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Modern Physics Letters B

Phase sensitivity and entanglement of superposition coherent states in Mach–Zehnder interferometer

Gang Ren, Feng Chen

Published Jun 16, 2023• 0 citations
Publisher

Abstract

In this paper, we mainly focus on analyzing the fidelity, parity measurement, phase sensitivity and entanglement properties of the output states corresponding to three quantum superposition coherent states, i.e. even coherent state (ECS), Yurke-Stoler state (YSS) and odd coherent state (OCS). Our results show that the OCS characterizes super-resolution in the phase measurement via parity measurement at the output ports of a Mach–Zehnder interferometer. In addition, we find that the optimal phase sensitivity may approach the Heisenberg limit which is independent of the superposition coefficient of the coherent states. An interesting finding is that the macroscopically entangled coherent states can be experimentally prepared by adjusting the parameters of the nonlinear phase shifter of the MZI.

DOI
10.1142/s0217984923501014

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In this paper, we mainly focus on analyzing the fidelity, parity measurement, phase sensitivity and entanglement properties of the output states corresponding to three quantum superposition coherent states, i.e. even coherent state (ECS), Yurke-Stoler state (YSS) and odd coherent state (OCS). Our results show that the OCS characterizes super-resolution in the phase measurement via parity measurement at the output ports of a Mach–Zehnder interferometer. In addition, we find that the optimal phase sensitivity may approach the Heisenberg limit which is independent of the superposition coefficient of the coherent states. An interesting finding is that the macroscopically entangled coherent states can be experimentally prepared by adjusting the parameters of the nonlinear phase shifter of the MZI.
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We investigate the phase sensitivity of the SU(1,1) interfereometer [SU(1,1)I] and the modified Mach–Zehnder interferometer (MMZI) with the entangled coherent states (ECS) as inputs. We consider the ideal case and the situations in which the photon losses are taken into account. We find that, under ideal conditions, the phase sensitivity of both the MMZI and the SU(1,1)I can beat the shot-noise limit (SNL) and approach the Heisenberg limit (HL). In the presence of photon losses, the ECS can beat the coherent and squeezed states as inputs in the SU(1,1)I, and the MMZI is more robust against internal photon losses than the SU(1,1)I.
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Here, we are investigating the enhancement in resolution and phase sensitivity of a Mach-Zehnder interferometer (MZI) based quantum LiDAR. We are using a multi-photonic state (MPS), superposition of four coherent states [ Int. J. Quantum Inf. 19 , 2150013 ( 2021 ) 0219-7499 10.1142/S0219749921500131 ], as the input state and binary outcome parity photon counting measurement and binary outcome zero non-zero photon counting measurement as the measurement schemes. We have thoroughly investigated the results in lossless as well as lossy cases. We found enhancement in resolution and phase sensitivity in comparison to the coherent state and even coherent superposition state (ECSS) based quantum LiDAR. Our analysis shows that MPS may be an alternative nonclassical resource in the field of quantum imaging and quantum sensing technologies, like in quantum LiDAR.
We study the improvement in the phase sensitivity of a Mach–Zehnder interferometer using the superposition of Schrödinger’s cat-like state with the Fock state (SCFS) and the coherent state as inputs. With this setup, we examine the effect on phase sensitivity of the interferometer using a two-channel detection (TCD) scheme [ Opt. Express 29 , 95 ( 2021 ) OPEXFF 1094-4087 10.1364/OE.413391 ] in which we take the optimal combination of the intensities of both output ports. We find better phase sensitivity under some conditions for this setup as compared to other known combinations of inputs such as squeezed vacuum and coherent states, vacuum and coherent states, etc. Therefore, we expect that the SCFS may be an alternative nonclassical resource for improvement in the phase sensitivity of a Mach–Zehnder interferometer, having potential application in quantum sensing.