In recent years quantum optical interferometry has received a lot of attention due to its important applications in quantum metrology, quantum imaging, gravitational wave detection and quantum laser radar (LADAR). The classical standard scheme for sensing a phase-shift consists of a coherent state as input and an intensity measurement of the output state. This strategy leads to a shot-noise limited phase sensitivity: phase uncertainty < 1/N^(1/2), where N is the average number of photons, as well as a diffraction limited resolution.

We have developed and experimentally demonstrated a novel approach---based on coherent state input---that is capable of reaching super-resolution while retaining shot-noise limited performance. Our approach is based on standard homodyne detection and data post-selection which approximates a parity measurement.

      

This work is done in cooperation with group of prof. Ulrik L. Andersen, Department of Physics, Technical University of Denmark.