Phonon-Laser Ultrasensitive Force Sensor

Developing nanomechanical oscillators for ultrasensitive force detection is very useful in exploring science. We report our achievement of ultrasensitive detection of the external force regarding the radiofrequency electric field by a nanosensor made of a single trapped ⁴⁰Ca⁺ ion under injection locking, where squeezing is additionally applied to detection of the smallest force in the ion trap. The employed ion is confined stably in a surface electrode trap and works as a phonon laser that is very sensitive to the external disturbance. The injection locking drove the ion's oscillation with phase synchronization, yielding the force detection with sensitivity of 347 ±500.2em0exyN/√Hz. Further with 3-dB squeezing applied on the oscillation phase variance, we achieve a successful detection of the smallest force to be 86.5±70.1 yN.