Quantum non-demolition measurement of the photon number: an application to radiometry
Stefania Castelletto, Ivo Pietro Degiovanni, Maria Luisa Rastello · Journal of Optics B Quantum and Semiclassical Optics · 2001
This paper proposes a realistically feasible experiment, within the realm of existing technology and proved techniques, to measure the mean photon number of a coherent source by means of a quantum non-demolition scheme, exploiting the parametric amplification of correlated photons in χ (2) media. We deduce the number of photons of an input source interacting with a high-intensity pump field in a nonlinear crystal, using as the probe the shift in the quadrature amplitude of the pump beam induced by the source under measurement. We perform a theoretical evaluation of the noise level associated with this measurement and compare it with the quantum limit. We explore the possible implications of this method for radiometry.