We find an upper bound for the sensitivity of Fabry-P\'erot interferometric length measurements using inefficient photodetectors. This bound applies to all possible quantum-mechanical states of the light entering the interferometer. It applies to standard photodetection, differenced photodetection, and homodyne detection. In the limit of large photon number we identify the optimal detection scheme and input states. They are homodyne detection with a coherent state in one input port, and a nonvacuum quadrature squeezed state in the other. No other quantum states of the input light give better sensitivity, provided that the interferometer output is measured by either photodetection or homodyning, and that the photodetectors are inefficient.We find an upper bound for the sensitivity of Fabry-P\'erot interferometric length measurements using inefficient photodetectors. This bound applies to all possible quantum-mechanical states of the light entering the interferometer. It applies to standard photodetection, differenced photodetection, and homodyne detection. In the limit of large photon number we identify the optimal detection scheme and input states. They are homodyne detection with a coherent state in one input port, and a nonvacuum quadrature squeezed state in the other. No other quantum states of the input light give better sensitivity, provided that the interferometer output is measured by either photodetection or homodyning, and that the photodetectors are inefficient.

Physical Review AFeb 1, 19911 citation

Open questions in closed-loop photodetection

Jeffrey H. Shapiro

Jan 1, 19870 citations

Improving single-photon sources via linear optics and photodetection

Dominic William Berry, Stefan Scheel, Barry C. Sanders +1 more

Triggered single-photon sources produce the vacuum state with nonzero probability, but produce a much smaller multiphoton component. It is therefore reasonable to approximate the output of these photon sources as a mixture of the vacuum and single-photon states with probabilities $1\ensuremath{-}p$ and $p$ , respectively. Here we are concerned with increasing the efficiency $p$ by directing multiple copies of the single-photon-vacuum mixture into a linear optical device and applying photodetection on some outputs. We prove that it is impossible, under certain conditions, to increase $p$ via linear optics and conditional preparation based on photodetection. We also establish a class of photodetection events for which $p$ can be improved, although with an added multiphoton component. In addition we prove that it is not possible to obtain perfect single-photon states via this method from imperfect $(p<1)$ inputs.Triggered single-photon sources produce the vacuum state with nonzero probability, but produce a much smaller multiphoton component. It is therefore reasonable to approximate the output of these photon sources as a mixture of the vacuum and single-photon states with probabilities $1\ensuremath{-}p$ and $p$, respectively. Here we are concerned with increasing the efficiency $p$ by directing multiple copies of the single-photon-vacuum mixture into a linear optical device and applying photodetection on some outputs. We prove that it is impossible, under certain conditions, to increase $p$ via linear optics and conditional preparation based on photodetection. We also establish a class of photodetection events for which $p$ can be improved, although with an added multiphoton component. In addition we prove that it is not possible to obtain perfect single-photon states via this method from imperfect $(p<1)$ inputs.

arXiv:quant-ph/0309140Physical Review AMar 1, 200421 citations

p

, respectively. Here we are concerned with increasing the efficiency

p

by directing multiple copies of the single-photon-vacuum mixture into a linear optical device and applying photodetection on some outputs. We prove that it is impossible, under certain conditions, to increase

p

via linear optics and conditional preparation based on photodetection. We also establish a class of photodetection events for which

p

can be improved, although with an added multiphoton component. In addition we prove that it is not possible to obtain perfect single-photon states via this method from imperfect

(p<1)

inputs.