Josephsonjunctions
A Josephson junction is a quantum electronic device formed by two superconductors separated by a thin non-superconducting barrier, such as an insulating oxide or a normal metal. The barrier allows Cooper-pair tunneling, enabling a supercurrent to flow across the junction without any voltage drop up to a critical current I_c. The junction’s behavior is governed by its critical current, resistance in the normal state, and capacitance, and it acts as a nonlinear, non-dissipative element at low temperatures.
The key relations governing Josephson junctions are the Josephson equations. The direct current relation states that
In circuit models, the resistively and capacitively shunted junction (RCSJ) model describes the total current as
Josephson junctions come in several realizations, notably SIS (superconductor–insulator–superconductor) tunnel junctions and SNS (superconductor–normal–superconductor) weak links.
Applications span superconducting qubits (such as transmons and phase qubits), superconducting quantum interference devices (SQUIDs) for
Josephson junctions were predicted by Brian D. Josephson in 1962 and quickly confirmed experimentally, becoming foundational