Experimental sub-Rayleigh resolution by an unseeded high-gain optical   parametric amplifier for quantum lithography
  Quantum lithography proposes to adopt entangled quantum states in order to increase resolution in interferometry. In the present paper we experimentally demonstrate that the output of a high-gain optical parametric amplifier can be intense yet exhibits quantum features, namely, sub-Rayleigh fringes, as proposed by Agarwal et al. (Phys. Rev. Lett. 86, 1389 (2001)). We investigate multiphoton states generated by a high-gain optical parametric amplifier operating with a quantum vacuum input for a gain values up to 2.5. The visibility has then been increased by means of three-photon absorption. The present article opens interesting perspectives for the implementation of such an advanced interferometrical setup. 
Fabio Sciarrino, Chiara Vitelli, Francesco De Martini, Ryan Glasser,   Hugo Cable, and Jonathan P. Dowling