Subwavelength interference with an effective entangled source

Abstract

We propose a two-photon subwavelength interference scheme for classical light in which multiple quantum-like entangled two-photon paths play an essential role. These entangled two-photon paths are introduced through a specially designed source composed of many point sources $j$ with $j$'s complex amplitude being a superposition of modes ${e}^{i{\ensuremath{\phi}}_{j}}$ and ${e}^{i{\ensuremath{\phi}}_{j}^{(1)}}$, where ${\ensuremath{\phi}}_{j}$ and ${\ensuremath{\phi}}_{j}^{(1)}$ are temporally random phases but satisfying ${\ensuremath{\phi}}_{j}+{\ensuremath{\phi}}_{j}^{(1)}={\ensuremath{\phi}}_{0}$, with ${\ensuremath{\phi}}_{0}$ being either a constant or a random phase in time. Interference between the entangled two-photon paths could lead to second-order subwavelength interference of an object put in front of the source plane. In a proof-of-principle experiment, by using a spatial light modulator to modulate the wave front of a coherent light, we have generated such a source and observed subwavelength interference of a double-slit mask via two-photon measurement.