  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.
