Controlling Atom-Atom Interaction at Ultralow Temperatures by dc Electric Fields

Abstract

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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