# Transmon qubit in a magnetic field: Evolution of coherence and transition frequency

Schneider, Andre; Wolz, Tim; Pfirrmann, Marco; Spiecker, Martin; Rotzinger, Hannes; Ustinov, Alexey V.; Weides, Martin

##### Abstract (englisch):
We report on spectroscopic and time-domain measurements on a fixed-frequency concentric transmon qubit in an applied in-plane magnetic field to explore its limits of magnetic field compatibility. We demonstrate quantum coherence of the qubit up to field values of $B=40\,\mathrm{mT}$, even without an optimized chip design or material combination of the qubit. The dephasing rate $\Gamma_\varphi$ is shown to be unaffected by the magnetic field in a broad range of the qubit transition frequency. For the evolution of the qubit transition frequency, we find the unintended second junction created in the shadow angle evaporation process to be non-negligible and deduce an analytic formula for the field-dependent qubit energies. We discuss the relevant field-dependent loss channels, which cannot be distinguished by our measurements, inviting further theoretical and experimental investigation. Using well-known and well-studied standard components of the superconducting quantum architecture, we are able to reach a field regime relevant for quantum sensing and hybrid applications of magnetic spins and spin systems.

 Zugehörige Institution(en) am KIT Physikalisches Institut (PHI) Publikationstyp Zeitschriftenaufsatz Publikationsdatum 04.09.2019 Sprache Englisch Identifikator ISSN: 2643-1564 KITopen-ID: 1000117440 Erschienen in Physical review research Band 1 Heft 2 Seiten 023003 Schlagwörter qubit, quantum bit, quantum sensing Relationen in KITopen Verweist aufQuantum Sensing Experiments with Superconducting Qubits. Schneider, Andre (2020) Hochschulschrift (1000117442)
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