Human: With regards to superconductivity and Josephson junctions, how do you know that a superconductor is superconducting? Assistant: 
You can test for superconductivity using a Josephson junction. A Josephson junction is a device that allows electric current to flow through a superconductor. It is made from two superconductors that are separated by a thin insulating barrier. When a voltage is applied across the junction, it can produce a current that flows indefinitely without any resistance.