
What does it mean for light to be stopped or stored? - ColinWright
http://www.askamathematician.com/2013/07/q-what-does-it-mean-for-light-to-be-stopped-or-stored/
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KennyCason
I think that was the easiest to understand/intro to quantam information
handling that I have read.

I also enjoyed how they went from: Heinze, Hubrich, and Halfmann -> H and H
and H -> the three H's. I kind of expected it to go to "triple H"

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wbhart
H^3 perhaps. There is a precedent. The Lenstra-Lenstra-Lovasz algorithm (LLL)
is often called L^3, admittedly because the complexity is O(L^3) in the bit
size L. Later a quadratic algorithm was discovered, cheekily called the L^2
algorithm. Later still it was done in quasilinear time. Unfortunately, the
authors of those papers did not have the sense to have names starting with L.

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ColinWright
I was unaware of an L^2 (or better) algorithm - can you provide a reference?
Even just a term to search for - my Search-fu is failing.

Thanks.

 _Added in edit:_

OK, I've found these - hoping I'm on the right track:

    
    
        1982    LLL    Lenstra Lenstra Lovász
        1987    BKZ    Block Korkine Zolotarev
        2002    RSR    Random Sampling Reduction
        2002    PDR    Primal Dual Reduction

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acqq
I've tried to read the paper (note IANP, I'm not a physicist) and some
additional descriptions, remembering what I've read in Feynman lectures. The
principles really sound like reading about the DRAM (with the pulses to write,
to read and to "refresh" the content of memory) but with photons in the input
and output instead of the electrons. Inside of the crystal, it's the electrons
that get to move to higher levels when the photons hit the atom they orbit and
then to the lower level emitting the photons out. That's how a plain glass
window works. The difference is that the researchers add carefully controlled
electromagnetic (light is also electromagnetic emission) signals (additional
controlling inputs and outputs) which gives them the possibility to "write" at
one point in time and "read" sometime later the same "image." The new
achievement is that they reach 40 seconds or more between the write and read,
which is a new record. There's even some application of genetic algorithms
described in the paper used for preparing the conditions to make such write
and read possible:

 _The loop starts with a random set (‘‘generation’’) of preparation pulses
(‘‘genetic individuals’’). Each individual is described by a temporal array of
intensity and frequency values (‘‘genes’’). The self-learning loop applies the
pulses for EIT and determines the individuals with the highest fitness, i.e.,
the best light storage efficiency. The next generation is built by imitating
concepts of evolutionary biology: The best individuals are copied into the
next generation (cloning). Other good individuals are modified by variations
of their genes (mutation) or combination with other fit individuals
(inheritance). The loop goes through several hundred generations, until the
gene sequences (i.e., pulse shapes) converge toward an optimum. Figure 3 shows
the progress of the self-learning loop, i.e., the increase of signal pulse
energy after light storage vs number of completed generations. As expected,
the fitness increases monotonically with the generations._

I'd appreciate comments from anybody who knows and understands more.

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thehme
An actually readable explanation that can be understood. However, it seems to
me that the actual accomplishment, as the author mentioned, is our newly
acquired ability of "storing quantum information" and not actually "stopping
light". I like the "H's" references...how interesting that they all have H
last names - perhaps there is a German stat of last names starting with H.

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morpher
The article discusses at the outset that the distinction between "storing
info" and "stopping light" is subtle, I not nonexistent in this case. When
light travels through a material, one can treat it either at a macro level of
a light wave slowing down, or at a micro level of light travelling at vacuum
speed but being continuously absorbed and re-emitted. The former is a much
simpler picture and captures the essence of what is happening. So, if you use
a material (as H^3 have done) in which the effective speed becomes vanishingly
small, this is "stopping light" in the only sense one can talk about.

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JulianMorrison
What I wonder is if this could be used to bridge across decoherence.

Current problem: a quantum system is used to do a calculation, but it
decoheres to fast to be useful, or to scale.

Possible solution: do part of a calculation, shove the result in one of these
light storage thingies, decohere, reboot and re-establish coherence, feed in
result from light storage thingy, continue calculating.

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agf
Are you saying the light would somehow allow you to easily reconstruct the
lost state of the quantum computer? Or that it's easier to read out and store
the quantum state as light than another way?

I don't think either of those things are true, so I don't think this would
work to solve that problem.

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mariuolo
Could it also conceivably be used to store energy?

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beloch
Light is energy, so yes.

A slightly better question might be whether EIT could store energy in amounts
large enough to make it useful as a capacitor. At present, this is not likely.
This technology is striving towards optical RAM, not caps.

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DennisP
Maybe someday we'll have slow glass:
[http://en.wikipedia.org/wiki/Slow_light#Slow_light_in_fictio...](http://en.wikipedia.org/wiki/Slow_light#Slow_light_in_fiction)

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deletes
Is this a possible way to store information in quantum computers?

EDIT: Note to self, reading is tech.

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czr80
FTA: "What makes the experiment most exciting is that this experiment has
proven to be an extremely long term method for storing quantum information,
which has traditionally been a major hurdle. Normally a quantum computer (such
as they are) has to get all of its work done in a fraction of a second."

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TeMPOraL
Take note, all you commenters who asked "what's the practical value?" when
discussing that experiment last week.

