  There has been much recent interest in quantum optical interferometry for
applications to metrology, sub-wavelength imaging, and remote sensing, such as
in quantum laser radar (LADAR). For quantum LADAR, atmospheric absorption
rapidly degrades any quantum state of light, so that for high-photon loss the
optimal strategy is to transmit coherent states of light, which suffer no worse
loss than the Beer law for classical optical attenuation, and which provides
sensitivity at the shot-noise limit. This approach leaves open the question --
what is the optimal detection scheme for such states in order to provide the
best possible resolution? We show that coherent light coupled with photon
number resolving detectors can provide a super-resolution much below the
Rayleigh diffraction limit, with sensitivity no worse than shot-noise in terms
of the detected photon power.
