OPTIMAL QUANTUM MEASUREMENTS FOR PHASE ESTIMATION

Quantum information theory is applied to practical interferometer-base d phase measurements to deduce the optimal phase measurement scheme wi th two optical modes. Optimal phase measurements, given ideal input st ates, reveal an asymptotic 1/n decrease in phase uncertainty Delta the ta for n the mean photon number of the input state. In contradistincti on to previous schemes for realizing the number-phase uncertainty limi t, the 1/n limit achieved here is independent of the interferometer ph ase shift; prior information about the expected phase shift is not nec essary to attain this limit. These results apply more generally to su( 2) and so(3) phase parameter estimation.