Quantum Enhanced Integrated Single Photon Nonlinear Interferometer
Kai-Hong Luo, Matteo Santandrea, Michael Stefszky, Harald Herrmann, Christine Silberhorn · 2023
The standard quantum limit (SQL) describes the best precision that can be achieved for phase measurements using a classical interferometer. For such an interferometer, this limit is given by$1/\sqrt{N}$where$N$is the total number of photons launched into the interferometer. The SQL can be circumvented through the utilisation of quantum states combined with advanced low-loss detection schemes. Such overcoming of the SQL has been demonstrated, for example, by replacing the unused vacuum input port of the linear interferometer with a non-classical state [1], and by exploiting nonlinear SU (1,1) interferometers in the high-gain regime [2]. However, the impact of the experimental losses on the ability of nonlinear interferometers to beat the SQL is often neglected, particularly in the low-gain regime. In this work, we close this gap by studying the performance of lossy SU (1,1) interferometers in the single-photon pair regime, with particular attention to the different amount of information contained in the measurement of single counts and of coincidences at the output of the interferometer.