Light completely stopped for a record- breaking minute

The fastest thing in the universe has come to a
complete stop for a record-breaking minute.
At full pelt, light would travel about 18 million
kilometres in that time – that's more than 20
round trips to the moon.
"One minute is extremely, extremely long,"
says Thomas Krauss at the University of St
Andrews, UK. "This is indeed a major
milestone."
The feat could allow secure quantum
communications to work over long distances.
While light normally travels at just under 300
million metres per second in a vacuum,
physicists managed to slow it down to just 17
metres per second in 1999 and then halt it
completely two years later, though only for a
fraction of a second. Earlier this year,
researchers kept it still for 16 seconds using
cold atoms .
Stripy light
To break the minute barrier, George Heinze
and colleagues at the University of Darmstadt,
Germany, fired a control laser at an opaque
crystal, sending its atoms into a quantum
superposition of two states. This made it
transparent to a narrow range of frequencies.
Heinze's team then halted a second beam that
entered the crystal by switching off the first
laser and hence the transparency.
The storage time depends on the crystal's
superposition. A magnetic field extends it but
complicates the control laser configuration.
Heinze's team used an algorithm to "breed"
combinations of magnet and laser, leading
them to one that trapped light for a minute.
They also used the trap to store and then
retrieve an image consisting of three stripes.
"We showed you can imprint complex
information on your light beam," says Heinze.
Tens of seconds of light storage are needed for
a device called a quantum repeater, which
would stop and then re-emit photons used in
secure communications, to preserve their
quantum state over long distances.
It should even be possible to achieve longer
light storage times with other crystals, says
Heinze, as they have pushed their current
material close to its physical limit.