Suppression of two-body collisional loss in an ultracold gas via the Fano effect

TL;DR

This paper demonstrates how the Fano effect can be used to completely suppress two-body inelastic collisional losses in ultracold gases by coupling scattering channels to bound states, enabling control over atomic interactions.

Contribution

The authors generalize the Fano effect to strong coupling regimes and analytically prove the suppression of inelastic scattering amplitudes to zero in ultracold atomic systems.

Findings

Inelastic scattering can be fully suppressed via Fano coupling.

Elastic scattering length can remain large despite suppression of inelastic losses.

Independent control of elastic and inelastic scattering amplitudes is achievable.

Abstract

The Fano effect (U. Fano, Phys. Rev. \textbf{15},1866 (1961) shows that an inelastic scattering process can be suppressed when the output channel (OC) is coupled to an isolated bound state. In this paper we investigate the application of this effect for the suppression of two-body collisional losses of ultracold atoms. The Fano effect is originally derived via a first-order perturbation treatment for coupling between the incident channel (IC) and the OC. We generalize the Fano effect to systems with arbitrarily strong IC--OC couplings. We analytically prove that, in a system with one IC and one OC, when the inter-atomic interaction potentials are real functions of the inter-atomic distance, the exact s-wave inelastic scattering amplitude can always be suppressed to \emph{zero} by coupling between the IC or the OC (or both of them) and an extra isolated bound state. We further show that when the low-energy inelastic collision between two ultracold atoms is suppressed by this effect, the real part of the elastic scattering length between the atoms is still possible to be much larger than the range of inter-atomic interaction.In addition, when open scattering channels are coupled to two bound states, with the help of the Fano effect, independent control of the elastic and inelastic scattering amplitudes of two ultracold atoms can be achieved. Possible experimental realizations of our scheme are also discussed.