Fuhrer, Andreas

Date:   Thursday, November 19, 2020
Time:   10:00
Place:   scheduled Zoom meeting
Host:    Klaus Ensslin

From Qubits to Transistors and Back

Andreas Fuhrer
IBM Research Zurich

Superconducting qubits have seen tremendous improvements in coherence over the past decade facilitated by improved circuit design, fabrication processes, integrated packaging and dedicated control hardware. However, qubit coherence is known to depend on the microscopic environment near the Josephson junctions affected e.g. by molecular adsorbates or amorphous oxides. In order to study the impact of such defects we have developed a UHV-treatment system that allows us to clean the qubit chips using UV-light, ion milling or active reagents such as ammonia before loading the chips into the dilution refrigerator under vacuum. We show how these treatments affect qubit coherence and can be used to trim the qubit frequency of fixed frequency transmons after fabrication without affecting coherence. Furthermore, we demonstrate a compact superconducting switch that operates similar to a transistor by application of a gate voltage to a thin superconducting nanowire. We discuss the physics of the switching mechanism and potential applications of such devices for routing microwave signals at millikelvin temperatures with minimal power dissipation.
Finally, we show how silicon fin field-effect-transistors can be used as spin qubits. These devices were developed in a QSIT collaboration and will be further studied in the new NCCR SPIN.

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[5] S. Geyer et al., arXiv:2007.15400 (2020)