Quantum non-demolition measurement of photon number with atom-light interferometers

Abstract

When atoms are illuminated by an off-resonant field, the AC Stark effect will lead to phase shifts in atomic states. The phase shifts are proportional to the photon number of the off-resonant illuminating field. By measuring the atomic phase with newly developed atom-light hybrid interferometers, we can achieve quantum non-demolition measurement of the photon number of the optical field. In this paper, we analyze theoretically the performance of this QND measurement scheme by using the QND measurement criteria established by Holland et al [Phys. Rev. A 42, 2995 (1990)]. We find the quality of the QND measurement depends on the phase resolution of the atom-light hybrid interferometers. We apply this QND measurement scheme to a twin-photon state from parametric amplifier to verify the photon correlation in the twin beams. Furthermore, a sequential QND measurement procedure is analyzed for verifying the projection property of quantum measurement and for the quantum information tapping. Finally, we discuss the possibility for single-photon-number-resolving detection via QND measurement.

Quantum non-demolition measurement based on an SU(1,1)-SU(2)-concatenated atom-light hybrid interferometer

“…Compared to a conventional SU(1,1) interferometer, the number of phase-sensing particles is further increased due to input field â(0) W . In the previous scheme [32], a strong stimulated Raman process can indeed be used to excite most of the atoms to the |m state to improve the number of phase-sensing particles. However, this will produce additional nonlinear effects and noise light fields [39][40][41].…”

“…To have single-photon resolution, we need AC-Stark coefficient κ ∼ 1/gN 1/2 α . Compared to the traditional SU(2) interferometer [32], the required coefficient is smaller by a factor of 1/g . This is due to the method of active correlation output readout for the SU(2) interferometer [38], in which the SNR is greater than the SU(2) interferometer by a factor of g of NRP.…”

“…However, we can adjust the gain parameter of the NRP in readout stage to reduce the impact due to losses. Compared to the previous works [32,33], the actively correlated atom-light hybrid interferometer can be realized QND measurement of photon number with higher precision.…”

“…The second type is the SU(1,1) nonlinear interferometer utilizing nonlinear Raman process (NRP) for wave split- ting and recombination [29]. This new type interferometer can be applied to QND measurement of photon number based on the AC-Stark effect [32,33]. However, due to the requirements of detection of laser source stability in LIGO, the intensity stabilization justments are very strict across the gravitational wave band [34] and higher accuracy is required for QND measurement of high photon number.…”

Sensing performance enhancement via asymmetric gain optimization in the atom-light hybrid interferometer

“…Atom interferometers can measure the atomic phase sensitive parameters, and have been demonstrated to measure the rotation rate [19], acceleration of gravity [20][21][22] and magnetic field [23,24]. The ALHI is sensitive to both the optical and atomic phases, which has the potential to combine the advantages of optical wave and atomic systems in precision measurement, and has been utilized to measure angular velocity, electric field and magnetic field [14,15,25,26].…”