CALL them the alternative Higgs hunters. A group of researchers has glimpsed a simulated version of the elusive particle in the behaviour of a handful of atoms on a lab bench.
In marked contrast to the high-energy collisions of the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland, where the real Higgs boson was made, the atoms in the new work were arranged in an ultracold, flat array. The work suggests that something like the Higgs mechanism, which is thought to have given mass to elementary particles in the hot, early universe, operates in a range of physical situations. Similar physics could even be at play in the alternate universes that pop up in some versions of string theory, if they turn out to exist.
"It says a lot about the unity of physics, and how this is a deep and fundamental concept that appears in many different physical situations," says Subir Sachdev of Harvard University, who studies ultracold systems but was not involved in the new work.
The Higgs boson that appears in the standard model of particle physics is the calling card of the omnipresent Higgs field. The field cannot be observed, but high-energy protons smashing into each other inside the LHC can "shake" the field and produce Higgs bosons.
Thanks to the wave-particle duality of quantum mechanics, Higgs bosons can also be thought of as waves that appear in the Higgs field when it is shaken. This idea allowed a team led by Immanuel Bloch of the Max-Planck Institute of Quantum Optics in Munich, Germany, to test whether the Higgs mechanism could be at play in a cold, two-dimensional system.
The team trapped about 500 rubidium atoms in a vacuum chamber and cooled them to a few billionths of a degree above absolute zero. Then the team exposed the atoms to a pattern of criss-crossed laser beams. To the atoms, the pattern looked like an egg carton: the bright areas were wells where the atoms tended to settle, and the dark areas were barriers in between.
When the laser light was intense, the wells were deep, and each held one atom. But when the light was fainter, the wells grew shallow, allowing the atoms to tunnel between them, then spread out and form a single quantum entity. At the boundary between those two phases, the equations governing the atoms are the same as those that govern the Higgs field. So the transition from one atom per well to the single quantum state is analogous to shaking the Higgs field.
When the team brightened and then dimmed the lasers, the atoms collectively made a wave. This "Higgs mode" was the equivalent of the Higgs boson in their simulated Higgs field, report the team (Nature, DOI: 10.1038/nature11255). "We are calling it Higgs in Flatland," says Bloch, referring to the 1884 novella set in a two-dimensional world
But the two-dimensional Higgs mode could have real effects. For example, some suggest that the mathematics behind such flat systems could come into play in versions of string theory. "It's remarkable how there's this beautiful experiment here, and the LHC, all coming about at the same time," adds Sachdev.
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