513 research outputs found
Dressed Feshbach molecules in the BEC-BCS crossover
We present the RPA theory of the BEC-BCS crossover in an atomic Fermi gas
near a Feshbach resonance that includes the relevant two-body atomic physics
exactly. This allows us to determine the probability for the dressed
molecules in the Bose-Einstein condensate to be in the closed channel of the
Feshbach resonance and to compare with the recent experiments of Partridge {\it
et al.} [cond-mat/0505353] with Li. We determine for this extremely broad
resonance also the condensate density of the dressed molecules throughout the
BEC-BCS crossover.Comment: 4 pages, 3 figure
Sarma Phase in Trapped Unbalanced Fermi Gases
We consider a trapped unbalanced Fermi gas at nonzero temperatures where the
superfluid Sarma phase is stable. We determine in particular the phase
boundaries between the superfluid, normal, and phase separated regions of the
trapped unbalanced Fermi mixture. We show that the physics of the Sarma phase
is sufficient to understand the recent observations of Zwierlein et al.
[Science 311, 492 (2006); Nature 442, 54 (2006)] and indicate how the apparent
contradictions between this experiment and the experiment of Partridge et al.
[Science 311, 503 (2006)] may be resolved.Comment: Replaced with published version; 4 pages, 3 figure
Quantum phase transition in an atomic Bose gas with a Feshbach resonance
We show that in an atomic Bose gas near a Feshbach resonance a quantum phase
transition occurs between a phase with only a molecular Bose-Einstein
condensate and a phase with both an atomic and a molecular Bose-Einstein
condensate. We show that the transition is characterized by an Ising order
parameter. We also determine the phase diagram of the gas as a function of
magnetic field and temperature: the quantum critical point extends into a line
of finite temperature Ising transitions.Comment: 4 pages, 2 figure
Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs
NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance âŒ170 nΊ0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1â2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise
Black holes and membranes in AdS_7
We investigate maximal gauged supergravity in seven dimensions and some of
its solitonic solutions. By focusing on a truncation of the gauged SO(5)
R-symmetry group to its U(1)^2 Cartan subgroup, we construct general two charge
black holes that are asymptotically anti-de Sitter. We demonstrate that 1- and
2-charge black holes preserve 1/2 and 1/4 of the supersymmetries respectively.
Additionally, we examine the odd-dimensional self-duality equation governing
the three-form potential transforming as the 5 of SO(5), and provide some
insight on the construction of membrane solutions in anti-de Sitter
backgrounds.Comment: 13 pages, harvmac (big option
Bogoliubov theory of Feshbach molecules in the BEC-BCS crossover
We present the Bogoliubov theory for the Bose-Einstein condensation of
Feshbach molecules in a balanced Fermi mixture. Because the Bogoliubov theory
includes (Gaussian) fluctuations, we can in this manner accurately incorporate
both the two-body and many-body aspects of the BEC-BCS crossover that occurs
near a Feshbach resonance. We apply the theory in particular to the very broad
Feshbach resonance in atomic Li-6 at a magnetic field of B_0 = 834 G and find
good agreement with experiments in that case. The BEC-BCS crossover for more
narrow Feshbach resonances is also discussed.Comment: 13 pages of RevTex and 12 Figures. Submitted for publication in
Physical review
Anti-de Sitter space, branes, singletons, superconformal field theories and all that
There has recently been a revival of interest in anti de-Sitter space (AdS)
brought about by the conjectured duality beteeen physics in the bulk of AdS and
a conformal field theory on the boundary. Since the whole subject of branes,
singletons and superconformal field theories on the AdS boundary was an active
area of research about ten years ago, I begin with a historical review,
including the ``Membrane at the end of the universe'' idea. Next I discuss two
recent papers with Lu and Pope on on and on , respectively. In each case we note that odd-dimensional spheres
may be regarded as U(1) bundles over and that this
permits an unconventional ``Hopf''duality along the U(1) fibre. This leads in
particular to the phenomenon of BPS without BPS whereby states which appear to
be non-BPS in one picture are seen to be BPS in the dual picture.Comment: Minor improvements. 37 pages Latex. Based on talks delivered at the
the PASCOS 98 conference, Northeastern University, March 1998; the
Superfivebranes and Physics in 5+1 Dimensions conference, ICTP, Trieste,
Italy, April 1998; the Arnowitt Fest, Texas A&M University, April 1998; the
Strings 98 conference, ITP, Santa Barbara, June 199
Localization of supergravity on the brane
A supersymmetric Randall-Sundrum brane-world demands that not merely the
graviton but the entire supergravity multiplet be trapped on the brane. To
demonstrate this, we present a complete ansatz for the reduction of (D=5,N=4)
gauged supergravity to (D=4,N=2) ungauged supergravity in the Randall-Sundrum
geometry. We verify that it is consistent to lowest order in fermion terms. In
particular, we show how the graviphotons avoid the `no photons on the brane'
result because they do not originate from Maxwell's equations in D=5 but rather
from odd-dimensional self-duality equations. In the case of the fivebrane, the
Randall-Sundrum mechanism also provides a new Kaluza-Klein way of obtaining
chiral supergravity starting from non-chiral.Comment: 12 pages, Latex, minor improvements, references adde
Four Dimensional String/String/String Triality
In six spacetime dimensions, the heterotic string is dual to a Type
string. On further toroidal compactification to four spacetime dimensions, the
heterotic string acquires an SL(2,\BbbZ)_S strong/weak coupling duality and
an SL(2,\BbbZ)_T \times SL(2,\BbbZ)_U target space duality acting on the
dilaton/axion, complex Kahler form and the complex structure fields
respectively. Strong/weak duality in interchanges the roles of and
in yielding a Type string with fields . This suggests
the existence of a third string (whose six-dimensional interpretation is more
obscure) that interchanges the roles of and . It corresponds in fact to
a Type string with fields leading to a four-dimensional
string/string/string triality. Since SL(2,\BbbZ)_S is perturbative for the
Type string, this triality implies -duality for the heterotic
string and thus fills a gap left by duality. For all three strings the
total symmetry is SL(2,\BbbZ)_S \times O(6,22;\BbbZ)_{TU}. The
O(6,22;\BbbZ) is {\it perturbative} for the heterotic string but contains the
conjectured {\it non-perturbative} SL(2,\BbbZ)_X, where is the complex
scalar of the Type string. Thus four-dimensional triality also
provides a (post-compactification) justification for this conjecture. We
interpret the Bogomol'nyi spectrum from all three points of view. In
particular we generalize the Sen-Schwarz formula for short multiplets to
include intermediate multiplets also and discuss the corresponding black hole
spectrum both for the theory and for a truncated ---- symmetric
theory. Just as the first two strings are described by the
four-dimensional {\it elementary} and {\it dual solitonic} solutions, so theComment: 36 pages, Latex, 2 figures, some references changed, minor changes in
formulas and tables; to appear in Nucl. Phys.
- âŠ