Persistent current switch

A chip having integrated thereon a persistent current switch for controlling a persistent current in a superconductor loop, the persistent current switch comprising:

• a piece of superconductor material that is part of the superconductor loop, and
• an illumination system that is configured to direct, using a light-guiding system, light onto the piece of superconductor material for influencing an electrical resistance of the piece of superconductor material,
• wherein the illumination system is configured such that the light impinging on the piece of superconductor material substantially does not heat the piece of superconductor material, and
• wherein the light impinging on the piece of superconductor material has a power of less than 1 μW.

A method for initiating a persistent current in a superconductor loop comprising a piece of superconductor material, the method comprising

• cooling the superconductor loop to below a critical temperature, and
• causing an illumination system to direct light onto the piece of superconductor material so that the piece of superconductor material does not adopt a superconducting state, wherein the illumination system is configured such that the light impinging on the piece of superconductor material substantially does not heat the piece of superconductor material and wherein the light impinging on the piece of superconductor material has a power of less than 1 μW, and
• energizing the superconductor loop comprising causing an electrical current through at least part of the superconductor loop, and
• while the electrical current is flowing through at least part of the superconductor loop, causing the illumination system to not direct light onto the piece of superconductor material so that the piece of superconductor material adopts the superconductive state so that the superconductor loop becomes superconductive and conducts the persistent current.