Josephson effect

The Josephson effect is the counterintuitive current flow between two superconductors put in contact through a thin insulating layer without applied voltage. This is the so-called dc Josephson effect. Applying a voltage does not increase the dc current but turns it into an ac current, the so-called ac Josephson effect. This was predicted by Brian Josephson. This led to an interesting controversy with the pope of superconductivity, John Bardeen (Josephson was a Ph.D student by then)! The experimental verification led Bardeen to withdraw his criticisms.

The Josephson effect has important applications, most famously, the SQUID.

There are many variants, includin in bosonic systems, in which case one speaks of Bosonic Josephson Junctions. For the particular case of polaritons, I call those Polaritonic Josephson Junctions.

In the case of superfluid, for instance, the dc Josephson effect consists in a steady flow. Applying pressure leds to oscillations.

Important works:

• Possible new effects in superconductive tunnelling. B.D. Josephson in Phys. Lett. 1:251 (1962). — the seminal paper.
• Quantum Coherent Atomic Tunneling between Two Trapped Bose-Einstein Condensates. A. Smerzi, S. Fantoni, S. Giovanazzi and S. Shenoy in Phys. Rev. Lett. 79:4950 (1997). — double-well BEC system.
• Relation between ac Josephson effect and double-well Bose-Einstein-condensate oscillations. L. Radzihovsky and V. Gurarie in Phys. Rev. A 81:063609 (2010). — ac Josephson vs double well.

It is reviewed in Refs.