Interferometry Beyond Exact Time Reversal

In this chapter we study the situation that arises when the two durations of spin exchange do not match in length. If the nonlinear readout is shorter than the initial entangled state preparation only an incomplete time reversal can be carried out. Consequently, the probe state does not get fully disentangled and only partial absorption of fluctuations is achieved. In the opposite case the duration of the nonlinear readout is prolonged. This overcompensating regime is the most interesting as it provides benefits for approaching a Heisenberg-limited phase sensitivity in presence of technical fluctuations. This relies on the noiseless amplification that allows magnifying the output signal to an extent that spurious noise can be rendered less significant.