Abstract: The disclosure relates to a trench capacitor device for a superconducting electronic circuit. The trench capacitor device includes a substrate, a first capacitor electrode, and a second capacitor electrode, each electrode including a superconductor and extending into the substrate. The first electrode is circumferentially enclosed by the second electrode such that an inwardly facing surface of the second electrode faces an outwardly facing surface of the first electrode.

Abstract: A method for forming a modified resonator is provided. In one aspect, the method includes obtaining a resonator on top of a substrate, thereby forming an interface area between a bottom surface of the resonator and a top surface of the substrate. The resonator can include niobium or tantalum. The method also includes contacting the resonator and the substrate with a liquid acidic etching solution selected so as to have a higher etch rate towards the substrate than towards the resonator and a nonzero etch rate towards the resonator.

Abstract: Superconducting solder bumps are produced on a qubit substrate by electrodeposition. The substrate comprises qubit areas, and superconducting contact pads connected to the qubit areas. First a protection layer is formed on the substrate, and patterned so as to cover at least the qubit areas. Then one or more thin layers are deposited conformally on the patterned protection layer, the thin layers comprising at least a non-superconducting layer suitable for acting as a seed layer for the electrodeposition of the solder bumps. The seed layer is removed locally in areas which lie within the surface area of respective contact pads. This is done by producing and patterning a mask layer, so that openings are formed therein, and by removing the seed layer from the bottom of the openings. The solder bumps are formed by electrodeposition of the solder material on the bottom of the openings. After the formation of the solder bumps, the seed layer and the protection layer are removed.

Abstract: The disclosure relates to a trench capacitor device for a superconducting electronic circuit. The trench capacitor device includes a substrate, a first capacitor electrode, and a second capacitor electrode, each electrode including a superconductor and extending into the substrate. The first electrode is circumferentially enclosed by the second electrode such that an inwardly facing surface of the second electrode faces an outwardly facing surface of the first electrode.

Abstract: A method for forming a modified resonator is provided. In one aspect, the method includes obtaining a resonator on top of a substrate, thereby forming an interface area between a bottom surface of the resonator and a top surface of the substrate. The resonator can include niobium or tantalum. The method also includes contacting the resonator and the substrate with a liquid acidic etching solution selected so as to have a higher etch rate towards the substrate than towards the resonator and a nonzero etch rate towards the resonator.