Optical Control of the Scattering Length and Effective Range for Magnetically Tunable Feshbach Resonances in Ultracold Gases

TL;DR

This paper introduces two-field optical techniques to precisely control the scattering length and effective range in ultracold gases, enabling manipulation of interactions via a molecular dark state that suppresses optical scattering.

Contribution

The work presents a novel dark-state method for optical control of Feshbach resonances, allowing independent tuning of the scattering length and effective range in ultracold gases.

Findings

Suppresses optical scattering compared to single-field methods

Enables control of the effective range and scattering amplitude

Provides a way to modify energy dependence of scattering phase shift

Abstract

We describe two-field optical techniques to control interactions in Feshbach resonances for two-body scattering in ultra-cold gases. These techniques create a molecular dark state in the closed channel of a magnetically tunable Feshbach resonance, greatly suppressing optical scattering compared to single optical field methods. The dark-state method enables control of the effective range, by creating narrow features that modify the energy dependence of the scattering phase shift, as well as control of the elastic and inelastic parts of the zero-energy s-wave scattering amplitude. We determine the scattering length and the effective range from an effective range expansion, by calculating the momentum-dependent scattering phase shift from the two-body scattering state.