Atomic nucleus excited with laser: A breakthrough after decades

[drakebake]

Hey, I'm one of the authors on the paper and see that people are curious about things. I'm happy to answer any questions, cool to find this here!

[fsh]

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.

[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.

[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.

[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...

[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.

[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

[MilStdJunkie]

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!

[blackoil]

> it's sort of shocking how little we know

To my feeble mind, it's shocking how much we know.

[javajosh]

Yeah and maybe we could do GR experiments on a table top. Gravity goes as 1/r^2 so a small r might make the mass terms irrelevant, and you could check GR in various ways [1] especially Shapiro delay[2]. This would, in turn, give a way to probe quantum gravity effects.

1 - https://en.wikipedia.org/wiki/Tests_of_general_relativity

2 - https://en.wikipedia.org/wiki/Shapiro_time_delay

[avsteele]

Nice to see this happen! When this was attempted with trapped ions, I and my colleagues at GaTech were the first to trap and laser cool Th(232) 3+

https://sites.lsa.umich.edu/kuzmich-lab/wp-content/uploads/s...

[est]

> 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]

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

[rolph]

this technology can be weaponized.

[tlb]

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.

[pfdietz]

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

[jhart99]

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?

[moconnor]

Interesting... there must be some error tolerance though, right? So there can be _some_ excess energy - where do they dump that to and what is the tolerance?

[andrewflnr]

Where do electron transitions usually dump excess energy?

[lifeisstillgood]

>>> 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

[fodkodrasz]

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.

[rpastuszak]

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]

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

[meindnoch]

https://apps.dtic.mil/sti/pdfs/AD1012150.pdf

Gravitational Detection of Submarines, PM Moser 1989

[MadnessASAP]

If you didn't know, deflections in earth's magnetic field are already used to detect submarines, amongst other things. Any large ferrous object will cause a small but detectable deflection in the magnetic field.

Range is pretty short but still large enough that you can do it from an airplane flying over.

[noqc]

Submarines are basically exactly the same mass as the water they displace.

[bobmcnamara]

Does the average density of most submarines approaching the density of water make that more difficult?

Are you looking for density variation between the parts and airspaces of a submarine?

[jncfhnb]

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]

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]

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.

[ISL]

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]

> this is extremely exciting

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

[dtx1]

What does "exciting a nucleus" mean?

[Geenkaas]

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?

[danans]

> 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!

[shadowtree]

Man, Vienna is killing it in physics.

Nobel in 2022 for Zeilinger

Nobel in 2023 for Kraus, who did his work at TU Wien

Now this. Giving a lot of other unis a run for their money.

[femto]

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-...

[rbanffy]

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

[galangalalgol]

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

[v3ss0n]

Odin must be proud.

[alexey-salmin]

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).

[einpoklum]

> 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]

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]

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

Resources companies are salivating