Time-reversal and super-resolving phase measurements

Phys Rev Lett. 2007 Jun 1;98(22):223601. doi: 10.1103/PhysRevLett.98.223601. Epub 2007 May 31.

Abstract

We demonstrate phase super-resolution in the absence of entangled states. The key insight is to use the inherent time-reversal symmetry of quantum mechanics: our theory shows that it is possible to measure, as opposed to prepare, entangled states. Our approach is robust, requiring only photons that exhibit classical interference: we experimentally demonstrate high-visibility phase super-resolution with three, four, and six photons using a standard laser and photon counters. Our six-photon experiment demonstrates the best phase super-resolution yet reported with high visibility and resolution.