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Ultracold matter

Ultracold matter

Flash Physics: Cavity-cooling multiple atoms, space dust makes radio waves, UK creates funding super-body

03 May 2017 Hamish Johnston

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World's team of editors and reporters

Cool technique: the cavity is tuned to absorb scattered light

Cavity cooling extended to multiple atoms

Physicists in the US are the first to cool multiple atoms using cavity cooling – a technique that had been restricted to cooling single atoms. As well as making it possible to create a wider range of ultracold atomic gases, the breakthrough could lead to the cooling of ensembles of molecules. Cooling in an optical cavity involves the scattering of photons from an atom (or other tiny objects) such that the scattered photons have more energy than the incident photons. This reduces the random motion of the object and therefore its temperature. This process can be done very efficiently by tuning the cavity so that it readily absorbs the scattered photons. Cavity cooling is attractive because it does not require the atom to have specific energy levels. This is unlike laser-cooling techniques, which only work if the atoms can undergo transitions between specific energy levels. Trapping large numbers of atoms in a finely tuned cavity, however, is very difficult, but now, Vladan Vuletič and colleagues at the Massachusetts Institute of Technology have achieved just that. They succeeded in cooling a few hundred caesium atoms from a temperature of 200 μK to a chilly 10 μK. Writing in Physical Review Letters, the team also points out that its technique could be modified to cool ensembles of molecules, something that is very difficult to do using laser cooling.

Why colliding space dust emits radio waves

The long-standing mystery of why radio waves are emitted when nanometre and micron-sized space dust collides with a spacecraft may have been solved by Alex Fletcher and Sigrid Close at Stanford University in the US. The research suggests that emissions associated with dust collisions could be responsible for some electrical failures on board satellites. Fletcher and Close built on previous work suggesting that when a dust particle strikes a satellite surface it vaporizes and ionizes material, creating a cloud of dust, gas and plasma that expands into the emptiness of space. The pair assumed that the electrons in the expanding plasma travel faster than the much heavier ions, creating a large electric field. Computer simulations done by Fletcher and Close suggest that the coherent motion of electrons within this electric field generates the radio waves – however, the radio emissions predicted are higher frequency than that measured in laboratory experiments. The researchers are now doing a more detailed study of the electron motion and also the effect of dust on the process. The research is described in Physics of Plasmas.

UK creates new funding super-body

The UK government has pushed through its higher-education and research bill that includes the creation of UK Research and Innovation (UKRI) – a new umbrella organization that will oversee the country’s seven research councils such as the Science and Technology Facilities Council and the Engineering and Physical Sciences Research Council. The UKRI will be responsible for £6bn in research grants and funding each year and is now expected to come into operation early next year. It was announced in February that Mark Walport, the UK government’s chief scientific adviser, will head the new body. The bill was pushed through before the UK government shut down for the general election on 8 June.

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