
Quantum Physics Leads To Perfect Mirror - jonbaer
http://www.scientificamerican.com/podcast/episode.cfm?id=quantum-physics-leads-to-perfect-mi-13-07-24
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ISL
The Nature article on the subject is considerably more informative. The
research shows a curve that's not inconsistent with 'perfect'. The measured Q
is about 10^6, and roughly consistent with their wavefunction model of
reflection. It's an excellent Q for the substrate.

The model allows for infinite reflectance, so this work opens an interesting
window into future improvements. When the reported Q passes 10^12, you'll know
that they're on to something truly special. Bulletproof measurements of Qs
greater than 10^5 are a challenge, so it may be a while.

This paper was the coolest thing (to me) in last week's Nature.

Paywalled links (the authors have not chosen to put it on the arXiv):

[http://www.nature.com/nature/journal/v499/n7457/full/499159a...](http://www.nature.com/nature/journal/v499/n7457/full/499159a.html)
[http://www.nature.com/nature/journal/v499/n7457/full/nature1...](http://www.nature.com/nature/journal/v499/n7457/full/nature12289.html)

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ErsatzVerkehr
> the authors have not chosen to put it on the arXiv

Doesn't Nature forbid authors from uploading pre-prints to the arXiv?

[http://www.nature.com/nature/authors/policy/embargo.html](http://www.nature.com/nature/authors/policy/embargo.html)

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ISL
Doesn't look like an explicit ban on preprints, though Nature might prefer
that you not do it. I'm pretty sure I've seen a Nature paper or two appear on
the arXiv around the time of publication.

"Nature does not wish to hinder communication between scientists. For that
reason, different embargo guidelines apply to work that has been discussed at
a conference or displayed on a preprint server and picked up by the media as a
result. (Neither conference presentations nor posting on recognized preprint
servers constitute prior publication.)

Our guidelines for authors and potential authors in such circumstances are
clear-cut in principle: communicate with other researchers as much as you
wish, but do not encourage premature publication by discussion with the press
(beyond a formal presentation, if at a conference)."

Looks like they say "It's okay to talk among scientists, but don't talk with
the media at all until we've released it. We'll pull your paper if you do."

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ErsatzVerkehr
Looks like you're right:

"1\. You are welcome to post pre-submission versions or the original submitted
version of the manuscript on a personal blog, a collaborative wiki or a
preprint server at any time (but not subsequent pre-accept versions that
evolve due to the editorial process)."

[http://www.nature.com/authors/policies/confidentiality.html](http://www.nature.com/authors/policies/confidentiality.html)

... But I can see how authors, anticipating a possible Nature publication,
would choose to maximize "impact" by not jumping the gun.

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tocomment
I'm wondering if this would be a good defense against laser weapons? I've
heard that normal mirrors are worthless for this since even a minut
imperfections can be enough to quickly heat up and destroy the mirror.

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jacquesm
Use a cylindrical mirror and make it spin fast enough, possibly with movement
along multiple axis to spread the energy out over as large an area as
possible, and return the beam back to the sender?

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dodo53
If you have a perfect mirror, can you store energy in lasers indefinitely?

I guess you'd still lose energy to the air

~~~
ISL
The short answer is yes.

Aside from tiny losses like tunnelling, scattering from vacuum excitations and
thermally-generated fields, etc., a perfect optical cavity will store light
indefinitely. No laser required, only light of the appropriate wavelength and
phase.

The combination of Fabry-Perot cavities and power-recycling in the optics of
the LIGO gravitational wave observatory "gains" a ~100 W laser up to a few
megawatts. If a cavity is formed in free space, like LIGO, then careful
attention to vacuum is required to prevent loss.

ULE clock reference cavities have quality factors that are much higher, and
need no vacuum, as the light propagates entirely within a glass substrate.

 _Edit:_ I should add that the "tiny losses" mentioned at the outset are
precisely what prevent you from making a "perfect cavity". As the quality of a
cavity/oscillator increases, the number and deviousness of loss mechanisms
does too. This is especially the case at frequencies that are low compared to
those at which an experimenter can iterate.

For HN, consider building a host that can run uninterrupted for 10^12 seconds
(30,000 years).

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ErsatzVerkehr
...but the effective storage time of the power recycling cavity in LIGO is
about 1 second. This is a rather long time by optical standards, but I'd say
it's a long way from "indefinitely".

~~~
ISL
Agreed. My post may have been more tautological than I'd hoped (in the absence
of loss, a cavity is lossless). Thank you for the important reminder that in
nature, there is no DC.

In the sense in which I'd understood the question "Cavity losses are often
dominated by reflectivity losses at the mirrors: does an improved mirror make
a big difference?", I think my reply is relevant.

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ape4
Its funny. Quantum Mechanics was invented about 90 years ago but the first
cool applications are coming out today.

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mistercow
Arguably, LASERS and modern semiconductors both rely on our understanding of
QM. Hard drives using GMR have been around for at least 16 years. Erasing of
flash drives uses quantum tunneling. MRIs probably would not be possible
without an understanding of QM. Computational chemistry relies heavily on QM.

So no, I don't think your statement is accurate. QM has been giving us cool
applications for decades. The amazing thing is that it's still giving us
amazing _new_ advances even after all this time.

~~~
ISL
Agreed entirely; an upvote wasn't enough. Quantum Mechanics has been
delivering the goods since their invention.

While the maser surely is an explicit application of quantum mechanics,
placing theoretical chemistry onto a solid physical framework may have had the
greatest aggregate impact on humanity. From a scientific perspective, much of
what we know about the universe requires spectroscopy. Everything we know
about subatomic processes requires quantum understanding as a prerequisite.

Quantum effects are so curious/clever that we should continue to expect
interesting surprises into the foreseeable future.

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dreen
What, no pics?

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balsam
sciam didn't mention it, but the last two authors are the same guys who
modernized wireless cellphone charging (Tesla's coils were deemed too
dangerous)

[http://en.wikipedia.org/wiki/WiTricity](http://en.wikipedia.org/wiki/WiTricity)

