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Nature 431, 159-162 (9 September 2004) | doi:10.1038/nature02831; Received 25 May 2004; Accepted 5 July 2004

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Coherent dynamics of a flux qubit coupled to a harmonic oscillator

I. Chiorescu1,4, P. Bertet1, K. Semba1,2, Y. Nakamura1,3, C. J. P. M. Harmans1 & J. E. Mooij1

  1. Quantum Transport group, Kavli Institute of NanoScience, Delft University of Technology and Delft Institute for Micro Electronics and Submicron Technology (DIMES), Lorentzweg 1, 2628 CJ, Delft, The Netherlands
  2. NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi 243-0198, Japan
  3. NEC Fundamental Research Laboratories, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan
  4. Present address: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA

Correspondence to: I. Chiorescu1,4J. E. Mooij1 Email: chiorescu@pa.msu.edu
Email: mooij@qt.tn.tudelft.nl

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In the emerging field of quantum computation1 and quantum information, superconducting devices are promising candidates for the implementation of solid-state quantum bits (qubits). Single-qubit operations2, 3, 4, 5, 6, direct coupling between two qubits7, 8, 9, 10 and the realization of a quantum gate11 have been reported. However, complex manipulation of entangled states—such as the coupling of a two-level system to a quantum harmonic oscillator, as demonstrated in ion/atom-trap experiments12, 13 and cavity quantum electrodynamics14—has yet to be achieved for superconducting devices. Here we demonstrate entanglement between a superconducting flux qubit (a two-level system) and a superconducting quantum interference device (SQUID). The latter provides the measurement system for detecting the quantum states; it is also an effective inductance that, in parallel with an external shunt capacitance, acts as a harmonic oscillator. We achieve generation and control of the entangled state by performing microwave spectroscopy and detecting the resultant Rabi oscillations of the coupled system.

  1. Quantum Transport group, Kavli Institute of NanoScience, Delft University of Technology and Delft Institute for Micro Electronics and Submicron Technology (DIMES), Lorentzweg 1, 2628 CJ, Delft, The Netherlands
  2. NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi 243-0198, Japan
  3. NEC Fundamental Research Laboratories, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan
  4. Present address: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA

Correspondence to: I. Chiorescu1,4J. E. Mooij1 Email: chiorescu@pa.msu.edu
Email: mooij@qt.tn.tudelft.nl