616 research outputs found
Adsorbate Electric Fields on a Cryogenic Atom Chip
We investigate the behaviour of electric fields originating from adsorbates
deposited on a cryogenic atom chip as it is cooled from room temperature to
cryogenic temperature. Using Rydberg electromagnetically induced transparency
we measure the field strength versus distance from a 1 mm square of YBCO
patterned onto a YSZ chip substrate. We find a localized and stable dipole
field at room temperature and attribute it to a saturated layer of chemically
adsorbed rubidium atoms on the YBCO. As the chip is cooled towards 83 K we
observe a change in sign of the electric field as well as a transition from a
localized to a delocalized dipole density. We relate these changes to the onset
of physisorption on the chip surface when the van der Waals attraction
overcomes the thermal desorption mechanisms. Our findings suggest that, through
careful selection of substrate materials, it may be possible to reduce the
electric fields caused by atomic adsorption on chips, opening up experiments to
controlled Rydberg-surface coupling schemes.Comment: 5 pages, 4 figure
Design of magnetic traps for neutral atoms with vortices in type-II superconducting micro-structures
We design magnetic traps for atoms based on the average magnetic field of
vortices induced in a type-II superconducting thin film. This magnetic field is
the critical ingredient of the demonstrated vortex-based atom traps, which
operate without transport current. We use Bean's critical-state method to model
the vortex field through mesoscopic supercurrents induced in the thin strip.
The resulting inhomogeneous magnetic fields are studied in detail and compared
to those generated by multiple normally-conducting wires with transport
currents. Various vortex patterns can be obtained by programming different
loading-field and transport current sequences. These variable magnetic fields
are employed to make versatile trapping potentials.Comment: 11 pages, 14 figure
Monitoring currents in cold-atom circuits
Complex circuits of cold atoms can be exploited to devise new protocols for
the diagnostics of cold-atoms systems. Specifically, we study the quench
dynamics of a condensate confined in a ring-shaped potential coupled with a
rectilinear guide of finite size. We find that the dynamics of the atoms inside
the guide is distinctive of the states with different winding numbers in the
ring condensate. We also observe that the depletion of the density, localized
around the tunneling region of the ring condensate, can decay in a pair of
excitations experiencing a Sagnac effect. In our approach, the current states
of the condensate in the ring can be read out by inspection of the rectilinear
guide only, leaving the ring condensate minimally affected by the measurement.
We believe that our results set the basis for definition of new quantum
rotation sensors. At the same time, our scheme can be employed to explore
fundamental questions involving dynamics of bosonic condensates.Comment: Figures are enlarged. Section IV is added. Journal reference adde
10 GeV dark matter candidates and cosmic-ray antiprotons
Recent measurements performed with some direct dark matter detection
experiments, e.g. CDMS-II and CoGENT (after DAMA/LIBRA), have unveiled a few
events compatible with weakly interacting massive particles. The preferred mass
range is around 10 GeV, with a quite large spin-independent cross section of
-. In this paper, we recall that a light dark
matter particle with dominant couplings to quarks should also generate
cosmic-ray antiprotons. Taking advantage of recent works constraining the
Galactic dark matter mass profile on the one hand and on cosmic-ray propagation
on the other hand, we point out that considering a thermal annihilation cross
section for such low mass candidates very likely results in an antiproton flux
in tension with the current data, which should be taken into account in
subsequent studies.Comment: 4 pages, 2 figures. V2: minor changes to match the published versio
Superfluid qubit systems with ring shaped optical lattices
We study an experimentally feasible qubit system employing neutral atomic
currents. Our system is based on bosonic cold atoms trapped in ring-shaped
optical lattice potentials. The lattice makes the system strictly one
dimensional and it provides the infrastructure to realize a tunable ring-ring
interaction. Our implementation combines the low decoherence rates of of
neutral cold atoms systems, overcoming single site addressing, with the
robustness of topologically protected solid state Josephson flux qubits.
Characteristic fluctuations in the magnetic fields affecting Josephson junction
based flux qubits are expected to be minimized employing neutral atoms as flux
carriers. By breaking the Galilean invariance we demonstrate how atomic
currents through the lattice provide a implementation of a qubit. This is
realized either by artificially creating a phase slip in a single ring, or by
tunnel coupling of two homogeneous ring lattices. The single qubit
infrastructure is experimentally investigated with tailored optical potentials.
Indeed, we have experimentally realized scaled ring-lattice potentials that
could host, in principle, of such ring-qubits, arranged in a stack
configuration, along the laser beam propagation axis.
An experimentally viable scheme of the two-ring-qubit is discussed, as well.
Based on our analysis, we provide protocols to initialize, address, and
read-out the qubit.Comment: 14 revtex4-1 pages, 7 figs; to be published in Scientific Report
Programmable trap geometries with superconducting atom chips
We employ the hysteretic behavior of a superconducting thin film in the
remanent state to generate different traps and flexible magnetic potentials for
ultra-cold atoms. The trap geometry can be programmed by externally applied
fields. This new approach for atom-optics is demonstrated by three different
trap types realized on a single micro-structure: a Z-type trap, a double trap
and a bias field free trap. Our studies show that superconductors in the
remanent state provide a new versatile platform for atom-optics and
applications in ultra-cold quantum gases
The Integrated Polarization of Spiral Galaxy Disks
We present integrated polarization properties of nearby spiral galaxies at
4.8 GHz, and models for the integrated polarization of spiral galaxy disks as a
function of inclination. Spiral galaxies in our sample have observed integrated
fractional polarization in the range < 1% to 17.6%. At inclinations less than
50 degrees, the fractional polarization depends mostly on the ratio of random
to regular magnetic field strength. At higher inclinations, Faraday
depolarization associated with the regular magnetic field becomes more
important. The observed degree of polarization is lower (<4%) for more luminous
galaxies, in particular those with L_{4.8} > 2 x 10^{21} W/Hz. The polarization
angle of the integrated emission is aligned with the apparent minor axis of the
disk for galaxies without a bar. In our axially symmetric models, the
polarization angle of the integrated emission is independent of wavelength.
Simulated distributions of fractional polarization for randomly oriented spiral
galaxies at 4.8 GHz and 1.4 GHz are presented. We conclude that polarization
measurements, e.g. with the SKA, of unresolved spiral galaxies allow
statistical studies of the magnetic field in disk galaxies using large samples
in the local universe and at high redshift. As these galaxies behave as
idealized background sources without internal Faraday rotation, they can be
used to detect large-scale magnetic fields in the intergalactic medium.Comment: 13 pages, 6 figures; Accepted for publication in The Astrophysical
Journa
Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits
We experimentally demonstrate novel structures for the realisation of
registers of atomic qubits: We trap neutral atoms in one and two-dimensional
arrays of far-detuned dipole traps obtained by focusing a red-detuned laser
beam with a microfabricated array of microlenses. We are able to selectively
address individual trap sites due to their large lateral separation of 125 mu
m. We initialize and read out different internal states for the individual
sites. We also create two interleaved sets of trap arrays with adjustable
separation, as required for many proposed implementations of quantum gate
operations
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