Controlling openness in quantum matter with Floquet engineering and quantum interferenceTBA

Coupling to the environment is a defining feature of quantum systems and often limits coherence, control, and performance in applications ranging from quantum simulation to sensing and information processing. Developing strategies to engineer and suppress unwanted dissipation therefore remains a central challenge across modern quantum science.

In this talk, I present how periodic driving can be used to gain unprecedented control over scattering processes in an ultracold gas of lithium-6 atoms. By Floquet engineering magnetic Feshbach resonances, we create tunable interaction resonances whose position, width, and loss properties can be tailored in situ. Interference between different Floquet pathways enables strong suppression of dissipation while preserving interaction control.

Building on these capabilities, we realize a bound state in the continuum (BIC), a counterintuitive quantum state that remains localized despite being energetically embedded in a continuum of scattering states. The BIC emerges from destructive interference between two coherently coupled Feshbach resonances and represents a controlled decoupling of a quantum state from its environment. Using loss spectroscopy, collective dynamics, and rf photoassociation, we directly observe the disappearance of coupling to the continuum and identify the state as a Friedrich–Wintgen BIC.

Our results demonstrate how Floquet engineering and quantum interference can be used to control openness in quantum systems, providing new tools for the design of dissipation-engineered and non-Hermitian quantum matter.