Abstract
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 not affected 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 can not 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.
Highlights
Superconducting quantum circuits render a versatile platform for realizing circuit quantum electrodynamic systems
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
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
Summary
Superconducting quantum circuits render a versatile platform for realizing circuit quantum electrodynamic systems Such systems are used in various applications as they offer a flexible and engineerable tool kit to build a physical model system and employ it to study quantum mechanics in depth. Studies of the limits of magnetic field compatibility of standard Josephson junction (JJ) qubits are lacking. We study the coherence time under the influence of a magnetic field and discuss different field-dependent loss channels. This behavior is reproducible and symmetric with respect to the applied fields up to B = ±20 mT.
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