Interqubit coupling mediated by a high-excitation-energy quantum object

S. Ashhab, Antti Niskanen, K. Harrabi, Y. Nakamura, T. Picot, P. C. De Groot, C. J. P. M. Harmans, J. E. Mooij, Franco Nori

Research output: Contribution to journalArticleScientificpeer-review

75 Citations (Scopus)


We consider a system composed of two qubits and a high excitation energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well-known results concerning the leading term in the mediated coupling, we obtain an expression for the residual coupling between the qubits in the off state. We also analyze the entanglement between the three objects, i.e., the two qubits and the coupler, in the eigenstates of the total Hamiltonian. Although we focus on the application of our results to the recently realized parametric-coupling scheme with two qubits, we also discuss extensions of our results to harmonic-oscillator couplers, couplers that are near resonance with the qubits and multiqubit systems. In particular, we find that certain errors that are absent for a two-qubit system arise when dealing with multiqubit systems.
Original languageEnglish
Article number014510
JournalPhysical Review B: Condensed Matter and Materials Physics
Issue number1
Publication statusPublished - 2008
MoE publication typeA1 Journal article-refereed


  • qubits
  • coupling
  • eigenvalues
  • eigenfunctions
  • harmonic oscillators
  • quantum computing
  • quantum entanglement
  • Josephson devices
  • Josephson junction


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