Something from nothing: Physicists model vacuum tunnelling in a 2D superfluid

(Press-News.org) In 1951, physicist Julian Schwinger theorized that by applying a uniform electrical field to a vacuum, electron-positron pairs would be spontaneously created out of nothing, through a phenomenon called quantum tunnelling.

The problem with turning the matter-out-of-nowhere theory into Star Trek replicators or transporters? Enormously high electric fields would be required—far beyond the limits of any direct physical experiments. 

As a result, the aptly named Schwinger effect has never been seen. 

Now theoretical physicists at the University of British Columbia (UBC) have described a parallel effect in a more manageable system. In their model, they substitute a thin film of superfluid helium for the vacuum, and the background flow of the superfluid for the massive electrical field.

“Superfluid Helium-4 is a wonder. At a few atomic layers thick it can be cooled very easily to a temperature where it's basically in a frictionless vacuum state,” explains Dr. Philip Stamp, a theorist at UBC working on condensed matter and quantum gravity, and author of the new findings published today in PNAS. 

“When we make that frictionless vacuum flow, instead of electron-positron pairs appearing, vortex/anti-vortex pairs will appear spontaneously, spinning in opposite directions to one another.”

In the paper, Dr. Stamp and UBC colleague Michael Desrochers outline the theory and the mathematics behind it—mapping out a detailed approach to conducting a direct experiment. 

Vacuum tunneling is a process of keen interest in quantum mechanics and quantum field theory. In quantum theory, vacuums aren’t empty, they’re filled with fluctuating fields that can lead to the temporary appearance and disappearance of virtual particles. 

“We believe the Helium-4 film provides a nice analog to several cosmic phenomena,” adds Dr. Stamp. “The vacuum in deep space, quantum black holes, even the very beginning of the Universe itself. And these are phenomena we can’t ever approach in any direct experimental way.” 

However, Dr. Stamp emphasizes that the real interest of the work may lie less in an analogs – which always have limitations – and more in the way it alters our understanding of superfluids, and of phase transitions in two-dimensional systems. 

“These are real physical systems in their own right, not analogs. And we can do experiments on these.”

At the mathematical level, the researchers needed several breakthroughs to make the theory work. For example, previous researchers looking at vortices in superfluids have treated the vortex mass as an unchanging constant. Dr. Stamp and Desrochers showed that this mass will vary dramatically as the vortices move, fundamentally changing our understanding of vortices in both fluids and the early universe. 

"It’s exciting to understand how and why the mass varies, and how this affects our understanding of quantum tunnelling processes, which are ubiquitous in physics, chemistry and biology," says Desrochers.

Stamp also argues that the same mass variability will occur with electron-positron pairs in the Schwinger effect, thence modifying Schwinger’s theory, in a kind of ‘revenge of the analog’.

The work was supported by the National Science and Engineering Research Council.

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