Harmonic oscillators are key elements of the physicist's toolkit for modeling the world. Back at the end of March I wrote about some recent results using silicon nitride membranes to make incredibly high quality (which is to say, low damping) harmonic oscillators. (Remember, the ideal harmonic oscillator that gets introduced in undergrad intro physics is a mass on a spring, with no friction or dissipation at all. An ideal oscillator would have a \(Q\) factor that is infinite, and it would keep ringing forever once started.) This past week, two papers appeared on the arxiv showing that it's possible to design networks of (again) silicon nitride beams that have resonances at room temperature (in vacuum) with \(Q > 10^{9}\).
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| (a) A perimeter mode of oscillation. (b) a false- color electron micrograph of such a device. |
The other paper gets to a very similar design, through a process that combines biological inspiration (spiderwebs), physics insight, and machine learning/optimization to really maximize \(Q\).
With tools like this, it's possible to do quantum mechanics experiments (that is, mechanics experiments where quantum effects are dominant) at or near room temperature with these. Amazing.
Why does the high Q require (or let?) you do quantum mechanics with them? Shouldn't there be a macroscopic number of vibration quanta since the fundamental frequency is much lower than kT?
ReplyDeleteYou need the oscillations to be so-called “coherent” therefore the rate at which your oscillator is being populated by thermal noise (let’s call them thermal phonons) should be lower than the oscillation frequency. And that rate is kT/hQ at each temperature. Depending on your readout parameters of either opto or electromechanical system this quantity could be beneficial for a certain application. One interesting regime is when you can do cold-damping and do feedback on the motion of these oscillators via a coupling force (through your optical cavity for example) and cool them to low occupations.
DeleteAs Douglas mentioned you can find it in more details here in the review article: https://arxiv.org/abs/0712.1618
Thanks for posting these Doug. Cool stuff that I would have probably missed otherwise.
ReplyDeleteDo you know how much is understood about why silicon nitride is so special and why there are no losses? 10^9 is pretty darn big. Even in a "perfect" crystal I would have thought that there would be *some* processes (maybe surface scattering) that result in higher losses than this.
[Also read: How to become a professor]
Hi! You can check out Fedorov et al PRB on the Generalized dissipation dilution of high stress nanomechanics. In a nutshell, the high Q of SiN comes from the high stress and the geometric nonlinearity of the modes.
DeleteThanks for the post! Very interesting blog!
ReplyDeleteI’m Mohammad Bereyhi from EPFL, the author of the polygon work! I would be more than happy to discuss if you have any questions!
Anon, I think the trick is that if the product of Q and frequency is sufficiently high, it is possible to do special mechanical cooling techniques to lower the temperature of the resonator drastically. Also, in NMR it is possible with pulsed techniques to see coherent oscillations even though the energy splitting is tiny compared with kT (though that’s an ensemble experiment). I think the answer is in this review, though I haven’t read it: https://arxiv.org/abs/0712.1618 . Perhaps Mohammad can explain :-)
ReplyDelete@Steve, I'm not sure it is completely understood, but this paper is relevant: https://doi.org/10.1103/PhysRevLett.105.027205
ReplyDeleteWhat is so great about the USA when it is hellbent to make money by creating instability in another part of the world. Just having developed infrastructure but doing sophisticated forms of corruption does not make a country great. In hindsight, was Trump a better choice than Biden? Scientists, profs do not like or don't want to talk about politics. It is a pity because the most intelligent minds are not available to take a country on the right path. They r just happy and satisfied doing research in their comfy lab.
ReplyDeleteThe sad reality of today is that there aren't enough brilliant minds to have mankind walk on the path of peace and development and I hope profs/scientists realise where they get the funds for their research from.
https://www.newsweek.com/how-isis-got-weapons-us-used-them-take-iraq-syria-748468
https://www.theguardian.com/commentisfree/2020/feb/17/joe-biden-role-iraq-war
https://www.nytimes.com/2020/01/12/us/politics/joe-biden-iraq-war.html
https://www.theguardian.com/commentisfree/2015/jun/03/us-isis-syria-iraq
https://www.voanews.com/east-asia-pacific/china-outpaces-us-arms-supply-pakistan
https://www.thehindu.com/news/international/indias-weapons-procurement-from-the-us-jumps-to-34-billion-in-2020/article33286380.ece
Anon, people who know me know that I'm not shy about talking politics - I just tend not to do it here, because that's not why I write this. If you want a political discussion about US foreign policy, there are many other places online where you can do that.
ReplyDelete