[cantrevealname]

> If the wavelength of the laser is chosen exactly right ... then maybe a special atomic nucleus could be manipulated with a laser, namely thorium-229. On November 21, 2023, the team was finally successful: the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time.

So what's the wavelength? I felt like the article left me hanging.

The answer is: 148.3821 nm

Yes, I admit that it's meaningless to me. It's sort of like a big news story announcing that Malaysia Airlines MH-370 has been located somewhere in the world's oceans, but not saying where because a number like 148.3821 km SSE of the Cocos Islands is going to be meaningless to most people.

[whatshisface]

148nm is on the lower end of UV-C. It's higher-energy than the furthest ultraviolet light that the sun produces (200nm). If it were produced artificially, it'd be heavily absorbed by the atmosphere to the point of near opacity. If the visible spectrum was an octave, where the "tone" of a color wrapped around from red back to blue the way G wraps to A, it'd be the blue one octave above visible blue.

[pmayrgundter]

Nice to hear the octave relation used!

"blue above visible blue" is a good name.. hmm, a little web tool to name these would be neat ;)

[Cthulhu_]

Out of curiosity I googled to see if there's formal names to things beyond UV and a SO question came up saying Klingon has a word for a color that falls within the UV spectrum, Amarklor; it "falls between violet amarklor (dark violet or purple) and amaklor-kalish (almost black)".

Else there's Octarine from the Discworld books, it's the colour of magic.

Another one in that same SO thread is err, quantifying synesthesia in the study of "chromophonics", where sound is assigned a color and vice-versa, that is, one could name a colour after a sound, which matches up with the earlier "octave" analogy.

[beretguy]

> "blue above visible blue"

Good name for a rock band. Or some tv series.

[NateEag]

But better would be a prog-rock album named:

Supravisiblue

[codethief]

Indeed. In German, "blue" (blau) is sometimes used to say "drunk/inebriated" which makes the name all the more appropriate for a rock band, I think. :)

[ethbr1]

Joni Mitchell - Blue (Blue)

https://m.youtube.com/watch?v=MvR7Dkg4NQU&t=820s

[adrianmonk]

Surely it would be a blues band.

[ngoldbaum]

Teeny nit, the sun produces light well into the x-rays (mostly from the corona though). You're probably talking about sunlight making it through the atmosphere.

[whatshisface]

I'm talking about the blackbody radiation of the sun's surface, which accounts for almost all of the light. The X-ray flux at earth is 11 orders of magnitude lower than the blackbody-related flux.

[Cthulhu_]

It looks like "chromophonics" is a thing to link colors with tones (synesthesia)

[roenxi]

Physics like this (really I'd call it materials science; it isn't but it has immediate practical applications on building things) is a bit of a sleeper in terms of importance. Small improvements in tolerances and materials drive huge changes in what is economically feasible at the other end of the science-engineering-machining pipeline. "We've built a higher precision thing" is usually huge news. Take semiconductors, where the entire industry is driving crazy value entirely from getting better at moving atoms around by a few nanometers.

Missing out on the magic number does seem like a bit of a problem, but really the expectations on the audience are already quite low. That number could easily turn out to be worth more than a trillion dollars to humanity at large, but I'd bet most readers just think of it as a party factoid.

[adrian_b]

This actually has significant practical importance, because it is hoped that using this transition of the thorium nucleus it will be possible to build atomic clocks even better than those using transitions in the spectra of ions or neutral atoms, because the energy levels of the nucleus are less sensitive to any external influences.

While in the best atomic clocks one must use single ions held in electromagnetic traps or a small number of neutral atoms held in an optical lattice with lasers, in both cases in vacuum, because the ions or neutral atoms must not be close to each other, to avoid influences, with thorium 229 it is hoped that a simple solid crystal can be used, because the nuclei will not influence each other.

The ability to use a solid crystal not only simplifies a lot the construction of the atomic clock, but it should enable the use of a greater number of nuclei than the number of ions or atoms used in the current atomic clocks, which would increase the signal to noise ratio, which would require shorter averaging times than today, when the best atomic clocks require averaging over many hours or days for reaching their limits in accuracy, making them useless for the measurement of short time intervals (except for removing the drift caused by aging of whatever clocks are used for short times).

[WitCanStain]

What could we do with more accurate atomic clocks that we cannot do with current ones?

[btilly]

The article points to a use I wouldn't have thought of.

The deeper you go into a gravitational field, the slower time goes. Therefore comparing clocks in different places gives a way to measure gravity. These clocks could be sufficiently precise to find mineral deposits underground from their gravity signature.

[defrost]

> These clocks could be sufficiently precise to find mineral deposits underground from their gravity signature.

We've been doing that since the 1960s at least with such things as the LaCoste & Romberg gravimeter (1936).

You can download, see online the "Geoid"

https://americanhistory.si.edu/collections/nmah_865074

https://en.wikipedia.org/wiki/Gravimetry

https://en.wikipedia.org/wiki/Geoid

Magnetic anomalies also highlight inteesting places for minerals, the issue with both magnetic and gravity fields variations lies with determining the "true" depth to target (medium sized shallow target, or massive deep taget?) which is known as an inversion problem.

[btilly]

Yes, but a better clock means more precise measurements, means we can locate smaller masses to higher precision.

[defrost]

For interest, Precision Vs Accuracy, Atomic Clocks Vs Sapphire Oscillator

https://news.ycombinator.com/item?id=28232645

Detecting gravity waves with large laser triangles required a few advances in technology - precision clocks was one.

Not so long ago had you asked your question the answer would have been "detect gravity waves".

[fanf2]

Most units of measurement are derived from the second, so the more precise our frequency standards, the more precise everything else can be. Things like interferometry and spectroscopy depend directly on very precise frequency standards.

[denton-scratch]

> clocks even better than those using transitions in the spectra of ions or neutral atoms

I'd be interested to know how much more accurate a nuclear-state-transition clock might be than a conventional Caesium or Rubidium clock.

TFA seems to make the point that a nuclear clock would be more resistant to external influences, such as EM radiation, than an atomic clock, and so could be used in experiments where such influences might introduce unwanted uncertainty. But I'd like to know what the claim for greater accuracy is based on, rather than simply greater reliability.

[wbl]

You have the math turned around. Because the nuclear resonance is much more stable and high frequency the Q factor and accuracy of the measurement is higher. With a cesium or rubidium clock it's very difficult to control all the influences on how tightly the nominal resonance is achieved and the Q while impressive is a bit less.

There are some real challenges in realization: this will take optical combs and all sorts of other stuff to really take advantage of.

[pfdietz]

They also point out that because the thorium atoms can be embedded in a solid, and have motion << the wavelength of the radiation, the emission and absorption are largely recoil-free. This eliminates Doppler broadening. What broadening there could be was below the resolution of their pump beam.

[infogulch]

Oh that's about 0.0000000014 football fields.

More seriously, apparently it takes a photon with a wavelength of 92nm to eject an electron from a hydrogen atom. Maybe this is a reasonable reference/refresher: https://web.archive.org/web/20210413042937/https://www.nagwa...

[shiandow]

More to the point >400nm is visible light, this puts 148nm well within the ultraviolet range. Though it's not too far removed from the visible spectrum, wouldn't surprise me if some animals could see it.

[LeifCarrotson]

148 doesn't feel too far removed from the visible spectrum, but it's in the wrong direction for animals to make use of it. I'm no biologist, but I'd be shocked if there were any animals that had adapted sensitivity to a type of radiation that they are never exposed to in nature. The sun doesn't really emit much UV-C light:

https://en.wikipedia.org/wiki/Solar_irradiance#Absorption_an...

and the light that is emitted is absorbed by the atmosphere:

https://en.wikipedia.org/wiki/Ultraviolet#Solar_ultraviolet

It's useful to be able to see a little UV-A, perhaps, and very useful for predators to see 'heat' into the IR range, but if your eyes were sensitive to 148nm, the world would be pretty dark.

Maybe after a few million years, in the grinding dust in the back of my shop, something will evolve that has a symbiotic relationship to arc welders...

[twic]

Also, even if there was some advantage to doing so, i'm not sure how animals could see a wavelength that short. They would need a photoreceptor protein which can absorb photons of that wavelength and turn them into some sort of chemical change which can trigger a signalling cascade. That protein would have to have a pair of molecular orbitals which are h * 148 nm apart. What can give you that?

The ethene double bond absorbs at ~165 nm, a benzene ring at ~180 nm, and building things out of those tends to increase the wavelength, not decrease it. 148 nm is single bond territory - could you have a chromophore which uses photons of the right wavelength to break a bond, and then somehow react to the presence of free radicals?!

[narag]

A long time ago I saw some UV photos of flowers, compared to visible and IR. There were some distinct features. That suggests some insects could see them, but of course it's just speculation.

[blincoln]

It's not speculation. Bee eyes have receptors for green, blue, and UV-A light, for example. But as BenjiWiebe mentioned, that's not the same as being sensitive to UV-C.

I'm sure there would be some value in seeing others parts of UV. Some minerals fluoresce from one type of UV light but not another, so they'd be dark in the bands that cause them to fluoresce. Mantis shrimp can apparently see into UV-B, but I'm not aware of anything living that can see UV-C.

[BenjiWiebe]

That would be UV-A, I believe. Not UV-C.

[nullc]

Many animals do have more UV extension than you might initially assume useful: due to scattering following the inverse fourth power of wavelength the sky is lit in the UV a long time before sunrise.

Presumably wouldn't apply anywhere near as far as 148nm since as you note that light doesn't make it to earth.

[shiandow]

Ah, yeah makes sense that animals couldn't see it if it's not really part of sunlight. I was thinking it was not physically impossible, but it would be remarkably pointless if the light is simply not there.

[pfdietz]

I don't see how it could get into an organism if it's absorbed by air and water.

[fanf2]

For comparison, over the last several years there has been a lot of research into optical frequency standards. Because they run at a higher frequency than (microwave) caesium frequency standards, optical frequency standards can be more precise. The current candidates https://iopscience.iop.org/article/10.1088/1681-7575/ad17d2 have wavelengths between 750nm and 250nm. Caesium frequency standards use a wavelength of 32.6mm, so about 100,000x bigger than optical frequency standards.

Based on just the frequency, I dunno what makes the thorium nuclear transition much better than optical transitions. Unless the excitement (as it were) is about scaling up to even higher frequencies.

[CamperBob2]

The key factor is the line width, or the range of frequencies over which the transition can be stimulated. The ratio of the stimulus frequency and line width is one way of expressing the resonator Q factor. In general, the lower the line width for a given transition, the higher the Q, the better the signal-to-noise ratio, and the more stable the resulting clock. (Imagine how much more precisely the frequency of a large bell could be measured compared to a cymbal or something else with a broader acoustical spectrum.)

Cs or Rb clocks give you a line width of a few hundred Hz at 9 GHz (Q=roughly 100 million), while quantum transitions in optical clocks can achieve line widths on the order of 1 Hz in the PHz region (equivalent Q in the quintillions.) There is a lot more to building a good clock than high Q, but it's a very important consideration ( http://www.leapsecond.com/pages/Q/ ).

What caught my eye is the ringdown time of the stimulated optical resonance, apparently in the hundreds of seconds. They talk about line widths in the GHz range, but that seems to refer to the laser rather than the underlying resonance being probed. It would have been interesting to hear more about what they expected regarding the actual transition line width. Probably the information is there but not in a form that I grokked, given insufficient background in that field.

[foxyv]

It's kind of funny, the 148.3821nm light being used to excite the nuclear transition is undoubtedly ultraviolet. However, the distinction between X-Rays and Gamma Rays is that Gamma rays originate from the nucleus. So in some lights, the photons emitted by the nuclear phase transition back to it's base state could be called "Gamma Ultra-Violet."

https://en.wikipedia.org/wiki/Gamma_ray#Distinction_from_X-r...

No one WOULD call them gamma rays, but just a fun thought!

[M95D]

They could at least say it was a UV laser.

[colecut]

I guess they could have said the laser frequency is about 2.02 petahertz

[zh3]

Typical LED wavelengths by colour:-

  UV    385nm
  Blue  450nm
  Green 525nm
  Red   630nm
  IR    880nm