Detecting magnetically guided atoms with an optical cavity

We show that a low-finesse cavity can be efficient for detecting neutral atoms. The low finesse can be compensated for by decreasing the mode waist of the cavity. We have used a near-concentric resonator with a beam waist of 12 microm and a finesse of only 1100 to detect magnetically guided Rb atoms with a detection sensitivity of 0.1 atom in the mode volume. For future experiments on single-atom detection and cavity QED applications, it should be beneficial to use miniaturized optical resonators integrated on atom chips.