Quantum interference heats up

A thermal effect predicted more than 40 years ago was nearly forgotten, while a related phenomenon stole the limelight. Now experimentally verified, the effect could spur the development of heat-controlling devices. See Letter p.401 Thermal 'Josephson effect' demonstrated When two superconductors are connected by a weak link, they form a 'Josephson junction', in which the electrical current crossing the junction is determined by the quantum phase difference between the two superconductors. Such structures form the basis of superconducting quantum interference devices (SQUIDs), widely used for the measurement of small magnetic fields. Nearly 50 years ago, Kazumi Maki and Allan Griffin predicted a thermal analogue of the Josephson junction. Now Francesco Giazotto and María José Martínez-Pérez have realized such a device, in which the flow of heat between the superconductors is also dependent on the quantum phase difference. This effect could potentially be harnessed for the manipulation of heat in solid-state nanocircuits.