據《自然》雜誌2007年2月8日報導﹐你如何先讓光波消失﹐接著再讓它們在別的地方現身？ 這聽上去似乎是天方夜譚﹐也許只有魔術師才能做到。 美國哈佛大學物理學家莉尼‧韋斯特加德‧哈烏 (Lene Vestergaard Hau) 及同事確實做到了這一點。 不過﹐他們並未使用魔術﹐而是利用量子力學的奇特原理﹐玩了一個乾坤大挪移的把戲。
首先﹐研究人員把光脈沖發送至擁有兩百萬個鈉原子的超冷雲團之中﹐讓其運行速度減緩。 接下來﹐他們徹底銷毀光束﹐將其“記憶”銘刻于鈉原子當中。 他們把這些原子分流于第二個雲團之中﹐再用另外一個激光束進行刺激。 隨即﹐原始脈沖的“記憶”便被觸動﹐雖然此時“記憶”已經減弱﹐但內容並無任何變化。
韋斯特加德說﹐在兩處雲之間移動的“信使原子”基本上就是原始脈沖的“物質拷貝”﹕投射于原子上的一絲光。 這一過程可被用于操作量子計算機上的信息﹐量子計算機通常比常規計算機的計算能力強得多。 另外﹐它在常規光通訊領域同樣用途廣泛﹐如用于把信息存儲在光束上。
Turning light into matter
by Philip Ball Published online 7 February 2007 | Nature | doi:10.1038/news070205-8
How do you make a light wave vanish and then reappear elsewhere?
It sounds like a conjuring trick. You shine a light into a gas, and the light gets
swallowed. ... ... ... ... ... ...
[圖片說明]： The light enters one cloud of atoms and is revived in another
Cool clouds turn light to matter
BBC News - Thursday, 8 February 2007, 17:50 GMT
A fleeting pulse of light has been captured and then made to reappear in a different location by US physicists.
The quantum sleight of hand exploits the properties of super-cooled matter known as a Bose-Einstein condensate.
The emerging pulse was slightly weaker than the high-speed beam that entered the experimental setup, but was identical in all other respects.
The work, published in the journal Nature, could one day lead to advances in
computing and optical communication.
"Instead of light shining through optical fibres into boxes full of wires and
semiconductor chips, intact data, messages, and images will be read directly from the light," said Professor Lene Vestergaard Hau of Harvard University and one of
the authors of the Nature paper.
Exotic freezer
The Harvard team rose to prominence in the late 1990s when it slowed light from
its constant 299,792km/s (186,282mps) to a leisurely 61km/h (38mph).
It applied the brakes by shining light into a cloud of sodium atoms trapped in a
vacuum and cooled to just above absolute zero (-273C), the theoretical state of
zero heat.
At this temperature the atoms coalesce to form a Bose-Einstein condensate, an
exotic quantum entity first predicted by Albert Einstein and created in the lab in
1995.
A second laser tuned the tiny atomic cloud to slow the pulse of light.
In 2001, working with a team from the Harvard Smithsonian Center for
Astrophysics, the same group brought light to a halt, by slowly turning off the
second control laser.
Switching the laser back on set the light free.
The new experiment builds on this work.
[圖片說明]： The team had previously "frozen" a beam of light in a gas cloud
Light switch
Instead of just one cloud of sodium atoms, the new setup used two, a fraction of a millimetre apart.
"The two atom clouds were separated and had never seen each other before,"
said Professor Hau.
A pulse of light was shone on the first cloud, impressing a "cast" of the pulse into a clump of spinning sodium atoms, nudged in the direction of the second
condensate.
This slowly moving clump was composed entirely of sodium atoms, effectively
turning light into matter.
Once the "messenger" group had merged with the second cloud, a second laser
was shone through the condensate to revive the original pulse of light.
From a standing start, the reconstructed beam sped back up to the normal speed
of light. Analysis showed that it possessed exactly the same shape and wavelength of the original beam, although it was slightly weaker.
Writing in an accompanying article in Nature, Professor Michael Fleischhauer of
the University of Kaiserslautern in Germany described the experiment as "striking
and intriguing."
He said that science was entering a period of "unprecedented experimental
control" of light and matter.
"That could bring very real technological benefits," he wrote.
Applications could include optical storage devices and quantum computers, far
quicker and more powerful than today's PCs.
[圖片說明]： Professor Lene Vestergaard Hau (Photo: Jay Penni Photography)
* 有關此項研究的更多資訊的網址：
http://www.seas.harvard.edu/haulab/slow_light_project/remote_revival/remote_revival.htm
* 哈佛大學 Hau Lab 的網址：
http://www.seas.harvard.edu/haulab/index.htm
(原於2008/01/18在Yahoo開設的部落格，2013/09/10搬遷到Blogger，特為之記。)
沒有留言:
張貼留言