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Nanomechanical measurements of a superconducting qubit


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 attention1,2,3,4,5,6,7,8,9,10,11,12,13 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.

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Figure 1: Device and measurement circuit description, and driven frequency response of the nanoresonator.
Figure 2: Nanoresonator frequency shift as function of CPB parameters VCPB and Φ/Φo.
Figure 3: Spectroscopy of the CPB using the nanomechanical frequency shift as a probe.
Figure 4: Landau–Zener interferometry using the nanomechanical frequency shift as a probe.


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The authors would like to thank T. Duty, C. Wilson, G. Milburn, A. Doherty, E. Babourina-Brooks, A. Armour, A. Clerk and I. Bargatin for discussions; S. Stryker and A. Sears for assistance in constructing the measurement apparatus; and R. E. Muller for electron beam lithography. K.C.S. acknowledges support from the US National Science Foundation (DMR-0804567) and the Foundational Questions Institute (RFP2-08-27). M.D.L. acknowledges support from the Center for the Physics of Information, California Institute of Technology. Part of the research described in this publication was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the US National Aeronautics and Space Administration.

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Correspondence to M. L. Roukes.

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LaHaye, M., Suh, J., Echternach, P. et al. Nanomechanical measurements of a superconducting qubit. Nature 459, 960–964 (2009).

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