Physicists say they have brought light to a complete halt for a fraction of a second and then sent it on its way. Harvard University staff held a light pulse still without taking away all of its energy, the journal Nature reports. Controlling the movement of light particles - so-called photons - to store and process data could lead to the development of quantum computers. In a 2001 experiment, light pulses were briefly stored when particles of light were taken up by atoms in a gas. The Harvard experiment tops that achievement by holding light and its energy at a standstill.

Light normally travels at about 299,000 kilometres per second (186,000 miles per second), but it slows down when passing through some materials, such as glass.

The team fired a light beam called a signal pulse through a sealed glass cylinder containing a hot gas containing atoms of the element rubidium, illuminated by a strong ray of light known as a control beam.

While the pulse was travelling through the rubidium gas, the researchers switched off the control beam, creating a holographic imprint of the signal pulse on the rubidium atoms.

Earlier experimental methods had then switched on a single control beam to recreate the signal pulse, which then continued on its way.


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