Enhancement of phase sensitivity by the additional resource in a Mach-Zehnder interferometer

Abstract Improving the phase sensitivity of the optical interferometer plays a key role in quantum metrology. We propose a novel scheme that two Mach-Zehnder interferometers (MZIs) are parallelly placed for investigating the single-phase and two-phase sensitivities. For single-phase estimation, we study the performance of phase sensitivity by difference-intensity detection. The results show that the external loss in the additional resource plays the role of enhancing the phase sensitivity. And the sub shot-noise phase sensitivity is obtained by adjusting the photon loss of the additional resource in the MZI even with the inputs of a vacuum state plus a coherent state. For two-phase estimation, we investigate the ultimate bounds of estimation precision and compare them with the case of single-phase estimation under optimized detection method. Our results could yield potential applications to quantum sensor, quantum imaging and quantum tomography.