2,019 research outputs found
Rapidly Rotating Fermi Gases
We show that the density profile of a Fermi gas in rapidly rotating potential
will develop prominent features reflecting the underlying Landau level like
energy spectrum. Depending on the aspect ratio of the trap, these features can
be a sequence of ellipsoidal volumes or a sequence of quantized steps.Comment: 4 pages, 1 postscript fil
Superfluidity in the interior-gap states
We investigate superfluidity in the interior-gap states proposed by Liu and
Wilczek. At weak coupling, we find the {\em gapless} interior-gap state
unstable in physically accessible regimes of the parameter space, where the
superfluid density is shown to be always negative. We therefore conclude that
the spatially-uniform interior-gap phase is extremely unstable unless it is
fully gapped; in this case, however, the state is rather similar to
conventional BCS states.Comment: To appear in Physical Review
Formation epochs, star formation histories and sizes of massive early-type galaxies in cluster and field environments at z=1.2: insights from the rest-frame UV
We derive stellar masses, ages and star formation histories of massive
early-type galaxies in the z=1.237 RDCS1252.9-2927 cluster and compare them
with those measured in a similarly mass-selected sample of field contemporaries
drawn from the GOODS South Field. Robust estimates of these parameters are
obtained by comparing a large grid of composite stellar population models with
8-9 band photometry in the rest-frame NUV, optical and IR, thus sampling the
entire relevant domain of emission of the different stellar populations.
Additionally, we present new, deep -band photometry of both fields, giving
access to the critical FUV rest-frame, in order to constrain empirically the
dependence on the environment of the most recent star formation processes. We
find that early-type galaxies, both in the cluster and in the field, show
analogous optical morphologies, follow comparable mass vs. size relation, have
congruent average surface stellar mass densities and lie on the same Kormendy
relation. We also that a fraction of early-type galaxies in the field employ
longer timescales, , to assemble their mass than their cluster
contemporaries. Hence we conclude that, while the formation epoch of early-type
only depends on their mass, the environment does regulate the timescales of
their star formation histories. Our deep -band imaging strongly supports
this conclusions. It shows that cluster galaxies are at least 0.5 mag fainter
than their field contemporaries of similar mass and optical-to-infrared colors,
implying that the last episode of star formation must have happened more
recently in the field than in the cluster.Comment: 20pages, 10 figures. to appear on Ap
Experimental demonstration of a technique to generate arbitrary quantum superposition states
Using a single, harmonically trapped Be ion, we experimentally
demonstrate a technique for generation of arbitrary states of a two-level
particle confined by a harmonic potential. Rather than engineering a single
Hamiltonian that evolves the system to a desired final sate, we implement a
technique that applies a sequence of simple operations to synthesize the state
Quantum information processing with trapped ions
Experiments directed towards the development of a quantum computer based on
trapped atomic ions are described briefly. We discuss the implementation of
single qubit operations and gates between qubits. A geometric phase gate
between two ion qubits is described. Limitations of the trapped-ion method such
as those caused by Stark shifts and spontaneous emission are addressed.
Finally, we describe a strategy to realize a large-scale device.Comment: Article submitted by D. J. Wineland ([email protected])
for proceeding of the Discussion Meeting on Practical Realisations of Quantum
Information Processing, held at the Royal Society, Nov. 13,14, 200
Pauli Blocking of Collisions in a Quantum Degenerate Atomic Fermi Gas
We have produced an interacting quantum degenerate Fermi gas of atoms
composed of two spin-states of magnetically trapped K. The relative
Fermi energies are adjusted by controlling the population in each spin-state.
Measurements of the thermodynamics reveal the resulting imbalance in the mean
energy per particle between the two species, which is as large as a factor of
1.4 at our lowest temperature. This imbalance of energy comes from a
suppression of collisions between atoms in the gas due to the Pauli exclusion
principle. Through measurements of the thermal relaxation rate we have directly
observed this Pauli blocking as a factor of two reduction in the effective
collision cross-section in the quantum degenerate regime.Comment: 11 pages, 4 figure
Application of artificial neural networks for accurate determination of the complex permittivity of biological tissue
Medical devices making use of radio frequency (RF) and microwave (MW) fields have
been studied as alternatives to existing diagnostic and therapeutic modalities since they offer several
advantages. However, the lack of accurate knowledge of the complex permittivity of different
biological tissues continues to hinder progress in of these technologies. The most convenient and
popular measurement method used to determine the complex permittivity of biological tissues is
the open-ended coaxial line, in combination with a vector network analyser (VNA) to measure the
reflection coefficient (S11) which is then converted to the corresponding tissue permittivity using
either full-wave analysis or through the use of equivalent circuit models. This paper proposes an
innovative method of using artificial neural networks (ANN) to convert measured S11 to tissue
permittivity, circumventing the requirement of extending the VNA measurement plane to the coaxial
line open end. The conventional three-step calibration technique used with coaxial open-ended
probes lacks repeatability, unless applied with extreme care by experienced persons, and is not
adaptable to alternative sensor antenna configurations necessitated by many potential diagnostic and
monitoring applications. The method being proposed does not require calibration at the tip of the
probe, thus simplifying the measurement procedure while allowing arbitrary sensor design, and was
experimentally validated using S11 measurements and the corresponding complex permittivity of 60
standard liquid and 42 porcine tissue samples. Following ANN training, validation and testing, we
obtained a prediction accuracy of 5% for the complex permittivity.peer-reviewe
Resonant control of elastic collisions in an optically trapped Fermi gas of atoms
We have loaded an ultracold gas of fermionic atoms into a far off resonance
optical dipole trap and precisely controlled the spin composition of the
trapped gas. We have measured a magnetic-field Feshbach resonance between atoms
in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The
resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a
width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the
elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure
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