Experiment Provides Further Insights into Higgs Boson Physics

A new experiment by physicists at the University of Bonn, Germany, has achieved a Higgs-like state in a system composed of ultracold atoms.

Excitation spectra of the Higgs-like state: (a) excitation spectra of the Higgs-like state for different interaction strengths, 1/(kFa); the different levels of background condensate fraction are due to the different 1/(kFa); the solid lines shows the Gaussian fit to the high-frequency side of the spectra; the error bars show the standard deviation of approximately four measurements; (b) time-of-flight image of the condensate with the thermal background subtracted at 1/(kFa)=−0.43; rings indicate momentum intervals of 0.02kF; (c) momentum-resolved analysis of the Higgs excitation inside the condensate by averaging the optical density in the color-coded rings in (b) for different modulation frequencies; the resonance occurs at the same modulation frequency for all momenta. Image credit: Behrle et al, doi: 10.1038/s41567-018-0128-6.

For their experiment, Professor Michael Köhl from the Physics Institute at the University of Bonn and co-authors used a superconducting gas made of ultracold lithium atoms.

“At a certain temperature, the state of the gas changes abruptly: it becomes a superconductor that conducts a current without any resistance,” they explained.

“The lithium gas changes to a more orderly state at its phase transition. This includes the formation of so-called Cooper pairs, which are combinations of two atoms that behave like a single particle to the outside.”

“Cooper pairs behave fundamentally differently from individual atoms: they move together and can do so without scattering on other atoms or pairs. This is the reason for the superconductivity. But what happens when you try to excite the pairs?”

The physicists then illuminated the gas with microwave radiation.

“This allowed us to create a state in which the pairs start to vibrate and the quality of the superconductivity therefore oscillated very quickly: one moment the gas was a good superconductor, the next a bad one,” Professor Köhl said.

This common oscillation of the Cooper pairs corresponds to the Higgs boson discovered by CERN’s CMS and ATLAS experiments in 2012.

“Our experiment is also interesting for another reason,” the researchers said.

“It shows a way to switch superconductivity on and off very quickly. Superconductors normally try to remain in their conductive state for as long as possible.”

“They can be dissuaded by heating, but this is a very slow process. The experiments show that in principle this can also be over a thousand times faster. This insight may open up completely new applications for superconductors.”

The team’s work appears in the journal Nature Physics.

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A. Behrle et al. Higgs mode in a strongly interacting fermionic superfluid. Nature Physics, published online May 21, 2018; doi: 10.1038/s41567-018-0128-6