Unconventional Geometric Sagnac Interferometer for Rotation Sensing.

Quantum information processing with geometric features of quantum states may provide promising noise-resilient schemes for quantum metrology. In this Letter, we theoretically explore geometric Sagnac interferometers with trapped atomic clocks for rotation sensing. We first present the Sagnac phase-matching condition (SPMC) which is critical and instrumental in experiments to extract the rotation frequency from the interference signal with high sensitivity. Otherwise, if certain temporal profiles of the sweeping angular velocity and the total interrogation time are improperly used, the sensitivity could be detrimentally small. Furthermore, base on the SPMC, an scheme for unconventional geometric Sagnac interferometer is proposed, which could be intrinsically robust to certain decoherence noises and be more accessible in experiments compared with its pure geometric counterpart, due to a zero initial sweeping angular velocity. Such geometric Sagnac interferometers are capable of saturating the ultimate precision given by the quantum Cramu0027er-Rao bound.