Hybrid circuit cavity quantum electrodynamics with a micromechanical resonator

• Published in: Nature (London) Vol. 494; no. 7436; pp. 211 - 215
• Main Authors: Pirkkalainen, J.-M., Cho, S. U., Li, Jian, Paraoanu, G. S., Hakonen, P. J., Sillanpää, M. A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 14.02.2013; Nature Publishing Group
• Subjects: 639/766/119; 639/766/483/481; Classical and quantum physics: mechanics and fields; Electrodynamics; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Humanities and Social Sciences; letter; multidisciplinary; Observations; Optics; Phonons; Physics; Properties; Quantum information; Quantum optics; Quantum theory; Science; Spin coupling; South Korea; Finland; Micromechanical devices; Quantum electrodynamics; Quantum optics; Rabi oscillation; Hybrid systems; Stark effect; Quantum information; Quantum bit
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature11821

The properties of a quantum bit coupled to both a microwave cavity and a phonon mode in a micromechanical resonator suggest that such systems may allow for storage of quantum information in long-lived phonon states and read-out via microwave photons, with applications in quantum information control. A functional hybrid quantum system In the emerging field of quantum information technologies the next advances are expected to involve the combination of different types of quantum systems to harness various degrees of freedom. In this spirit, this paper describes the construction of a solid-state system combining a memory element, which has long-lived quantum states, with a quantum interface that offers easy read-out. This is achieved by coupling an artificial two-level atom in the form of a superconducting transmon qubit, to two different resonant cavities — a microwave resonator and a nanomechanical resonator. In the resulting hybrid device the low-frequency phonon cavity stores the quantum information from the qubit, and the electrical microwave resonator communicates with the outside world. Hybrid quantum systems with inherently distinct degrees of freedom have a key role in many physical phenomena. Well-known examples include cavity quantum electrodynamics 1 , trapped ions 2 , and electrons and phonons in the solid state. In those systems, strong coupling makes the constituents lose their individual character and form dressed states, which represent a collective form of dynamics. As well as having fundamental importance, hybrid systems also have practical applications, notably in the emerging field of quantum information control. A promising approach is to combine long-lived atomic states 2 , 3 with the accessible electrical degrees of freedom in superconducting cavities and quantum bits 4 , 5 (qubits). Here we integrate circuit cavity quantum electrodynamics 6 , 7 with phonons. Apart from coupling to a microwave cavity, our superconducting transmon qubit 8 , consisting of tunnel junctions and a capacitor, interacts with a phonon mode in a micromechanical resonator, and thus acts like an atom coupled to two different cavities. We measure the phonon Stark shift, as well as the splitting of the qubit spectral line into motional sidebands, which feature transitions between the dressed electromechanical states. In the time domain, we observe coherent conversion of qubit excitation to phonons as sideband Rabi oscillations. This is a model system with potential for a quantum interface, which may allow for storage of quantum information in long-lived phonon states, coupling to optical photons or for investigations of strongly coupled quantum systems near the classical limit.