Nature 508, 369–372 (2014)

The resistance-free transport offered by superconductors is not so easily exploited by alternating currents. Radio waves can induce quasiparticle excitations, above the superconducting gap, which open dissipation channels. Incorporating these quasiparticles in a description of the tunnelling current across a Josephson junction still generates controversy despite the success of Josephson's theoretical predictions.

Ioan Pop and colleagues have now shown that controlling the phase across a Josephson junction allows the losses caused by quasiparticles to be suppressed. This idea, which effectively uses electron-like and hole-like quasiparticles to cancel each other out, confirms one of Josephson's original predictions. By introducing a π phase difference across a junction, Pop et al. showed that this cancelling technique increased the relaxation time of their superconductor-based qubit by more than an order of magnitude.

This method not only has technological implications, extending beyond quantum information processing, but also provides a powerful tool for characterizing the quasiparticle-induced dissipation mechanism in Josephson junctions.