Researchers Used Quantum Vacuum Fluctuations to Raise a Superconductor's Critical Temperature by Up to 5.4%

A team at the University of Science and Technology of China has raised the critical temperature of a superconductor by up to 5.4% by placing it in a cavity that amplifies the quantum fluctuations of empty space, according to ScienceDaily. The critical temperature is the point below which the material loses all electrical resistance.

Empty space is never quite empty

Quantum theory says that even a perfect vacuum is full of virtual particles that constantly appear and vanish, and these vacuum fluctuations are normally far too weak to affect a material. The researchers used a terahertz split-ring resonator, a so-called dark cavity, to reshape the electromagnetic environment around the sample and amplify them.

A six-layer sample of niobium diselenide

The sample was a six-layer device of niobium diselenide (NbSe₂). Placed in the cavity, its critical temperature rose by up to 5.4%, and its critical current and critical magnetic field were also significantly higher near the superconducting transition, according to the Chinese Academy of Sciences, which calls it the first experimental demonstration of vacuum-fluctuation-enhanced superconductivity. The study appeared in Nature on August 19, and ScienceDaily covered it on September 30.

“This work shows that the background itself can become an actor.” — Professor Zeng, University of Science and Technology of China

A narrow result with open questions

The gain was measured in an ultrathin sample, and whether the approach scales to larger or other materials is unclear. The material still has to be kept at cryogenic temperatures, and the researchers explain the effect through the exchange of virtual photons between the material and the cavity, a mechanism that theory and experiment have not yet fully reconciled. What the result offers, the team says, is a way to control quantum materials without touching them.