Exceptional points in tunable superconducting resonators

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Research units

  • Bayer Akad Wissensch, Walther Meissner Inst
  • NIST, National Institute of Standards & Technology (NIST) - USA
  • VTT Tech Res Ctr Finland Ltd, VTT Technical Research Center Finland, QTF Ctr Excellence
  • Univ Oulu, University of Oulu, Res Unit Nano & Mol Syst
  • VTT Technical Research Centre of Finland


Superconducting quantum circuits are potential candidates to realize a large-scale quantum computer. The envisioned large density of integrated components, however, requires a proper thermal management and control of dissipation. To this end, it is advantageous to utilize tunable dissipation channels and to exploit the optimized heat flow at exceptional points (EPs). Here, we experimentally realize an EP in a superconducting microwave circuit consisting of two resonators. The EP is a singularity point of the effective Hamiltonian, and corresponds to critical damping with the most efficient heat transfer between the resonators without back and forth oscillation of energy. We observe a crossover from underdamped to overdamped coupling across the EP by utilizing photon-assisted tunneling as an in situ tunable dissipative element in one of the resonators. These methods can be used to obtain fast dissipation, for example, for initializing qubits to their ground states. In addition, these results pave the way for thorough investigation of parity-time symmetry and the spontaneous symmetry breaking at the EP in superconducting quantum circuits operating at the level of single energy quanta.


Original languageEnglish
Article number134505
Pages (from-to)1-17
Number of pages17
JournalPhysical Review B
Issue number13
Publication statusPublished - 7 Oct 2019
MoE publication typeA1 Journal article-refereed

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