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.
Not completely. Can't find it now, but there was research cited in the book Alex's Adventures in Numberland showing a real statistical deviation, example: Lawrences' studying Law school more frequently.
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.
> 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.
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.
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.
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. :)
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.
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.
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.
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).
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.
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.
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.
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.
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?
In practice, that's what would happen. Move around until seeing some larger gravitational pull, likely indicating some deposit. However, formally, this is not correct due to the mere fact that the gravitational force is proportional to 1/R^2, just like a Columb force. Thus, there are infinite numbers of mass distributions that produce the exact same gravitational field on the surface. The planet could be hollow, and we would not know it only from the field measurements.
A practical constraint is mass density, which has maximum and minimum values. We can make a crude approximation that the planet's density is constant, evaluate the field on the surface from the planet's shape and compare it with measurement. This would be more useful, but still, it wouldn't tell us whether there is a combo of water reservoir and a large massive deposit below it.
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.
> 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.
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.
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.
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:
I've heard "handegg" before but a football is not shaped like an egg, it's vaguely egg-like but the teardrop shape of an egg is distinctly not what a football looks like.
• 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)
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.
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:
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...
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?!
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.
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.
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.
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.
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.
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.
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."
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!
Speaking for myself, as a layman, I had always been walking around thinking of hadrons as balls with other balls inside, with forces mediated by tiny/insubstantial yet-to-be-discovered balls.
Yes, I knew they weren't balls, exactly, but still. Newer models with greater sensitivity have sort of pulled a fast one: that maybe the balls are a side effect of the way we look at them. More precisely, to look at them, we need to smack them hella hard, to make the balls come out where we can see them. But the smacking might be a part of why the balls look like balls!
The native hadron in its natural habitat might be something fantastically more complex, a sort of cell biology of energies all competing and vibrating, and they're part of the interrelated forces of the nucleus itself - we might even use that obsolete term return, the "nucleon", to represent this complex. Jiving against all of this are new ideas about what mass actually is, defining spatial attributes as degrees of freedom, and all sorts of new thoughts. It's super exciting.
So that's what I mean by "shocked how little we know", because what we did think we knew got oversold as a World of Balls.
But who knows?! Maybe this neat laser thing can help find more answers.
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.
> 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
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.
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.
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?
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).
Arent gamma, x, and uv ALL em radiation? What makes a gamma with a wavelength near uv still allow it to be called gamma? Why dont we say the nucleon emits uv at 148 when it transitions to its ground state?
You could say that as well. Gamma is often (usually?) defined as any radiation that originates from nuclear state transitions rather than electrons; this tends to be very high energy but can overlap the range of EM radiation from electronic transitions. Th229 is the extreme outlier.
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".
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?
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.
For free atoms, yes. For atoms in a crystal lattice (or other solid), it's quite common for electrons to decay through phonon interactions, i.e. by emitting vibrations (i.e. heat) to the lattice.
>>> 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.
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.
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.
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).
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.
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.
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).
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.
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.
Yes, that's one possibility[0]. Or the energy can be sufficient to alter the decay rates of other nuclear reactions (alpha/beta decay, etc.) compared to the base isotope. A weird example: Excited tantalum-180[1] is more stable than its base state.
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.
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.
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.
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.
25 years ago, there were experiments to move element 72 hafnium (Hf) between its low and excited isomer states, which would allow for the creation of a nuclear battery that could store 100,000 times more energy than a chemical battery, with a 31 year half life, but without neutron release:
This would be Iron Man and Star Wars tech if it worked. Unfortunately experiments went dark after 2009, probably because it worked haha, but maybe because Hf is too rare to make a practical battery. So it looks like they tried spalling element 73 Tantalum (Ta), 74 Tungsten (W) and 75 Rhenium (Re) with protons at 90-650 MeV to create 72 Hf with atomic masses 178, 179 and high spin 178m2, 179m2 isomers if I read this right:
There's a lot here though, so I can't really get a clear picture of what the yields are, or simply how many joules it takes to store one joule in an excited isomer. Which is of course all that matters, but papers often leave off the one part we're curious about, forcing us to learn nearly the entirety of the subject matter to derive it ourselves. Although on the bright side, maybe that protects us from nuclear armageddon and stuff.
Maybe someone can fill us in?
Edit: dangit _Microft beat me by 17 minutes, please answer there :-)
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.
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.
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.
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.
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.
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?
> 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!
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.
The body of work called quantum field theory is a theory of relativistic quantum mechanics although many aspects of its foundations are difficult to pin down, its a very powerful and useful apparatus.
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.
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.
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?
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.
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:
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.
To build a laser, you would need at least three energy levels, and ideally four, with particular constraints in the transition probabilties so that you can create population inversion. And you would need to pump it with a higher-energy (shorter wavelength) laser.
Perhaps doable with a free electron laser, but probably not with traditional lasers, due to the energies involved.
But, yeah, not sure what the use would be. Maybe a form of lidar that allowed measuring speed of objects to extreme precision, by measuring the dopler shift of reflected light? (Assuming light at such a short wavelength is reflected sufficiently, which it probably wouldn't be).
If there happened to be one atom/matrix that could be tuned to the transition energy of another atom's fission transition energy, then you could use it to burn nuclear material / waste. But you could just do that with the pump laser directly.
I suppose you could maybe pump such a laser with a very high temperature plasma (like fusion temperatures hot), rather than with a free electron laser. Then maybe it might make more sense.
Very interesting! Two-photon pumping of traditional lasers with only 2 states would require absurd energy densities, but I guess the combination of a strong quadrupole coupling and long state decay times makes it feasible for a nuclear laser.
Still not clear what it would be useful for outside of clocks, but definitely a very cool physics project, and I'm sure someone would find other uses eventually.
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).
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
> 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?
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.
What impact could this have on the value of cesium? Some time ago, I remember reading about cesium’s importance to tech, particularly for atomic clocks. It was in an article about the potential discovery of a cesium mine that might have huge political impact because China owns most of the cesium mines. And I imagine being able to replace cesium entirely would have similar impact.
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?
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.
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
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.
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.
Sounds interesting. If you don't mind me asking, what sort of computation requires synchronization across data centers? And why couldn't it be done with NTP?
Essentially distributed consistency and co-ordination. NTP isn't accurate/consistent enough because of light speed being limited. This matters for applications like network management and large scale control.
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?
What's really neat about this is the technique of embedding Thorium atoms in a crystal, which makes it possible to start thinking about solid state devices (specifically: nuclear clocks) based on this.
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.
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.
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").
When the atom ejects an electron, the hole left behind gets filled by an electron from a neighboring atom. Then the same thing happens to the neighbor -- and so on. This is electrical current flowing. Eventually the loop closes and some hole somewhere in the universe gets filled by the original ejected electron.
The hole in one atom can get filled by an electron from a higher orbital in a neighboring atom. In that case the energy gained will be greater than the energy lost by the original electron ejection. This is the situation where you get a photon (x-ray) with a higher energy (= shorter wavelength) than the original incident photon (ultraviolet).
Of course there's no free lunch. The way this happens is that N thorium atoms eject electrons from some orbital with energy X, the electrons shuffle around, and those N holes get filled by donors from orbitals whose total energy is N*X even though some of the donors are at higher levels and some are at lower levels.
If one could make the UV source highly efficient perhaps it could be used as a battery with extremely good energy density.
Yeah I've been thinking that if we had really tiny VLSI-integrated UV lasers (which we absolutely don't, not even close) that a bunch of these 229Th atoms embedded in a silicon chip would be a device with totally fascinating properties.
We can build waveguides in silicon wafer processes pretty easily but I'm not sure we can do that at UV wavelengths. You could imagine a single, big, off-chip laser whose beam can be steered by waveguides to illuminate any of a few billion 229Th deposits. These could act like the configuration memory bits of an FPGA. They would be "almost nonvolatile" -- you'd have to refresh them every hour or so, instead of several thousand times per second (dram) or never (sram). At such a low refresh rate the steering doesn't need to be particularly fast, and having to share one laser across all the deposits would not be a problem.
Unfortunately 229Th is mildly radioactive, but so are household smoke detectors so hopefully people wouldn't freak out about this.
What i was wondering…exactly… how do you make this kind of a laser? And imagine an xray laser… you could fry the guidance system of drone very precisely
> 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):
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.