Quantum sensing with entangled light enabled a 50% enhancement in the sensitivity of microcantilever beam displacement measurements. This new approach could enable more than two orders of magnitude improvement in the sensitivity of scanning probe microscopes and enable the detection of more material properties at higher speeds than traditionally possible.
The entangled light source was designed to exhibit phase-sum and intensity-difference squeezing. This means that uncertainties in either phase- or intensity-based measurements could be reduced below classical limits without violating the Heisenberg uncertainty principle. The researchers used phase-sum squeezing to measure the displacement of an atomic force microscope microcantilever with 50% better sensitivity than was traditionally possible. For one-second measurements, the quantum-enhanced sensitivity was 1.7 femtometers. Intriguingly, the researchers demonstrated similar improvements in sensitivity when the entangled light did not interact directly with the microscope. This result means that the microscope can interact with the low-power entangled state if large optical powers are problematic or with the high-power reference signal if a lossy microscope interface attenuates squeezing. The result is relevant beyond scanning probe microscopy to any classically optimized interferometric microscope or sensor that uses lasers for signal readout. Critically, this finding is true even for lossy microscopes that would normally be incompatible with squeezed light.
Related Publication:
R. C. Pooser, N. Savino, E. Batson, J. L. Beckey, J. Garcia, and B. J. Lawrie, Truncated nonlinear interferometry for quantum enhanced atomic force microscopy, Phys. Rev. Lett. 124, 230504 (2020).
