Abstract: Topological superconductor devices with gates formed in two gate layers are described. A topological superconductor device includes a superconducting wire having a first junction near a first end of the superconducting wire and a second junction near a second end, opposite to the first end. The topological superconductor device further includes: (1) a first side-plunger gate and a second-side plunger gate formed in a first gate layer of the topological superconductor device, (2) a middle-plunger gate formed in the first gate layer of the topological superconductor device, (3) a first cutter gate formed in a second layer, different from the first layer, of the topological superconductor device, and (4) a second cutter gate formed in the second layer of the topological superconductor device. The plunger gates are operable to tune respective sections of the superconducting wire and the cutter gates are operable to open and close the respective junctions.

Abstract: A method to evaluate a semiconductor-superconductor heterojunction for use in a qubit register of a topological quantum computer includes (a) measuring one or both of a radio-frequency (RF) junction admittance of the semiconductor-superconductor heterojunction and a sub-RF conductance including a non-local conductance of the semiconductor-superconductor heterojunction, to obtain mapping data and refinement data; (b) finding by analysis of the mapping data one or more regions of a parameter space consistent with an unbroken topological phase of the semiconductor-superconductor heterojunction; and (c) finding by analysis of the refinement data a boundary of the unbroken topological phase in the parameter space and a topological gap of the semiconductor-superconductor heterojunction for at least one of the one or more regions of the parameter space.

Abstract: A system comprises a substrate having a planar surface; a first magnet configured to apply a first magnetic field parallel to the planar surface; a circuit arranged on the planar surface; and a superconducting quantum interference device, SQUID, operably linked to the circuit. The SQUID comprises a Josephson junction arranged in a superconductive loop. The superconductive loop includes a portion which extends perpendicular to the planar surface and is orientated such that the SQUID is tuneable by the first magnet. By allowing the SQUID to be tuned using a magnetic field which is parallel to the planar surface, a reduction in flux noise may be achieved. Also provided are a method of operating a SQUID, and a SQUID.

Abstract: A parametric amplifier for amplifying an input signal includes a resonator comprising a Josephson junction. The Josephson junction comprises a first superconductor component, a second superconductor component and a semiconductor component. The semiconductor component is configured to enable coupling of the first and second superconductor components. The parametric amplifier further comprises a gate electrode configured to apply an electrostatic field to the semiconductor component of the Josephson junction for tuning the parametric amplifier. Such parametric amplifiers are useful for amplifying signals in the microwave frequency range. Tuning the junction by electrostatic gating may allow for improved scalability compared to tuning using magnetic flux. Also provided are the use of the parametric amplifier to amplify a signal; and a method of amplifying a signal.

Abstract: A method to evaluate a semiconductor-superconductor heterojunction for use in a qubit register of a topological quantum computer includes (a) measuring one or both of a radio-frequency (RF) junction admittance of the semiconductor-superconductor heterojunction and a sub-RF conductance including a non-local conductance of the semiconductor-superconductor heterojunction, to obtain mapping data and refinement data; (b) finding by analysis of the mapping data one or more regions of a parameter space consistent with an unbroken topological phase of the semiconductor-superconductor heterojunction; and (c) finding by analysis of the refinement data a boundary of the unbroken topological phase in the parameter space and a topological gap of the semiconductor-superconductor heterojunction for at least one of the one or more regions of the parameter space.

Abstract: A method to evaluate a semiconductor-superconductor heterojunction for use in a qubit register of a topological quantum computer includes measuring a radio-frequency (RF) junction admittance of the semiconductor-superconductor heterojunction to obtain mapping data; finding by analysis of the mapping data one or more regions of a parameter space consistent with an unbroken topological phase of the semiconductor-superconductor heterojunction; measuring a sub-RF conductance including a non-local conductance of the semiconductor-superconductor heterojunction in each of the one or more regions of the parameter space, to obtain refinement data; and finding by analysis of the refinement data a boundary of the unbroken topological phase in the parameter space and a topological gap of the semiconductor-superconductor heterojunction for at least one of the one or more regions of the parameter space.

Abstract: A method to evaluate a semiconductor-superconductor heterojunction for use in a qubit register of a topological quantum computer includes measuring a radio-frequency (RF) junction admittance of the semiconductor-superconductor heterojunction to obtain mapping data; finding by analysis of the mapping data one or more regions of a parameter space consistent with an unbroken topological phase of the semiconductor-superconductor heterojunction; measuring a sub-RF conductance including a non-local conductance of the semiconductor-superconductor heterojunction in each of the one or more regions of the parameter space, to obtain refinement data; and finding by analysis of the refinement data a boundary of the unbroken topological phase in the parameter space and a topological gap of the semiconductor-superconductor heterojunction for at least one of the one or more regions of the parameter space.