Near-photon-number-eigenstate fields lead to dramatic signal-to-noise improvement beyond the standard shot-noise limit in many optical systems, including interferometric gravitational-wave detectors. These fields may be generated from parametric processes with measurement feedback. Degradation from nonideal photodetection can be overcome by appropriate optical preamplification. It is estimated that an order-of-magnitude improvement can already be obtained with existing devices.

• Received 20 November 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.2176