Journal Article

Preparation and detection of a mechanical resonator near the ground state of motion

Hertzberg, J. B., Ndukum, T., Rocheleau, T., Schwab, K. C., Macklin, C., Clerk, A. A.

2010

Overview

Closer to an exotic goal Placing a macroscopic object in its quantum-mechanical ground state of motion is an exciting experimental prospect. If achieved, it should reveal counter-intuitive physical behaviour — such as the existence of the system in two locations simultaneously. Rocheleau et al . come tantalizingly close to this goal. They have cooled a nanomechanical resonator to a point where the probability of it residing in its motional ground state is 0.21 (which in itself should be sufficient to enable direct measurement of some anticipated quantum phenomena), and have identified the experimental hurdles that need to be overcome to push the system more fully into this exotic quantum regime. Placing a macroscopic object in its quantum-mechanical ground state of motion is an exciting experimental target that should reveal counterintuitive physical behaviour — such as the existence of states in which the mechanical system is located in two places simultaneously. A nanomechanical resonator is now cooled to a point where the probability of its residing in the quantum ground state of motion is 0.21; this level of cooling should allow a series of fundamental quantum mechanical observations. Cold, macroscopic mechanical systems are expected to behave contrary to our usual classical understanding of reality; the most striking and counterintuitive predictions involve the existence of states in which the mechanical system is located in two places simultaneously. Various schemes have been proposed to generate and detect such states 1 , 2 , and all require starting from mechanical states that are close to the lowest energy eigenstate, the mechanical ground state. Here we report the cooling of the motion of a radio-frequency nanomechanical resonator by parametric coupling to a driven, microwave-frequency superconducting resonator. Starting from a thermal occupation of 480 quanta, we have observed occupation factors as low as 3.8 ± 1.3 and expect the mechanical resonator to be found with probability 0.21 in the quantum ground state of motion. Further cooling is limited by random excitation of the microwave resonator and heating of the dissipative mechanical bath. This level of cooling is expected to make possible a series of fundamental quantum mechanical observations including direct measurement of the Heisenberg uncertainty principle and quantum entanglement with qubits.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: Analysis / Applied sciences / Circuit properties / Cooling / Electric, optical and optoelectronic circuits / Electronics / Exact sciences and technology / Ground state / Humanities and Social Sciences / letter / Mechanical properties / Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits / multidisciplinary / Quantum theory / Resonators / Science / Science (multidisciplinary) / Superconductors / Thermal properties