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25th July 2013, 22:31
Light completely stopped for a record-breaking minute
2013 07 25
By Jacob Aron | NewScientist
http://www.newscientist.com/article/dn23925-light-completely-stopped-for-a-recordbreaking-minute.html?cmpid=RSS|NSNS|2012-GLOBAL|online-news#.UfGmlo2mjpV
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.
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Stopped Light and Image Storage by Electromagnetically Induced Transparency up to the Regime of One Minute
http://prl.aps.org/abstract/PRL/v111/i3/e033601
Georg Heinze*, Christian Hubrich, and Thomas Halfmann†
Institut für Angewandte Physik, Technische Universität Darmstadt, Hochschulstraße 6, 64289 Darmstadt, Germany
Selected for a Viewpoint in PhysicsEditors' Suggestion Received 28 March 2013; published 15 July 2013
See accompanying Physics Viewpoint
The maximal storage duration is an important benchmark for memories. In quantized media, storage times are typically limited due to stochastic interactions with the environment. Also, optical memories based on electromagnetically induced transparency (EIT) suffer strongly from such decoherent effects. External magnetic control fields may reduce decoherence and increase EIT storage times considerably but also lead to complicated multilevel structures. These are hard to prepare perfectly in order to push storage times toward the theoretical limit, i.e., the population lifetime T1. We present a self-learning evolutionary strategy to efficiently drive an EIT-based memory. By combination of the self-learning loop for optimized optical preparation and improved dynamical decoupling, we extend EIT storage times in a doped solid above 40 s. Moreover, we demonstrate storage of images by EIT for 1 min. These ultralong storage times set a new benchmark for EIT-based memories. The concepts are also applicable to other storage protocols.
© 2013 American Physical Society
URL: http://link.aps.org/doi/10.1103/PhysRevLett.111.033601
DOI: 10.1103/PhysRevLett.111.033601
PACS: 42.50.Gy, 42.50.-p, 42.30.-d, 42.30.Va
*georg.heinze@physik.tu-darmstadt.de
†http://www.iap.tu-darmstadt.de/nlq
2013 07 25
By Jacob Aron | NewScientist
http://www.newscientist.com/article/dn23925-light-completely-stopped-for-a-recordbreaking-minute.html?cmpid=RSS|NSNS|2012-GLOBAL|online-news#.UfGmlo2mjpV
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.
***********************************
Stopped Light and Image Storage by Electromagnetically Induced Transparency up to the Regime of One Minute
http://prl.aps.org/abstract/PRL/v111/i3/e033601
Georg Heinze*, Christian Hubrich, and Thomas Halfmann†
Institut für Angewandte Physik, Technische Universität Darmstadt, Hochschulstraße 6, 64289 Darmstadt, Germany
Selected for a Viewpoint in PhysicsEditors' Suggestion Received 28 March 2013; published 15 July 2013
See accompanying Physics Viewpoint
The maximal storage duration is an important benchmark for memories. In quantized media, storage times are typically limited due to stochastic interactions with the environment. Also, optical memories based on electromagnetically induced transparency (EIT) suffer strongly from such decoherent effects. External magnetic control fields may reduce decoherence and increase EIT storage times considerably but also lead to complicated multilevel structures. These are hard to prepare perfectly in order to push storage times toward the theoretical limit, i.e., the population lifetime T1. We present a self-learning evolutionary strategy to efficiently drive an EIT-based memory. By combination of the self-learning loop for optimized optical preparation and improved dynamical decoupling, we extend EIT storage times in a doped solid above 40 s. Moreover, we demonstrate storage of images by EIT for 1 min. These ultralong storage times set a new benchmark for EIT-based memories. The concepts are also applicable to other storage protocols.
© 2013 American Physical Society
URL: http://link.aps.org/doi/10.1103/PhysRevLett.111.033601
DOI: 10.1103/PhysRevLett.111.033601
PACS: 42.50.Gy, 42.50.-p, 42.30.-d, 42.30.Va
*georg.heinze@physik.tu-darmstadt.de
†http://www.iap.tu-darmstadt.de/nlq