Faithful conversion of propagating quantum information to mechanical motion

Abstract

Combining micrometre-sized mechanical resonators with superconducting quantum circuits, quantum information encoded with photons now can be converted to the motion of a macroscopic object. The motion of micrometre-sized mechanical resonators can now be controlled and measured at the fundamental limits imposed by quantum mechanics. These resonators have been prepared in their motional ground state1,2,3 or in squeezed states4,5,6, measured with quantum-limited precision7, and even entangled with microwave fields8. Such advances make it possible to process quantum information using the motion of a macroscopic object. In particular, recent experiments have combined mechanical resonators with superconducting quantum circuits to frequency-convert, store and amplify propagating microwave fields9,10,11,12. But these systems have not been used to manipulate states that encode quantum bits (qubits), which are required for quantum communication and modular quantum computation13,14. Here we demonstrate the conversion of propagating qubits encoded as superpositions of zero and one photons to the motion of a micromechanical resonator with a fidelity in excess of the classical bound. This ability is necessary for mechanical resonators to convert quantum information between the microwave and optical domains15,16,17 or to act as storage elements in a modular quantum information processor12,13,18. Additionally, these results are an important step towards testing speculative notions that quantum theory may not be valid for sufficiently massive systems19.