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Optical gratings could make quantum tech portable

Photonics Spectra
Aug 2013

GLASGOW, Scotland, and LONDON – A microfabricated chip that produces ultracold atoms could lead to portable, ultraprecise clocks and quantum sensors.

Many of the most accurate measurement devices, including atomic clocks, work by observing how atoms transfer between individual quantum states. The highest precision is obtained with long observation times, often using slow-moving ultracold atoms prepared in a large apparatus.

“The longer the transition of atoms can be observed, the more precisely they can be measured,” said Dr. Aidan Arnold of the University of Strathclyde’s physics department. “It is possible to shine laser light on atoms to slow them down using the Doppler effect. We can now do this in a really small device.”


A microfabricated grating transforms a single incoming laser beam into a light field specially tailored for trapping and cooling atoms.


In the research, a joint project between Strathclyde, the University of Glasgow, Imperial College London and the National Physical Laboratory (NPL), the surface of a semiconductor chip was patterned to form a diffraction grating that splits a laser into many atom-cooling beams. The technology is far more compact than previous setups but still can cool and trap large numbers of atoms for use in portable devices, they said.

“These specially microfabricated diffraction gratings create the perfect laser beams for trapping and cooling atoms,” said professor Ed Hinds, who directs the Centre for Cold Matter at Imperial College London. While advances have been made in producing portable sensors, simplifying atomic cooling and loading using microfabrication techniques has proved difficult, the researchers said. Their source addresses the problem by delivering “ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures,” they say in their paper. The same chip design can also provide a simpler way to form stable optical lattices.

“The miniaturization of atomic sensors using these optical gratings can make an important contribution to metrology and high-precision measurement,” said Dr. Alastair Sinclair, principal scientist at NPL.

Ultracold atoms are essential for precise, modern measurements and are increasingly important as an enabling technology in quantum information processing and matter-wave interferometry, among other applications. Ultraprecise portable clocks, magnetometers and accelerometers have wide-ranging uses, including navigation on Earth and in space, telecommunications, geological exploration and medical imaging. The diffraction gratings were co-designed by the groups, and some were microfabricated at the James Watt Nanofabrication Centre at the University of Glasgow.

The work appears in Nature Nanotechnology (doi:10.1038/nnano.2013.47).


GLOSSARY
diffraction grating
A glass substrate carrying a layer of deposited aluminum that has been pressure-ruled with a large number of fine equidistant grooves, using a diamond edge as a tool. Light falling on such a grating is dispersed into a series of spectra on both sides of the incident beam, the angular dispersion being inversely proportional to the line spacing. By proper shaping of the diamond edge, however, the grooves can be formed in such a way as to concentrate most of the energy into a single spectral...
optical lattice
A periodic structure formed by intersecting or superimposed laser beams. These beams can trap atoms in low-potential regions, forming a pattern of atoms resembling the structure of a crystal.
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