State and Process Characterisation

The cornerstone enabling time reversal is the process of parametric amplification which is realized by spin exchange. In this chapter we experimentally characterize the nonlinear process in detail. Emphasis is placed on the generated number fluctuations which are generic to the emerging entangled state. These fluctuations reflect the state’s ability for superior phase estimation. Finally, experimental limitations such as particle loss, pump depletion effects, and seeded dynamics are considered.