Noise mitigation using spectator quantum systems and continuous feedforward

There has been significant recent interest in using a set of so-called “spectator” qubits to detect correlated noise fluctuations and ultimately improve performance of a distinct set of “data” qubits (see e.g. [1-3]). Here we theoretically analyze a continuous-in-time version of this idea: use a spectator quantum system (i.e. a qubit or cavity) in a continuous measurement and feeforward scheme to continuously cancel the influence of correlated noise on the “data” system. We discuss fundamental limits placed on this approach by quantum measurement constraints, and also compare against autonomous spectator schemes based on reservoir engineering ideas. In addition to helping improve qubit performance, we discuss how analogous strategies could be used to improve force sensors.

[1] RS Gupta, et al PRA (2020)

[2] Majumder, et al npj quantum information (2020)

[3] Youssry, et al arXiv (2021)