There has been much recent interest in quantum metrology for applications tosub-Raleigh ranging and remote sensing such as in quantum radar. For quantumradar, atmospheric absorption and diffraction rapidly degrades any activelytransmitted quantum states of light, such as N00N states, so that for thishigh-loss regime the optimal strategy is to transmit coherent states of light,which suffer no worse loss than the linear Beer's law for classical radarattenuation, and which provide sensitivity at the shot-noise limit in thereturned power. We show that coherent radar radiation sources, coupled with aquantum homodyne detection scheme, provide both longitudinal and angularsuper-resolution much below the Rayleigh diffraction limit, with sensitivity atshot-noise in terms of the detected photon power. Our approach provides atemplate for the development of a complete super-resolving quantum radar systemwith currently available technology.
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