Showing papers by "Chris J. Vale published in 2010"
TL;DR: It is shown that short-range pair correlations in a strongly interacting Fermi gas follow a simple universal law described by Tan's relations, which is achieved through measurements of the static structure factor which displays a universal scaling proportional to the ratio of Tan's contact to the momentum C/q.
Abstract: We show that short-range pair correlations in a strongly interacting Fermi gas follow a simple universal law described by Tan's relations. This is achieved through measurements of the static structure factor which displays a universal scaling proportional to the ratio of Tan's contact to the momentum $\mathcal{C}/q$. Bragg spectroscopy of ultracold $^{6}\mathrm{Li}$ atoms from a periodic optical potential is used to measure the structure factor for a wide range of momenta and interaction strengths, providing broad confirmation of this universal law. We calibrate our Bragg spectra using the $f$-sum rule, which is found to improve the accuracy of the structure factor measurement.
167 citations
TL;DR: Theoretical predictions for the dynamic structure factor of a harmonically trapped Fermi superfluid near the BEC-BCS crossover are compared with recent Bragg spectroscopy measurements at large transferred momenta as mentioned in this paper.
Abstract: Theoretical predictions for the dynamic structure factor of a harmonically trapped Fermi superfluid near the Bose-Einstein condensate--Bardeen-Cooper-Schrieffer (BEC-BCS) crossover are compared with recent Bragg spectroscopy measurements at large transferred momenta. The calculations are based on a random-phase (or time-dependent Hartree-Fock-Gorkov) approximation generalized to the strongly interacting regime. Excellent agreement with experimental spectra at low temperatures is obtained, with no free parameters. Theoretical predictions for zero-temperature static structure factor are also found to agree well with the experimental results and independent theoretical calculations based on the exact Tan relations. The temperature dependence of the structure factors at unitarity is predicted.
26 citations
Posted Content•
TL;DR: In this paper, the authors consider dynamical tunnelling with Bose-Einstein condensates in magnetic micro-traps on atom chips and find the Floquet spectrum for one of these as a function of the potential strength, modulation, and effective Planck's constant.
Abstract: The study of dynamical tunnelling in a periodically driven anharmonic potential probes the quantum-classical transition via the experimental control of the effective Planck's constant for the system. In this paper we consider the prospects for observing dynamical tunnelling with Bose-Einstein condensates in magnetic micro-traps on atom chips. We outline the driven anharmonic potentials that are possible using standard magnetic traps, and find the Floquet spectrum for one of these as a function of the potential strength, modulation, and effective Planck's constant. We develop an integrable approximation to the non-integrable Hamiltonian and find that it can explain the behaviour of the tunnelling rate as a function of the effective Planck's constant in the regular region of parameter space. In the chaotic region we compare our results with the predictions of models that describe chaos-assisted tunnelling. Finally we examine the practicalities of performing these experiments in the laboratory.
9 citations
Posted Content•
19 Jan 2010
TL;DR: Tan as discussed by the authors developed exact relations for the BEC-BCS crossover, which connect the bulk thermodynamic properties to the microscopic parameters using a single shortrange parameter known as the contact, I.
Abstract: Universality is a remarkable property of strongly interacting systems of fermions. For sufficiently strong interactions, all dilute Fermi gases behave identically on a scale given by the average particle separation. Ultracold Fermi gases in the Bose-Einstein condensate (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluid crossover display such universality, although their universal properties are not exactly known. In 2005 Shina Tan [1] developed several elegant exact relations for the BEC-BCS crossover, which connect the bulk thermodynamic properties to the microscopic parameters using a single shortrange parameter known as the contact, I.
4 citations