Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session S48: Superconducting Qubits: Quasiparticles
8:00 AM–10:36 AM,
Thursday, March 7, 2024
Room: 200E
Sponsoring
Units:
DQI DCMP DMP
Chair: Jaseung Ku, Syracuse University
Abstract: S48.00010 : Quasiparticle effects in magnetic-field-resilient 3D transmons (Part 2 - Theory)*
9:48 AM–10:00 AM
Presenter:
Giampiero Marchegiani
(Technology Innovation Institute)
Authors:
Giampiero Marchegiani
(Technology Innovation Institute)
Jonas Krause
(University of Cologne)
Christian Dickel
(University of Cologne)
Lucas M Janssen
(University of Cologne)
Gianluigi Catelani
(Technology Innovation Institute)
Yoichi Ando
(University of Cologne)
We measure a non-monotonic evolution of τp with in-plane magnetic field, increasing up to 150 mT, followed by a decrease at higher fields (see Part 1). We understand this exotic behavior with a generalized approach to quasiparticle decoherence. The model accounts for the transmon being a SQUID measured mainly at the bottom sweetspot 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 resonant quasiparticle tunneling gives a sizable contribution to the parity-switching rate τp-1. With a higher magnetic field, f01 decreases and gets detuned from the gap difference, causing the initial increase of τp, while photon-assisted qubit transitions increase producing the subsequent decay at higher fields. At the highest field (300-400 mT) τp decays faster than the model predicts. We show that τp , the qubit lifetime T1, as well as residual transmon excitation due to quasiparticles can all be consistently described.
[1] J. Krause et al., Phys. Rev. Appl. 17, 034032 (2022)
[2] G. Marchegiani et al., PRX Quantum 3, 040338 (2022)
*This work was supported by the DFG through Cluster of Excellence ML4Q (EXC 2004/1 - 390534769)
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