. Using a variational model based on a
Gaussian-parabolic trial wavefunction we calculate chemical potential,
condensate size in time-of-flight, release energy and collective excitation
spectrum for varying trap geometries and atom numbers and find good agreement
with recent published experimental results.Comment: 7 pages, 4 figure
Single Atom Imaging with an sCMOS camera
Single atom imaging requires discrimination of weak photon count events above
background and has typically been performed using either EMCCD cameras,
photomultiplier tubes or single photon counting modules. sCMOS provides a cost
effective and highly scalable alternative to other single atom imaging
technologies, offering fast readout and larger sensor dimensions. We
demonstrate single atom resolved imaging of two site-addressable single atom
traps separated by 10~m using an sCMOS camera, offering a competitive
signal-to-noise ratio at intermediate count rates to allow high fidelity
readout discrimination (error ) and sub-m spatial resolution for
applications in quantum technologies.Comment: 4 pages, 4 figure
Novel techniques to cool and rotate Bose-Einstein condensates in time-averaged adiabatic potentials
We report two novel techniques for cooling and rotating Bose-Einstein
condensates in a dilute rubidium vapour that highlight the control and
versatility afforded over cold atom systems by time-averaged adiabatic
potentials (TAAPs). The intrinsic loss channel of the TAAP has been
successfully employed to evaporatively cool a sample of trapped atoms to
quantum degeneracy. The speed and efficiency of this process compares well with
that of conventional forced rf-evaporation. In an independent experiment, we
imparted angular momentum to a cloud of atoms forming a Bose-Einstein
condensate by introducing a rotating elliptical deformation to the TAAP
geometry. Triangular lattices of up to 60 vortices were created. All findings
reported herein result from straightforward adjustments of the magnetic fields
that give rise to the TAAP.Comment: The first two authors contributed equally to this wor
Supersymmetric 3-3-1 model with right-handed neutrinos
We consider the supersymmetric extension of the 3-3-1 model with right-handed
neutrinos. We study the mass spectra in the scalar and pseudoscalar sectors,
and for a given set of the input parameters, we find that the lightest scalar
in the model has a mass of 130 GeV and the lightest pseudoscalar has mass of 5
GeV. However, this pseudoscalar decouples from the at high energy scales
since it is almost a singlet under .Comment: Revtex4, 16 pages, no figure
Electric Charge Quantization
Experimentally it has been known for a long time that the electric charges of
the observed particles appear to be quantized. An approach to understanding
electric charge quantization that can be used for gauge theories with explicit
factors -- such as the standard model and its variants -- is
pedagogically reviewed and discussed in this article. This approach uses the
allowed invariances of the Lagrangian and their associated anomaly cancellation
equations. We demonstrate that charge may be de-quantized in the
three-generation standard model with massless neutrinos, because differences in
family-lepton--numbers are anomaly-free. We also review the relevant
experimental limits. Our approach to charge quantization suggests that the
minimal standard model should be extended so that family-lepton--number
differences are explicitly broken. We briefly discuss some candidate extensions
(e.g. the minimal standard model augmented by Majorana right-handed neutrinos).Comment: 18 pages, LaTeX, UM-P-92/5
Ultracold atoms in an optical lattice with dynamically variable periodicity
The use of a dynamic "accordion" lattice with ultracold atoms is
demonstrated. Ultracold atoms of Rb are trapped in a two-dimensional
optical lattice, and the spacing of the lattice is then increased in both
directions from 2.2 to 5.5 microns. Atoms remain bound for expansion times as
short as a few milliseconds, and the experimentally measured minimum ramp time
is found to agree well with numerical calculations. This technique allows an
experiment such as quantum simulations to be performed with a lattice spacing
smaller than the resolution limit of the imaging system, while allowing imaging
of the atoms at individual lattice sites by subsequent expansion of the optical
lattice.Comment: 4 pages, 3 figures. Minor changes made and references update
Observation of vortex nucleation in a rotating two-dimensional lattice of Bose-Einstein condensates
We report the observation of vortex nucleation in a rotating optical lattice.
A 87Rb Bose-Einstein condensate was loaded into a static two-dimensional
lattice and the rotation frequency of the lattice was then increased from zero.
We studied how vortex nucleation depended on optical lattice depth and rotation
frequency. For deep lattices above the chemical potential of the condensate we
observed a linear dependence of the number of vortices created with the
rotation frequency,even below the thermodynamic critical frequency required for
vortex nucleation. At these lattice depths the system formed an array of
Josephson-coupled condensates. The effective magnetic field produced by
rotation introduced characteristic relative phases between neighbouring
condensates, such that vortices were observed upon ramping down the lattice
depth and recombining the condensates.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let
Experimental observation of the 'Tilting Mode' of an array of vortices in a dilute Bose-Einstein Condensate
We have measured the precession frequency of a vortex lattice in a
Bose-Einstein condensate of 87Rb atoms. The observed mode corresponds to a
collective motion in which all the vortices in the array are tilted by a small
angle with respect to the z-axis (the symmetry axis of the trapping potential)
and synchronously rotate about this axis. This motion corresponds to excitation
of a Kelvin wave along the core of each vortex and we have verified that it has
the handedness expected for such helical waves, i.e. precession in the opposite
sense to the rotational flow around the vortices. The experimental method used
to excite this collective mode closely resembles that used to study the
scissors mode and excitation of the scissors mode for a condensate containing a
vortex array was used to determine the angular momentum of the system. Indeed,
the collective tilting of the array that we have observed has previously been
referred to as an `anomalous' scissors mode.Comment: 5 pages, 7 figures to be published in PR
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