Nanomechanical measurements of a superconducting qubit

• Published in: Nature (London) Vol. 459; no. 7249; pp. 960 - 964
• Main Authors: LaHaye, M. D., Suh, J., Echternach, P. M., Schwab, K. C., Roukes, M. L.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.06.2009; Nature Publishing Group
• Subjects: Analysis; Applied sciences; Design and construction; Electronics; Electrons; Energy; Exact sciences and technology; Humanities and Social Sciences; Influence; letter; Measurement; Mechanical properties; multidisciplinary; Nanotechnology; Properties; Quantum theory; Resonators; Science; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Silicon nitride; Superconducting devices; Superconductive devices; Vibration; United States; Frequency shift; Superconductor circuit; Quantum electrodynamics; Resonance frequency; Quantum interference; Cooper pair; Nanoelectromechanical device; Quantum bit
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature08093

Nanomechanical vibrations Fabricating tiny mechanical structures whose vibrational motion is purely quantum mechanical is a long-standing goal in physics, both from a fundamental perspective and in view of the applications that they could potentially enable. A parallel — and equally important — goal is the development of a scheme for observing and controlling such tiny motions. LaHaye et al . have made important progress in this direction by coupling a tiny mechanical resonator to a superconducting two-level quantum system (qubit). The state of the superconducting qubit can be measured through its influence on the vibrations of the resonator. Such a coupled device configuration should ultimately enable the preparation and measurement of exotic quantum states of motion. Fabricating tiny mechanical structures where the vibrational motion is purely quantum mechanical is a long-standing goal in physics, and a parallel goal is the development of a scheme for observing and controlling such tiny motions. By coupling a tiny mechanical resonator to a superconducting two-level quantum system (qubit), the state of the superconducting qubit can be measured through its influence on the vibrations of the resonator, a demonstration of nanomechanical read-out of quantum interference. The observation of the quantum states of motion of a macroscopic mechanical structure remains an open challenge in quantum-state preparation and measurement. One approach that has received extensive theoretical attention 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 is the integration of superconducting qubits as control and detection elements in nanoelectromechanical systems (NEMS). Here we report measurements of a NEMS resonator coupled to a superconducting qubit, a Cooper-pair box. We demonstrate that the coupling results in a dispersive shift of the nanomechanical frequency that is the mechanical analogue of the ‘single-atom index effect’ 14 experienced by electromagnetic resonators in cavity quantum electrodynamics. The large magnitude of the dispersive interaction allows us to perform NEMS-based spectroscopy of the superconducting qubit, and enables observation of Landau–Zener interference effects—a demonstration of nanomechanical read-out of quantum interference.