Device for eliminating trap of magnetic flux in a superconduction circuit

An apparatus for eliminating a magnetic flux from a superconducting circuit, said apparatus comprising:

• a substrate having an upper surface and a lower surface, said upper surface of the substrate having a region supporting the superconducting circuit;
• heating means, provided on the upper surface of the substrate, for inducing a temperature gradient in the superconducting circuit upon energization of the heating means;
• and
• driving means connected to the heating means for energizing the heating means.

An apparatus for eliminating a magnetic flux from a superconducting circuit said apparatus comprising:

• a substrate on which the superconducting circuit is formed;
• heating means comprising resistance heating elements, provided on the substrate;
• driving means connected to the heating means for energizing the heating means by supplying a drive current to each of the resistance heating elements in said heating means;
• wherein said heating means includes means for forming, upon energization of the resistance heating elements in the heating means, a region of normal conduction state characterized by a temperature that exceeds a critical temperature of the normal conduction-superconduction transition, in at least a part of the superconducting circuit, and for producing a minimized magnetic field upon the energization of the resistance heating elements, and
• wherein said driving means includes means for controlling energization of the heating means such that the region of normal conduction state moves consecutively and continuously to a periphery of said superconducting circuit.

A method for eliminating trapped magnetic flux from a superconducting circuit held at a temperature below a critical temperature of a normal conduction-superconduction transition, comprising the steps of:

• increasing the temperature of the superconducting circuit with a first temperature profile that changes periodically along the superconducting circuit in a predetermined direction thereof to form a plurality of normal conduction regions in which the temperature exceeds the critical temperature, said first temperature profile being so determined that said plurality of normal conduction regions are aligned in said predetermined direction and separated from each other by intervening superconducting regions, with a temperature peak formed in each of the normal conduction regions in correspondence to a first position defined in the superconducting circuit;
• decreasing the temperature of the superconducting circuit while maintaining the shape of the first temperature profile until the normal conduction regions substantially disappear, to collect a magnetic flux that has been trapped in the superconducting circuit in correspondence to the normal conduction region at said first position corresponding to the temperature peak caused by the first temperature profile;
• heating the superconducting circuit, after the step of decreasing the temperature of the superconducting circuit while maintaining the shape of the first temperature profile, with a second temperature profile that changes periodically along the superconducting circuit in the predetermined direction thereof to form a plurality of normal conduction regions in which the temperature exceeds the critical temperature, said second temperature profile being determined such that said plurality of normal conducting regions are aligned in said predetermined direction and separated from each other by intervening superconducting regions with a temperature peak formed in each of the normal conduction regions in correspondence to a second position of the superconducting circuit, said second temperature profile being so formed that the first position corresponding to the peak temperature of the first temperature profile is included in the normal conduction region that is formed by the second temperature profile;
• and
• decreasing the temperature of the superconducting circuit while maintaining the shape of the second temperature profile until the normal conduction regions formed as a result of the second temperature profile substantially disappear, to collect a magnetic flux that has been trapped in the superconducting circuit in correspondence to the normal conduction region at said second position corresponding to the temperature peak caused by the second temperature profile.