Sideband cooling of micromechanical motion to the quantum ground state

Abstract

It has been a long-standing goal in the field of cavity optomechanics to cool down a mechanical resonator to its motional quantum ground state by using light. Teufel et al. have now achieved just that with a recently developed system in which a drum-like flexible aluminium membrane is incorporated in a superconducting circuit. Ground-state cooling of a mechanical resonator was demonstrated for the first time last year in a different type of device, but the quantum states in this new device should be much longer lived, allowing direct tests of fundamental principles of quantum mechanics. As a first step, the authors perform a quantum-limited position measurement that is only a factor of about five away from the Heisenberg limit. The advent of laser cooling techniques revolutionized the study of many atomic-scale systems, fuelling progress towards quantum computing with trapped ions1 and generating new states of matter with Bose–Einstein condensates2. Analogous cooling techniques3,4 can provide a general and flexible method of preparing macroscopic objects in their motional ground state. Cavity optomechanical or electromechanical systems achieve sideband cooling through the strong interaction between light and motion5,6,7,8,9,10,11,12,13,14,15. However, entering the quantum regime—in which a system has less than a single quantum of motion—has been difficult because sideband cooling has not sufficiently overwhelmed the coupling of low-frequency mechanical systems to their hot environments. Here we demonstrate sideband cooling of an approximately 10-MHz micromechanical oscillator to the quantum ground state. This achievement required a large electromechanical interaction, which was obtained by embedding a micromechanical membrane into a superconducting microwave resonant circuit. To verify the cooling of the membrane motion to a phonon occupation of 0.34 ± 0.05 phonons, we perform a near-Heisenberg-limited position measurement3 within (5.1 ± 0.4)h/2π, where h is Planck’s constant. Furthermore, our device exhibits strong coupling, allowing coherent exchange of microwave photons and mechanical phonons16. Simultaneously achieving strong coupling, ground state preparation and efficient measurement sets the stage for rapid advances in the control and detection of non-classical states of motion17,18, possibly even testing quantum theory itself in the unexplored region of larger size and mass19. Because mechanical oscillators can couple to light of any frequency, they could also serve as a unique intermediary for transferring quantum information between microwave and optical domains20.