  Quantum fluctuations constitute the primary noise barrier limiting
cavity-based axion dark matter searches. In an experiment designed to mimic a
real axion search, we employ a quantum-enhanced sensing technique to detect a
synthetic axion-like microwave tone at an unknown frequency weakly coupled to a
resonator, demonstrating a factor of 5.6 acceleration relative to a
quantum-limited search for the same tone. The acceleration comes from increases
to both the visibility bandwidth and the peak visibility of a detector. This
speedup is achieved by dynamically coupling the resonator mode to a second
(readout) mode with balanced swapping and two-mode squeezing interactions. A
small fractional imbalance between the two interaction rates yields further
scan rate enhancement and we demonstrate that an 8-fold acceleration can be
achieved.
