Fig. 4: Local dynamical decoupling towards optimal metrology.
From: Multi-ensemble metrology by programming local rotations with atom movements
a, We split the array into three ensembles, and perform a local dynamical decoupling (DD) sequence such that even though the total Ramsey dark time is T, individual ensembles experience different effective evolution times of T/4, T/2 and T. The phase of each ensemble is then measured using dual-quadrature readout. b, Slower-evolving ensembles (those which experience less evolution time) can be used to detect phase slips in faster-evolving ensembles, extending the effective interrogation time of optical clocks. Following the sequence in a, we find the three ensembles evolve at relative rates of 1.00:1.99(1):4.10(4) with respect to the total evolution time T. The demonstrated scheme in a and b is effective for the case of slow frequency noise where the corresponding noise correlation time is longer than the total evolution time. c, To handle generic time-dependent noise with shorter correlation times, we envision breaking the total evolution time into k kernels of length τ, each of which is composed of local dynamical decoupling and free evolution. In this way, as long as τ is shorter than the correlation time of any time-dependent noise affecting the system, the different M ensembles (indexed by m = 0,…, M − 1) can accumulate phase in a correlated manner over the interleaved Ramsey interrogation periods.
