Ultrastrong coupling regime of cavity QED with phase-biased flux qubits

J. Bourassa, J. M. Gambetta, A. A. Abdumalikov, Jr., O. Astafiev, Y. Nakamura, and A. Blais
Phys. Rev. A 80, 032109 – Published 15 September 2009

Abstract

We theoretically study a circuit QED architecture based on a superconducting flux qubit directly coupled to the center conductor of a coplanar waveguide transmission-line resonator. As already shown experimentally [A. A. Abdumalikov, Jr. et al., Phys. Rev. B 78, 180502(R) (2008)], the strong coupling regime of cavity QED can readily be achieved by optimizing the local inductance of the resonator in the vicinity of the qubit. In addition to yielding stronger coupling with respect to other proposals for flux qubit based circuit QED, this approach leads to a qubit-resonator coupling strength g which does not scale as the area of the qubit but is proportional to the total inductance shared between the resonator and the qubit. Strong coupling can thus be attained while still minimizing sensitivity to flux noise. Finally, we show that by taking advantage of the large kinetic inductance of a Josephson junction in the center conductor of the resonator can lead to coupling energies of several tens of percent of the resonator frequency, reaching the ultrastrong coupling regime of cavity QED where the rotating-wave approximation breaks down. This should allow an on-chip implementation of the Eβ Jahn-Teller model.

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  • Received 8 June 2009

DOI:https://doi.org/10.1103/PhysRevA.80.032109

©2009 American Physical Society

Authors & Affiliations

J. Bourassa1, J. M. Gambetta2, A. A. Abdumalikov, Jr.3, O. Astafiev3,4, Y. Nakamura3,4, and A. Blais1

  • 1Département de Physique et Regroupement Québécois sur les Matériaux de Pointe (RQMP), Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1
  • 2Department of Physics and Astronomy and Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
  • 3The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
  • 4NEC Nano Electronics Research Laboratories, Tsukuba, Ibaraki 305-8501, Japan

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Issue

Vol. 80, Iss. 3 — September 2009

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