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TT: Fachverband Tiefe Temperaturen

TT 50: Superconducting Electronics: SQUIDs, Qubits, Circuit QED II

TT 50.2: Vortrag

Donnerstag, 20. März 2025, 15:15–15:30, H36

Superconducting Pb stripline resonators: Role of coupling and applications in spectroscopy — Elies Ben Achour, Cenk Beydeda, Gabriele Untereiner, Martin Dressel, and •Marc Scheffler — 1. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany

Planar superconducting microwave resonators play an important role for various research directions in solid state physics and quantum technologies. Here we investigate superconducting lead (Pb) stripline resonators, which we probe at various harmonics between 0.7 GHz and 6 GHz and at temperatures between 1.5 K and 7 K.

We discuss on general grounds how the loaded quality factor Q_L of a planar microwave resonator made of a conventional superconductor should depend on temperature and frequency. We consider contributions due to dissipation by thermal quasiparticles Q_QP, due to residual dissipation Q_Res, and due to coupling Q_C. We focus on the role of coupling, and we compare resonators with different coupling capacitance. For the Pb resonators, we find a strongly frequency- and temperature-dependent Q_L, which we can describe by a lumped element model. For certain resonators at the lowest studied temperatures we observe a maximum in the frequency-dependent Q_L when Q_Res and Q_C match, and here the measured Q_L can exceed 2 × 10⁵.

We also present the application of such Pb stripline resonators for microwave spectroscopy at temperatures down to the mK range.

Keywords: superconducting microwave resonators; microwave spectroscopy; superconductivity of Pb; resonator quality factors