Sagnac interferometry based on ultraslow polaritons in cold atomic vapors.

The advantages of light and matter-wave Sagnac interferometers--large area on one hand and high rotational sensitivity per unit area on the other--can be combined utilizing ultraslow light in cold atomic gases. While a group-velocity reduction alone does not affect the Sagnac phase shift, the associated momentum transfer from light to atoms generates a coherent matter-wave component which gives rise to a substantially enhanced rotational signal. It is shown that matter-wave sensitivity in a large-area interferometer can be achieved if an optically dense vapor at subrecoil temperatures is used. Already a noticeable enhancement of the Sagnac phase shift is possible, however, with far fewer cooling requirements.