429 research outputs found
Trapping of ultra-cold atoms with the magnetic field of vortices in a thin film superconducting micro-structure
We store and control ultra-cold atoms in a new type of trap using magnetic
fields of vortices in a high temperature superconducting micro-structure. This
is the first time ultra-cold atoms have been trapped in the field of magnetic
flux quanta. We generate the attractive trapping potential for the atoms by
combining the magnetic field of a superconductor in the remanent state with
external homogeneous magnetic fields. We show the control of crucial atom trap
characteristics such as an efficient intrinsic loading mechanism, spatial
positioning of the trapped atoms and the vortex density in the superconductor.
The measured trap characteristics are in good agreement with our numerical
simulations.Comment: 4pages, comments are welcom
Tapered optical fibers as tools for probing magneto-optical trap characteristics
We present a novel technique for measuring the characteristics of a
magneto-optical trap for cold atoms by monitoring the spontaneous emission from
trapped atoms coupled into the guided mode of a tapered optical nanofiber. We
show that the nanofiber is highly sensitive to very small numbers of atoms
close to its surface. The size and shape of the MOT, determined by translating
the cold atom cloud across the tapered fiber, is in excellent agreement with
measurements obtained using the conventional method of fluorescence imaging
using a CCD camera. The coupling of atomic fluorescence into the tapered fiber
also allows us to monitor the loading and lifetime of the trap. The results are
compared to those achieved by focusing the MOT fluorescence onto a photodiode
and it was seen that the tapered fiber gives slightly longer loading and
lifetime measurements due to the sensitivity of the fiber, even when very few
atoms are present.Comment: 21 pages, 5 figure
Single-Electron Traps: A Quantitative Comparison of Theory and Experiment
We have carried out a coordinated experimental and theoretical study of
single-electron traps based on submicron aluminum islands and aluminum oxide
tunnel junctions. The results of geometrical modeling using a modified version
of MIT's FastCap were used as input data for the general-purpose
single-electron circuit simulator MOSES. The analysis indicates reasonable
quantitative agreement between theory and experiment for those trap
characteristics which are not affected by random offset charges. The observed
differences between theory and experiment (ranging from a few to fifty percent)
can be readily explained by the uncertainty in the exact geometry of the
experimental nanostructures.Comment: 17 pages, 21 figures, RevTex, eps
Maxwell's Demon at work: Two types of Bose condensate fluctuations in power-law traps
After discussing the key idea underlying the Maxwell's Demon ensemble, we
employ this idea for calculating fluctuations of ideal Bose gas condensates in
traps with power-law single-particle energy spectra. Two essentially different
cases have to be distinguished. If the heat capacity remains continuous at the
condensation point in the large-N-limit, the fluctuations of the number of
condensate particles vanish linearly with temperature, independent of the trap
characteristics. If the heat capacity becomes discontinuous, the fluctuations
vanish algebraically with temperature, with an exponent determined by the trap.
Our results are based on an integral representation that yields the solution to
both the canonical and the microcanonical fluctuation problem in a singularly
transparent manner.Comment: 10 pages LaTeX and 3 eps-figures, published versio
A ring trap for ultracold atoms
We propose a new kind of toroidal trap, designed for ultracold atoms. It
relies on a combination of a magnetic trap for rf-dressed atoms, which creates
a bubble-like trap, and a standing wave of light. This new trap is well suited
for investigating questions of low dimensionality in a ring potential. We study
the trap characteristics for a set of experimentally accessible parameters. A
loading procedure from a conventional magnetic trap is also proposed. The
flexible nature of this new ring trap, including an adjustable radius and
adjustable transverse oscillation frequencies, will allow the study of
superfluidity in variable geometries and dimensionalities.Comment: 4 figures, 10 pages ; the order of the sections has been changed ; to
appear in Phys. Rev.
Charge trapping and detrapping in polymeric materials: Trapping parameters
Space charge formation in polymeric materials can cause some serious concern for design engineers as the electric field may severely be distorted, leading to part of the material being overstressed. This may result in material degradation and possibly premature failure at the worst. It is therefore important to understand charge generation, trapping, and detrapping processes in the material. Trap depths and density of trapping states in materials are important as they are potentially related to microstructure of the material. Changes in these parameters may reflect the aging taken place in the material. In the present paper, characteristics of charge trapping and detrapping in low density polyethylene (LDPE) under dc electric field have been investigated using the pulsed electroacoustic (PEA) technique. A simple trapping and detrapping model based on two trapping levels has been used to qualitatively explain the observation. Numerical simulation based on the above model has been carried out to extract parameters related to trapping characteristics in the material. It has been found that the space charge decaying during the first few hundred seconds corresponding to the fast changing part of the slope was trapped with the shallow trap depth 0.88 eV, with trap density 1.47 × 1020 m-3 in the sample volume measured. At the same time, the space charge that decays at longer time corresponding to the slower part of the slope was trapped with the deep trap depth 1.01 eV, with its trap density 3.54 × 1018 m-3. The results also indicate that trap depths and density of both shallow and deep traps may be used as aging markers as changes in the material will certainly affect trapping characteristics in terms of trap depth and density
Charge Transfer Inefficiency Studies for CCD Vertex Detectors at a LC
The Linear Collider Flavour Identification (LCFI) collaboration studies CCD
detectors for quark flavour identification in the framework of a future linear
e+e- collider. The flavour identification is based on precision reconstruction
of charged tracks very close to the interaction point. Therefore, this detector
will be exposed to a high level of radiation and thus an important aspect of
the vertex detector development are radiation hardness studies. Results of
detailed simulations of the charged transport properties of a CCD prototype
chip are reported and compared with initial measurements. The simulation
program allows to study the effect of radiation damage after the exposure of
the detector to a realistic radiation dose, which is expected in the
environment of detector operation at a future LC.Comment: 6 pages, 10 figures, Proceedings 2005 International Linear Collider
Workshop - Stanford, U.S.
Manipulating and measuring single atoms in the Maltese cross geometry
Background: Optical microtraps at the focus of high numerical aperture (high-NA) imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms for quantum technology and studies of optical physics associated with super- and sub-radiant states. The recently developed “Maltese cross” geometry (MCG) atom trap uses four in-vacuum lenses to achieve four-directional high-NA optical coupling to single trapped atoms and small atomic arrays. This article presents the first extensive characterisation of atomic behaviour in a MCG atom trap. Methods: We employ a MCG system optimised for high coupling efficiency and characterise the resulting properties of the trap and trapped atoms. Using current best practices, we measure occupancy, loading rate, lifetime, temperature, fluorescence anti-bunching and trap frequencies. We also use the four-directional access to implement a new method to map the spatial distribution of collection efficiency from high-NA optics: we use the two on-trap-axis lenses to produce a 1D optical lattice, the sites of which are stochastically filled and emptied by the trap loading process. The two off-trap-axis lenses are used for imaging and single-mode collection. Correlations of single-mode and imaging fluorescence signals are then used to map the single-mode collection efficiency.Results: We observe trap characteristics comparable to what has been reported for single-atom traps with one- or two-lens optical systems. The collection efficiency distribution in the axial and transverse directions is directly observed to be in agreement with expected collection efficiency distribution from Gaussian beam optics. Conclusions: The multi-directional high-NA access provided by the Maltese cross geometry enables complex manipulations and measurements not possible in geometries with fewer directions of access, and can be achieved while preserving other trap characteristics such as lifetime, temperature, and trap size.Peer ReviewedPostprint (published version
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