In superconductivity, a Josepshon vortex (after Brian Josephson from Cambridge University) is a vortex of supercurrent in a long Josephson junction (LJJ). The supercurrents circulate around the vortex center which is situated inside the Josephson barrier, unlike Abrikosov vortices in type-II superconductors, located in the superconducting condensate.

Abrikosov vortices in superconductors are characterized by normal cores where the superconducting condensate is destroyed on a scale of the superconducting coherence length ^[1]. The cores of Josephson vortices are more complex and depend on physical nature of the barrier. In Superconductor-Normal Metal-Superconductor (SNS) LJJ there exist measurable superconducting correlations induced in the barrier from two superconducting electrodes by proximity effect. Similarly to Abrikosov vortices in superconductors, Josephson vortices in SNS LJJ are characterized by normal cores in which the correlations are suppressed by destructive quantum interference and the normal state is recovered ^[2]. Unlike Abrikosov cores, the size of the Josephson ones is not fixed. Rather, it depends on supercurrents currents circulating in superconducting electrodes and applied magnetic field. In Superconductor-Insulator-Superconductor (SIS) LJJ the cores are not expected to have any specific spectral signature; they were not observed.

Usually the Josephson vortex's supercurrents create a magnetic field with the total flux equal to ${\displaystyle \Phi _{0))$—a single flux quantum. Such a vortex is therefore called a (Josephson) fluxon. It has been shown that under certain conditions a propagating Josephson vortex can initiate another Josephson vortex. This effect is called flux cloning (or fluxon cloning). Although a second vortex appears, this does not violate the conservation of the single flux quantum.

Recently^[when?] it was demonstrated by Hilgenkamp et al. that Josephson vortices in the so-called 0-π LJJ can also carry half of the flux quantum, and are called semifluxons.