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Emission spectrum of helium.

The emission spectrum of helium. Laser pulses can expose quantum aspects of pairs of helium atoms. Credit: Dept. of Physics, Imperial College/SPL

Atomic and molecular physics

Taking tenuous helium molecules for a spin

Zapping helium ‘dimers’ with lasers allows a glimpse into a fleeting relationship.

Helium atoms are stand-offish, rarely interacting with atoms of other elements or with one another. But physicists know that helium atoms cooled close to absolute zero can be coaxed into forming fragile pairs, or dimers, of a particularly quantum nature.

To better understand these tentative dance partners, Maksim Kunitski and Reinhard Dörner at Goethe University in Frankfurt, Germany, and their colleagues have given helium dimers a ‘kick’ by exposing them to a strong laser field. The team shot a laser pulse at helium dimers, imparting angular momentum to the pairs. A second, shorter laser pulse quickly knocked electrons off the atoms. The remaining positively-charged ions repelled one another, flying apart so they could be measured.

By varying the time between the first and second laser pulses, the group could see the dimer’s quantum response. The team’s technique could be used to study the less-explored helium trimer — a grouping of three helium atoms — as well as other low-energy molecules. It could also open a window onto the dynamics of exotic quantum states.

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Pulsar wind nebula illustration

Curving purple lines in this artist’s impression represent the magnetic field of a neutron star (white sphere) left over from a brilliant supernova. Credit: Salvatore Orlando/INAF-Osservatorio Astronomico di Palermo

Astronomy and astrophysics

X-rays expose a clue to the mystery of the missing neutron star

Astronomers might have spotted the long-sought debris of a famous stellar explosion.
A bone fragment next to a dime

A bone fragment excavated in Southeast Alaska belonged to one of the earliest known domestic dogs in the Americas. Credit: Douglas Levere/University at Buffalo

Genomics

An ancient Alaskan dog’s DNA hints at an epic shared journey

To scientists’ surprise, a 10,000-year-old bone found in an Alaskan cave belonged to a domestic dog — one of the earliest known from the Americas.
Emissions billow from smokestacks at a coal-fired power plant as the sun sets, India.

Black carbon emitted by power plants and other sources in Asia wafts to the Arctic, where the pollution accelerates the melting of ice and snow. Credit: Kuni Takahashi/Bloomberg/Getty

Atmospheric science

Soot from Asia travels express on a highway to the high Arctic

Black carbon from fuel combustion in South Asia bolsters the effects of climate change on northern ice and snow.
Prevotella copri bacteria, computer illustration

The gut bacterium Prevotella copri (artist’s impression) has been linked to a reduction in the health benefits of a diet that skimps on red meat in favour of fish and vegetables. Credit: Kateryna Kon/Science Photo Library

Microbiology

Trying a Mediterranean diet? Gut microbes might sway the outcome

The composition of a person’s microbiome could influence the health effects of swapping steak for vegetables and olive oil.
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