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.
Highlights
Quantum nondemolition (QND) measurement [1,2] is a special type of measurement of a quantum system in which the physical observable to be measured is not altered in the measurement process
AC Stark effect was suggested for QND measurement of photon number by using EIT method for atomic phase shift measurement [24]
A new type of hybrid interferometers involving both atomic ensemble and light was demonstrated [25,26,27,28], and attracts lots of attention. This type of interferometers is based on Raman interaction between atoms and light, and is sensitive to both optical and atomic phase shift, so can be used to measure the atomic AC Stark phase shift induced by an optical probe field
Summary
Quantum nondemolition (QND) measurement [1,2] is a special type of measurement of a quantum system in which the physical observable to be measured is not altered in the measurement process. AC Stark effect was suggested for QND measurement of photon number by using EIT method for atomic phase shift measurement [24]. A new type of hybrid interferometers involving both atomic ensemble and light was demonstrated [25,26,27,28], and attracts lots of attention This type of interferometers is based on Raman interaction between atoms and light, and is sensitive to both optical and atomic phase shift, so can be used to measure the atomic AC Stark phase shift induced by an optical probe field. Compared with the EIT scheme, the QND measurement based on the hybrid interferometers can work for short and off-resonant probe pulse. We conclude in Sect.(6) with a summary and a discussion on the possiblility for single-photon-number-resolving detection via this QND measurement
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