|DATE||July 27 (Tue), 2021|
|TITLE||Optimal observables for Gaussian illumination|
Quantum illumination (QI) is the most noise-robust protocol since it pursues to enhance a target detection capability with input entangled states in a heavy noise environment, while classical illumination (CI) utilizes un-entangled states. Gaussian illumination is to detect the target using Gaussian states: coherent, thermal, squeezed vacuum, and two-mode squeezed vacuum (TMSV) states. Here I propose optimal observables for Gaussian illumination in order to maximize the signal-to-noise ratio (SNR). The observables are constructed from the output states after the interaction between a signal and a target, with the corresponding measurement setups. In QI using a TMSV state, we show that the SNR using the observable outperforms the SNRs using other observables for any number of signal power, thermal noise, and target reflectance. In the limit of low signal power, asymptotically, it approaches a half of exponent of the TMSV state QCB. In CI using coherent and thermal states, the SNR using the observable approaches the coherent state QCB in the limit of large idler power while the thermal state cannot outperform the coherent state.