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We propose a physical mechanism for tuning the atomatom interaction strength at ultra-low temperatures. In the presence of a dc electric field the interatomic potential is changed due to the effective dipole-dipole interaction between the polarized atoms. Detailed multi-channel scattering calculations reveal features never before discussed for ultra-cold atomic collisions. We demonstrate that optimal control of the effective atom-atom interactions can be achieved under reasonable laboratory conditions. Implications of this research on the physics of atomic Bose-Einstein condensation (BEC) and on the pursuit for atomic degenerate fermion gases will be discussed. 34.50.Cf,05.30.Jp,05.30.Fk The study of weakly interacting quantum gases has attracted significant attention since the initial success of Bose-Einstein condensation (BEC) [1]. Tremendous progress has been made over the last three years in both theory and experiment. One of the recent interests is the study of controlling the strength of atom-atom interaction. Several groups have discussed mechanisms for changing the scattering length of the atom-atom interaction using near resonant lasers [2], radio frequency fields This letter concerns the physics of adjusting the effective low energy atomic interactions. We propose the use of an external dc electric field (dc-E) to influence the low energy atomic collisions by means of modifying the shape of the interaction potential between atoms. This letter is organized as follows: We start with a brief discussion of the effective interaction potential between two alkalimetal atoms in the presence of a dc-E, followed by an outline of the main results of multi-channel collision formalism for two polarized atoms at ultralow temperatures. Illustrative results are presented, using a typical model potential for the atom-atom interaction. For collisions between bosonic atoms, we show that: (i) the sign of the scattering length a sc may be determined by measuring the relative deviation of the total elastic cross section in the presence of a dc-E, (ii) it is possible to tune the value of a sc smoothly in a broad range, (iii) a dc-E can induce strong anisotropic interactions between the atoms, and (iv) a dc-E can induce zero energy resonances (these are shape resonances in contrast to Feschbach resonances recently observed [5]). For collisions between fermionic atoms we show that (v) the dc-E can induce strong interactions between atoms in spin symmetrized states even at zero temperature. We believe these results open the door for a new area of studies of quantum degenerate atomic gases with adjustable and anisotropic interactions.In the usual treatment of the binary interaction between two spherically symmetric atoms in the ground state, the long-range interaction potential is given [in the London-van der Waals (LvW) formalism] by the following expressionwhere C 6 , C 8 , and C 10 are the dispersion coefficients, and R is the internuclear distance. This is a "short-range" potential; therefore, the zero energy scattering i...

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We address a growing interest in trapping and cooling of mixed-species alkali-metal atoms. Long-range coefficients that arise in the multipole expansion of molecular potentials for unlike alkali-metal dimers are calculated. The coefficients for the heteronuclear alkali-metal dimers corresponding to different molecular symmetries that separate to nS-nЈS,nS-nЈP,nS-nЈD, and nP-nЈP atomic levels are computed with high precision. We consider cases where in the infinite separation limit, one atom is in the ground state and the other is in one of the lowest S, P, and D excited states and both atoms are in their lowest excited P states. We find the long-range potentials for Rb(5S)-Cs(6S),Rb(6S)-Cs(6S),K(4S)-Rb(5 P) 1,3 ⌺,K(4P)-Cs(6 P) 1,3 ⌺, and Rb(5S)-Na(3D) 1,3 ⌺ molecules to be the most attractive. The K(4S)-Rb(5 P) dimer represents the best candidate molecule for ultracold photoassociative spectroscopy. We also find the K(4 P)-Cs(6 P) and Rb(5S)-K(4 P) dimers to form, respectively, the most attractive and the most repulsive long-range potentials. The present calculation is in good agreement with experimentally determined value for the 1/R 6 van der Waals coefficient for the interaction between Cs(6S) and Li(2 P) atoms. ͓S1050-2947͑99͒07101-2͔

We present theoretical prospects for creating p-wave paired BCS states of magnetic trapped fermionic atoms. Based on our earlier proposal of using dc electric fields to control both the strength and anisotropic characteristic of atom-atom interaction and our recently completed multi-channel atomic collision calculations we discover that p-wave pairing with 40 K and 82,84,86 Rb in the low field seeking maximum spin polarized state represent excellent choices for achieving superfluid BCS states; and may be realizable with current technology in laser cooling, magnetic trapping, and evaporative/sympathetic cooling, provided the required strong electric field can be applied. We also comment on the prospects of similar p-wave paired BCS states in 6 Li, and more generally on creating other types exotic BCS states. Our study will open a new area in the vigorous pursuit to create a quantum degenerate fermionic atom vapor. 03.75.Fi, 32.80.Pj, 42.50.Vk