Molecular interaction and vortex core size

Weiping, Zhang, Ling +3 more

Jacques Tempere, Michiel Wouters, J. T. Devreese

We derive a path-integral description of the vortex state of a fermionic superfluid in the crossover region between the molecular condensate (BEC) regime and the Cooper pairing (BCS) regime. This path-integral formalism, supplemented by a suitable choice for the saddle point value of the pairing field in the presence of a vortex, offers a unified description that encompasses both the BEC and BCS limits. The vortex core size is studied as a function of the tunable interaction strength between the fermionic atoms. We find that in the BEC regime, the core size is determined by the molecular healing length, whereas in the BCS regime, the core size is proportional only to the Fermi wavelength. The observation of such quantized vortices in dilute Fermi gases would provide an unambiguous proof of the realization of superfluidity in these gases.

Yisa S. Rumala, A. E. Leanhardt

Optical vortices with a vortex core size that is at least two orders of magnitude smaller than the laser beam waist is presented. The optical vortex is generated by a spiral phase plate (SPP) and counterrotating optical vortex pairs are created in a modified Mach–Zehnder interferometer surrounded by a 4f lens arrangement. The azimuthal variation of the counterrotating optical vortex forms a sinusoidal intensity modulation for which the winding number of the optical vortex is deduced accurately and precisely by fitting it to a sinusoidal function. These results are of interest in designing novel optical vortex gratings for manipulating matter waves (e.g., in Kapitza–Dirac scattering). A theory of atomic angular Kapitza–Dirac scattering with optical vortices is presented. The large beam waist combined with a small optical vortex core size would also be of interest when using an optical vortex to perform spectroscopy in a wide range of matter systems including solid, liquid, atomic, and molecular systems, as well as in short-range optical communication.

Bose-Einstein Condensates

Lihao Yan, Boldizsár Jankó, Xiaoyu Ma +1 more

Xuebing Luo, Kezhao Zhou, Zhang Zhi-dong

We use the path-integral formalism to investigate the vortex properties of a quasi-two dimensional (2D) Fermi superfluid system trapped in an optical lattice potential. Within the framework of mean-field theory, the cooper pair density, the atom number density, and the vortex core size are calculated from weakly interacting BCS regime to strongly coupled while weakly interacting BEC regime. Numerical results show that the atoms gradually penetrate into the vortex core as the system evolves from BEC to BCS regime. Meanwhile, the presence of the optical lattice allows us to analyze the vortex properties in the crossover from three-dimensional (3D) to 2D case. Furthermore, using a simple re-normalization procedure, we find that the two-body bound state exists only when the interaction is stronger than a critical one denoted by G c which is obtained as a function of the lattice potential’s parameter. Finally, we investigate the vortex core size and find that it grows with increasing interaction strength. In particular, by analyzing the behavior of the vortex core size in both BCS and BEC regimes, we find that the vortex core size behaves quite differently for positive and negative chemical potentials.