Surpassing spectator qubits with photonic modes and continuous measurement for Heisenberg-limited noise mitigation

TL;DR

This paper introduces a photonic mode-based continuous measurement approach for noise mitigation in quantum systems, surpassing previous spectator qubit methods and achieving Heisenberg-limited scaling with potential for autonomous implementation.

Contribution

It generalizes spectator qubits to spectator modes, enabling continuous noise measurement and correction with many photon states, surpassing quantum measurement constraints.

Findings

Spectator modes can outperform spectator qubits in noise mitigation.

Long-time dephasing can be arbitrarily suppressed, even for white noise.

Heisenberg-limited scaling achieved using squeezing drives.

Abstract

Noise is an ever-present challenge to the creation and preservation of fragile quantum states. Recent work suggests that spatial noise correlations can be harnessed as a resource for noise mitigation via the use of spectator qubits to measure environmental noise. In this work we generalize this concept from spectator qubits to a spectator mode: a photonic mode which continuously measures spatially correlated classical dephasing noise and applies a continuous correction drive to frequency-tunable data qubits. Our analysis shows that by using many photon states, spectator modes can surpass many of the quantum measurement constraints that limit spectator qubit approaches. We also find that long-time data qubit dephasing can be arbitrarily suppressed, even for white noise dephasing. Further, using a squeezing (parametric) drive, the error in the spectator mode approach can exhibit Heisenberg-limited scaling in the number of photons used. We also show that spectator mode noise mitigation can be implemented completely autonomously using engineered dissipation. In this case no explicit measurement or processing of a classical measurement record is needed. Our work establishes spectator modes as a potentially powerful alternative to spectator qubits for noise mitigation.