Understanding Floquet Resonances in Ultracold Quantum Gas Scattering

It is demonstrated that the effective scattering length can be highly manipulated via time-periodic driving of a short-range interparticle potential. By developing a Floquet-scattering theory we show that sharp Floquet resonances occur at which the effective interaction can be tuned to very large attractive or repulsive values. The resulting s-wave scattering length can be obtained in analytic form and the shape of these resonances is given by a simple formula describing how resonance position and width can be altered by the driving strength. Our approach allows the identification of the underlying physical mechanism of the scattering resonances as Floquet bound states with positive energies, which are dynamically created by the drive. This insight is valuable for a detailed analysis and uncovers a general resource for enhanced or reduced scattering in Floquet systems, as was recently confirmed experimentally.