We investigate the statistical arrow of time for a quantum system being monitored by a sequence of measurements. For a continuous qubit measurement example, we demonstrate that time-reversed evolution is always physically possible, provided that the measurement record is also negated. Despite this restoration of dynamical reversibility, a statistical arrow of time emerges, and may be quantified by the log-likelihood difference between forward and backward propagation hypotheses. We then show that such reversibility is a universal feature of nonprojective measurements, with forward or backward Janus measurement sequences that are time-reversed inverses of each other.
J. Dressel, A. Chantasri, A. N. Jordan, and A. Korotkov, Phys. Rev. Lett. 119, 220507 (2017).
American Physical Society
This article was originally published in Physical Review Letters, volume 119, in 2017. DOI:10.1103/PhysRevLett.119.220507