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We investigate the superfluid properties of a one-component Fermi gas with a uniaxially anisotropic p-wave pairing interaction, Ux > Uy = Uz [where Ui (i = x,y,z) is a pi-wave pairing interaction]. This type of interaction is considered to be realized in a 40K Fermi gas. Including pairing fluctuations within a strong-coupling T-matrix theory, we determine the px-wave superfluid phase transition temperature ..., as well as the other phase transition temperature ... (...), below which the superfluid order parameter has the px + ipy-wave symmetry. In the normal state near ..., px-wave pairing fluctuations are shown to induce an anisotropic pseudogap phenomenon, where a dip structure in the angle-resolved density of states around ω = 0 is the most remarkable in the px direction. In the px-wave superfluid phase (...), while the pseudogap in the px direction continuously changes to the superfluid gap, the pseudogap in the perpendicular direction to the Px axis is found to continue developing because of enhanced py-wave and pz-wave pairing fluctuations around the node of the px-wave superfluid order parameter. Since pairing fluctuations are always suppressed in the isotropic s-wave superfluid state, this phenomenon is peculiar to an unconventional Fermi superfluid with a nodal superfluid order parameter. Since the p-wave Fermi superfluid is the most promising non-s-wave pairing state in an ultracold Fermi gas, our results would contribute to understanding how the anisotropic pairing fluctuations, as well as the existence of plural superfluid phases, affect many-body properties of this unconventional Fermi superfluid. [ABSTRACT FROM AUTHOR]

Understanding the formation of Cooper pairs and the resulting thermodynamic properties of low-dimensional Fermi gases is an important area of research, which may help build our understanding of other low-dimensional systems, such as high-temperature superconductors. In lower dimensions, quantum fluctuations are expected to play an increasingly important role, and the reliability of strong-coupling theories becomes questionable. Here, we present a comparison of recent thermodynamic measurements and theoretical predictions from different many-body T-matrix theories for a two-dimensional strongly interacting Fermi gas in the normal state. We find that the fully self-consistent T-matrix theory provides the best description of the experimental data over a wide range of temperatures and interatomic interactions. [ABSTRACT FROM AUTHOR]

The polaronic system consisting of an impurity in a dilute Bose-Einstein condensate is considered in the presence of a narrow Feshbach resonance. For this purpose a coupled-channel model is used, which at the mean-field level predicts the formation of quasiparticles that are a superposition of the impurity and the molecular states. The impurity-boson interactions and the coupling between the open and closed channels are then considered weak and a perturbative calculation of the corrections to the mean-field results is presented. This allows us to examine the properties of the quasiparticles, such as the lifetime and the effective mass. The relation between the model parameters and the experimental parameters is determined by identifying the low-energy T matrix and applying a proper renormalization scheme. [ABSTRACT FROM AUTHOR]

We report the implementation of the relativistic equation-of-motion coupled-cluster method to calculate the double-ionization spectra (DI-EOMCC) of the closed-shell atomic systems. This method is employed to calculate the principal valence double-ionization potential values of He and alkaline-earth-metal (Be, Mg, Ca, Sr, and Ba) atoms. Our results are compared with the results available from the NIST database and other ab initio calculations. We have achieved an accuracy of ~ 0.1 %, which is an improvement over the first-principles T-matrix calculations [Y. Noguchi et al., J. Chem. Phys. 123,144112 (2005)]. We also present results using the second-order many-body perturbation theory and the random-phase approximation in the equation-of-motion framework, and these results are compared with the DI-EOMCC results. [ABSTRACT FROM AUTHOR]

We consider a Bose-Fermi mixture in the molecular limit of the attractive interaction between fermions and bosons. For a boson density smaller than or equal to the fermion density, we show analytically how a T-matrix approach for the constituent bosons and fermions recovers the expected physical limit of a Fermi-Fermi mixture of molecules and atoms. In this limit, we derive simple expressions for the self-energies, the momentum distribution function, and the chemical potentials. By extending these equations to a trapped system, we determine how to tailor the experimental parameters of a Bose-Fermi mixture in order to enhance the indirect Pauli exclusion effect on the boson momentum distribution function. For the homogeneous system, we present finally a diffusion Monte Carlo simulation which confirms the occurrence of such a peculiar effect. [ABSTRACT FROM AUTHOR]

Boson-fermion pair correlations in a mixture are considered at zero temperature in the T-matrix approximation. Special attention is paid to the Luttinger theorem. In a strict random-phase approximation variant of the Nozières-Schmitt-Rink approach, it is shown that this theorem is respected also in the homogeneous infinite matter case. We calculate the corresponding occupation numbers of fermions and bosons and the condensate depletion. We also show that in the limit of very small boson density, our results are in good agreement with the results found in the literature for the Fermi polaron in strongly imbalanced Fermi-Fermi mixtures. [ABSTRACT FROM AUTHOR]

We study the equilibrium correlations of a Bose gas in an elongated three-dimensional harmonic trap using a grand-canonical classical-field method. We focus in particular on the progressive transformation of the gas from the normal phase, through a phase-fluctuating quasicondensate regime to the so-called true-condensate regime, with decreasing temperature. Choosing realistic experimental parameters, we quantify the density fluctuations and phase coherence of the atomic field as functions of the system temperature. We identify the onset of Bose condensation through analysis of both the generalized Binder cumulant appropriate to the inhomogeneous system, and the suppression of the effective many-body T matrix that characterizes interactions between condensate atoms in the finite-temperature field. We find that the system undergoes a second-order transition to condensation near the critical temperature for an ideal Bose gas in the strongly anisotropic three-dimensional geometry but remains in a strongly phase-fluctuating quasicondensate regime until significantly lower temperatures. We characterize the crossover from a quasicondensate to a true condensate by a qualitative change in the form of the nonlocal first-order coherence function of the field and compare our results to those of previous works employing a density-phase Bogoliubov-de Gennes analysis. [ABSTRACT FROM AUTHOR]

In this paper, taking into account the effect of the induced interaction, we calculate the superfluid-transition temperature of ultracold Fermi gases within the framework of the non-self-consistent T-matrix approximation. The result shows that the transition temperature is reduced by about 10% at unitarity due to the induced interaction. In the Bardeen-Cooper-Schrieffer (BCS) limit, the critical temperature is about 0.45TcBCS and it is the same as the result of the usual Gorkov and Melik-Barkhudarov correction, whereas in the Bose-Einstein condensate (BEC) limit, the influence of the induced interaction can be neglected and the critical temperature turns out to be the transition temperature of ideal Bose gases. Our results show that the induced interaction cannot be neglected in the study of the BCS-BEC crossover. [ABSTRACT FROM AUTHOR]

We study the dilute Fermi gas at unitarity using molecular dynamics with an effective quantum potential constructed to reproduce the quantum two-body density matrix at unitarity. Results for the equation of state, the pair-correlation function, and the shear viscosity are presented. These quantities are well understood in the dilute, high-temperature limit. Using molecular dynamics we determine higher-order corrections in the diluteness parameter nλ³, where n is the density and λ is the thermal de Broglie wavelength. In the case of the contact density, which parameterizes the short distance behavior of the correlation function, we find that the results of molecular dynamics interpolate between the truncated second- and third-order virial expansion and are in excellent agreement with existing T-matrix calculations. For the shear viscosity we reproduce the expected scaling behavior at high temperature, n ~ 1/λ³, and we determine the leading density-dependent correction to this result. [ABSTRACT FROM AUTHOR]

We study nonequilibrium dynamics of ultracold two-component Fermi gases in low-dimensional geometries after the interactions are quenched from a weakly interacting to a strongly interacting regime. We develop a T-matrix formalism that takes into account the interplay between Pauli blocking and tight confinement in low-dimensional geometries. We employ our formalism to study the formation of molecules in quasi-two-dimensional Fermi gases near Feshbach resonance and show that the rate at which molecules form depends strongly on the transverse confinement. Furthermore, Pauli blocking gives rise to a sizable correction to the binding energy of molecules. [ABSTRACT FROM AUTHOR]

We study ultracold bosons in three dimensions with an anisotropic Rashba-Dresselhaus spin-orbit coupling. We first carry out the exact summation of ladder diagrams for the two-boson t matrix at zero energy. Then, with the t matrix as the effective interaction, we find the ground-state phase diagrams of bosons in mean field as a function of the spin-orbit coupling, the anisotropy, and the scattering lengths between particles in the same and in different pseudospin states. The resulting phase diagrams have much richer structures than those obtained using mean-field couplings, exhibiting three different phases: a plane-wave condensate, a striped condensate, and an unstable phase. The differences between the present approach using the t matrix compared to using mean-field couplings is significant for large scattering lengths, large spin-orbit-coupling strength, or small anisotropy. [ABSTRACT FROM AUTHOR]

We calculate the single-particle spectral density of a normal (nonsuperfluid) two-component gas of fermions in the BCS-BEC crossover within a T-matrix approximation. We review how noncondensed pairs lead to a spectral density reminiscent of the ordered state, and explore how a gaplike feature in the spectrum evolves as one changes the polarization of the gas. As the gas is polarized, we find that this pseudogap becomes more diffuse and moves away from the Fermi level, reflecting the fact that fewer pairs are present but that they still play an important role in the excitations. [ABSTRACT FROM AUTHOR]

The conventional orientation-averaging procedure developed in the framework of the superposition T-matrix approach is generalized to include the case of illumination by a Gaussian beam (GB). The resulting computer code is parallelized and used to perform extensive numerically exact calculations of electromagnetic scattering by volumes of discrete random medium consisting of monodisperse spherical particles. The size parameters of the scattering volumes are 40, 50, and 60, while their packing density is fixed at 5%. We demonstrate that all scattering patterns observed in the far-field zone of a random multisphere target and their evolution with decreasing width of the incident GB can be interpreted in terms of idealized theoretical concepts such as forward-scattering interference, coherent backscattering (CB), and diffuse multiple scattering. It is shown that the increasing violation of electromagnetic reciprocity with decreasing GB width suppresses and eventually eradicates all observable manifestations of CB. This result supplements the previous demonstration of the effects of broken reciprocity in the case of magneto-optically active particles subjected to an external magnetic field. [ABSTRACT FROM AUTHOR]