Quantum Optics Laboratory

Atoms based velocimeter typically relies on measuring the first order Doppler shift of individual atoms. To determine the center-of-mass motion of an atomic ensemble, one usually needs to map out or truncate the velocity distribution of the ensemble. Here, I will describe the light dragging effect in a moving electromagnetically induced transparent (EIT) medium and use it to sense the center-of-mass motion of an atomic ensemble directly. The light dragging effect or the deviation of phase velocity from the speed of light c in a moving medium was first observed by Fizeau in a flowing water experiment for the study of ether in the pre Einstein’s special theory of relativity era. It was later explained by the Lorentz velocity addition to the first order. We enhance the dragging effect in a cold atomic medium under EIT condition and demonstrate a velocity sensor at a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. This new type of sensor depends on the collective motion of the atomic ensemble and could lead to a new design of motional sensor beyond the limitation of Doppler broadening of atoms. In this talk, I will also present our recent results and progress on atom interferometry inside a hollow-core photonic crystal fiber.