A Josephson Junction is a quantum device made of two superconductors separated by a thin insulating barrier. It allows for the flow of supercurrent, which is a current that can pass through the junction without any voltage applied. This phenomenon occurs due to the quantum tunneling of Cooper pairs, which are pairs of electrons that move together in a superconducting state. These junctions are essential in various applications, including quantum computing and superconducting qubits. They can also be used in sensitive magnetometers known as SQUIDs (Superconducting Quantum Interference Devices), which detect extremely weak magnetic fields.