光を止める実験に成功

■光を止める実験に成功　米ハーバード大、世界初

自然界で最も速く制御が難しい光を、ある種のガスの中で止め再び放出することに、
米ハーバード大の二つの研究チームが世界で初めて成功した。
通信に使う光の制御だけでなく、今のコンピューターで解けない問題も
解けるといわれる未来の「量子コンピューター」に応用可能な成果としても注目を集めている。

どういう原理？

とうとう止まりましたか。
速くしたり遅くしたり、大変ですなぁ。。。。

止まってるんじゃなくて中で乱反射してただけとか・・・・・・
んなことぁないか（＾＾；

ソースはどこ？

ガスが吸収、放射をするだけってこたあないよなぁ？

＞３
なんかそれっぽそうな気が、、、
光を３００倍に加速　のときも思ったけど、
どうして、研究ってのは誇大広告になりがちなんでしょうね。
報道するマスコミが単なるバカなのか、
研究者側が研究費を引き出すために、大風呂敷をひろげるのか、

でどうやって光を止めたんでしょう。
ソースきぼーーん

ちょっと宣伝するんですが、うちも同じようなことやっている。

原理はいわゆる電磁場誘起透明化（EIT)である：
レーザー場で媒質の光学応答を変えて
吸収が０、屈折率分散が急峻になる。
その媒質にプロブ光を通すと群速度が極端に遅くなる。
最近の実験は、レス１が言ったグループnatureに発表した
Na原子のBECを媒質につかって、17m/sの群速度を観測した実験。

我々は現時点はＢＥＣ使わないで 6km/s　達成。
詳しいことは前回＆今回の物理学会に来てください。

　　　 ／￣￣￣￣ヽ
　　／　　／￣＼　　ヽ
　/　　 /　　　　　ヽ､､､ヽ
　|　　/　　　ー 　　ー | |
　|　　|　　　　・　　　・ | | 　 ／￣￣￣￣￣￣￣￣
　|　　|　　 ●　 ー　●| | ＜　　太るのも止めて欲しいべさ・・・
　ゝ‐ｲ＼　　　　　　 ／ノ　　＼＿＿＿＿＿＿＿＿

清水研？

＞９
違います

ついでに光速より速い伝播の話ですが、
そもそもパルスの形が崩れて群速度が定義できない。
肝心なfront velocityはｃに越えられない。

相対論は不滅だ！

どこの研究室？言えるでしょ？

Ｈ研

あ゛ーーー。なんではっきりいわんのだ。
面倒だ。JPSのプログラムから探し出してやる。

白○センセイのところね。
実験って昔からやってたのかな？理論だけかと思ってた。

止めたって言うんだから、以前より遅くなったんじゃないのかな？

昔計算したことあるみたいが、大した遅くならなかった。
緩和の遅い媒質がないから。
最近極低温（ＢＥＣとか）の原子なら実現できる。

うちは固体水素を使ってる。

まぁ、そうだろうね。
止めたっていうのは新しい成果かな？
たぶん新しい成果なんじゃないの？
ＢＥＣのガスの実験で進展があったということなんだろ？

止まったとしたら、その状態って、、、キャビティ中の電場と似たようなモノ
になるのかな？

完全に速度が０じゃないと思う
屈折率分散が無限大なら別だが。

速度が遅い分相互作用が大きくなり→巨大非線形効果→
単一光子スイッチとか応用できる
あと、光子が媒質に’凍りつく’ので光子の量子状態を
媒質に移る、量子メモリとか
などなど

現実の媒質で、無限大は無いだろうね。

相互作用が大きくなると言うのは、キャビティでも同じことだよね。
キャビティと違うところはどこなんだろうか？
もちろん、キャビティがなくても済むというのは除いて。

その場合、光閉じ込めるにはHigh Q cavity必要
うちもやっている。微小球のＷＧＭモード
（球の中ぐるぐる回る）を使って。

Scientists Hold Light Particles Captive

Last updated: 18 Jan 2001 20:55 GMT (Reuters)

By Maggie Fox＠｀ Health and Science Correspondent

WASHINGTON (Reuters) - It may be impossible to grasp a sunbeam＠｀ but
physicists said on Thursday they had managed to capture light＠｀ play with it
a while＠｀ and then let it go.

They said their achievement could speed the development of quantum
computers＠｀ which would calculate millions of times faster than present-day
computers＠｀ and inventions that no one has yet dreamed of.

The secret was slowing down atoms of rubidium so they would not absorb the
photons＠｀ as atoms usually do＠｀ the team at the Harvard-Smithsonian Center for
Astrophysics in Cambridge＠｀ Massachusetts said.

Instead＠｀ they report in the Jan. 29 issue of Physical Review Letters＠｀ the
atoms change their magnetic spin just slightly -- a change that allows them
to store information from the photons. Hitting the cloud of hot rubidium gas
with another laser pulse releases the first pulse＠｀ they said.

Usually＠｀ when a photon hits an atom -- even an atom in a highly reflective
mirror -- it gets absorbed and heats up the atom＠｀ putting it into what
physicists call a higher energy state.

"Here＠｀ the light pulse does get dimmer and dimmer and slower and slower＠｀"
Ben Stein＠｀ a spokesman for the American Institute of Physics＠｀ said in a
telephone interview.

"The light does disappear but instead of getting absorbed in the usual way
as it heats up atoms＠｀ it goes to storing its information in the atoms in the
form of something called spin."

This little change could work just like the switches in computers. "You
could store zeros and ones just like they are stored in computers＠｀" Stein
said. But it would happen much faster and＠｀ using the sometimes weird laws of
quantum mechanics＠｀ one photon could have more than one "on-off" position at
the same time.

ULTRA-FAST QUANTUM COMPUTERS

This property could be used to make ultra-fast quantum computers.

Even better＠｀ the physicists were able to get the light back out of the
rubidium.

"Later on＠｀ you can shine another light pulse which coaxes the atoms into
spitting out the original light wave＠｀" Stein said. "The beam of light will
come out again."

Stein said the applications＠｀ beyond the use of light in a quantum computer＠｀
are not clear. But the same was true of lasers when they were first
invented.

"No one foresaw their use in supermarket scanners and so on＠｀" he said.

In a second paper＠｀ to be published in next week's issue of the journal
Nature＠｀ Lene Hau and colleagues at the Harvard/Rowland Institute of Science
said they had done a similar experiment using ultra-cold gas.

They used sodium atoms for their experiment＠｀ and were also able to store the
light and get it back out again.

"We believe that this system could be used for quantum information
transfer＠｀" they wrote in their report.

Light travels in packages called photons＠｀ which have properties resembling
both waves and particles. In nature it moves at 186＠｀000 miles (300＠｀000 km)
per second＠｀ the fastest speed possible according to Einstein's theories.


=============================================================
January 18＠｀ 2001 The New York Times

Scientists Bring Light to Full Stop＠｀ Hold It＠｀ Then Send It on Its Way
By JAMES GLANZ

----------------------------------------------------------------------------
Researchers say they have slowed light to a dead stop＠｀ stored it and then
released it as if it were an ordinary material particle.

The achievement is a landmark feat that＠｀ by reining in nature's swiftest and
most ethereal form of energy for the first time＠｀ could help realize what are
now theoretical concepts for vastly increasing the speed of computers and
the security of communications.

Two independent teams of physicists have achieved the result＠｀ one led by Dr.
Lene Vestergaard Hau of Harvard University and the Rowland Institute for
Science in Cambridge＠｀ Mass.＠｀ and the other by Dr. Ronald L. Walsworth and
Dr. Mikhail D. Lukin of the Harvard-Smithsonian Center for Astrophysics＠｀
also in Cambridge.

Light normally moves through space at 186＠｀000 miles a second. Ordinary
transparent media like water＠｀ glass and crystal slow light slightly＠｀ an
effect that causes the bending of light rays that allows lenses to focus
images and prisms to produce spectra.

Using a distantly related but much more powerful effect＠｀ the Walsworth-Lukin
team first slowed and then stopped the light in a medium that consisted of
specially prepared containers of gas. In this medium＠｀ the light became
fainter and fainter as it slowed and then stopped. By flashing a second
light through the gas＠｀ the team could essentially revive the original beam.

The beam then left the chamber carrying nearly the same shape＠｀ intensity and
other properties it had when it entered. The experiments led by Dr. Hau
achieved similar results with closely related techniques.

"Essentially＠｀ the light becomes stuck in the medium＠｀ and it can't get out
until the experimenters say so＠｀" said Dr. Seth Lloyd＠｀ an associate professor
of mechanical engineering at the Massachusetts Institute of Technology who
is familiar with the work.

Dr. Lloyd added＠｀ "Who ever thought that you could make light stand still?"

He said the work's biggest impact could come in futuristic technologies
called quantum computing and quantum communication. Both concepts rely
heavily on the ability of light to carry so-called quantum information＠｀
involving particles that can exist in many places or states at once.

Quantum computers could crank through certain operations vastly faster than
existing machines; quantum commmunications could never be eavesdropped upon.
For both these systems＠｀ light is needed to form large networks of computers.
But those connections are difficult without temporary storage of light＠｀ a
problem that the new work could help solve.

A paper by Dr. Walsworth＠｀ Dr. Lukin and three collaborators ・Dr. David
Phillips＠｀ Annet Fleischhauer and Dr. Alois Mair＠｀ all at Harvard- Smithsonian
・is scheduled to appear in the Jan. 29 issue of Physical Review Letters.

Citing restrictions imposed by the journal Nature＠｀ where her report is to
appear＠｀ Dr. Hau refused to discuss her work in detail.

Two years ago＠｀ however＠｀ Nature published Dr. Hau's description of work in
which she slowed light to about 38 miles an hour in a system involving beams
of light shone through a chilled sodium gas.

Dr. Walsworth and Dr. Lukin mentioned Dr. Hau's new work in their paper＠｀
saying she achieved her latest results using a similarly chilled gas. Dr.
Lukin cited her earlier work＠｀ which Dr. Hau produced in collaboration with
Dr. Stephen Harris of Stanford University＠｀ as the inspiration for the new
experiments.

Those experiments take the next step＠｀ stopping the light's propagation
completely.

"We've been able to hold it there and just let it go＠｀ and what comes out is
the same as what we sent in＠｀" Dr. Walsworth said. "So it's like a freeze
frame."

Dr. Walsworth＠｀ Dr. Lukin and their team slowed light in a gas form of
rubidium＠｀ an alkaline metal element.

The deceleration of the light in the rubidium differed in several ways from
how light slows through an ordinary lens. For one thing＠｀ the light dimmed as
it slowed through the rubidium.

Another change involved the behavior of atoms in the gas＠｀ which developed a
sort of impression of the slowing wave.

This impression＠｀ actually consisting of patterns in a property of the atoms
called their spin＠｀ was a kind of record of the light's passing and was
enough to allow the experimenters to revive or reconstitute the original
beam.

Both Dr. Hau's original experiments on slowing light＠｀ and the new ones on
stopping it＠｀ rely on a complex phenomenon in certain gases called
electromagnetically induced transparency＠｀ or E.I.T.

This property allows certain gases＠｀ like rubidium＠｀ that are normally opaque
to become transparent when specially treated.

For example＠｀ rubidium would normally absorb the dark red laser light used by
Dr. Walsworth and his colleagues＠｀ because rubidium atoms are easily excited
by the frequency of that light.

But by shining a second laser＠｀ with a slightly different frequency＠｀ through
the gas＠｀ the researchers rendered it transparent.

The reason is that the two lasers create the sort of "beat frequency" that
occurs when two tuning forks simultaneously sound slightly different notes.

The gas does not easily absorb that frequency＠｀ so it allows the light to
pass through it; that is＠｀ the gas becomes transparent.

But another property of the atoms＠｀ called their spin＠｀ is still sensitive to
the new frequency. Atoms do not actually spin but the property is a
quantum-mechanical effect analagous to a tiny bar magnet that can be twisted
by the light.

As the light passes through＠｀ it alters those spins＠｀ in effect flipping them.
Though the gas remains transparent＠｀ the interaction serves as a friction or
weight on the light＠｀ slowing it.

Using that technique＠｀ Dr. Hau and Dr. Harris in the earlier experiment
slowed light to a crawl. But they could not stop it＠｀ because the transparent
"window" in the gas became increasingly narrower＠｀ and more difficult to pass
through＠｀ as the light moved slower and slower.

In a recent theoretical advance＠｀ Dr. Lukin＠｀ with Dr. Suzanne Yelin of
Harvard-Smithsonian and Dr. Michael Fleischhauer of the University of
Kaiserslautern in Germany＠｀ discovered a way around this constraint.

They suggested waiting for the beam to enter the gas container＠｀ then
smoothly reducing the intensity of the second beam.

The three physicists calculated that this procedure would narrow the window＠｀
slowing the first beam＠｀ but also "tune" the system so that the beam always
passes through.

The first beam＠｀ they theorized＠｀ should slow to an infinitesimally slow
speed＠｀ finally present only as an imprint on the spins＠｀ with no visible
light remaining. Turning the second beam back on＠｀ they speculated＠｀ should
reconstitute the first beam.

The new experiments bore those ideas out.

"The light is actually brought to a stop and stored completely in the
atoms＠｀" Dr. Harris said. "There's no other way to do that. It's been done ・
done very convincingly＠｀ and beautifully."

光が止まったら観測できないんじゃ・・・。

ほとんど止まったということかな？
１０秒ぐらいしてから、ガスから入射パルスが出現するとか。

もう相対論も過去の遺物。
さよなら２０世紀の古典。

↑光速度不変は真空中での話ですよー？わかってますか？

あれ？光って止まったら存在しなくなるんじゃなかったっけ？

>>30
停まるとエネルギーが消耗して一瞬で消えるってやつ？