Quantum metrology via repeated quantum nondemolition measurements in a photon box
Yu-Ran Zhang, Jie-Dong Yue, Heng Fan · Physical Review A · 2015
In quantum metrology schemes, one generally needs to prepare $m$ copies of $N$ entangled particles, such as entangled photon states, and then they are detected in a destructive process to estimate an unknown parameter. Here we present an experimental scheme for estimating this parameter by using repeated indirect quantum nondemolition measurements in the setup consisting of a photon in a superconducting cavity (called a photon box). This interaction-based scheme is able to achieve the phase sensitivity scaling as $1/N$ with a Fock state of $N$ photons. Moreover, we only need to prepare one initial $N$-photon state and it can be used repetitively for $m$ trials of measurements. This scheme is shown to sustain the quantum advantage for a much longer time than the damping time of Fock state and be more robust than the common strategy with exotic entangled states. To overcome the $2\ensuremath{\pi}/N$ periodic error in the estimation of the true parameter, we can employ a cascaded strategy by adding a real-time feedback interferometric layout.