D. W. Berry, M. J. Hall, M. Zwierz, and H. M. Wiseman, "Universality of the Heisenberg Limit for Estimates of Random Phase Shifts,"
in Conference on Lasers and Electro-Optics 2012,
OSA Technical Digest
(Optical Society of America, 2012), paper QTu2E.7.
Recent work has suggested that it is possible to perform phase measurements more accurately than the Heisenberg limit. We show that, when one averages over random phase shifts, the Heisenberg limit is universal.