Brief science items and news

As I distract myself from work-related writing that I really need to do, here are a few science-related links:

• This article in ars technica is about this paper, in which a quantum interference experiment is performed that, in the most straightforward interpretation, involves superpositions of states where "event A preceded event B" and "event B preceded event A".  This is in the same mind-zapping vein as quantum eraser experiments.  I haven't read this in detail, but my typical takeaway from these things is two-fold:  (1) the math of the usual quantum mechanics formalism is in excellent agreement with experiment every time it's been checked, and (2) nature doesn't care about our hang-ups about interpretation, especially when phrasing questions about quantum in terms of, "what classical past history should have happened here, when we weren't actually making observations?"
• This paper in Advanced Materials is a very nice overview about application-relevant magnetic materials (e.g., rare-earth magnets like Nd2Fe14B) and where we might want to look to find new ones.  
• This youtube video is a great discussion and experimental proof of the Feynman inverse sprinkler problem.  The short version:  suppose an ordinary water sprinkler rotates clockwise when it's spewing water out of its arms, the momentum flux of the water generating a torque.  If instead you immersed the sprinkler in water and had suction bring water in through the arms, which way would it spin, if it spins at all?  I don't want to spoil it for you.  Watch the video - it's very nicely done.
• I'm not sure the link will work for everyone, but there is an article in The Atlantic called "The Shocking Speed of China's Scientific Rise".  For anyone paying the slightest bit of attention for the last decade, this must be some new definition of "shocking" with which I was previously unfamiliar.  
• Info is beginning to trickle out about the likely presidential budget request for FY27, and guess what:  some of the same folks who freak out that China might surpass the US as a science power are again going to pitch big budget cuts (article is about NIH, but it's hard to imagine other agencies won't be similarly viewed).  Congress largely pushed back against the PBR this past year, but this is an annual exercise in the US - it never stops.

AI and the practice of theoretical physics

Matthew Schwartz of Harvard has made a big recent splash, between his public Aspen talk "10000 Einsteins" a year ago about the role of AI and the future of physics, and his talk last week at the APS Global Physics summit on the same topic, and now with this essay, "Vibe Physics:  The AI Grad Student", on the website of Anthropic (producers of the AI tool Claude).

The essay talks about how Prof. Schwartz used Claude to write this paper, and he states that the AI tool functions roughly like a 2nd year grad student (one who also doesn't get tired or complain, but does need close checking and supervision).  The claim is that with this approach to doing calculations and writing papers, he was able to come out with a piece of work that would've taken literally ten times longer if done by working with a human student.  Note that he's not exactly unbiased, and he concludes his essay (on anthropic's site) saying you should spend the $20/month Claude subscription fee and it will change your life.  

There is no doubt that AI tools can speed up certain kinds of work, and there is a every hope that applying this in science will lead to increased pace of progress.  That said, right now these tools are (unsurprisingly) best at working in areas that are well-known and explored - one of my colleagues has tried applying these to really underexplored higher dimensional problems, and they're much less effective there.  The essay's claim that "LLMs are profoundly creative" is provocative.   There is also no discussion here about the cost of these tools, in financial, energy, and environmental terms.  

Still, Schwartz raises many questions about the future of the field and graduate education in general.   (His paragraph about how human beings will still be needed in science for getting experimental data, at least for a while, is really something.)  University research is not just about answering scholarly questions; it's about educating people.  Maybe some faculty will revel in writing papers without that kind of interaction, but somehow I don't think we're quite at the stage yet where we don't need to worry anymore about training experts in technical fields.  I do agree that it's good advice for everyone to pay close attention to where these capabilities are going.  We certainly live in interesting times.

APS March Meeting 2026, Day 4 and wrap-up

Since I headed home early this afternoon, I was only able to go to a couple of talks this morning.  Here are those highlights, and a couple of general observations about the meeting.

• Piers Coleman gave a very interesting talk that put me onto an experimental puzzle I'm sorry to say I had not seen previously.  Some context:  It is now well-established that one can do spin-polarized scanning tunneling microscopy, which (given certain constraints) can image magnetic contrast in conductors down to the atomic scale.  The mechanism is basically the same as tunneling magnetoresistance:  there is a difference in the density of states for spin-up and spin-down electrons, and so a spin-polarized (magnetic) tip results in a tunneling current into/out of a magnetic sample that depends on the local magnetization.  That is, the sign of the current doesn't affect the sign of the magnetic contrast.  I had missed this 2022 Science paper, where instead of a magnetic tip, the investigators used a tip made from a nanowire of SmB6.  That peculiar material is widely (though not universally) viewed as a topological Kondo insulator that can host special surface states in which the spin direction is locked to the current direction.  With that tip, they see magnetic contrast (!) that flips sign with the sign of the current (!!), which is at least hand-wavingly what you'd expect if the direction of the tunneling electron's spin is tied to the current direction.  A more recent paper does something similar with a (BiBr)4 tip (another topologically nontrivial material).  In the talk and related paper, the argument is made that something special happens to the surface states (the effect in SmB6 turns on below about 10 K) and that this tied to the condensed matter analog of axion physics.
• On a completely different note, I saw a talk by John Davis about a new, clever kind of continuously running refrigerator that has a base temperature of around 500 mK and uses only a couple of gas liters of 3He.  One can pump on liquid 3He and get down to about 270 mK in one-shot mode, or about 450 mK if recondensing the 3He gas with a heat exchanger to get continuous operation, but 3He is very expensive.  The new design works with a mixture that's mostly 4He.  After condensing, pumping on this can cool it sufficiently that the 3He phase separates and rises to the top of the liquid, and then the 3He can be preferentially pumped (and recirculated back in).  Very cute.
• Tangentially, one nice feature of conferences is that you can stumble upon facts you didn't know.  For example, during that talk, Prof. Davis mentioned, off-handedly, that in 2D turbulence as studied in things like helium films, you can end up with long-time persistent vortices, and that this is similar to how cyclonic storms persist for centuries on Jupiter.
• Regarding the meeting in general, the APS is aware that there were some AV issues, including some of the rooms having 50" monitors rather than projectors.  This was a surprise to the organizers.  I'm still not sure how much I like the merger of the March and April meetings into one super-meeting.  On the plus side, there are opportunities for cross-over events (e.g., the Kavli symposium, which I didn't see this time), and there are some financial benefits to the society via economies of scale.  Still, 14,000 attendees makes things unwieldy for sure.
• I don't understand some of the choices re the meeting website and the meeting app.  For example, people can upload their slides and make them available.  However, on the meeting website, even when you're logged in, there's apparently no way to get to them.  You can only find the files using the APS meetings app, and even then it's not trivial.  

For those at the meeting the rest of today and Friday, if there are big stories that I missed because of my travel, please feel free to discuss in the comments.

APS March Meeting 2026, Day 3

It was another eclectic day at the APS Global Physics Summit.  Here is a selection of highlights based on my stochastic sampling of talks.

• I've written before about CISS (the chirality-induced spin selection effect).  Joe Subotnik gave a neat invited talk related to this, based on something I'd never really considered.  In physics we learn about the Born-Oppenheimer approximation, which basically says that electrons are fast and nuclei are slow, so we can often solve electronic problems without worrying about nuclear motion.  In practice, as usually done, B-O theory does not strictly conserve momentum or angular momentum, so it cannot explain something like the Einstein-de Haas effect, where flipping electronic spins eventually results in actual mechanical rotation of a solid.  Similarly, ordinary Marcus theory of electron transfer doesn't worry about angular momentum conservation.   The talk focused on a recent approach (and here) that looks carefully at wavefunctions, involves the equivalent of Berry phase and quantum geometry and recaptures the key physics, and this may explain CISS.
• Javad Shabani presented his group's recent work on growing epitaxial layers of germanium substitutionally doped with gallium, at carrier densities around \(5 \times 10^{21}\) carriers per cc, basically around 1 Ga atom in each 8-atom unit cell.   This hole-dopes the material enormously.  The resulting films superconduct with a \(T_{c}\sim\) 3 K and good critical fields, and look very nice structurally.  This is potentially a route toward creating arrays of millions of epitaxially nice Josephson junctions.
• I attended the AI Town Hall, which featured Hal Finkel from DOE talking about the Genesis Mission; Rachel Burley, chief publication officer of the APS, speaking about the challenges that AI presents to all facets of journals and scientific publishing; and Sarah Demers, chair of the physics department at Yale and chair of the APS's Panel on Public Affairs, discussing the community's effort to formulate an enduring position on physics and AI in this rapidly changing landscape.  
• In the last session of the day, I attended the DCMP prize session, and it was very interesting to hear from this year's Buckley Prize winners about their journeys and what they've been doing lately.  

In addition to a lot of fun conversations, I popped in and out of a few other talks, and apologies for not covering everything.

APS March Meeting 2026, Day 2

Today was again a bit random, as I had talks for both one of my students and me, and meetings with folks.  Some highlights:

• Edoardo Baldini gave a very nice talk about exotic phases and collective excitations in van der Waals magnets.  This included using second harmonic generation microscopy and polarimetry to look at the evolution of magnetic phases in NiPS3 as a function of thickness, ending up at the monolayer which acts like a 2D XY magnet.  In the paper, they see clear evidence of a BKT transition, plus a second lower temperature ordering of some kind.
• After some AV issues (seem like quite a few of those this year), Barry Zink gave an interesting presentation about using Cr as a spin detector in spin Seebeck measurements on YIG, and looking at how the antiferromagnetism of the Cr affects the measurement (see here).  In new results, they have been adding in an intervening layer of antiferromagnetic IrMn, looking at how magnons in the IrMn affect the results.
• This was followed by a talk by Romain LeBrun all about spintronics in the GHz and THz, using hematite (Fe2O3) as an example antiferromagnetic insulator.  They see some interesting nonlinear dynamics and rectification in antiferromagnetic resonance in Fe2O3.  In NiO, they use optical excitation to drive coherent phonons, exciting a spin current, which then leads to a THz pulse when the spin current hits an inverse spin Hall detector (Pt or W).  Similar experiments in BiFeO3 show that THz generation in that multiferroic system can arise just from oscillating the ferroelectric polarization.
• Andrew Dane from IBM gave a great presentation to a more-than-packed room about their recent studies of two-level systems in qubits.  From waaaaay in the back, I learned about their use of nearby suspended electrodes to apply electric fields to try to shift the energies of some of the TLS (the ones with electric dipole moments and at the surface of the devices).  TLS drastically suppress the coherence of superconducting qubits, and understanding their origins and ways to work around them (to characterize fab processes, for example) is very important.  As I said in that post linked above, once again we see that TLS are everywhere, and they are evil.  I need to think about whether there's anything I could contribute on this.  The real highlight of the talk was the use of "percussive maintenance" (banging the side of the cryostat) to alter the not-field-tunable TLS distribution via some unknown mechanism.
• Bonking the experiment was taken to a new level in this talk about mechanoluminescence, which involved shooting the sample with an airsoft pellet gun under controlled conditions.

There were other talks as well - some fun stuff.  I also want to give a shoutout to the free-to-play vintage arcade games in the exhibit hall.  Galaga and the stand-up vector graphics Star Wars game were great consumers of my time and my quarters back in the day.

APS March Meeting 2026, Day 1

I hit a pretty random assortment of talks on my first day at the APS Global Physics Summit, after catching a very early flight to get to Denver.  Here are a few highlights:

• My colleague Hanyu Zhu gave a nice talk about the coupling between chiral phonons (vibrational excitations of atomic motion that carry net orbital angular momentum) and their coupling to electronic spins.  For example, chiral ionic motion can effectively generate enormous local magnetic fields (see here).
• I went to part of a session about magnons (quantized spin waves) and their connection to quantum information.  There was a theory talk by Silvia Viola Kusminskiy about cavity manipulation of magnons, and there was an experimental talk by Mathias Weiler about using surface acoustic waves plus magnetoelastic coupling to set up all sorts of interesting nonreciprocal magnetoacoustic devices. 
• My former postdoc Longji Cui gave a talk about molecular phononics - measuring thermal transport (by phonons) down to the single molecule level.  For a nice review of the overall topic, see here.  He then discussed extending this to measurements of polymers.
• There was a session about strange metals and the cuprates, which included a talk by Dragana Popovic about how there is evidence for persistent vortex-liquid-like phase fluctuations in these materials even into the normal state.  This was followed by Nigel Hussey showing systematic studies of the magnetoresistance in both electron-doped and hole-doped cuprates.  The upshot is that in the electron-doped materials, there is a clear anisotropic inelastic scattering rate (from spin fluctuations) that scales with the superconducting transition, implying that spin fluctuations are the "glue".  In contrast, the hole-doped system has different systematics, implying that perhaps the strange metal fraction of material is what leads to superconductivity.
• For maybe the second time in my long attendance at the meeting, I attended the APS prize session, where they present the certificates associated with the various honors.  It was very nice.

Now I just need to get some sleep and figure out what to see tomorrow....

Some science leading into the APS Global Physics Summit

Next week is the annual APS conference that was once the March Meeting and is now the combined March/April "Global Physics Summit".  As I've done annually, I will try to give some impressions of interesting talks that I see, hopefully at an understandable level.  This year I'm only there from Monday through late Thursday morning, so I may miss exciting things - hopefully people will still discuss such things here as has happened in past years.

A few science tidbits in the meantime:

• People sometimes time arXiv submissions to coincide with the APS meeting, and sometimes it's just coincidence.  Two preprints (here and here) popped up very recently, both experiments on interferometry and braiding of anyons in bilayer graphene.  There are many subtleties in such experiments.  The colorized electron microscope images of the devices show how sophisticated fabrication has become in these systems, where very small amounts of disorder can disrupt the fragile many-body quantum states of interest.
• On a much more classical physics note, this preprint uses some sophisticated multiscale modeling to address the question, why is ice so slippery?  A super-thin layer of water on the surface of the ice under sliding conditions is crucial, and the roles of frictional heating and heat transfer have been tricky to quantify.
• Meanwhile, across town from me at the University of Houston, Paul Chu and company have published this paper in PNAS, where they have demonstrated ambient pressure superconductivity in a mercury-based cuprate at 151 K, breaking the old ambient pressure record by 18 K (!).  The trick here has been pressure annealing.  Many superconductors, particularly the cuprates, tend to have higher transition temperatures at elevated pressures.  One idea is that pressure distortion of certain bond angles favors superconductivity in this system, and Chu et al. have been exploring the idea of cycling pressure and temperature to "lock in" the altered crystal structure.
• Moving away from condensed matter and turning to science used in the aid of history:  When Vesuvius erupted in 79 CE, the pyroclastic flow swept through Herculaneum and a nearby Roman villa, housing a library of more than 1800 now-carbonized scrolls.  Using 3D x-ray tomography, it is hoped that these scrolls may actually be read without trying to physically unroll them, prompting the Vesuvius Prize.  This effort, involving x-ray imaging and AI methods, seems to be bearing fruit.  There may be many more scrolls still buried as well.  It would be amazing if great lost works of ancient Greek and Roman literature could be recovered.
• Tangentially related to science, the arXiv is looking for a CEO - here is the position description.  It's hard to overstate the impact of the arXiv and its relations in terms of open science, and in the chaotic world of scientific publishing, it's more important than ever.
• If you need evidence of how screwed up scientific publishing is, apparently Springer-Nature has been surveying people to see how willing they would be to pay an up-front fee (e.g. $299) just for the privilege of submitting an article.