Subluminal light propagation through an ultracold atom-molecule coupled resonant medium

We theoretically investigate light propagation through a Feshbach-resonant atom-molecule coupled system. We show that when a diatomic molecular state in an electronically ground-state potential is coupled to the continuum of Feshbach-resonant atom-atom scattering states via an excited molecular state with a control (strong) and a probe (weak) laser field, the dispersive behaviour of the medium is significantly influenced by the Feshbach resonance. In particular, a Feshbach resonance helps to make the dispersion characteristics quite sharp, leading to the subluminal propagation of the probe. Our model calculations with realistic parameters show that it is possible to reduce the group velocity to 50 m s(-1) with nearly 80% transmission. Furthermore, we demonstrate that it is possible to achieve significant enhancement of the delay-bandwidth product (DBP) of the probe by narrowing the width of the resonance, opening up new prospects for using a resonant atom-molecule coupled medium for efficient slow-light production and applications.