The speed of light in a vacuum (c) is the immutable constant. Every shadow in the world is proof absolute that it can be prevented from reaching some places (by prior reflection and absorption). But light can also be slowed-down and stopped and even stored.
Light propagates at speeds less than (c) in different media.
In 1999, Danish physicist Lene Vestergaard Hau led a combined team from Harvard University and the Rowland Institute for Science which succeeded in slowing a beam of light to about 17 meters per second, and researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 9.7 km/s in 2004. Hau later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted.This was in an effort to develop computers that will use only a fraction of the energy of today’s machines.
Back in 2007, Lene Hau showed that light could be “stopped” and then “restarted” a little distance away.
Lene Hau (image photonics.com)
CAMBRIDGE, Mass., Feb. 8, 2007 — By converting light into matter and then back again, physicists have for the first time stopped a light pulse and then restarted it a small distance away. This “quantum mechanical magic trick” provides unprecedented control over light and could have applications in fiber-optic communication and quantum information processing.
In quantum networks, information optically transmitted over the network is converted into matter, processed, and then converted back into light. The physicists at Harvard University hope that their discovery could provide a possible way to do this, since matter, unlike light, can easily be manipulated. Their findings were published this week in the journal Nature.
“We demonstrate that we can stop a light pulse in a supercooled sodium cloud, store the data contained within it, and totally extinguish it, only to reincarnate the pulse in another cloud two-tenths of a millimeter away,” said Lene Vestergaard Hau, Mallinckrodt Professor of Physics and of Applied Physics in Harvard’s Faculty of Arts and Sciences and School of Engineering and Applied Sciences.
But now comes evidence that it can be “stopped” and stored for a whole minute – and maybe even longer.
Georg Heinze, Christian Hubrich, Thomas Halfmann. Stopped Light and Image Storage by Electromagnetically Induced Transparency up to the Regime of One Minute. Physical Review Letters, 2013; 111 (3) DOI: 10.1103/PhysRevLett.111.033601
Abstract: 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.
Hugues de Riedmatten writes in Physics:
A solid-state device can now store light coherently for up to one minute.
The ability to store light while keeping its quantum coherence properties (e.g., entanglement) plays an important role in quantum information science. It makes it possible to build quantum memories for light, which could become crucial elements in many quantum information processing schemes based on the use of photons, from quantum communication networks to quantum computing protocols. A critical parameter for applications is the duration over which light can be stored. For example, the distribution of quantum bits over complex quantum information networks, and their storage for further manipulation, might require quantum memories with storage time from a few seconds to a few minutes. Writing in Physical Review Letters, Georg Heinze at the University of Darmstadt, Germany, and colleagues report an important step towards this goal by demonstrating a solid-state coherent optical memory capable of storing a classical light pulse, and even a full image, for a duration of more than one minute—the longest light-storage time reported in any system to date.
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