Viewpoint: Seeing the “Quantum” in Quantum Zero-Point Fluctuations

A technique from ion spectroscopy reveals the quantum nature of a mechanical system at low temperature.

Quantum zero-point motion, the fluctuation in the position of an object necessitated by the Heisenberg uncertainty principle, is among the most basic of quantum phenomena. While the origin of such fluctuations may be textbook material, unambiguously detecting them in a large mechanical structure (i.e., large compared to atomic scales) and, moreover, detecting their quantum nature, have remained elusive goals. These two tasks have now been accomplished by Amir Safavi-Naeini and co-workers at the California Institute of Technology in Pasadena [1]. As described in Physical Review Letters, this group coupled the motion of a patterned silicon nanomechanical beam to photons in an effective optical cavity formed in the beam. By laser cooling a mode of the beam’s motion to close to the quantum ground state, and by using a technique borrowed from ion-trap physics [2], they were able to clearly detect the quantum nature of the beam’s position fluctuations. This measurement of a truly nonclassical aspect of mechanical zero-point motion represents a milestone in the quest to measure and control the quantum nature of mechanical systems.