Gain sensitivity of the Mach-Zehnder interferometer by photon subtraction strategy

TL;DR

This paper demonstrates that photon subtraction from two-mode squeezed vacuum states significantly enhances the phase sensitivity of a Mach-Zehnder interferometer, surpassing quantum limits with practical squeezing levels.

Contribution

It introduces a photon subtraction strategy to improve phase sensitivity in MZ interferometers, achieving Heisenberg scaling and surpassing quantum Cramer-Rao bounds with realistic squeezing.

Findings

Photon subtraction yields over 20 dB sensitivity gain.

Sensitivity surpasses quantum Cramer-Rao bound at 5 dB squeezing.

Strategy enables practical enhancement of interferometric measurements.

Abstract

We study sensitivity of phase estimation of Mach-Zehnder (MZ) interferometer with original two-mode squeezed vacuum (TMSV) state. At the initial stage, the TMSV state is converted into two single-mode squeezed vacuum (SMSV) states, from each of which photons are subtracted by measurement by photon-number resolving (PNR) detector in auxiliary modes. New measurement-induced continuous variable (CV) states of a certain parity can already demonstrate gain sensitivity more than 20 dB in relation to the initial SMSV states at the output from the MZ interferometer and follow to Heisenberg scaling in the case of subtracting a large number of photons in the measuring channels for practical values of the SMSV squeezing 5 dB>. Using only one measurement-induced CV state of a certain parity together with the SMSV state shows an increase in sensitivity of no more than 11 dB. We show that the sensitivity of the phase estimation obtained by measuring the intensity difference of two measurement-induced CV states in two arms of the MZ interferometer can surpass quantum Cramer-Rao (QCR) boundary of the original two SMSV states just in the practical range of input squeezing 5 dB>. In general, the strategy with preliminary subtraction of photons from two SMSV enables greatly enhance the sensitivity of the MZ interferometer in the practical case of small values of squeezing.