Cavity-QED based approaches have succeeded in generating large amounts of entanglement enhancements beyond the standard quantum limit (SQL), which sets a fundamental imprecision on all quantum sensors with unentangled atoms [1,2]. It is now of great interest to apply these cavity-QED approaches to enhance a broad range of quantum sensors including atomic clocks  and matterwave interferometers. Here, we demonstrate a rubidium matterwave interferometer with atoms guided by a blue-detuned hollow optical dipole trap as they free-fall along the axis of a high-finesse cavity with cooperativity C≈1. We also demonstrate cavity-enhanced quantum non-demolition (QND) readout of the matterwave interferometer with added readout noise as much as 10 dB below the projection noise level. We will conclude by discussing our efforts to further improve the QND measurements to realize an entangled interferometer with sensitivity surpassing the SQL.
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