Quantum Physics Leads To Perfect Mirror | Hacker News Reader

Quantum Physics Leads To Perfect Mirror

scientificamerican.com

33 pointsjonbaer28 comments

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/nature1...

> 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

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."

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

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

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.

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?

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

I guess you'd still lose energy to the air

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).

...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".

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.

Since the effect only works at an angle of 35 degrees, you couldn't just use two mirrors. Maybe you could arrange them in a ring... all you have to do is find a regular polygon with internal angles of 35 degrees :)

Could you construct a closed cycle path of 35 deg internal angles in 3D?

For 35 degrees, you don't need 3D; a ring of 72 35-degree angles is a cycle (with a star pattern, rather than a polygon). There is a similar solution for any rational fraction of a full revolution (equivalently, any angle which is rational when measured in degrees (or gradians), but not radians).

However, the article said “about 35 degrees” so the actual number is probably something 34.5 ≤ x ≤ 35.5 but not actually 35.

My geometric intuition says that in 3D you can always construct a cycle but I don't know how to formalize it. Imagine a flat zig-zag chain of alternating bends; you can reshape it to a curve of arbitrary radius (around the axis of the width of the chain) by turning each bend slightly relative to its neighbors (about the axis of the beam), in alternating directions. Then you can choose a radius which makes the ends meet exactly.

Lasers even LEDs have terrible effecency vs battery's. What's worse is converting light back to electricity is also terribly inefficient so even if these worked as advertised you would be stuck with a terrible battery.

Even in a vacuum, you'll have diffractive losses unless the mirrors are infinitely large.

It doesn't have to have 100% efficiency, it only needs to be a significant improvement over existing battery technology.

Ah... a "can of light" as a practical energy storage mechanism. I think it's safe to say that this will remain a complete fantasy for the foreseeable future.

Example: my laptop battery has an energy storage of about 100 Watt-hours = 360 kJ. Suppose we want to store the same amount of power in an optical cavity (two mirrors pointed at each other) with a length of 0.5 meter. The time required by light to make a roundtrip in this cavity is 2L/c = 3 nanoseconds. Thus the power incident on the mirror at any given instant is (360 kJ)/(3 nanoseconds) = 10^14 watts!

This power is high enough that I suspect that even the vacuum itself couldn't conduct it without strange effects (production of particles, for instance).

This is the kind of thinking that could lead to better battery technology. Wouldn't it be amazing if the energy density of a system like this beat out gasoline?

Only if you ignore some of the operative words in the announcement: "virtually", "Just the right angle (about 35 degrees)".

For this to work as a storage medium it would have to work at an angle much closer to 90 degrees to avoid excessively large equipment and there would have to be a near perfect conversion both on the input side and on the output side (which as far as I know we currently don't have).

Perfect mirror in a vacuum?

> ... in a vacuum?

Aaah, good old "in a vacuum," surely one of physics most convenient simplifications, together with frictionless surface, the point particle and it's big-boned cousin perfect sphere and of course the infinite featureless plane. Except that a vacuum is actually kinda sorta possible in the real world too.

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

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.

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.

There are infinitely many real world applications of the quantum theory, from the spectrum of neon lamps to the nuclear magnetic resonance images. Another is all the solid state physics, and in particular superconductors and in particular modern computers, are based in quantum theory applications.

If you want a direct quantum phenomena that you use at your home everyday, you can choose giant magnetoresistance used in hard disk heads: http://en.wikipedia.org/wiki/Giant_magnetoresistance . This is my favorite case to explain that strange quantum effects have real world direct applications. Just start talking about the spin in currents in magnetic conductors and then add the sandwich with non-magnetic conductors, and then suddenly explain how it is used in hard disks.

It's difficult to choose a cool application because there are too many, but let's try:

A cool application: LEDs!

A cooler application: Laser diodes!!

A coolest application: Green Laser pointers!!! (They are actually an infrared laser diode that pumps another infrared laser that passes through a frequency doubling crystal to make it green.) ( See the last image of http://searchwarp.com/swa141478.htm )

Discovered not invented.

What, no pics?

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

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