A classical oscillator takes the sideband route to the quantum ground state

Last year researchers at the University of California, Santa Barbara, demonstrated quantum effects in the motion of a macroscopic object. They achieved control of phonon energy states in a high-frequency (6-GHz) micromechanical oscillator after cryogenically cooling it to its ground state. Now, researchers at NIST , JILA, and the University of Colorado Boulder have employed photon–phonon coupling to reduce the vibrational energy of a low-frequency (10-MHz) micromechanical oscillator to the ground state. Their setup consisted of a flexible 15-μm-diameter aluminum membrane (the gray disk in the image) coupled to a superconducting microwave resonant circuit. After cooling their system to 15 mK, the researchers applied a microwave field at a frequency just below resonance, generating so-called sideband photons that effectively steal energy from membrane’s phonons. For applied photon numbers on the order of 10⁴, the oscillator’s motion enters the quantum regime, possessing on average less than one phonon. The researchers also detected the oscillator’s displacement with a precision that comes closest to date to the theoretical Heisenberg limit. The low-frequency system’s relatively longer phonon lifetimes and larger displacements could pave the way to storage of quantum information and generation of entangled states in mechanical systems. (J. D. Teufel et al., Nature, in press, doi: 10.1038/nature10261 .)—Jermey N. A. Matthews