Past quantum state analysis of the photon number evolution in a cavity
T. Rybarczyk, Stefan Gerlich, Bruno Peaudecerf, Mariane Penasa, Brian Julsgaard, Klaus Moelmer, S. Gleyzes, M. Brune, J. M. Raimond, S. Haroche, I. Dotsenko · arXiv (Cornell University) · 2014
A quantum system can be monitored through repeated interactions with meters, followed by their detection. The state of the system at time t is thus conditioned on the information obtained until that time. More insight in the state dynamics is provided, however, by the past quantum state (PQS) [S. Gammelmark et al. Phys. Rev. Lett. 111, 160401 (2013)]. It relies on all aspects of the system evolution which are recorded in the past and in the future of t. Using PQS analysis for the quantum non-demolition photon number counting in a cavity, we can reveal information hidden in the standard approach and resolve a wider range of number states. This experiment demonstrates the strong potential of PQS analysis.