Faithful conversion of propagating quantum information to mechanical motion

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 state(1-3) or in squeezed states(4-6), measured with quantum-limited precision(7), and even entangled with microwave fields(8). 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 fields(9-12). But these systems have not been used to manipulate states that encode quantum bits (qubits), which are required for quantum communication and modular quantum computation(13,14). 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 domains(15-17) or to act as storage elements in a modular quantum information processor(12,13,18) . Additionally, these results are an important step towards testing speculative notions that quantum theory may not be valid for sufficiently massive systems(19).