Combining cryogenic cooling (~20 K) with backaction laser cooling, our researchers probe optomechanical oscillators near their quantum "ground state" — driving macroscopic devices consisting of billions of atoms into single quantum states.
Achieving quantum ground state operating conditions on macroscopic devices has been a major objective in quantum physics. As with atoms, molecules, and ions, reaching the ground state is the first step towards observing macroscopic quantum phenomena. In optomechanics, light field forces (radiation pressure) in resonant optical cavities damp and cool nanomechanical motion down to quantum levels.
Our silicon nanobeams are fabricated from silicon-on-insulator (SOI) wafers consisting of a 220 nm silicon layer on top of a 2 µm SiO₂ oxide layer. These optomechanical crystals feature periodic array holes that simultaneously confine 1550 nm telecom photons and ~4 GHz phonons within the same microscopic volume.
This high co-localization results in extremely strong optomechanical coupling rates, enabling the laser cooling beam to efficiently extract thermal phonons from the mechanical resonator.
Unlike classical oscillators, quantum mechanical oscillators exhibit zero-point motion in their lowest energy state. By coupling high-Q GHz mechanical oscillators with optical cavity photons, we achieve laser back-action cooling down to an average phonon occupancy of 0.85 ± 0.08.
These techniques pave the way for using mesoscopic mechanical resonators as quantum transducers, quantum memory elements, and precision sensors for quantum metrology.