What is "static electricity"/"contact electrification"/triboelectricity?

An early physics demonstration that many of us see in elementary school is that of static electricity:  an electrical insulator like a wool cloth or animal fur is rubbed on a glass or plastic rod, and suddenly the rod can pick up pieces of styrofoam or little bits of paper.  Alternately, a rubber balloon is rubbed against a kid's hair, and afterward the balloon is able to stick to a wall with sufficient force that static friction keeps the balloon from sliding down the surface.  The physics here is that when materials are rubbed together, there can be a net transfer of electrical charge from one to the other, a phenomenon called triboelectricity.  The electrostatic attraction between net charge on the balloon and the polarizable surface of the wall is enough to hold up the balloon.  

Balloons electrostatically clinging to a wall, from here.

The big mysteries are, how and why do charges transfer between materials when they are rubbed together?  As I wrote about once before, this is still not understood, despite more than 2500 years of observations.  The electrostatic potentials that can be built up through triboelectricity are not small.  They can be tens of kV, enough to cause electrons accelerating across those potentials to emit x-rays when they smack into the positively charged surface.  Whatever is going on, it's a way to effectively concentrate the energy from mechanical work into displacing charges.  This is how Wimshurst machines and Van de Graaff generators work, even though we don't understand the microscopic physics of the charge generation and separation.

There are disagreements to this day about the mechanisms at work in triboelectricity, including the role of adsorbates, surface chemistry, whether the charges transferred are electrons or ions, etc.  From how electronic charge transfer works between metals, or between metals and semiconductors, it's not crazy to imagine that somehow this should all come down to work functions or the equivalent.  Depending on the composition and structure of materials, the electrons in there can be bound more tightly (energetically deeper compared to the energy of an electron far away, also called "the vacuum" level) or more loosely (energetically shallower, closer to the energy of a free electron).  It's credible that bringing two such materials in contact could lead to electrons "falling down hill" from the more loosely-binding material into the more tightly binding one.   That clearly is not the whole story, though, or this would've been figured out long ago.

This week, a new paper revealed an interesting wrinkle.  The net preference for picking up or losing charge seems to depend very clearly on the history of repeated contacts.  The authors used PDMS silicone rubber, and they find that repeated contacting can deterministically bake in a tendency for charge to flow one direction.  Using various surface spectroscopy methods, they find no obvious differences at the PDMS surface before/after the contacting procedures, but charge transfer is affected.  

My sneaking suspicion is that adsorbates will turn out to play a huge role in all of this.  This may be one of those issues like friction (see here too), where there is a general emergent phenomenon (net charge transfer) that can take place via multiple different underlying pathways.  Experiments in ultrahigh vacuum with ultraclean surfaces will undoubtedly show quantitatively different results than experiments in ambient conditions, but they may both show triboelectricity.

The National Science Foundation - this is not business as usual

The National Science Foundation was created 75 years ago, at the behest of Vannevar Bush, who put together the famed study, Science, The Endless Frontier, in 1945.  The NSF has played a critical role in a huge amount of science and engineering research since its inception, including advanced development of the laser, the page rank algorithm that ended up in google, and too many other contributions to list.  

The NSF funds university research as well as some national facilities.  Organizationally, the NSF is an independent agency, meaning that it doesn’t reside under a particular cabinet secretary, though its Director is a presidential appointee who is confirmed by the US Senate.  The NSF comprises a number of directorates (most relevant for readers of this blog are probably Mathematical and Physical Sciences; Engineering;  and STEM Education, though there are several others).  Within the directorates are divisions (for example, MPS → Division of Materials Research; Division of Chemistry; Division of Physics; Division of Mathematics etc.).   Within each division are a variety of programs, spanning from individual investigator grants to medium to large center proposals, to group training grants, to individual graduate and postdoctoral fellowships.  Each program is administered by one or more program officers who are either scientists who have become civil servants, or "rotators", academics who take a leave of absence from their university positions to serve at the NSF for some number of years.  The NSF is the only agency whose mission historically has explicitly included science education.  The NSF's budget has been about $9B/yr (though until very recently there was supposedly bipartisan support for large increases), and 94% of its funds are spent on research, education, and related activities.  NSF funds more than 1/4 of all basic research done at universities in the US, and it also funds tech development, like small business innovation grants.

The NSF, more than any other agency that funds physical science and engineering research, relies on peer review.  Grants are reviewed by individual reviewers and/or panels.  Compared to other agencies, the influence of program officers in the review process is minimal.  If a grant doesn't excite the reviewers, it won't get funded.  This has its pluses and minuses, but it's less of a personal networking process than other agencies.  The success rate for many NSF programs is low, averaging around 25% in DMR, and 15% or so for graduate fellowships.  Every NSF program officer with whom I've ever interacted has been dedicated and professional.  

Well, yesterday the NSF laid off 11% of its workforce.  I had an exchange last night with a long-time NSF program director, who gave permission for me to share the gist, suitably anonymized.  (I also corrected typos.)  This person says that they want people to be aware of what's going on.  They say that NSF leadership is apparently helping with layoffs, and that "permanent Program Directors (feds such as myself) will be undergoing RIF or Reduction In Force process within the next month or so. So far, through buyout and firing today we lost about 16% of the workforce, and RIF is expected to bring it up to 50%."  When I asked further, this person said this was "fairly certain".   They went on:  "Another danger is budget.  We do no know what happens after the current CR [continuing resolution] ends March 14.  A long shutdown or another CR are possible.  For FY26 we are told about plans to reduce the NSF budget by 50%-75% - such reduction will mean no new awards for at least a year, elimination of divisions, merging of programs.  Individual researchers and professional societies can help by raising the voice of objection.  But realistically, we need to win the midterms to start real change.  For now we are losing this battle.  I can only promise you that NSF PDs are united as never before in our dedication to serve our communities of reesarchers and educators.  We will continue to do so as long as we are here."  On a related note, here is a thread by a just laid off NSF program officer.  Note that congress has historically ignored presidential budget requests to cut NSF, but it's not at all clear that this can be relied upon now.  

Voluntarily hobbling the NSF is, in my view, a terrible mistake that will take decades to fix.  The argument that this is a fiscally responsible thing to do is weak.  The total federal budget expenditures in FY24 was $6.75T.  The NSF budget was $9B, or 0.13% of the total.  The secretary of defense today said that their plan is to cut 8% of the DOD budget every year for the next several years.  That's a reduction of 9 NSF budgets per year.  

I fully recognize that many other things are going on in the world right now, and many agencies are under similar pressures, but I wanted to highlight the NSF in particular.  Acting like this is business as usual, the kind of thing that happens whenever there is a change of administration, is disingenuous.  

What are parastatistics?

While I could certainly write more about what is going on in the US these days (ahh, trying to dismantle organizations you don't understand), instead I want to briefly highlight a very exciting result from my colleagues, published in Nature last month.  (I almost titled this post "Lies, Damn Lies, and (para)Statistics", but that sounds like I don't like the paper.)

When we teach students about the properties of quantum objects (and about thermodynamics), we often talk about the "statistics" obeyed by indistinguishable particles.  I've written about aspects of this before.  "Statistics" in this sense means, what happens mathematically to the multiparticle quantum state \(|\Psi\rangle\) when two particles are swapped.  If we use the label \(\mathbf{1}\) to mean the set of quantum numbers associated with particle 1, etc., then the question is, how are \(|\Psi(\mathbf{1},\mathbf{2})\rangle\) and \(|\Psi(\mathbf{2},\mathbf{1})\rangle\) related to each other.  We know that probabilities have to be conserved, so \(\langle \Psi(\mathbf{1},\mathbf{2}) | \Psi(\mathbf{1},\mathbf{2})\rangle = \langle \Psi(\mathbf{2},\mathbf{1}) | \Psi(\mathbf{2},\mathbf{1})\rangle\).   

The usual situation is to assume \(|\Psi(\mathbf{2},\mathbf{1})\rangle\ = c |\Psi(\mathbf{1},\mathbf{2})\rangle\), where \(c\) is a complex number of magnitude 1.  If \(c = 1\), which is sort of the "common sense" expectation from classical physics, the particles are bosons, obeying Bose-Einstein stastistics.   If \(c = -1\), the particles are fermions and obey Fermi-Dirac statistics.  In principle, one could have \(c = \exp(i\alpha)\), where \(\alpha\) is some phase angle.  Particles in that general case are called anyons, and I wrote about them here.  Low energy excitations of electrons (fermions) confined in 2D in the presence of a magnetic field can act like anyons, but it seems there can't be anyons in higher dimensions.

 Being imprecise, when particles are "dilute" -- "far" from each other in terms of position and momentum -- we typically don't really need to worry much about what kind of quantum statistics govern the particles.  The distribution function - the average occupancy of a typical single-particle quantum state (labeled by a coordinate \(\mathbf{r}\), a wavevector \(\mathbf{k}\), and a spin \(\mathbf{\sigma}\) as one possibility) - is much less than 1.  When particles are much more dense, though, the quantum statistics matter enormously.  At low temperatures, bosons can all pile into the (single-particle, in the absence of interactions) ground state - that's Bose-Einstein condensation.   In contrast, fermions have to stack up into higher energy states, since FD statistics imply that no two indistinguishable fermions can be in the same state - this is the Pauli Exclusion Principle, and it's basically why solids are solid.  If a gas of particles is at a temperature \(T\) and a chemical potential \(\mu\), then the distribution function and a function of energy \(\epsilon\) for bosons or fermions is given by \(f(\epsilon,\mu,T) = 1/ (\exp((\epsilon-\mu)/k_{\mathrm{B}}T) \pm 1 )\), where the \(+\) sign is the fermion case and the \(-\) sign is the boson case.  

In the paper at hand, the authors take on parastatistics, the question of what happens if, besides spin, there are other "internal degrees of freedom" that are attached to particles described by additional indices that obey different algebras.  As they point out, this is not a new idea, but what they have done here is show that it is possible to have mathematically consistent versions of this that do not trivially reduce to fermions and bosons and can survive in, say, 3 spatial dimensions.  They argue that low energy excitations (quasiparticles) of some quantum spin systems can have these properties.  That's cool but not necessarily surprising - there are quasiparticles in condensed matter systems that are argued to obey a variety of exotic relations originally proposed in the world of high energy theory (Weyl fermions, Majorana fermions, massless Dirac fermions).  They also put forward the possibility that elementary particles could obey these statistics as well.  (Ideas transferring over from condensed matter or AMO physics to high energy is also not a new thing; see the Anderson-Higgs mechanism, and the concept of unparticles, which has connections to condensed matter systems where electronic quasiparticles may not be well defined.)

Fig. 1 from this paper, showing distribution functions for fermions, bosons, 
and more exotic systems studied in the paper.

Interestingly, the authors work out what the distribution function can look like for these exotic particles, as shown here (fig 1 from the paper).  The left panel shows how many particles can be in a single-particle spatial state for fermions (zero or one), bosons (up to \(\infty\)), and funky parastatistics-obeying particles of different types.  The right panel shows the distribution functions for these cases.  I think this is very cool.  When I've taught statistical physics to undergrads, I've told the students that no one has written down a general distribution function for systems like this.  Guess I'll have to revise my statements on this!

Indirect costs + potential unintended consequences

It's been another exciting week where I feel compelled to write about the practice of university-based research in the US.  I've written about "indirect costs" before, but it's been a while.  I will try to get readers caught up on the basics of the university research ecosystem in the US, what indirect costs are, the latest (ahh, the classic Friday evening news dump) from NIH, and what might happen.  (A note up front:  there are federal laws regulating indirect costs, so the move by NIH will very likely face immediate legal challenges.  Update:  And here come the lawsuits.  Update 2:  Here is a useful explanatory video.)  Update 3:  This post is now closed (7:53pm CST 13 Feb).  When we get to the "bulldozer going to pile you lot onto the trash" level of discourse, there is no more useful discussion happening.

How does university-based sponsored technical research work in the US?  Since WWII, but particularly since the 1960s, many US universities conduct a lot of science and engineering research sponsored by US government agencies, foundations, and industry.  By "sponsored", I mean there is a grant or contract between a sponsor and the university that sends funds to the university in exchange for research to be conducted by one or more faculty principal investigators, doctoral students, postdocs, undergrads, staff scientists, etc.  When a PI writes a proposal to a sponsor, a budget is almost always required that spells out how much funding is being requested and how it will be spent.  For example, a proposal could say, we are going to study superconductivity in 2D materials, and the budget (which comes with a budget justification) says, to do this, I need $37000 per year to pay a graduate research assistant for 12 months, plus $12000 per year for graduate student tuition, plus $8000 in for the first year for a special amplifier, plus $10000 to cover materials, supplies, and equipment usage fees.  Those are called direct costs.  

In addition, the budget asks for funds to cover indirect costs.  Indirect costs are meant to cover the facilities and administrative costs that the university will incur doing the research - that includes things like, maintaining the lab building, electricity, air conditioning, IT infrastructure, research accountants to keep track of the expenses and generate financial reports, etc.  Indirect costs are computed as some percentage of some subset of the direct costs (e.g.,  there are no indirect costs charged on grad tuition or pieces of equipment more expensive than $5K).  Indirect cost rates have varied over the years but historically have been negotiated between universities and the federal government.  As I wrote eight years ago, "the magic (ahem) is all hidden away in OMB Circular A21 (wiki about it, pdf of the actual doc).  Universities periodically go through an elaborate negotiation process with the federal government (see here for a description of this regarding MIT), and determine an indirect cost rate for that university."  Rice's indirect cost rate is 56.5% for on-campus fed or industrial sponsored projects.  Off-campus rates are lower (if you're really doing the research at CERN, then logically your university doesn't need as much indirect).  Foundations historically try to negotiate lower indirect cost rates, often arguing that their resources are limited and paying for administration is not what their charters endorse.  The true effective indirect rate for universities is always lower than the stated number because of such negotiations.

PIs are required to submit technical progress reports, and universities are required to submit detailed financial reports, to track these grants.  

This basic framework has been in place for decades, and it has resulted in the growth of research universities, with enormous economic and societal benefit.  Especially as industrial long term research has waned in the US (another screed I have written before), the university research ecosystem has been hugely important in contributing to modern technological society.  We would not have the internet now, for example, if not for federally sponsored research.

Is it ideal?  No.  Are there inefficiencies?  Sure.  Should the whole thing be burned down?  Not in my opinion, no.

"All universities lose money doing research."  This is a quote from my colleague who was provost when I arrived at Rice, and was said to me tongue-in-cheek, but also with more than a grain of truth.  If you look at how much it really takes to run the research apparatus, the funds brought in via indirect costs do not cover those costs.  I have always said that this is a bit like Hollywood accounting - if research was a true financial disaster, universities wouldn't do it.  The fact is that research universities have been willing to subsidize the additional real indirect costs because having thriving research programs brings benefits that are not simple to quantify financially - reputation, star faculty, opportunities for their undergrads that would not exist in the absence of research, potential patent income and startup companies, etc.

Reasonable people can disagree on what is the optimal percentage number for indirect costs.   It's worth noting that the indirect cost rate at Bell Labs back when I was there was something close to 100%.  Think about that.  In a globally elite industrial research environment, with business-level financial pressure to be frugal, the indirect rate was 100%.  

The fact is, if indirect cost rates are set too low, universities really will be faced with existential choices about whether to continue to support sponsored research.  The overall benefits of having research programs will not outweigh the large financial costs of supporting this business.

Congress has made these true indirect costs steadily higher.  Over the last decades, both because it is responsible stewardship and because it's good politics, Congress has passed laws requiring more and more oversight of research expenditures and security.  Compliance with these rules has meant that universities have had to hire more administrators - on financial accounting and reporting, research security, tech transfer and intellectual property, supervisory folks for animal- and human-based research, etc.  Agencies can impose their own requirements as well.  Some large center-type grants from NIH/HHS and DOD require preparation and submission of monthly financial reports. 

What did NIH do yesterday?  NIH put out new guidance (linked above) setting their indirect cost rate to 15% effective this coming Monday.  This applies not just to new grants, but also to awards already underway.  There is also a not very veiled threat in there that says, we have chosen for now not to retroactively go back to the start of current awards and ask for funds (already spent) to be returned to us, but we think we would be justified in doing so.   The NIH twitter feed proudly says that this change will produce an immediate savings to US taxpayers of $4B. 

What does this mean?  What are the intended and possible unintended consequences?  It seems very likely that other agencies will come under immense pressure to make similar changes.  If all agencies do so, and nothing else changes, this will mean tens of millions fewer dollars flowing to typical research universities every year.   If a university has $300M annually in federally sponsored research, then that would be generating under the old rules (assume 55% indirect rate) $194M of direct and $106M of indirect costs.  If the rate is dropped to 15% and the direct costs stay the same at $194M, then that would generate $29M of indirect costs, a net cut to the university of $77M per year.

There will be legal challenges to all of this, I suspect. 

The intended consequences are supposedly to save taxpayer dollars and force universities to streamline their administrative processes.  However, given that Congress and the agencies are unlikely to lessen their reporting and oversight requirements, it's very hard for me to see how there can be some radical reduction in accounting and compliance staffs.  There seems to be a sentiment that this will really teach those wealthy elite universities a lesson, that with their big endowments they should pick up more of the costs.

One unintended consequence:  If this broadly goes through and sticks, universities will want to start making new direct costs.  For a grant like the one I described above, you could imagine asking for $1200 per year for electricity, $1000/yr for IT support, $3000/yr for lab space maintenance, etc.  This will create a ton of work for lawyers, as there will be a fight over what is or is not an allowable direct cost.  This will also create the need for even more accounting types to track all of this.  This is the exact opposite of "streamlined" administrative processes.

A second unintended consequence:  Universities for whom doing research is financially a lot more of a marginal proposition would likely get out of those activities,  if they truly can't recover the costs of operating their offices of research.  This is the opposite of improving the situation and student opportunities at the less elite universities.

From a purely real politik perspective that often appeals to legislators:  Everything that harms the US research enterprise effectively helps adversaries.  The US benefitted enormously after WWII by building a global premier research environment.  Risking that should not be done lightly.

Don't panic.  There is nothing gained by freaking out.  Whatever happens, it will likely be a drawn out process.  It's best to be aware of what's happening, educated about what it means, and deliberate in formulating strategies that will preserve research excellence and capabilities.

(So help me, I really want my next post to be about condensed matter physics or nanoscale science!)

NSF targeted with mass layoffs, acc to Politico; huge cuts in president’s budget request

According to this article at politico, there was an all-hands meeting at NSF today (at least for the engineering directorate) where they were told that there will be staff layoffs of 25-50% over the next two months.

This is an absolute catastrophe if it is accurately reported and comes to pass.  NSF is already understaffed.  This goes far beyond anything involving DEI, and is essentially a declaration that the US is planning to abrogate the federal role in supporting science and engineering research.  

Moreover, I strongly suspect that if this conversation is being had at NSF, it is likely being had at DOE and NIH.

I don't even know how to react to this, beyond encouraging my fellow US citizens to call their representatives and senators and make it clear that this would be an unmitigated disaster.

Update: looks like the presidential budget request will be for a 2/3 cut to the NSF.  Congress often goes against such recommendations, but this is certainly an indicator of what the executive branch seems to want.  

An update, + a paper as a fun distraction

My post last week clearly stimulated some discussion.  I know people don't come here for political news, but as a professional scientist it's hard to ignore the chaotic present situation, so here are some things to read, before I talk about a fun paper:

• Science reports on what is happening with NSF.  The short version: As of Friday afternoon, panels are delayed and funds (salary) are still not accessible for NSF postdoctoral fellows.  Here is NPR's take.
• As of Friday afternoon, there is a new court order that specifically names the agency heads (including the NSF director), saying to disburse already approved funds according to statute.  
• Update: The NSF is now allowing postdocs and GRF recipients to get paid; they are obeying the new court order.  See here and the FAQ specifically.

Looks like on this and a variety of other issues, we will see whether court orders actually compel actions anymore.

Now to distract ourselves with dreams of the future, this paper was published in Nature Photonics, measuring radiation pressure exerted by a laser on a 50 nm thick silicon nitride membrane.  The motivation is a grand one:  using laser-powered light sails to propel interstellar probes up to a decent fraction (say 10% or more) of the velocity of light.  It's easy to sketch out the basic idea on a napkin, and it has been considered seriously for decades (see this 1984 paper).  Imagine a reflective sail say 10 m\(^{2}\) and 100 nm thick.  When photons at normal incidence bounce from a reflective surface, they transfer momentum \(2\hbar \omega/c) normal to the surface.  If the reflective surface is very thin and low mass, and you can bounce enough photons off it, you can get decent accelerations.  Part of the appeal is, this is a spacecraft where you effectively keep the engine (the whopping laser) here at home and don't have to carry it with you.  There are braking schemes so that you could try to slow the craft down when it reaches your favorite target system.

A laser-powered lightsail (image from CalTech)

Of course, actually doing this on a scale where it would be useful faces enormous engineering challenges (beyond building whopping lasers and operating them for years at a time with outstanding collimation and positioning).  Reflection won't be perfect, so there will be heating.  Ideally, you'd want a light sail that passively stabilizes itself in the center of the beam.  In this paper, the investigators implement a clever scheme to measure radiation forces, and they test ideas involving dielectric gratings etched into the sail to generate self-stabilization.   Definitely more fun to think about such futuristic ideas than to read the news.

(An old favorite science fiction story of mine is "The Fourth Profession", by Larry Niven.  The imminent arrival of an alien ship at earth is heralded by the appearance of a bright point in the sky, whose emission turns out to be the highly blue-shifted, reflected spectrum of the sun, bouncing off an incoming alien light sail.  The aliens really need humanity to build them a launching laser to get to their next destination.)

Turbulent times

While I've been absolutely buried under deadlines, it's been a crazy week for US science, and things are unlikely to calm down anytime soon.  As I've written before, I largely try to keep my political views off here, since that's not what people want to read from me, and I want to keep the focus on the amazing physics of materials and nanoscale systems.  (Come on, this is just cool - using light to dynamically change the chirality of crystals?  That's really nifty.)   

Still, it's hard to be silent, even just limiting the discussion to science-related issues.  Changes of presidential administrations always carry a certain amount of perturbation, as the heads of many federal agencies are executive branch appointees who serve at the pleasure of the president.  That said, the past week was exceptional for multiple reasons, including pulling the US out of the WHO as everyone frets about H5N1 bird flu; a highly disruptive freeze of activity within HHS (lots of negative consequences even if it wraps up quickly); and immediate purging of various agency websites of any programs or language related to DEI, with threatened punishment for employees who don't report their colleagues for insufficient reporting of any continued DEI-related activities.

Treating other people with respect, trying to make science (and engineering) welcoming to all, and trying to engage and educate the widest possible population in expanding human knowledge should not be controversial positions.  Saying that we should try to broaden the technical workforce, or that medical trials should involve women and multiple races should not be controversial positions.

What I wrote eight years ago is still true.  It is easier to break things than to build things.  Rash steps very often have lingering unintended consequences.  

Panic is not helpful.  Doomscrolling is not helpful.  Getting through challenging times requires determination, focus, and commitment to not losing one's principles.  

Ok, enough out of me.  Next week (deadlines permitting) I'll be back with some science, because that's what I do.

This week in the arXiv: quantum geometry, fluid momentum "tunneling", and pasta sauce

Three papers caught my eye the other day on the arXiv at the start of the new year:

arXiv:2501.00098 - J. Yu et al., "Quantum geometry in quantum materials" - I hope to write up something about quantum geometry soon, but I wanted to point out this nice review even if I haven't done my legwork yet.  The ultrabrief point:  The single-particle electronic states in crystalline solids may be written as Bloch waves, of the form \(u_{n \mathbf{k}}(\mathbf{r}) \exp(i \mathbf{k} \cdot \mathbf{r})\), where the (crystal) momentum is given by \(\hbar \mathbf{k}\) and \(u_{n \mathbf{k}}\) is a function with the real-space periodicity of the crystal lattice and contains an implicit \(\mathbf{k}\) dependence.  You can get very far in understanding solid-state physics without worrying about this, but it turns out that there are a number of very important phenomena that originate from the oft-neglected \(\mathbf{k}\) dependence of \(u_{n \mathbf{k}}\).  These include the anomalous Hall effect, the (intrinsic) spin Hall effect, the orbital Hall effect, etc.  Basically the \(\mathbf{k}\) dependence of \(u_{n \mathbf{k}}\) in the form of derivatives defines an internal "quantum" geometry of the electronic structure.  This review is a look at the consequences of quantum geometry on things like superconductivity, magnetic excitations, excitons, Chern insulators, etc. in quantum materials.

Fig. 1 from arXiv:2501.01253

arXiv:2501.01253 - B. Coquinot et al., "Momentum tunnelling between nanoscale liquid flows" - In electronic materials there is a phenomenon known as Coulomb drag, in which a current driven through one electronic system (often a 2D electron gas) leads, through Coulomb interactions, to a current in adjacent but otherwise electrically isolated electronic system (say another 2D electron gas separated from the first by a few-nm insulating layer).  This paper argues that there should be a similar-in-spirit phenomenon when a polar liquid (like water) flows on one side of a thin membrane (like one or few-layer graphene, which can support electronic excitations like plasmons) - that this could drive flow of a polar fluid on the other side of the membrane (see figure).  They cast this in the language of momentum tunneling across the membrane, but the point is that it's some inelastic scattering process mediated by excitations in the membrane.  Neat idea.

arXiv:2501.00536 - G. Bartolucci et al., "Phase behavior of Cacio and Pepe sauce" - Cacio e pepe is a wonderful Italian pasta dish with a sauce made from pecorino cheese, pepper, and hot pasta cooking water that contains dissolved starch.  When prepared well, it's incredibly creamy, smooth, and satisfying.  The authors here perform a systematic study of the sauce properties as a function of temperature and starch concentration relative to cheese content, finding the part of parameter space to avoid if you don't want the sauce to "break" (condensing out clumps of cheese-rich material and ruining the sauce texture).  That's cool, but what is impressive is that they are actually able to model the phase stability mathematically and come up with a scientifically justified version of the recipe.  Very fun.

End of the year thoughts - scientific philanthropy and impact

As we head into 2025, and the prospects for increased (US) government investment in science, engineering, and STEM education seem very limited, I wanted to revisit a topic that I wrote about over a decade ago (!!!), the role of philanthropy and foundations in these areas.  

Personally I think the case for government support of scientific research and education is overwhelmingly clear; while companies depend on having an educated technical workforce (at least for now) and continually improving technology, they are under great short-term financial pressures and genuinely long-term investment in research is rare.  Foundations are not a substitute for nation-state levels of support, but they are a critical component of the research and education landscape.  

Annual citations of the EPR paper from Web of Science,

a case study in the long-term impact of some "pure" scientific

research, and giving hope to practicing scientists that surely

our groundbreaking work will be appreciated sixty years 

after publication.  

A key question I've wondered about for a long time is how to properly judge the impact that research-supporting foundations are making.  The Science Philanthropy Alliance is a great organization that considers these issues deeply.

The nature of long-term research is that it often takes a long time for its true impact (I don't mean just citation counts, but those are an indicator of activity) to be felt.  One (admittedly extreme) example is shown here, the citations-per-year (from Web of Science) of the 1935 Einstein/Podolsky/Rosen paper about entanglement.  (Side note:  You have to love the provocative title, "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?", which from the point of view of the authors at the time satisfies Betteridge's Law of Headlines.)  There are few companies that would be willing to invest in supporting research that won't have its true heyday for five or six decades.

One additional tricky bit is that grants are usually given to people and organizations who are already active.  It's often not simple to point to some clear result or change in output that absolutely would not have happened without foundation support.  This is exacerbated by the fact that grants in science and engineering are often given to people and organizations who are not just active but already very well supported - betting on an odds-on favorite is a low risk strategy. 

Many foundations do think very carefully about what areas to support, because they want to "move the needle".  For example, some scientific foundations are consciously reluctant to support closer-to-clinical-stage cancer research, since the total annual investment by governments and pharmaceutical companies in that area numbers in the many billions of dollars, and a modest foundation contribution would be a tiny delta on top of that.  

Here is a list of the wealthiest charitable foundations (only a few of which support scientific research and/or education) and their endowments.  Nearly all of the science-related ones are also plugged in here.  A rough estimate of annual expenditures from endowed entities is about 5% of their holdings.  Recently I've come to think about private universities as one crude comparator for impact.  If a foundation has the same size endowment as a prestigious research university, I think it's worth thinking about the relative downstream impacts of those entities.  (Novo Nordisk Foundation has an endowment three times the size of Harvard's endowment.)  

Another comparator would be the annual research expenditures of a relevant funding agency.  The US NSF put forward $234M into major research instrumentation and facilities in FY2024.  A foundation with a $5B endowment could in principle support all of that from endowment returns.  This lets me make my semiregular pitch about foundational or corporate support for research infrastructure and user facilities around the US.  The entire annual budget for the NSF's NNCI, which supports shared nanofabrication and characterization facilities around the US, is about $16M.   That's a niche where comparatively modest foundation (or corporate) support could have serious impact for interdisciplinary research and education across the country.  I'm sure there are other similar areas out there, and I hope someone is thinking about this.  

Anyway, thanks to my readers - this is now the 20th year of this blog's existence (!!! again), and I hope to be able to keep it up well in the new year.

Technological civilization and losing object permanence

In the grand tradition of physicists writing about areas outside their expertise, I wanted to put down some thoughts on a societal trend.  This isn't physics or nanoscience, so feel free to skip this post.

Object permanence is a term from developmental psychology.  A person (or animal) has object permanence if they understand that something still exists even if they can't directly see it or interact with it in the moment.  If a kid realizes that their toy still exists even though they can't see it right now, they've got the concept.  

I'm wondering if modern technological civilization has an issue with an analog of object permanence.  Let me explain what I mean, why it's a serious problem, and end on a hopeful note by pointing out that even if this is the case, we have the tools needed to overcome this.

By the standards of basically any previous era, a substantial fraction of humanity lives in a golden age.  We have a technologically advanced, globe-spanning civilization.  A lot of people (though geographically very unevenly distributed) have grown up with comparatively clean water; comparatively plentiful food available through means other than subsistence agriculture; electricity; access to radio, television, and for the last couple of decades nearly instant access to communications and a big fraction of the sum total of human factual knowledge.  

Whether it's just human nature or a consequence of relative prosperity, there seems to be some timescale on the order of a few decades over which a non-negligible fraction of even the most fortunate seem to forget the hard lessons that got us to this point.  If they haven't seen something with their own eyes or experienced it directly, they decide it must not be a real issue.  I'm not talking about Holocaust deniers or conspiracy theorists who think the moon landings were fake.  There are a bunch of privileged people who have never personally known a time when tens of thousands of their neighbors died from childhood disease (you know, like 75 years ago, when 21,000 Americans were paralyzed every year from polio (!), proportionately like 50,000 today), who now think we should get rid of vaccines, and maybe germs aren't real.  Most people alive today were not alive the last time nuclear weapons were used, so some of them argue that nuclear weapons really aren't that bad (e.g. setting off 2000 one megaton bombs spread across the US would directly destroy less than 5% of the land area, so we're good, right?).  Or, we haven't had massive bank runs in the US since the 1930s, so some people now think that insuring bank deposits is a waste of resources and should stop.  I'll stop the list here, before veering into even more politically fraught territory.  I think you get my point, though - somehow chunks of modern society seem to develop collective amnesia, as if problems that we've never personally witnessed must have been overblown before or don't exist at all.  (Interestingly, this does not seem to happen for most technological problems.  You don't see many people saying, you know, maybe building fires weren't that big a deal, let's go back to the good old days before smoke alarms and sprinklers.)  

While the internet has downsides, including the ability to spread disinformation very effectively, all the available and stored knowledge also has an enormous benefit:  It should make it much harder than ever before for people to collectively forget the achievements of our species.  Sanitation, pasteurization, antibiotics, vaccinations - these are absolutely astonishing technical capabilities that were hard-won and have saved many millions of lives.  It's unconscionable that we are literally risking mass death by voluntarily forgetting or ignoring that.  Nuclear weapons are, in fact, terrible.  Insuring bank deposits with proper supervision of risk is a key factor that has helped stabilize economies for the last century.  We need to remember historical problems and their solutions, and make sure that the people setting policy are educated about these things. They say that those who cannot remember the past are doomed to repeat it.  As we look toward the new year, I hope that those who are familiar with the hard earned lessons of history are able to make themselves heard over the part of the populace who simply don't believe that old problems were real and could return.

Items for discussion, including google's latest quantum computing result

As we head toward the end of the calendar year, a few items:

• Google published a new result in Nature a few days ago.  This made a big news splash, including this accompanying press piece from google themselves, this nice article in Quanta, and the always thoughtful blog post by Scott Aaronson.  The short version:  Physical qubits as made today in the superconducting platform favored by google don't have the low error rates that you'd really like if you want to run general quantum algorithms on a quantum computer, which could certainly require millions of steps.  The hope of the community is to get around this using quantum error correction, where some number of physical qubits are used to function as one "logical" qubit.  If physical qubit error rates are sufficiently low, and these errors can be corrected with enough efficacy, the logical qubits can function better than the physical qubits, ideally being able to undergo a sequential operations indefinitely without degradation of their information.   One technique for this is called a surface code.  Google have implemented this in their most recent chip 105 physical qubit chip ("Willow"), and they seem to have crossed a huge threshold:  When they increase the size of their correction scheme (going from a 3 (physical qubit) \(\times\) 3 (physical qubit) to 5 \(\times\) 5 to 7 \(\times\) 7), the error rates of the resulting logical qubits fall as hoped.  This is a big deal, as it implies that larger chips, if they could be implemented, should scale toward the desired performance.  This does not mean that general purpose quantum computers are just around the corner, but it's very encouraging.  There are many severe engineering challenges still in place.  For example, the present superconducting qubits must be tweaked and tuned.  The reason google only has 105 of them on the Willow chip is not that they can't fit more - it's that they have to have wires and control capacity to tune and run them.  A few thousand really good logical qubits would be needed to break RSA encryption, and there is no practical way to put millions of wires down a dilution refrigerator.  Rather, one will need cryogenic control electronics. 
• On a closely related point, google's article talks about how it would take a classical computer ten septillion years to do what its Willow chip can do.  This is based on a very particularly chosen problem (as I mentioned here five years ago) called random circuit sampling, looking at the statistical properties of the outcome of applying random gate sequences to a quantum computer.  From what I can tell, this is very different than what most people mean when they think of a problem to benchmark a quantum computer's advantage over a classical computer.  I suspect the typical tech-literate person considering quantum computing wants to know, if I ask a quantum computer and a classical computer to factor huge numbers or do some optimization problem, how much faster is the quantum computer for a given size of problem?  Random circuit sampling feels instead much more to me like comparing an experiment to a classical theory calculation.  For a purely classical analog, consider putting an airfoil in a windtunnel and measuring turbulent flow, and comparing with a computational fluids calculation.  Yes, the windtunnel can get you an answer very quickly, but it's not "doing" a calculation, from my perspective.  This doesn't mean random circuit sampling is a poor benchmark, just that people should understand it's rather different from the kind of quantum/classical comparison they may envision.
• On one unrelated note:  Thanks to a timey inquiry from a reader, I have now added a search bar to the top of the blog.  (Just in time to capture the final decline of science blogging?)
• On a second unrelated note:  I'd be curious to hear from my academic readers on how they are approaching generative AI, both on the instructional side (e.g., should we abandon traditional assignments and take-home exams?  How do we check to see if students are really learning vs. becoming dependent on tools that have dubious reliability?) and on the research side (e.g., what level of generative AI tool use is acceptable in paper or proposal writing?  What aspects of these tools are proving genuinely useful to PIs?  To students?  Clearly generative AI's ability to help with coding is very nice indeed!)

Seeing through your head - diffuse imaging

From the medical diagnostic perspective (and for many other applications), you can understand why it might be very convenient to be able to perform some kind of optical imaging of the interior of what you'd ordinarily consider opaque objects.  Even when a wavelength range is chosen so that absorption is minimized, photons can scatter many times as they make their way through dense tissue like a breast.  We now have serious computing power and extremely sensitive photodetectors, which has led to the development of imaging techniques to perform imaging through media that absorb and diffuse photons.  Here is a review of this topic from 2005, and another more recent one (pdf link here).  There are many cool approaches that can be combined, including using pulsed lasers to do time-of-flight measurements (review here), and using "structured illumination" (review here).   

Sure, point that laser at my head.  (Adapted from
Figure 1 of this paper.)

I mention all of this to set the stage for this fun preprint, titled "Photon transport through the entire adult human head".  Sure, you think your head is opaque, but it only attenuates photon fluxes by a factor of around \(10^{18}\).  With 1 Watt of incident power at 800 nm wavelength spread out over a 25 mm diameter circle and pulsed 80 million times a second, time-resolved single-photon detectors like photomultiplier tubes can readily detect the many-times-scattered photons that straggle their way out of your head around 2 nanoseconds later.  (The distribution of arrival times contains a bunch of information.  Note that the speed of light in free space is around 30 cm/ns; even accounting for the index of refraction of tissue, those photons have bounced around a lot before getting through.)  The point of this is that those photons have passed through parts of the brain that are usually considered inaccessible.  This shows that one could credibly use spectroscopic methods to get information out of there, like blood oxygen levels.

Foams! (or, why my split pea side dish boils over every Thanksgiving)

Foams can be great examples of mechanical metamaterials.  

Adapted from TOC figure of this paper

Consider my shaving cream.  You might imagine that the (mostly water) material would just pool as a homogeneous liquid, since water molecules have a strong attraction for one another.  However, my shaving cream contains surfactant molecules.  These little beasties have a hydrophilic/polar end and a hydrophobic/nonpolar end.  The surfactant molecules can lower the overall energy of the fluid+air system by lowering the energy cost of the liquid/surfactant/air interface compared with the liquid/air interface.  There is a balancing act between air pressure, surface tension/energy, and gravity that has to be played, but under the right circumstances you end up with formation of a dense foam comprising many many tiny bubbles.  On the macroscale (much larger than the size of individual bubbles), the foam can look like a very squishy but somewhat mechanically integral solid - it can resist shear, at least a bit, and maintain its own shape against gravity.  For a recent review about this, try this paper (apologies for the paywall) or a taste of this in a post from last year. 

What brought this to mind was my annual annoyance yesterday in preparing what has become a regular side dish at our family Thanksgiving.  That recipe begins with rinsing, soaking, and then boiling split peas in preparation for making a puree.  Every year, without fail, I try to keep a close eye on the split peas as they cook, because they tend to foam up.  A lot.  Interestingly, this happens regardless of how carefully I rinse them before soaking, and the foaming (a dense white foam of few-micron-scale bubbles) begins well before the liquid starts to boil.  I have now learned two things about this.  First, pea protein, which leaches out of the split peas, is apparently a well-known foam-inducing surfactant, as explained in this paper (which taught me that there is a journal called Food Hydrocolloids).  Second, next time I need to use a bigger pot and try adding a few drops of oil to see if that suppresses the foam formation.

Nanopasta, no, really

Fig. 1 from the linked paper

Here is a light-hearted bit of research that touches on some fun physics.  As you might readily imagine, there is a good deal of interdisciplinary and industrial interest in wanting to create fine fibers out of solution-based materials.  One approach, which has historical roots that go back even two hundred years before this 1887 paper, is electrospinning.  Take a material of interest, dissolve it in a solvent, and feed a drop of that solution onto the tip of an extremely sharp metal needle.  Then apply a big voltage (say a few to tens of kV) between that tip and a nearby grounded substrate.  If the solution has some amount of conductivity, the liquid will form a cone on the tip, and at sufficiently large voltages and small target distances, the droplet will be come unstable and form a jet off into the tip-target space.  With the right range of fluid properties (viscosity, conductivity, density, concentration) and the right evaporation rate for the solvent, the result is a continuously forming, drying fiber that flows off the end of the tip.  A further instability amplifies any curves in the fiber path, so that you get a spiraling fiber spinning off onto the substrate.   There are many uses for such fibers, which can be very thin.

The authors of the paper in question wanted to make fibers from starch, which is nicely biocompatible for medical applications.  So, starting from wheat flour and formic acid, they worked out viable parameters and were able to electrospin fibers of wheat starch (including some gluten - sorry, for those of you with gluten intolerances) into nanofibers 300-400 nm in diameter.  The underlying material is amorphous (so, no appreciable starch crystallization).  The authors had fun with this and called the result "nanopasta", but it may actually be useful for certain applications.

Brief items

 A few tidbits that I encountered recently:

• The saga of Ranga Dias at Rochester draws to a close, as described by the Wall Street Journal.  It took quite some time for this to propagate through their system.  This is after multiple internal investigations that somehow were ineffective, an external investigation, and a lengthy path through university procedures (presumably because universities have to be careful not to shortcut any of their processes, or they open themselves up to lawsuits).
• At around the same time, Mikhail Eremets passed away.  He was a pioneer in high pressure measurements of material properties and in superconductivity in hydrides.
• Also coincident, this preprint appeared on the arXiv, a brief statement summarizing some of the evidence for relatively high temperature superconductivity in hydrides at high pressure.
• Last week Carl Bender gave a very nice colloquium at Rice, where he spoke about a surprising result.  When we teach undergrad quantum mechanics, we tell students that the Hamiltonian (the expression with operators that gives the total energy of a quantum system) has to be Hermitian, because this guarantees that the energy eigenvalues have to be real numbers.  Generically, non-hermitian Hamiltonians would imply complex energies, which would imply non-conservation of total probability. That is one way of treating open quantum systems, when particles can come and go, but for closed quantum systems, we like real energies.  Anyway, it turns out that one can write an explicitly complex Hamiltonian that nonetheless has a completely real energy spectrum, and this has deep connections to PT symmetry conservation.  Here is a nice treatment of this.
• Just tossing this out:  The entire annual budget for the state of Arkansas is $6.5B.  The annual budget for Stanford University is $9.5B.  

More soon.

Really doing mechanics at the quantum level

A helpful ad from Science Made Stupid.

Since before the development of micro- and nanoelectromechanical techniques, there has been an interest in making actual mechanical widgets that show quantum behavior.  There is no reason that we should not be able to make a mechanical resonator, like a guitar string or a cantilevered beam, with a high enough resonance frequency so that when it is placed at low temperatures ( \(\hbar \omega \gg k_{\mathrm{B}}T\)), the resonator can sit in its quantum mechanical ground state.  Indeed, achieving this was Science's breakthrough of the year in 2010.  

This past week, a paper was published from ETH Zurich in which an aluminum nitride mechanical resonator was actually used as a qubit, where the ground and first excited states of this quantum (an)harmonic oscillator represented \(|0 \rangle\) and \(|1 \rangle\).  They demonstrate actual quantum gate operations on this mechanical system (which is coupled to a more traditional transmon qubit - the setup is explained in this earlier paper).  

One key trick to being able to make a qubit out of a mechanical oscillator is to have sufficiently large anharmonicity.  An ideal, perfectly harmonic quantum oscillator has an energy spectrum given by \((n + 1/2)\hbar \omega\), where \(n\) is the number of quanta of excitations in the resonator.  In that situation, the energy difference between adjacent levels is always \(\hbar \omega\).  The problem with this from the qubit perspective is, you want to have a quantum two-level system, and how can you controllably drive transitions just between a particular pair of levels when all of the adjacent level transitions cost the same energy?  The authors of this recent paper have achieved a strong anharmonicity, basically making the "spring" of the mechanical resonator softer in one displacement direction than the other.  The result is that the energy difference between levels \(|0\rangle\) and \(|1\rangle\) is very different than the energy difference between levels \(|1\rangle\) and \(|2\rangle\), etc.  (In typical superconducting qubits, the resonance is not mechanical but an electrical \(LC\)-type, and a Josephson junction acts like a non-linear inductor, giving the desired anharmonic properties.)  This kind of mechanical anharmonicity means that you can effectively have interactions between vibrational excitations ("phonon-phonon"), analogous to what the circuit QED folks can do.  Neat stuff.

Recent papers to distract....

Time for blogging has continued to be scarce, but here are a few papers to distract (and for readers who are US citizens:  vote if you have not already done so!).

• Reaching back, this preprint by Aharonov, Collins, Popescu talks about a thought experiment in which angular momentum can seemingly be transferred from one region to another even though the probability of detecting spin-carrying particles between the two regions can be made arbitrarily low.  I've always found these kinds of discussions to be fun, even when the upshot for me is usually, "I must not really understand the subtleties of weak measurements in quantum mechanics."  This is a specific development based on the quantum Cheshire cat idea.  I know enough to understand that when one is talking about post-selection in quantum experiments, some questions are just not well-posed.  If we send a wavepacked of photons at a barrier, and we detect with a click a photon that (if it was in the middle of the incident wavepacket) seems to have therefore traversed the barrier faster than c, that doesn't mean much, since the italicized parenthetical clause above is uncheckable in principle.  
• Much more recently, this paper out last week in Nature reports the observation of superconductivity below 200 mK in a twisted bilayer of WSe2.  I believe that this is the first observation of superconductivity in a twisted bilayer of an otherwise nonsuperconducting 2D semiconductor other than graphene.  As in the graphene case, the superconductivity shows up at a particular filling of the moiré lattice, and interestingly seems to happen around zero applied vertical electric field (displacement field) in the device.  I don't have much to say here beyond that it's good to see interesting results in a broader class of materials - that suggests that there is a more general principle at work than "graphene is special".
• This preprint from last week from Klein et al. is pretty impressive.  It's been known for over 25 years (see here) that it is possible to use a single-electron transistor (SET) as a scannable charge sensor and potentiometer.  Historically, making these devices and operating them has been a real art.  They are fragile, static-sensitive, and fabricating them from evaporated metal on the tips of drawn optical fibers is touchy.  There have been advances in recent years from multiple quarters, and this paper demonstrates a particularly interesting idea: Use a single charge trap in a layer of WSe2 as the SET, and effectively put the sample of interest on the scannable tip.  This is an outgrowth of the quantum twisting microscope.

Guide to faculty searches, 2024 edition

As you can tell from my posting frequency lately, I have been unusually busy.  I hope to be writing about more condensed matter and nano science soon.   In the meantime, I realized that I have not re-posted or updated my primer on how tenure-track faculty searches work in physics since 2015.  Academia hasn't changed much since then, but even though the previous posts can be found via search engines, it's probably a good idea to put this out there again.  Interestingly, here is a link to a Physics Today article from 2001 about this topic, and here is a link to the same author's 2020 updated version.

Here are the steps in the typical tenure-track faculty search process.  Non-tenure-track hiring can be very similar depending on the institution.  (Just to define the terminology:  "Teaching professor" usually = non-tenure-track, expected to teach several courses per semester, usually no expectations of research except perhaps education research, no lab space.  "Research professor" usually = non-tenure-track, research responsibilities and usually not expected to teach; often entirely paid on research grant funds, either their own or those of a tenure-track PI.)

• The search gets authorized. This is a big step - it determines what the position is, exactly: junior vs. junior or senior; a new faculty line vs. a replacement vs. a bridging position (i.e. we'll hire now, and when X retires in three years, we won't look for a replacement then). The main challenges are two-fold: (1) Ideally the department has some strategic plan in place to determine the area that they'd like to fill. Note that not all departments do this - occasionally you'll see a very general ad out there that basically says, "ABC University Dept. of Physics is authorized to search for a tenure-track position in, umm, physics. We want to hire the smartest person that we can, regardless of subject area." The challenge with this is that there may actually be divisions within the department about where the position should go, and these divisions can play out in a process where different factions within the department veto each other. This is pretty rare, but not unheard of. (2) The university needs to have the resources in place to make a hire.  In tight financial times, this can become more challenging. I know of public universities having to cancel searches in 2008/2009 even after the authorization if the budget cuts get too severe. A well-run university will be able to make these judgments with some lead time and not have to back-track.
• Note that some universities and colleges/schools within universities have other processes outside the traditional "department argues for and gets a faculty line to fill" method.  "Cluster hiring", for example, is when, say, the university decides to hire several faculty members whose research is all thematically related to "energy and sustainability", a broad topic that could clearly involve chemistry, physics, materials science, chemical engineering, electrical engineering, etc.  The logistics of cluster hiring can vary quite a bit from place to place.  I have opinions about the best ways to do this; one aspect that my own institution does well is to recognize that anyone hired has to have an actual primary departmental home - that way the tenure process and the teaching responsibilities are unambiguous.

• The search committee gets put together. In my dept., the chair asks people to serve. If the search is in condensed matter, for example, there will be several condensed matter people on the committee, as well as representation from the other major groups in the department, and one knowledgeable person from outside the department (in chemistry or ECE, for example). The chairperson or chairpeople of the committee meet with the committee or at least those in the focus area, and come up with draft text for the ad.  In cross-departmental searches (as in the cluster hiring described above), a dean or equivalent would likely put together the committee.

• The ad gets placed, and canvassing begins of lots of people who might know promising candidates. A committed effort is made to make sure that all qualified women and underrepresented minority candidates know about the position and are asked to apply (reaching out through relevant professional societies, social media, society mailing lists - this is in the search plan). Generally, the ad really does list what the department is interested in. It's a huge waste of everyone's time to have an ad that draws a large number of inappropriate (i.e. don't fit the dept.'s needs) applicants. The exception to this is the generic ad like the type I mentioned above. Back when I was applying for jobs, MIT and Berkeley had run the same ad every year, grazing for talent. They seem to do just fine. The other exception is when a university already knows who they want to get for a senior position, and writes an ad so narrow that only one person is really qualified. I've never seen this personally, but I've heard anecdotes.

• In the meantime, a search plan is formulated and approved by the dean. The plan details how the search will work, what the timeline is, etc. This plan is largely a checklist to make sure that we follow all the right procedures and don't screw anything up. It also brings to the fore the importance of "beating the bushes" - see above. A couple of people on the search committee will be particularly in charge of oversight on affirmative action/equal opportunity issues.

• The dean usually meets with the committee and we go over the plan, including a refresher for everyone on what is or is not appropriate for discussion in an interview (for an obvious example, you can't ask about someone's religion, or their marital status).

• Applications come in.  This is all done electronically, thank goodness.  The fact that I feel this way tells you about how old I am.  Some online systems can be clunky, since occasionally universities try to use the same software to hire faculty as they do to hire groundskeepers, but generally things go smoothly.  The two most common software systems out there in the US are Interfolio and Academic Jobs Online.  Each have their own idiosyncracies.  Every year when I post this, someone argues that it's ridiculous to make references write letters, and that the committee should do a sort first and ask for letters later.  I understand this perspective, but I tend to disagree. Letters can contain an enormous amount of information, and sometimes it is possible to identify outstanding candidates due to input from the letters that might otherwise be missed. (For example, suppose someone's got an incredible piece of postdoctoral work about to come out that hasn't been published yet. It carries more weight for letters to highlight this, since the candidate isn't exactly unbiased about their own forthcoming publications.)  

• The committee begins to review the applications. Generally the members of the committee who are from the target discipline do a first pass, to at least weed out the inevitable applications from people who are not qualified according to the ad (i.e. no PhD; senior people wanting a senior position even though the ad is explicitly for a junior slot; people with research interests or expertise in the wrong area). Applications are roughly rated by everyone into a top, middle, and bottom category. Each committee member comes up with their own ratings, so there is naturally some variability from person to person. Some people are "harsh graders". Some value high impact publications more than numbers of papers. Others place more of an emphasis on the research plan, the teaching statement, or the rec letters. Yes, people do value the teaching statement - we wouldn't waste everyone's time with it if we didn't care. Interestingly, often (not always) the people who are the strongest researchers also have very good ideas and actually care about teaching. This shouldn't be that surprising. Creative people can want to express their creativity in the classroom as well as the lab.  "Type A" organized people often bring that intensity to teaching as well.

• Once all the folders have been reviewed and rated, a relatively short list (say 20-25 or so out of 120 applications) is formed, and the committee meets to hash that down to, in the end, four or five to invite for interviews. In my experience, this happens by consensus, with the target discipline members having a bit more sway in practice since they know the area and can appreciate subtleties - the feasibility and originality of the proposed research, the calibration of the letter writers (are they first-rate folks? Do they always claim every candidate is the best postdoc they've ever seen?). I'm not kidding about consensus; I can't recall a case where there really was a big, hard argument within a committee on which I've served. I know I've been lucky in this respect, and that other institutions can be much more fiesty. The best, meaning most useful, letters, by the way, are the ones who say things like "This candidate is very much like CCC and DDD were at this stage in their careers." Real comparisons like that are much more helpful than "The candidate is bright, creative, and a good communicator." Regarding research plans, the best ones (for me, anyway) give a good sense of near-term plans, medium-term ideas, and the long-term big picture, all while being relatively brief and written so that a general committee member can understand much of it (why the work is important, what is new) without being an expert in the target field. It's also good to know that, at least at my university, if we come across an applicant that doesn't really fit our needs, but meshes well with an open search in another department, we send over the file. This, like the consensus stuff above, is a benefit of good, nonpathological communication within the department and between departments.

That's pretty much it up to the interview stage. No big secrets. No automated ranking schemes based exclusively on h numbers or citation counts.  

Update:  As pointed out by a commenter, a relatively recent wrinkle is the use of zoom interviews.  Rather than inviting 5-ish candidates to campus for interviews, many places are now doing some zoom interviews with a larger pool (more like 10 candidates) and then down-selecting to a smaller number to invite to campus.   Making sure that the interview formats are identical across all the candidates (e.g., having scripts to make sure that the same questions are always asked in the same order) is one way to mitigate unintentional biases that can otherwise be present.

Tips for candidates:

• Don't wrap your self-worth up in this any more than is unavoidable. It's a game of small numbers, and who gets interviewed where can easily be dominated by factors extrinsic to the candidates - what a department's pressing needs are, what the demographics of a subdiscipline are like, etc. Every candidate takes job searches personally to some degree because of our culture and human nature, but don't feel like this is some evaluation of you as a human being.

• Don't automatically limit your job search because of geography unless you have some overwhelming personal reasons.  I almost didn't apply to Rice because neither my wife nor I were particularly thrilled about Texas, despite the fact that neither of us had ever actually visited the place. Limiting my search that way would've been a really poor decision - I've now been here 24+ years, and we've enjoyed ourselves (my occasional Texas politics blog posts aside).

• Really read the ads carefully and make sure that you don't leave anything out. If a place asks for a teaching statement or a statement about mentoring or inclusion, put some real thought into what you say - they want to see that you have actually given this some thought, or they wouldn't have asked for it.
• Proof-read cover letters and other documents.  Saying that you're very excited about the possibilities at University A when you sent that application to University B is a bit awkward.

• Research statements are challenging because you need to appeal to both the specialists on the committee and the people who are way outside your area. My own research statement back in the day was around three pages. If you want to write a lot more, I recommend having a brief (2-3 page) summary at the beginning followed by more details for the specialists. It's good to identify near-term, mid-range, and long-term goals - you need to think about those timescales anyway. Don't get bogged down in specific technique details unless they're essential. You need committee members to come away from the proposal knowing "These are the Scientific Questions I'm trying to answer", not just "These are the kinds of techniques I know". I know that some people may think that research statements are more of an issue for experimentalists, since the statements indicate a lot about lab and equipment needs. Believe me - research statements are important for all candidates. Committee members need to know where you're coming from and what you want to do - what kinds of problems interest you and why. The committee also wants to see that you actually plan ahead. These days it's extremely hard to be successful in academia by "winging it" in terms of your research program.  I would steer clear of any use of AI help in writing any of the materials, unless it's purely at the "please check this for grammatical mistakes and typographical errors" level. 

• Be realistic about what undergrads, grad students, and postdocs are each capable of doing. If you're applying for a job at a four-year college, don't propose to do work that would require $1.5M in startup and an experienced grad student putting in 60 hours a week.

• Even if they don't ask for it explicitly, you need to think about what resources you'll need to accomplish your research goals. This includes equipment for your lab as well as space and shared facilities. Talk to colleagues and get a sense of what the going rate is for start-up in your area. Remember that four-year colleges do not have the resources of major research universities. Start-up packages at a four-year college are likely to be 1/4 of what they would be at a big research school (though there are occasional exceptions). Don't shave pennies - this is the one prime chance you get to ask for stuff! On the other hand, don't make unreasonable requests. No one is going to give a junior person a start-up package comparable to that of a mid-career scientist.

• Pick letter-writers intelligently. Actually check with them that they're willing to write you a nice letter - it's polite and it's common sense. (I should point out that truly negative letters are very rare.) Beyond the obvious two (thesis advisor, postdoctoral mentor), it can sometimes be tough finding an additional person who can really say something about your research or teaching abilities. Sometimes you can ask those two for advice about this. Make sure your letter-writers know the deadlines and the addresses. The more you can do to make life easier for your letter writers, the better.

As always, more feedback in the comments is appreciated.