Detection of the phase shift from a single quantized superconducting vortex

TL;DR

This paper demonstrates that a single superconducting vortex induces a measurable phase shift in a Josephson junction, enabling controllable quantum state switching and potential applications as a tunable phase element in quantum electronics.

Contribution

It introduces a method to detect vortex-induced phase shifts using Josephson interferometry, revealing a controllable 0-pi state transition caused by a vortex.

Findings

Vortex induces a Josephson phase shift equal to its polar angle.

Close vortex induces a pi-step in the Josephson phase difference.

Vortex acts as a tunable phase battery for quantum devices.

Abstract

An Abrikosov vortex in a superconductor carries a flux quantum, Phi_0 = hc/2e, localized at its center, but induces a global 2pi phase rotation in the superconducting condensate. This long-range gauge field outside the area pierced by a magnetic field is due to the Aharonov-Bohm effect, which is a non-classical phenomenon that illustrates the significance of potentials rather than forces in quantum mechanics. In the London gauge, the phase of the condensate is given by the polar angle around the vortex. Here we raise the question whether this phase shift could be detected by means of Cooper pair interferometry using Josephson junctions as phase-sensitive detectors. We introduce a single Abrikosov vortex into a superconducting lead with a detector junction made at the edge of the lead. We observe that the vortex induces a Josephson phase shift equal to the polar angle of the vortex within the junction length. When the vortex is close to the junction it induces a pi-step in the Josephson phase difference, leading to a controllable and reversible switching of the junction into the 0 - pi state. This in turn results in an unusual Phi_0/2 quantization of the flux in the junction. The vortex may hence act as a tunable "phase battery" for quantum electronics.