Response Current from Spin-Vortex-Induced Loop Current System to Feeding Current

The spin-vortex-induced loop current (SVILC) is a loop current generated around a spin-vortex formed by itinerant electrons. It is generated by a U(1) instanton created by the single-valued requirement of wave functions with respect to the coordinate, and protected by the topological number, "winding number". In a system with SVILCs, a macroscopic persistent current is generated as a collection of SVILCs. In the present work, we consider the situation where external currents are fed in the SVILC system and response currents are measured as spontaneous currents that flow through leads attached to the SVILC system. The response currents from SVILC systems are markedly different from the feeding currents in their directions and magnitude, and depend on the original current pattern of the SVILC system; thus, they may be used in the readout process in the recently proposed SVILC quantum computer, a quantum computer that utilizes SVILCs as qubits. We also consider the use of the response current to detect SVILCs.