Max Planck team pushes a superconductor to its true limit with picosecond pulses

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Researchers led by Eryin Wang at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have measured something that has been very hard to reach. ScienceAlert's Ivan Farkas reports on the work, which is published in Nature Physics. The team probed the depairing limit of superconductors, the point where a current becomes strong enough to break apart the electron pairs that carry it without resistance

Normal measurements cannot reach that limit. When a strong steady current flows, swirling quantum vortices start moving within billionths of a second, and their movement creates resistance before the true limit is reached. In effect, the vortices get in the way of the measurement

The team's solution was speed. They fired 300 femtosecond green laser pulses at a switch that produced current pulses lasting only picoseconds. That is several orders of magnitude faster than the vortices can respond, even though they move at tens of kilometres per second. The current simply came and went before the vortices could cause trouble

The results revealed clear differences between materials. Niobium nitride, a conventional superconductor, stayed superconducting up to a sharp threshold and then failed suddenly. A copper oxide high temperature superconductor weakened gradually instead, because its energy gap depends on direction. Andrea Cavalleri says picosecond measurements can reveal properties like this gap symmetry

This is materials physics rather than quantum computing, but superconductors are at the heart of many quantum technologies, from superconducting qubits to sensitive detectors. A new way to probe their limits could help engineers design better materials. An outside expert called the method a powerful new tool

Could ultrafast measurements like this help design better superconducting qubits? And how important is basic materials research to the future of quantum technology?

A Major Superconductor 'Speed Limit' Was Just Brokenwww.sciencealert.com