Transmission estimation at the quantum Cramér-Rao bound with macroscopic quantum light

Abstract

The field of quantum metrology seeks to apply quantum techniques and/or resources to classical sensing approaches with the goal of enhancing the precision in the estimation of a parameter beyond what can be achieved with classical resources. Theoretically, the fundamental minimum uncertainty in the estimation of a parameter for a given probing state is bounded by the quantum Cramér-Rao bound. From a practical perspective, it is necessary to find physical measurements that can saturate this fundamental limit and to show experimentally that it is possible to perform measurements with the required precision to do so. Here we perform experiments that saturate the quantum Cramér-Rao bound for transmission estimation over a wide range of transmissions when probing the system under study with a continuous wave bright two-mode squeezed state. To properly take into account the imperfections in the generation of the quantum state, we extend our previous theoretical results to incorporate the measured properties of the generated quantum state. For our largest transmission level of 84%, we show a 62% reduction over the optimal classical protocol in the variance in transmission estimation when probing with a bright two-mode squeezed state with −8 dB of intensity-difference squeezing. Given that transmission estimation is an integral part of many sensing protocols, such as plasmonic sensing, spectroscopy, calibration of the quantum efficiency of detectors, etc., the results presented promise to have a significant impact on a number of applications in various fields of research.

Parallel Quantum-Enhanced Sensing

“…It has been shown that a transmission-based sensing scheme with an optimized intensity-difference measurement, in which electronic gain or attenuation is used to compensate for the effect of optical losses, can reach the fundamental limit of sensitivity given by the quantum Crameŕ−Rao bound. 51,52 In our experiment, given that the optical losses introduced by the plasmonic sensors are significantly larger than the ones introduced by the mask, electronic attenuation is used in the conjugate's photocurrent to minimize the intensity-difference noise between correlated quadrants (see the Supporting Information). We implement the optimized intensity-difference measurements with a home-built quadrant detection system that provides access to the low (DC) and high (RF) frequency components of the photocurrent for each of the eight separate quadrants: four for the probe and four for the conjugate.…”

Quantum-enhanced Doppler lidar

“…Quantum metrology exploits quantum mechanical resources, such as entanglement and squeezing, to measure a physical parameter with higher resolution than any strategy with classical resources. Many quantum metrology protocols in the photonic regime 1 have been proposed such as quantum illumination (QI) [2][3][4][5][6] , quantumenhanced position and velocity estimation [7][8][9][10][11][12][13] , quantum phase estimation 14,15 , transmission parameter estimation [16][17][18][19][20] , noise estimation 21 and estimation of separation between objects 22,23 , among others. In these protocols, information about an object is retrieved by interrogating it with a signal beam.…”