Sideband cooling of micromechanical motion to the quantum ground state

Abstract

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 techniques^3,4 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 motion^{5,6,7,8,9,10,11,12,13,14,15}. 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 motion^17,18, 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.