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Atomic nucleus excited with laser: A breakthrough after decades

cantrevealname
52 replies
11h16m

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.

infogulch
22 replies
10h52m

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...

thebruce87m
12 replies
8h51m

American football or European football? This is like the gallon thing all over again.

tzs
4 replies
4h55m

Note: I will use the term "soccer" for the most common football of Europe, "Association football", and "football" for American football. And before anyone says that soccer fields should be called "pitches" not "fields" I will note that FIFA's "Laws of the Game" call it "field" 184 times. They only mention "pitch" in the glossary where the heading for "field" is "Field of play (pitch)".

Generally you want to use American football fields for this because American football fields have a standard size, 100 yards x 160 feet (91.44 x 53.3 meters). That size field is used in professional, college, and high school football.

Soccer fields on the other hand not only vary from country to country, they aren't even always all the same size within a league. The English Premier League for example is trying to standardize on 105 x 68 meters but several clubs are not yet there: Brentford (105 x 65), Chelsea (103 x 67), Crystal Palace (100 x 67), Everton (103 x 70), Fullham (100 x 65), Liverpool (101 x 68), and Nottingham Forest (105 x 70).

For international play the standard is a range. 100-110 meters length and 64-70 meters width.

There are parts of soccer fields that are standardized to specific values rather than ranges so would be good for unambiguous length or area comparisons. The amusing thing is that those all have fractional values in metric but integer values in Imperial/US units:

• Radius of circle around center mark: 10 yards.

• Penalty area: 44 x 18 yards.

• Distance from penalty mark to goal: 12 yards.

• Goal area: 20 x 6 yards.

• Distance between goal posts: 8 yards.

• Height of crossbar: 8 feet.

airstrike
2 replies
4h51m

> I will use the term "soccer" for the most common football of Europe, "Association football", and "football" for American football.

I appreciate your valiant efforts but to my mind this is extra confusing because "soccer" is short for "association football"

Time to rename American Football to "handegg" once and for all. Ok, ok, I'll settle for "American Rugby"

vonzepp
0 replies
1h34m

Or just American Handball

smegger001
0 replies
1h49m

Or just go back to calling it gridiron football.

Galatians4_16
0 replies
4h18m

European soccer, or American soccer? (there are significant differences)

lionkor
4 replies
8h6m

standard football field size, or empirical average?

defrost
2 replies
8h1m

I suspect the average football field size across the former British Empire is close to the FIFA standard.

Throw in Australian Rules Football fields if you're looking for a maximum, particularly if orginal marn-grook is in the mix.

Someone
1 replies
6h20m

suspect the average football field size across the former British Empire is close to the FIFA standard.

The FIFA standard (https://downloads.theifab.com/downloads/laws-of-the-game-202...) leaves a lot of leeway:

“3. Dimensions

The touchline must be longer than the goal line.

• Length (touchline): minimum 90 m (100 yds), maximum 120m (130 yds)

• Length (goal line): minimum 45 m (50 yds), maximum 90m (100 yds)”

So, a field can be almost square at 90m × 89m or approaching thrice as long as wide, at 120m × 45m.

Reason for this is prior art that can be hard to change (if there’s a stadium around your field, and it’s deemed too small, you’d have to demolish it to make the field fit the standard)

Various competitions restrict this, though.

defrost
0 replies
6h11m

Interesting .. I hadn't realised there'd be so much give in the FIFA specs!

Thankyou for looking that up.

wil421
0 replies
7h15m

Laden or unladen?

passwordoops
1 replies
7h10m

Or Canadian or Aussie rules football?

greggsy
0 replies
6h58m

Gaelic, obviously

shiandow
7 replies
6h57m

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
6 replies
6h8m

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
3 replies
5h6m

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
2 replies
3h23m

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
0 replies
1h50m

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
0 replies
2h27m

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

shiandow
1 replies
5h33m

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
0 replies
1h40m

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

megous
0 replies
7h15m

Ah, imperial units...

roenxi
14 replies
9h3m

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
13 replies
7h7m

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
9 replies
6h58m

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

btilly
6 replies
6h26m

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
5 replies
6h18m

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
4 replies
5h50m

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

defrost
1 replies
5h25m

Does it?

Inversion is rarely unique, and it's not due to the precision with which the field is measured.

https://earthsciences.anu.edu.au/study/student-projects/nove...

https://inside.mines.edu/~rsnieder/snieder_trampert_00.pdf

Epilogue:

    Linear inverse problem theory is an extremely powerful tool for solving inverse problems. Much of the information that we currently have on the Earth’s interior is based on linear inverse problems

    Despite the success of linear inverse theory, one should be aware that for many practical problems our ability to solve inverse problems is largely confined to the estimation problem.

btilly
0 replies
2h45m

Yes, inverse problems are hard. And not always possible in practice. See, for example, https://www.ams.org/publicoutreach/feature-column/fcarc-1997... for a case where one isn't possible.

That said, the gravity technique is one that actually gets used today. With better precision, it can be even more useful than it already is.

JanisErdmanis
1 replies
2h37m

The problem is that the planet could be hollow and produce the same gravitational measurements on the surface and outside. It needs to be coupled with a model that introduces constraints for the inverse problem to be defined.

blincoln
0 replies
1h37m

Since mining is only concerned with material that's within maybe 0.1% of the distance from the surface to the core, seems like you'd just need to move the sensor around and make sure the signal changes about where you'd expect for a mass of X Kg at a depth of Y meters instead of a supermassive chunk of dense material much deeper. Or, to put it another way, build a grid map of the area and subtract any background signal. Would that not work for some reason?

fanf2
0 replies
6h40m

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.

defrost
0 replies
6h50m

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".

denton-scratch
2 replies
4h57m

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
1 replies
3h55m

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
0 replies
1h39m

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.

whatshisface
9 replies
9h50m

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
5 replies
7h35m

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 ;)

beretguy
3 replies
5h0m

"blue above visible blue"

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

adrianmonk
0 replies
3h58m

Surely it would be a blues band.

NateEag
0 replies
4h40m

But better would be a prog-rock album named:

Supravisiblue

Cthulhu_
0 replies
3h52m

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.

ngoldbaum
1 replies
3h28m

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
0 replies
19m

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_
0 replies
3h48m

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

fanf2
1 replies
6h45m

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
0 replies
4h17m

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.

colecut
0 replies
11h6m

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

M95D
0 replies
10h0m

They could at least say it was a UV laser.

dtx1
21 replies
11h10m

What does "exciting a nucleus" mean?

guidedlight
8 replies
10h58m

Thorium-229 has two energy states. A ground state, and an excited isometric state.

The laser is used to transition the nucleus from the ground state to the excited isometric state.

bboygravity
3 replies
10h45m

And then?

topspin
2 replies
9h47m

And then the nuclei return to the ground state. That process is probabilistic and measured in half-lives. The key point is that the decay back to ground state happens at a very precise rate that is not influenced by effectively anything, and can be measured accurately. Thus, a clock.

dtx1
1 replies
9h43m

That process is probabilistic and measured in half-lives

The decay back to ground state happens at a very precise rate that is not influenced by effectively anything

That sounds contradictory to me.

topspin
0 replies
9h25m

I suppose it could: the term "probabilistic" applies to the quantum probability of any one metastable isomer (excited nucleus) decaying to ground state. In application you measure large numbers of decays, and in great numbers the decay curve is extremely precise.

phendrenad2
2 replies
10h32m

Isometric? Like, is the nucleus gaining a virtual proton or something?

pfdietz
0 replies
4h21m

The correct word is "isomeric", as in the state of a nuclear isomer.

nullc
0 replies
9h14m

Nucleons occupy orbital energy states like electrons. The application of energy can shift the state of the nucleus, and some of these alternative states are relatively stable.

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

tinco
0 replies
9h34m

Not a physicist, so this comment is more of a guess with the intention of someone correcting me, but I think the thing all the physicists leave out because it's probably very obvious is that when an excited nucleus returns to its ground state, it will emit radiation.

So they hit their thorium with a laser, and then instead of the laser passing through, it gets absorbed, and then they get a flash of radiation back, letting them know the thorium was excited. The delay between the laser pulse and the flash of radiation is a property of the particular thorium nucleus, and is not affected by environmental circumstances like temperature or electric/magnetic fields, so can be relied on as a very precise measurement of time.

cshimmin
5 replies
10h52m

It means getting the nucleus to absorb a certain energy above its ground state. Since it is a quantum object, it can only absorb/emit energy in very specific amounts at once (“quanta”).

The details of how the nucleus manifests that extra energy are complicated, but you can imagine it as like, picking up a certain vibrational frequency.

huytersd
2 replies
9h48m

But then what happens? Does it expel an electron/release energy etc.?

greenbit
1 replies
9h22m

Probably just emits another photon of the exact same wavelength a short time later. The time would be probabilistic, like 50% chance of emission in X amount of time.

graycat
0 replies
8h52m

Physics does not emphasize this, but the half life concept essentially assumes a Poisson process (Cinlar, Stochastic Processes) which has a Markov (past and future conditionally independent given the present, details from the Radon-Nikodym theorem, with a cute von Neumann polynomial proof, Rudin, Real and Complex Analysis) assumption.

The half life concept seems to be standard over much of physics.

That a Markov assumption could hold might suggest some new physics.

euroderf
1 replies
9h53m

With enough absorptions, can the nucleus tear itself apart (i.e. fission) ?

gilgoomesh
3 replies
11h3m

Applying energy to lift its electrons across a band gap. In this case, applying 8.35574 electron volts.

mypalmike
1 replies
10h33m

I thought this was an excitation of the state of the nucleus rather than that of electrons.

popol12
0 replies
10h2m

You’re right, parent read too fast

Turneyboy
0 replies
10h6m

We know how to do this and have observed this tons of times at this point. This would not be novel in any way. This is about exciting the nucleus which is completely different.

sebws
0 replies
11h3m

The article mentions switching between "energy states":

This nucleus has two very closely adjacent energy states – so closely adjacent that a laser should in principle be sufficient to change the state of the atomic nucleus.

the correct energy of the thorium transition was hit exactly, the thorium nuclei delivered a clear signal for the first time. The laser beam had actually switched their state.

I don't know enough to explain any further.

atoav
0 replies
11h5m

Not a physicist but "exciting" a thing means to make it oscillate e.g. by adding energy into the system. A violin player is exciting the string of her instrument using a bow.

Now in this case they use lasers. I suspect if you choose the right wavelenght (=frequency) of light there is some sort of resonance phenomenom.

fsh
14 replies
11h32m

The measurement was already confirmed by a different group: https://arxiv.org/abs/2404.12311

This is important since impurities in the crystals used lead to all kinds of fluorescence that could be mistaken for a signal from the Thorium ions. Now two groups have seen exactly the same signal in different Thorium-doped crystals which is very covincing that they have found the actual nuclear transition.

tromp
9 replies
7h30m

I find it satisfying to see a researcher called THORsten SchUMm devoting his research to THORiUM.

lordfrito
4 replies
7h24m

Lol that's a comic book name if I ever heard one. He's only one lab accident away from becoming a super hero/villain.

pfdietz
1 replies
4h39m

And he's working with a dangerous radioactive isotope!

kingkawn
0 replies
4h21m

We’re so close! Send some spiders into the reaction chamber!

AnimalMuppet
1 replies
4h6m

But then I'm only a name change and a lab accident away. And a name change isn't that hard...

deepsun
0 replies
3h38m

It doesn't work with name changes, unfortunately.

mananaysiempre
1 replies
7h5m

For what it’s worth, the names of both the element and the researcher do in fact refer to the Norse god of thunder Thor.

twic
0 replies
5h22m

Even better, Thorsten = Thor's stone!

data_maan
1 replies
8h3m

Who will claim priority now?

jahnu
0 replies
7h16m

As I understand it, that is not an independent discovery but rather replication/confirmation of the results described in the original 14th of March paper by PTB & TU Wien.

ChuckMcM
0 replies
50m

Thanks for that, I wondered if it had been confirmed.

I am always in awe of folks who come into the lab every day and work on figuring out the one thing. I envy that level of focus.

yread
9 replies
10h23m

Is there some direct application? Like using the excitation states of different atoms for storing information?

irjustin
6 replies
10h13m

The article directly stated more precise atomic clocks.

pzs
4 replies
9h59m

Not a physicist, so I am asking out of curiosity and to learn: have the limitations to the precision of current atomic clocks posed any problems?

was_a_dev
0 replies
3h43m

If atomic clocks become a few orders of magntidude better than the current state of the art (see atomic lattice clocks) then such clocks would do direct gravitational wave measurements and measure some fundemental constants.

The latter is important in physics to determine if these constants are truly constant in space and time. Which is a large assumption we have about the universe.

sgt101
0 replies
9h43m

synchronization of compute across data centers is something I've used atomic clocks for, precision and cost are an issue.

nullc
0 replies
8h56m

We derrive most of our other units from time, so differences in time accuracy translate into metrology improvements more generally.

Existing atomic clocks based on electrical interactions are extremely sensitive to the surrounding magnetic and electrical environment-- so for example accuracy is limited by collisions with other atoms, so state of the art atomic clocks have optically trapped clouds in high vacuums. Beyond limiting their accuracy generally makes the instruments very complex.

One could imagine an optical-nuclear atomic clock in entirely solid state form on a single chip with minimal support equipment achieving superior stability to a room sized instrument.

huytersd
0 replies
9h51m

If I remember correctly GPS is effected but the ultra precise version the gov uses can error correct pretty well. I would think greater GPS precision at a lower cost?

raverbashing
0 replies
9h32m

Usually these application, while they're good, they're just the initial idea people have given the current understanding

The cool applications usually come later (or they're more esoteric). The researchers were more excited to determine the actual frequency than think about clocks

limbicsystem
1 replies
8h14m

I >think< that this will enable more accurate magnetometers (see OPM-MEG and atomic clock magnetometers). Which can be used, among other things, for measuring neuronal activity.

nebben64
0 replies
41m

Can you explain your reply a bit; how will MEG tech evolve from this breakthrough?

danans
8 replies
11h55m

This makes it possible to combine two areas of physics that previously had little to do with each other: classical quantum physics and nuclear physics.

Is quantum physics now considered part of classical physics? If so then man, time flies!

emblaegh
3 replies
11h23m

Classical there is used in the sense of “non relativistic”.

denton-scratch
2 replies
4h49m

I thought relativistic quantum physics was not a thing (yet).

omnicognate
0 replies
47m

Special vs general. Quantum field theory is special relativistic and quantum mechanical. The grand unified theory stuff is about uniting general relativity and quantum mechanics.

itishappy
0 replies
3h50m

Nope, it's a thing! The Dirac Equation is one example. It explains the Pauli exclusion principle and predicts anti-matter.

It is consistent with both the principles of quantum mechanics and the theory of special relativity, and was the first theory to account fully for special relativity in the context of quantum mechanics.

What we don't have is a grand unified theory (a single set of rules that generates both theories), but we can consider relativistic effects in QM theories, and (I assume) vice versa.

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

dxuh
1 replies
11h42m

There is a big difference between "classical" quantum mechanics (about 100 years old now!) and quantum field theory (~50 years old). Maybe that's what they mean?

snthpy
0 replies
11h17m

When I was at university about 25 years ago, QM was about electron transition energies, with QED being a refinement of that for things like fine structure. In experimental HEP you had QCD and quark gluon plasma which informs things like the LHC experiments at CERN.

IIRC nuclear physics was largely phenomenological with a lot of observations that had simple models fit to them without being able to reduce those to the particle physics models. This might be about establishing a link between the phenomenological nuclear models and the fundamental QM models.

scotty79
0 replies
11h24m

I think they want to convey that nucleus is a really weird place so quantum physics of everything else is classical by comparison.

JanisErdmanis
0 replies
10h39m

We currently don’t know how to calculate the nucleus’s bound state despite a thorough understanding of individual pieces that make it together, as explored in colliders like CERN and others. The problem is similar to telling at what temperature water is boiling, freezing, and its density from knowing the properties of a single water molecule. We understand quantum mechanics and Columb forces govern the properties; it is incredibly hard to renormalise the system from an energy scale of a gas to a liquid or solid. Similarly, it is for a quark-gluon plasma; thus, phenomenological models are used, like how the nuclear potential could look and the masses for different combinations of nuclei.

tlb
7 replies
11h33m

From the paper, the light is UV-C at around 140nm or 8.4 eV. But it has to be very precisely the right energy to cause the transition, since nuclear states don’t have any place to dump excess energy to.

jhart99
2 replies
7h30m

Ahhh thank you! I was wondering why the energy had to be so precise. That makes a ton of sense why it has to be so accurate. What makes this transition so low energy? The only other atomic excited state I have any knowledge of is the iron excited state used in Mossbauer spectroscopy. That transition is much higher energy. Also that one has some coupling to the electronic state of the nucleus. Does this Thorium transition have some special reason that it isn't coupled to the electronic state?

twic
0 replies
4h51m

I found a paper which measured the energy of the transition [0], but it doesn't talk about why it's so low. Might be a starting point if you have more time to read than i do, though!

EDIT Hmm [1]:

Interestingly, the existence of a nuclear excited state of such low energy seems to be a coincidence and there is currently no conclusive theoretical calculation that allows to predict nuclear levels to this precision.

And there is a paper with a ton of detail and some nice diagrams of energy levels [2], but i'm not sure it really gets at "why".

[0] https://arxiv.org/abs/1905.06308

[1] https://link.springer.com/article/10.1140/epja/s10050-020-00...

[2] https://iopscience.iop.org/article/10.1088/1361-6455/ab29b8

adrian_b
0 replies
6h44m

The radiation emitted when nuclei transition between their internal energy levels is known as gamma rays.

The gamma rays normally have energies per photon many orders of magnitude greater than for visible light and also much greater than for X-rays (which are produced by electrons accelerated by very high voltages when hitting a target).

The thorium 229 nucleus is the only one that can emit gamma rays that are so low in energy that their energy is not only lower than for X-rays, but it is also lower than for many sources of ultraviolet light. For instance the ultraviolet light used in state-of-the-art lithography for semiconductor manufacturing has much higher frequency (shorter wavelength), by about ten times.

These gamma rays of the Th229 have a wavelength that is not much shorter than the 184-nm ultraviolet light that can be obtained with a mercury-vapor lamp.

What is important is that for such a frequency/wavelength it is possible to build laser sources, which enables the design of an atomic clock that will use thorium 229 nuclei instead of neutral atoms or ions of other elements (like ytterbium, lutetium, strontium, aluminum).

andrewflnr
2 replies
3h29m

Where do electron transitions usually dump excess energy?

infogulch
0 replies
11m

In general it's possible for electrons to jump to sub-orbitals which gives them a wider band of wavelengths that they can emit and absorb photons. The jumps between sub-orbitals are usually in microwave or radio bands.

ChrisClark
0 replies
2h6m

Don't they usually create a photon with that energy?

pfdietz
0 replies
4h32m

The Q of nuclear transitions is just insane (as reflected by their long half life, something in excess of 1700 seconds here for free atoms.) The uncertainty relationship is normally written as delta-p delta-x > hbar/2, but it can also be written as delta-t delta-E > hbar/2. So, if the half life is very long, delta-E can be very small.

This fact is used in Mössbauer spectroscopy (recoilless gamma emission in solids). The peak is so sharp that it was famously used by Pound and Rebka to detect the gravitational red shift in the lab at Harvard in 1960, reaching 1% accuracy by 1964.

https://en.wikipedia.org/wiki/Pound%E2%80%93Rebka_experiment

lifeisstillgood
7 replies
9h24m

>> For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources

Hold on how does that work?

I have had a sort of sci-fi idea that sufficiently sensitive gravitational field measurements coukd detect the passing of submarines (I am not sure on the maths tbh) - which would render a lot of nuclear strategy moot.

Just need to get a grasp on the maths

perihelions
1 replies
8h55m

Look at what paper actually says: flat "not achievable" in the abstract; and the scaling laws on page 4 are third- and fourth- inverse powers of distance (!!!!); and on page 7 they're considering ranges of the same length scale as a submarine itself (few hundreds of meters), and even there it's hopeless.

This one's never going to happen.

Geologic mass concentrations are an entirely different story: you get a gravitational monopole, which is a more reasonable inverse square law. (No monopoles for a submarine, because by design they have a mean density equal to water—as the paper explains).

Eliezer
0 replies
6h24m

What an excellent retrospectively obvious point!

moffkalast
0 replies
9h12m

That then makes single SLBM drone swarms the new meta. Spread them over a large enough area and it'll just seem like tectonic activity.

rpastuszak
0 replies
8h57m

Check out quantum navigation systems. They're not used to track submarines, but rather as an alternative to GPS for submarines (using tiny differences in the Earth's gravitational field to determine position).

(IIRC) Royal Navy trialed it (officially) for the first time last year.

limbicsystem
0 replies
7h39m

Sufficiently accurate clocks can act as 'relativity sensors' - measuring changes in the 'time' bit of spacetime due to small changes in gravity.

fodkodrasz
0 replies
8h41m

Actually the method of detecting mineral deposits by mapping gravitational field is already in use since a long time!

The Eotvos pendulum (an instrument aka. Eotvos torsion balance) designed in 1888 started this kind of measurement. It was used commonly by the 1920s by geophysicist for mapping underground deposits by measuring the gradient of the gravitational field very precisely.

This instrument was deprecated later by even better tools for surveying.

The instrument was initially constructed for the experiment showing that inertial and gravitational mass are the same (well, linearly correlated) to a great precision: https://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_experiment

https://www.nature.com/articles/118406a0 (pretty useless link, but a famed periodical)

Detecting submarines is way harder, practically impossible. as others have already pointed out.

rbanffy
3 replies
9h6m

Professor Thorsten discovering a mystery of Thorium... How appropriate. Thor must be proud.

v3ss0n
1 replies
8h16m

Odin must be proud.

B1FF_PSUVM
0 replies
7h58m

This is where I slip in my recommendation of the little book titled Votan, by John James.

galangalalgol
0 replies
7h23m

Also, it was submitted on the 18th, which was a Thorsday...

nullc
3 replies
10h25m

Now how the heck do you generate ~148.38nm light with a narrow linewidth? Their approach using four-wave mixing inherently results in short pulses.

.. and given that it decays through gamma emission, does this mean we could now build an optically pumped gamma ray laser?

M95D
1 replies
9h53m

The gamma emission would have to re-excite other atoms in a cascade to create a laser. Since the exciting energy is UV, not gamma => no cascade amplification.

A "wavelength converter" might be possible.

PS: Are you sure it's gamma emission? That takes more energy than the exciting UV photon.

karma_pharmer
0 replies
9h9m

PS: Are you sure it's gamma emission? That takes more energy than the exciting UV photon.

Apparently it is neither:

Decay of the 229Th isomeric state of the neutral thorium atom occurs predominantly by internal conversion (IC) with emission of an electron

https://www.nature.com/articles/nature17669

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

This is pretty weird. You shine UV light (with exactly the right wavelength) on 229Th, and it spits out electrons. But not like the photoelectric effect, where the electrons stop as soon as you turn off the light. No no. The Thorium keeps spitting out an exponentially-decaying stream of electrons for hours after you stop illuminating it.

Almost like an exponentially-discharging solar-powered current source (for a very specific wavelength of "solar").

karma_pharmer
0 replies
9h24m

The last sentence of the paper seems to imply that this result will give people a reason to want to develop those:

The development of dedicated VUV lasers with narrow linewidth will make it possible to access a new regime of resolution and accuracy in laser M¨ossbauer spectroscopy and to perform coherent control of a nuclear excitation"

Previously, if you wanted to manipulate nuclear states, you needed a synchrotron. Now, you need an infinitely less expensive instrument. I suppose the idea is that that will generate a lot of interest in improving the less-expensive instrument.

jncfhnb
2 replies
7h20m

1) does this have any relevance to thorium as nuclear fuel? Looks like no.

2) is there any significance to the units of the wave length? Like they’ve narrowed it down to a number. Does that granularity map to anything? Some sort of discrete scale? Or is there going to be a range of values that work +/- a super tiny value.

adrian_b
0 replies
6h34m

This has indeed no relationship with nuclear energy, except that thorium 229 is produced in nuclear reactors.

This achievement is a step (the most important one) towards the goal of making an atomic clock that uses thorium 229 (which has important advantages mentioned in another posting).

acidburnNSA
0 replies
4h55m

Not yet. But if someone could condition nuclear fuel atoms so that when they do fission, they consistently break into one delayed neutron precursor and one stable or near stable atom with no long-term afterglow heat, that could revolutionize nuclear power. I've been told that this dream is impossible but it's still my 1 genie wish. Right now they break into 50% of the periodic table and cause all sorts of grief.

alexey-salmin
2 replies
9h39m

Did anyone understand how they hold a nucleus (not an atom) in a crystal? Nucleus is charged and seeks electrons, I thought you need an electromagnetic trap for that (which the article says they don't use).

spuz
0 replies
9h33m

They use Th4+ ions, not nuclei. The lack of 4 electrons in the Th cations is compensated for by the surrounding F- anions.

rsfern
0 replies
8h2m

They grew CaF2 crystals with a small amount of thorium, which take the place of some of the Ca atoms in the crystal lattice. There’s an illustration in fig 1 of the preprint of what the substitutional defects look like

Like the other poster mentions, CaF2 is an ionic crystal, but I don’t think that’s an important detail because you wouldn’t expect a nuclear transition to be affected by the bonding state of the electrons. My guess is it’s just a convenient way to get a very dilute collection of thorium atoms without using an ion trap

gwd
1 replies
10h37m

It could be used, for example, to build an nuclear clock that could measure time more precisely than the best atomic clocks available today.

Are today's atomic clocks really so imprecise? Without further explanation of this, it reminds me of this comic (which is alas showing its age both by mentioning flash, and by implying that 1024 is already a uselessly high number of cpus to support):

https://xkcd.com/619/

fancy_pantser
0 replies
10h35m

Intel GPU joke in the alt text, truly timeless.

est
1 replies
9h29m

But it is not just time that could be measured much more precisely in this way than before. For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources or earthquakes

This has military applications as well, right?

Replacing GPS for nuclear submarines.

https://news.ycombinator.com/item?id=29213751

https://news.ycombinator.com/item?id=36222625

hargup
0 replies
6h49m

My buddy works for such a company, https://www.atomionics.com/ and they are doing pilots with mining companies.

einpoklum
1 replies
3h39m

For the first time, it has been possible to use a laser to transfer an atomic nucleus into a state of higher energy and then precisely track its return to its original state.

We've known about photon-atom interactions for well over 100 years, with excitation of electrons which are either released or drop back to the original orbit, right?

So, ok, the Nucleus is smaller and the energies to alter the quantum state are probably higher, but - why is this so special, and why Thorium in particular rather than any old nuclei?

Disclaimer: I'm not a physicist.

was_a_dev
0 replies
3h22m

The energy required to alter nuclear states is often in the MeV energy range, where Thorium is a rare example that has a very close state to the ground state, seperated by 8.4eV (100,000 less energy)

This means that to exicte to this nuclear state is possible using an ultraviolet laser

It has important applications for nuclear theory, nuclear atomic clocks and fundemental constant metrology.

bamboozled
1 replies
9h42m

For example, the Earth's gravitational field could be analyzed so precisely that it could provide indications of mineral resources

Resources companies are salivating

worldsayshi
0 replies
9h4m

It wouldn't be precise enough to measure things like what type of rock you have underneath when you're thinking about digging a tunnel or to find land mines in dirt right?

MilStdJunkie
1 replies
3h6m

When you stop and look at QCD in the big picture, it's sort of shocking how little we know - like, really, really know - about the internal structure of the proton, or even the nucleon!

It's the curse of "probing" with massive energies. No one's a hundred percent certain of whether they're detecting something that's actually there - like there there - or whether they're looking at by-product of enormous collision energies.

Physicists are smart people! I could never do what they do. But there's a limit to certainty, and inside the proton especially there's unknown first principles at work. Bringing the precision of photons and lasers into this nucleon party is going to be huge. I can't wait!

ISL
1 replies
3h56m

No time to elaborate at the moment. Just want to say that this is extremely exciting news.

Finding the thorium line is one of the most important open problems in precision/fundamental measurement.

einpoklum
0 replies
3h37m

this is extremely exciting

That's what the Thorium said! [rim shot]

swamp40
0 replies
21m

> thorium crystal clock

Take note, science fiction writers.

sharpshadow
0 replies
10h15m

That’s great news! As far as I understand constants are not an easy topic and being able to analyse more precisely is a big win.

femto
0 replies
7h34m

An obvious question is whether this be used to build a nuclear analogue of a laser, using nuclear transitions instead of electron transitions. It turns out to have already been asked:

https://physics.stackexchange.com/questions/296237/nuclear-t...

In summary, the answer seems to be "maybe, but why?". The laser was originally called "a solution in search of a problem", which would suggest that "why" isn't really a reason not to.

https://ask.metafilter.com/148055/Who-first-called-lasers-a-...

enslavedrobot
0 replies
3h36m

Very cool. Probably impossible but I wonder if you could see non-linear nuclear effects if you hit it with enough intensity.

Laser induced fission anyone?

dharma1
0 replies
6h27m

What stocks do I long, armed with this information :)

davidwritesbugs
0 replies
3h29m

Would this have any relevance to inertial navigation sensors?

cwillu
0 replies
3h7m

Literally over 50% of the viewport is taken up by sticky toolbar crap, depending on the window size.

Geenkaas
0 replies
9h42m

My high school physics class flashes back to me, I don't think I understand a fraction of it but it seems very exciting (pun intended).

I was reading up on this (now outdated) wiki page: https://en.wikipedia.org/wiki/Isotopes_of_thorium#Thorium-22...

And it mentions the application as qubit for quantum computers. If the state change is relatively simple, cheap and stable, what could this do for quantum computing? I picture a crystalline processor holding Thorium nuclei as the brains of a new supercomputer? Would that be viable?