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QI: Fachverband Quanteninformation

QI 19: Superconducting Electronics: Qubits I (joint session TT/QI)

QI 19.8: Vortrag

Mittwoch, 20. März 2024, 16:45–17:00, H 0104

Measuring and understanding quasiparticle effects in magnetic-field-resilient 3D transmons (Theory)Jonas Krause1, Christian Dickel1, Giampiero Marchegiani2, •Luc Janssen1, Gianluigi Catelani2,3, and Yoichi Ando11Physics Institute II, University of Cologne, Germany — 2Quantum Research Center, Technology Innovation Institute, UAE — 3JARA Institute for Quantum Information (PGI-11), Forschungszentrum Juelich, Germany

In this talk, we present the modeling of the charge-parity lifetime (τp) of a magnetic-field resilient 3D transmon [1]. Experimentally, the lifetime τp depends non-monotonically on the in-plane magnetic field. We explain this unexpected behavior within a generalized approach to quasiparticle decoherence. The model accounts for the transmon being a SQUID measured mainly at the bottom sweet spot and for the magnetic field tuning (Fraunhofer effect). It also incorporates effects of temperatures on the order of the transmon frequency. At zero field, the qubit frequency f01 is nearly resonant with the superconducting gap difference [2], so quasiparticle tunneling gives a sizable contribution to the parity-switching rate 1/τp. Increasing the in-plane field, f01 decreases and becomes detuned from the gap difference, causing the initial growth in τp, while photon-assisted qubit transitions increase producing the subsequent decay at higher fields. We show that τp and the qubit lifetime T1 can be consistently described by the model.

[1] J. Krause et al., Phys. Rev. Appl. 17 (2022) 034032

[2] G. Marchegiani et al., PRX Quantum 3 (2022) 040338

Keywords: quasiparticles; Fraunhofer effect; transmon

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