QUROPE Quantum Information Processing and Communication in Europe

I. M. Pop, K. Geerlings, G. Catelani, R. J. Schoelkopf, L.I. Glazman, M. H. Devoret Nature 508, 369–372 (2014)

While superconducting qubits represent a promising technological platform for quantum computation, a good enough control of the mechanisms of decoherence and dissipation in these systems is still an experimental challenge. In particular, Josephson’s key theoretical prediction that quasiparticle dissipation should vanish in transport through a junction when the phase difference across the junction is π has never been observed.

In their work, Pop and co-workers report the experimental observation of this quantum coherent suppression of the quasiparticle dissipation across a Josephson junction. The suppression of dissipation, despite the presence of lossy quasiparticle excitations above the superconducting gap, provides a powerful tool for minimizing decoherence in quantum electronic systems and could be directly exploited in quantum information experiments with superconducting quantum bits. In particular, coherence times, which have always been determined by extrinsic factors, are now limited by physics intrinsic to Josephson tunneling, achieving relaxation times well above 1  ms in artificial atoms (an increase by two orders of magnitude from previous works).