Time-reversal and super-resolving phase measurements
  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 \emph{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. 
K. J. Resch, K. L. Pregnell, R. Prevedel, A. Gilchrist, G. J. Pryde,   J. L. O'Brien and A. G. White