Semifluxon molecule under control

TL;DR

This paper demonstrates the controlled manipulation of a semifluxon molecule in a long Josephson junction, showing potential for use as bits or qubits in classical and quantum electronics.

Contribution

It introduces a method to control and switch the states of a semifluxon molecule, advancing the use of semifluxons in digital electronic applications.

Findings

Controlled switching between up-down and down-up states achieved

Flux states measured by on-chip SQUIDs

Demonstrates potential for semifluxons as digital bits or qubits

Abstract

Josephson junctions with a phase drop pi in the ground state allow to create vortices of supercurrent carrying only half of the magnetic flux quantum Phi_0~2.07*10^-15 Wb. Such semifluxons have two-fold degenerate ground states denoted up (with flux +Phi_0/2 and supercurrent circulating clockwise) and down (with flux -Phi_0/2 and supercurrent circulating counterclockwise). We investigate a molecule consisting of two coupled semifluxons in a 0-pi-0 long Josephson junction. The fluxes (polarities) of semifluxons are measured by two on-chip SQUIDs. By varying the dc bias current applied to the 0-pi-0 junction, we demonstrate controllable manipulation and switching between two states, up-down and down-up, of a semifluxon molecule. These results provide a major step towards employing semifluxons as bits or qubits for classical and quantum digital electronics.