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TT: Fachverband Tiefe Temperaturen

TT 35: Superconducting Electronics: SQUIDs, Circuit QED

TT 35.13: Talk

Wednesday, March 20, 2024, 12:45–13:00, H 2053

Circuit QED with two PT-symmetric non-Hermitian qubits — •Mikhail Fistul¹, Grigory A. Starkov², and Ilya M. Eremin¹ — ¹Institut für Theoretische Physik III, Ruhr-Universität Bochum, Bochum, Germany — ²Theoretische Physik IV, Universität Würzburg, Würzburg, Germany

Motivated by recent experiments on single non-Hermitian superconducting [1] or spin-qubits [2] we present here a detailed analysis of an exmplary PT-symmetric circuit QED composed of two biased non-Hermitian qubits embedded in a lossless resonator [3]. We consider a resonant quantum circuit as |ω_r−Ω| ≪ ω_r, where Ω and ω_r are qubits and resonator frequencies, respectively, providing well-defined groups of quasidegenerate resonant states. Non-Hermiticity is introduced via a staggered gain/loss parameter, γ of individual qubits. Using the direct numerical diagonalization and the generalized Schrieffer-Wolff transformation we obtain the dependence of low-lying eigenspectrum on the interaction strength between a single qubit and the resonator, g, identify the PT-symmetry broken and unbroken phases, and exeptional points of second and third order. We also show that in PT-symmetric circuit QED non-Hermiticity mixes the "dark" and the "bright" states.

[1] W. Chen, M. Abbasi, Y. N. Joglekar, K. W. Murch, Phys. Rev. Lett. 127 (2021) 140504

[2] Y. Wu, et. al., Science 364 (2019) 878

[3] G. A. Starkov, M. V. Fistul, I. M. Eremin, arXiv:2309.09829

Keywords: PT-symmetric non-Hermitian qubits; circuit QED; quasidegenerate resonant states; exeptional points; dark and bright states