Abstract

The estimation of the state of a quantum system is a central task in quantum information and quantum-enabled metrology. A quantum system can be monitored indirectly through its successive interaction with meters, whose final detection provides information on the system’s state. In the standard, forward, approach, the system’s density operator, ρ, at time t is deduced from all measurements performed up to time t and from our knowledge of the system’s dynamics, including relaxation. The recently introduced past quantum state (PQS) formalism [1] provides us with a simple method to include in the state estimation also information gathered after t. We present here an experiment applying the PQS analysis to a system with a high-dimensional Hilbert space [2].

© 2015 IEEE