Dynamical Response of Fermi Condensate to Varying Magnetic Fields

We investigate the dynamical response of strongly interacting ultra-cold fermionic atoms near Feshbach resonance to varying magnetic fields. Following the experimental practices, we calculate the response of the atoms to oscillating and to linearly ramped magnetic fields respectively. For oscillating magnetic fields, depending on the frequencies and the amplitudes of the oscillations, the response of the pair excitation gap shows either linear or rich non-linear behaviour. In addition, both the spectral studies through the linear response theory and the time-domain simulations suggest the existence of a resonant frequency corresponding to the pair dissociation threshold. For linearly ramped magnetic fields, the response of the excitation gap shows damped oscillations. The final value of the excitation gap depends on the rate of the field sweep.Comment: 6 pages, 6 figure

Superfluid shells for trapped fermions with mass and population imbalance

We map out the phase diagram of strongly interacting fermions in a potential trap with mass and population imbalance between the two spin components. As a unique feature distinctively different from the equal-mass case, we show that the superfluid here forms a shell structure which is not simply connected in space. Different types of normal states occupy the trap regions inside and outside this superfluid shell. We calculate the atomic density profiles, which provide an experimental signature for the superfluid shell structure.Comment: 4 pages, 3 figure

Detecting the breached pair phase in a polarized ultracold Fermi gas

We propose a method for the experimental detection of a new quantum phase, the breached pair state, in a strongly interacting ultracold Fermi gas with population imbalance. We show that through the time-of-flight Raman imaging, the presence of such a phase can be unambiguously determined with a measurement of the momentum-space phase separation of the minority spin component. To guide the experimental efforts, the momentum-space density profiles are calculated under typical experimental conditions.Comment: 4 pages, 3 figures, replaced with the published versio

Trapped Fermions across a Feshbach resonance with population imbalance

We investigate the phase separation of resonantly interacting fermions in a trap with imbalanced spin populations, both at zero and at finite temperatures. We directly minimize the thermodynamical potential under the local density approximation instead of using the gap equation, as the latter may give unstable solutions. On the BEC side of the resonance, one may cross three different phases from the trap center to the edge; while on the BCS side or at resonance, typically only two phases show up. We compare our results with the recent experiment, and the agreement is remarkable.Comment: 4 pages, 3 figures, replaced with the published versio

BCS-BEC crossover and quantum phase transition for 6Li and 40K atoms across Feshbach resonance

We systematically study the BCS-BEC crossover and the quantum phase transition in ultracold 6Li and 40K atoms across a wide Feshbach resonance. The background scattering lengths for 6Li and 40K have opposite signs, which lead to very different behaviors for these two types of atoms. For 40K, both the two-body and the many-body calculations show that the system always has two branches of solutions: one corresponds to a deeply bound molecule state; and the other, the one accessed by the current experiments, corresponds to a weakly bound state with population always dominantly in the open channel. For 6Li, there is only a unique solution with the standard crossover from the weakly bound Cooper pairs to the deeply bound molecules as one sweeps the magnetic field through the crossover region. Because of this difference, for the experimentally accessible state of 40K, there is a quantum phase transition at zero temperature from the superfluid to the normal fermi gas at the positive detuning of the magnetic field where the s-wave scattering length passes its zero point. For 6Li, however, the system changes continuously across the zero point of the scattering length. For both types of atoms, we also give detailed comparison between the results from the two-channel and the single-channel model over the whole region of the magnetic field detuning.Comment: 7 pages, 6 figure

Effective Hamiltonian for fermions in an optical lattice across Feshbach resonance

We derive the Hamiltonian for cold fermionic atoms in an optical lattice across a broad Feshbach resonance, taking into account of both multiband occupations and neighboring-site collisions. Under typical configurations, the resulting Hamiltonian can be dramatically simplified to an effective single-band model, which describes a new type of resonance between the local dressed molecules and the valence bond states of fermionic atoms at neighboring sites. On different sides of such a resonance, the effective Hamiltonian is reduced to either a t-J model for the fermionic atoms or an XXZ model for the dressed molecules. The parameters in these models are experimentally tunable in the full range, which allows for observation of various phase transitions.Comment: 5 pages, 2 figure

Piscine (Sparus aurata) transthyretin cDNA cloning and characterization

Transthyretin (TTR) is one of the three plasma proteins that participate in the transport of thyroid hormones, thyroxine (T4) and triiodothyronine (T3); it is also involved in the carriage of retinol through the mediation of retinol-binding protein.1 The liver and choroid plexus are the major sites of TTR synthesis in mammals, birds, and diprotodont marsupials; in reptiles, TTR is only synthesized in the choroid plexus. 2 cDNA coding for TTR has been cloned from several mammalian, reptilian, and avian species and is highly conserved especially in the domains involved in binding to thyroid hormones.3 TTR expression has never been reported in fish, in which albumin is considered to be the main carrier for T3 and T4.2 We report the cloning of a TTR cDNA from sea bream (Sparus aurata) and demonstrate the presence of TTR mRNA in the liver of this fish

Superfluidity of fermions with repulsive on-site interaction in an anisotropic optical lattice near a Feshbach resonance

We present a numerical study on ground state properties of a one-dimensional (1D) general Hubbard model (GHM) with particle-assisted tunnelling rates and repulsive on-site interaction (positive-U), which describes fermionic atoms in an anisotropic optical lattice near a wide Feshbach resonance. For our calculation, we utilize the time evolving block decimation (TEBD) algorithm, which is an extension of the density matrix renormalization group and provides a well-controlled method for 1D systems. We show that the positive-U GHM, when hole-doped from half-filling, exhibits a phase with coexistence of quasi-long-range superfluid and charge-density-wave orders. This feature is different from the property of the conventional Hubbard model with positive-U, indicating the particle-assisted tunnelling mechanism in GHM brings in qualitatively new physics.Comment: updated with published version

Correlations in interference and diffraction

Quantum formalism of Fraunhofer diffraction is obtained. The state of the diffraction optical field is connected with the state of the incident optical field by a diffraction factor. Based on this formalism, correlations of the diffraction modes are calculated with different kinds of incident optical fields. Influence of correlations of the incident modes on the diffraction pattern is analyzed and an explanation of the ''ghost'' diffraction is proposed.Comment: 16 pages, 2 figures, Latex, to appear in J. Mod. Op