Abstract
Cavity optomechanics is a tool to study the interaction between light and micromechanical motion. Here we observe optomechanical physics in a truly macroscopic oscillator close to the quantum ground state. As the mechanical system, we use a mm-sized piezoelectric quartz disk oscillator. Its motion is coupled to a charge qubit which translates the piezo-induced charge into an effective radiation–pressure interaction between the disk and a microwave cavity. We measure the thermal motion of the lowest mechanical shear mode at 7 MHz down to 30 mK, corresponding to roughly 102 quanta in a 20 mg oscillator. We estimate that with realistic parameters, it is possible to utilize the back-action cooling by the qubit in order to control macroscopic motion by a single Cooper pair. The work opens up opportunities for macroscopic quantum experiments.
Highlights
Small but macroscopic systems have been operated in the limit where they exhibit quantum mechanical behavior in some of their degrees of freedom
Detection of piezo thermal motion The benchmark of cavity optomechanics is the measurement of the motional sidebands due to thermally excited vibrations
Monolithic quartz oscillators are a promising platform for physical experiments
Summary
Small but macroscopic systems have been operated in the limit where they exhibit quantum mechanical behavior in some of their degrees of freedom. We propose and demonstrate a new cavity optomechanical scheme which involves a genuinely macroscopic mechanical oscillator relatively near the ground state (see figure 1). The quartz disk is used both as the mechanical oscillator, and as a substrate for fabricating a superconducting micro circuit The latter includes a charge qubit and a transmission line resonator. The work is based on a generic idea where a quantum two-level system, a qubit, mediates and enhances an interaction between a linear mechanical oscillator and a linear cavity. In a recent theory proposal [29], a related system was introduced where a coupling between a transmon qubit and piezo vibrations was mediated via a low-frequency cavity, but the optomechanical aspect was not considered
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