Loss-tolerant and supersensitive angular rotation estimation based on quantum-enhanced interferometers

Quantum resources have been proven to drive the measurement sensitivity to beyond standard quantum limit in quantum metrology. However, quantum advantage degrades with optical losses. Aiming at angular rotation estimation, we theoretically investigate three loss-tolerant (external loss) quantum-enhanced interferometers---the degenerate SU(1,1) interferometer (DSI), nondegenerate hybrid interferometer (NHI), and degenerate hybrid interferometer (DHI)---to achieve supersensitive angular rotation estimation, without strict requirement of external losses. Analysis results show that these interferometers are perfectly applicable to angular rotation estimation. Moreover, the sensitivity, which is the same as in the case of no external losses, can always be retrieved by taking full advantage of the second optical parametric amplifier as a phase-sensitive amplification. The sensitivity bound that originates from laser power restriction in the DSI scheme can be overcome by the employment of the NHI or DHI scheme. These results are critical in real time variation of the angle measurement and tracking an object in circular motion.