In this paper, we propose two protocols for generating super-resolving textit{single-photon} path-entangled states from general maximally path-entangled N00N states. We also show that both protocols generate the desired state with different probabili
ties depending on the type of detectors being used. Such super-resolving single-photon path-entangled states preserve high resolving power but lack the requirement of a multi-photon absorbing resist, which makes this state a perfect candidate for quantum lithography.
We study effects of phase fluctuations on phase sensitivity and visibility of a class of robust path-entangled photon Fock states (known as mm states) as compared to the maximally path-entangled N00N states in presence of realistic phase fluctuations
such as turbulence noise. Our results demonstrate that the mm states, which are more robust than the N00N state against photon loss, perform equally well when subject to such fluctuations. We show that the phase sensitivity with parity detection for both of the above states saturates the quantum Cramer-Rao bound in presence of such noise, suggesting that the parity detection presents an optimal detection strategy.
There has been much recent interest in quantum metrology for applications to sub-Raleigh ranging and remote sensing such as in quantum radar. For quantum radar, atmospheric absorption and diffraction rapidly degrades any actively transmitted quantum
states of light, such as N00N states, so that for this high-loss regime the optimal strategy is to transmit coherent states of light, which suffer no worse loss than the linear Beers law for classical radar attenuation, and which provide sensitivity at the shot-noise limit in the returned power. We show that coherent radar radiation sources, coupled with a quantum homodyne detection scheme, provide both longitudinal and angular super-resolution much below the Rayleigh diffraction limit, with sensitivity at shot-noise in terms of the detected photon power. Our approach provides a template for the development of a complete super-resolving quantum radar system with currently available technology.
To acquire the best path-entangled photon Fock states for robust quantum optical metrology with parity detection, we calculate phase information from a lossy interferometer by using twin entangled Fock states. We show that (a) when loss is less than
50% twin entangled Fock states with large photon number difference give higher visibility while when loss is higher than 50% the ones with less photon number difference give higher visibility; (b) twin entangled Fock states with large photon number difference give sub-shot-noise limit sensitivity for phase detection in a lossy environment. This result provides a reference on what particular path-entangled Fock states are useful for real world metrology applications.
