This paper demonstrates a frequency measurement technique using a single laser-cooled barium ion as a quantum probe that surpasses the Heisenberg limit. The uncertainty in the frequency measurement scales as 1/T^1.75±0.03, exceeding the 1/T scaling predicted by the Heisenberg limit for time-independent Hamiltonians. This improved precision, achieved through controlled feedback Hamiltonian, enables precise noise frequency measurement in the kHz range. The authors propose adapting this protocol for enhanced sensitivity in detecting certain types of light mass axion-like dark matter particles.

T. Dutta, M. Mukherjee