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 $Z$ 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 $^{6}$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 ∼170 nΦ0 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 1–2 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 $AdS_{5} \times S^{5}$ and on $AdS_{3} \times S^{3}$, respectively. In each case we note that odd-dimensional spheres $S^{{2n+1}}$ may be regarded as U(1) bundles over $CP^{n}$ 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 $IIA$ 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 $S,T,U$ respectively. Strong/weak duality in $D=6$ interchanges the roles of $S$ and $T$ in $D=4$ yielding a Type $IIA$ string with fields $T,S,U$. This suggests the existence of a third string (whose six-dimensional interpretation is more obscure) that interchanges the roles of $S$ and $U$. It corresponds in fact to a Type $IIB$ string with fields $U,T,S$ leading to a four-dimensional string/string/string triality. Since SL(2,\BbbZ)_S is perturbative for the Type $IIB$ string, this $D=4$ triality implies $S$-duality for the heterotic string and thus fills a gap left by $D=6$ 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 $X$ is the complex scalar of the $D=10$ Type $IIB$ string. Thus four-dimensional triality also provides a (post-compactification) justification for this conjecture. We interpret the $N=4$ 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 $N=4$ theory and for a truncated $S$--$T$--$U$ symmetric $N=2$ 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.