Phase-conjugate quantum communication with optical heterodyne detection
Jeffrey H. Shapiro · Optics Letters · 1995
A quantum heterodyne-detection system is described that affords K-ary phase-based digital communication at zero error probability at an average photon number of approximately K3/2. In phase-based precision measurement—at the same average photon number—this system can measure an arbitrary c-number phase shift to within ±π/K rad with probability one.