An investigation into the manufacture and measurement of superconducting microwave devices

N. Sekiya, M. Mukaida, Atsushi SAITO +2 more

Eric T. Holland, Yaniv Jacob Rosen, Nicholas Materise +7 more

Investigations into the microwave surface impedance of superconducting resonators have led to the development of single photon counters that rely on kinetic inductance for their operation, while concurrent progress in additive manufacturing, “3D printing,” opens up a previously inaccessible design space for waveguide resonators. In this manuscript, we present results from the synthesis of these two technologies in a titanium, aluminum, vanadium (Ti-6Al-4V) superconducting radio frequency resonator which exploits a design unattainable through conventional fabrication means. We find that Ti-6Al-4V has two distinct superconducting transition temperatures observable in heat capacity measurements. The higher transition temperature is in agreement with DC resistance measurements, while the lower transition temperature, not previously known in the literature, is consistent with the observed temperature dependence of the superconducting microwave surface impedance. From the surface reactance, we extract a London penetration depth of 8 ± 3 μm—roughly an order of magnitude larger than other titanium alloys and several orders of magnitude larger than other conventional elemental superconductors.

Pierre HARTEMANN

Yongxin Song, Dominic Hagmann, Kieran Dalton +5 more

Microwave crosstalk poses a major challenge to scaling superconducting quantum devices as it introduces excess control errors. Although its magnitude and impact have been explored in various experimental settings, quantitative physical models capable of explaining measured crosstalk for a given device geometry remain scarce. Here, we address this gap by investigating microwave crosstalk in planar superconducting devices with crossovers. We identify two structures that can lead to strong crosstalk: a drive line routed in close proximity to another qubit, and a drive line crossing a qubit-qubit coupler using an air bridge. We design and characterize devices involving these structures and develop physical models that quantitatively explain the experimentally observed crosstalk. Based on these models, we discuss the design considerations for reducing microwave crosstalk. Our results provide practical guidance for low-crosstalk device layouts and establish a basis for the systematic investigation of weaker crosstalk mechanisms.

D. Quenter, T. Doderer, Rudolf Peter Huebener

We measured the spatial distribution of microwave fields and dissipative surface currents in various passive and active superconducting thin-film devices during their operation at a temperature of about 4 K. We used low-temperature scanning electron microscopy which offers a spatial resolution of about 1 μm and we present sample response models for interpreting the imaging results. Such investigations may have important consequences for the improvement of the design and preparation of superconducting thin-film microwave devices.

E. Carlsson