Extended Data Fig. 1: Schematic illustrating the auto-balanced feedback loop.
From: Quantum-enhanced sensing of a single-ion mechanical oscillator
The feedback is applied to the LO, a frequency source used as a reference to compare to the ion’s oscillation frequency. The LO controls the phases and frequencies of the BSB and RSB laser pulses (see Fig. 1a) during the mode-frequency tracking experiments. The difference between the populations measured after a pair of Ramsey experiments with long waiting times provides an error signal, plong, which is used to feed back on the LO frequency, ωLO. Similarly, a second pair of Ramsey experiments with short waiting times provides and error signal, pshort, which is used to feed back on an additional LO phase offset ϕLO between the first and second effective π/2-pulses (“π/2”). The long- and short-waiting-time Ramsey experiments are interleaved, with ϕLO and ωLO applied equally to both. For more details on auto-balanced Ramsey experiments, see ref. 30.
