Haldane on the second quantum revolution

This week I attended a great public lecture by Duncan Haldane: "Quantum Mechanics After One Hundred Years, and the 'Second Quantum Revolution' Today"

Starting from the discovery of quantum mechanics, he explained how the concept of quantum entanglement is fueling today's second quantum revolution and its connection to his Nobel Prize-winning work.

Haldane remarked that his work on quantum spin chains was controversial. He had theorists accosting him at conferences arguing he was wrong. These kinds of disputes among theorists are best settled by experiment. Undoubtedly, Haldane would not have received his Nobel Prize if his predictions had not been validated by experiments. How can you motivate some experimental group to be interested in your theory? If it generates controversy!

Similarly, experiments often are the drive for fresh theoretical advances. For example, the experimental discovery of the quantum Hall and fractional quantum Hall effects came before the theoretical predictions or understanding. 

A good example of this is a second important work by Haldane also cited in his prize: quantum Hall effects in absence of Landau levels. This now-seminal work went largely unnoticed for a decade, because the model based on a two-dimensional honeycomb lattice seemed unfeasible to realize in an experiment. Later, the unanticipated work experimental isolation of graphene drove theorists to this fresh area. Haldane's early theory work was recognised as the foundation for the discovery of time reversal-symmetric topological insulators and the whole "zoo" of topological materials that followed.

Haldane also emphasized the importance of luck in making ground-breaking discoveries. von Klitzing was not the first person to attempt quantum Hall measurements, but previous attempts had used a different experimental setup: varying current with a fixed magnetic field. Imperfections in the current source led to fluctuations in the measured resistivity, which seemed to be consistent with previous approximate theoretical calculations based on perturbation theory. von Klitzing's approach of measuring resistivity as a function of magnetic field strength, with current kept fixed, led to unexpectedly precise quantization which needed new theory to explain. 

Haldane's take-home message was thus: anyone can win a Nobel Prize, but you need luck and the perseverance to defend your work if it is challenged.

An earlier iteration of this talk is available here. A more detailed write-up is available here. 

   

2025 in review

I was sad to hear that my former workplace, the Center for Theoretical Physics of Complex Systems, is winding down. It was such a great academic environment with time to think and ample opportunities to learn from colleagues and the regular seminars and international workshops. From the Center's last Scientific Report:

Outlook: The center counts 492 publications, a total of 12813 citations, and an h-index h = 56 on Google Scholar. Despite its tremendous success, a continuation with a new division headed by a new director could not be realized by IBS, which is a pity and raises other IBS related questions which are not part of the current report. As a result of the foreseeable retirement of the current director, the PCS is winding down by the end of 2025. Practically all members of the PCS quickly found or are successfully securing new positions in research institutes and universities worldwide. The successful concept of the PCS will continue to exist through its alumni who carry the message into the world. These include twenty three (23!) faculties worldwide, including eight (8!) in Korea, six (6!) in China, and five (5!) in India, but also in Singapore, Vietnam, Brazil, USA, and the Philippines.

It's a real shame, especially since support for similar theory-focused research centers is so limited. Short term grants promote "safe" topics rather than giving researchers the time and freedom to follow their curiosity and try new ideas.

Looking back, memorable moments at PCS include:

• A visit and seminar in 2018 by J. Michael Kosterlitz in which he recounted his unusual journey to his Nobel Prize-winning work, including the important role played by job rejections and rock climbing. We didn't record his talk, but what seems to be a similar version can be found here.
• Workshop weeks, particularly the ability to sit in on workshops beyond one's own areas of expertise and get a first-hand glimpse of how informal interactions differ between different fields. Sometimes the welcome reception and evening activities would wind down within an hour or so, other times they would continue into the early morning, prime time for forging new collaborations and hearing important gossip. This is also why online conferences are a poor substitute for in-person events. 
• We went through a period where we were required (as a government institute) to have personal identifying information in all job applications be anonymised, to eliminate bias in their evaluation. Whoever came up with this didn't understand you cannot anonymise academic CVs - the publication list will inevitably give the name away!

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Physical Review A saw a significant increase in submissions, including some LLM-written papers. When used properly, LLMs can be a great productivity enhancer, particularly for non-native English speakers. On the other hand, if one uses the LLM to "cheat" and write the paper entirely, it is really easy to spot. Some dead giveaways: formatting, em-dashes, fake references, overly wordy text that doesn't say much (or makes no sense at all). 

For similar reasons it is easy to spot when a referee report (or student homework assignment) has been prepared using an LLM instead of real intelligence! During one of my classes this year, I was sad to see some students completing their hand-written humanities assignment by directly copying the output from ChatGPT. At the end of the day, tedious "homework" like unpaid reviews are not just a box to tick off, they are exercise for your mind. By looking carefully for flaws and inconsistencies in someone else's work, you are also developing the critical thinking skills that will improve your own writing and research. Don't short-change yourself by delegating to an LLM!

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My own research is going at a slower pace. A lot of thinking time has been replaced with grant-writing. I hope to see some payoff for this substantial effort in 2026! 

Tenure review and impact: Named equations

To get tenure your work needs to have a clear impact. Impact can't be captured by simple rules such as publish at least x papers in a high impact journal. Standards differ too much between different research disciplines, so impact must be judged on a case by case basis.

Stronger cases for impact can be made more concisely. If you have a widely used equation named after you then likely you will "automatically" get tenure - no need to prepare a lengthy tenure dossier, since it is a clear cut case of lasting impact. 

While getting an equation named after you might seem like a daunting task, there are actually many examples of named new equations, models, or algorithms that have been adopted relatively recently. These examples give hints as to how you should strategise your own research directions if you want to use this method to secure tenure!

To start, the Lugiato-Lefever equation used to model Kerr frequency combs was first formulated in 1987. The first reference to it by others as the Lugiato-Lefever equation I can find is in 1997, after the original paper had already accumulated about 150 citations - a relatively long time.

Quantum algorithms are often named after their creators: Shor's algorithm, Grover search, and HHL immediately come to mind. But others are not: the quantum approximate optimization algorithm, quantum phase estimation, and quantum signal processing, to name a few.

The field of topological insulators provides numerous examples:

• Immediately after Haldane's key 1988 paper was published, others referred to it as "a model introduced by Haldane" and "Haldane's model". This continued for a long time, even including the seminal quantum spin Hall effect paper. The first reference to it as "the Haldane model" was the 2005 PRL paper "Orbital Magnetization in Periodic Insulators". A few papers followed this phrasing in the next two years, with it becoming widely adopted from 2008.
  
• The Kane-Mele model that started the field of topological insulators was named that way by others within a year and this name quickly stuck. 
• More recently, the first model of a quadrupole topological phase proposed by Benalcazar, Bernevig, and Hughes in 2017 started being called the Benalcazar-Bernevig-Hughes model in 2019. 
• In topological photonics we have the "Wu-Hu model" proposed in 2015, which effectively opened up the study of topological phases using all-dielectric photonic crystals. For many years this model lacked a catchy name, with many papers referring to shrunken/expanded photonic crystal designs. Then in 2023 something changed - 6 papers, all by different authors, started calling it the Wu-Hu model and now this name is being widely used!
  

Why do some equations or models get named after their creators and others don't? What makes a named equation special?

The examples taken from topological insulators relate to widely-used prototypical models. The models might lack rigorous justification from first principles or experimental feasibility, but they embody some phenomenon of interest and are simple enough to understand, boiling a mysterious effect down to its key ingredients - the heart of physics.

Names are used to allow specialists to communicate some complicated concept more concisely. Thus, naming after authors is less popular when a simple and sufficiently descriptive name exists. For example, "Berry phase" and "geometric phase" are both widely used. Similarly, if there are too many authors it becomes too cumbersome to refer to the model by their names. TKNN formula (from 4 authors' surnames) is widely used, but examples with more than four authors seem rare.

Finally, while it can help if a leading authority in the field starts using the name first, in all of the above examples the impact came before the name. But once the name is coined it becomes a lot more compelling for authors to work with your model, amplifying its impact.

2024 in review

It was a busy year for me, hence the substantially lower posting frequency.

I became a dad in February. It really puts the insignificance of the academic rat race in perspective. I had a lot less sleep and less uninterrupted time for deep work, but thankfully as of mid-December we are finally able to sleep more than 4 hours uninterrupted.

After a tough 9 years as a postdoc I started at tenure track position at SUTD in July. I have had a bit of a breather before research students join next year. I'm looking forward towards starting some research with a more longer term horizon than "get something publishable out within a year" as is typical for postdoc positions. And teaching undergraduates for the first time has also been highly rewarding even if it does take up a lot of time.

Before joining SUTD I was encouraged to apply for a start-up grant. Proposal writing really was a struggle with a newborn. My proposal was extremely rushed and unpolished - my aim was to just get out something that met the requirements. And thankfully it was funded. Take-home message: your grant proposal doesn't need to be perfect, sometimes the topic and the timing are more important than getting everything just right. The only certainty we have is that a proposal that is not submitted will never be funded.

On the research side, I was a collaborator on 8 papers submitted or published, with a few more promising ideas in the pipeline. I also managed to give 8 conference/seminar presentations, including at a graduate school in Indonesia. While I didn't participate in any big international conferences or workshops, I did enjoy attending a few meetings in Singapore.

On the editorial side, I've already finished 3 years of work with Physical Review A and will continue for another term. Since June I have also been serving temporarily as an editor for Physical Review Letters, handling more than 100 submissions. While there is a lot wrong with academic publishing today, one shouldn't lump journals of academic societies such as the American Physical Society with profit-driven publishers.

Happy 2025 to all readers! And if there's anything you'd like to see more of next year, let me know in the comments or drop me an email.

What to do when a reviewer asks for irrelevant citations

This paper has been circulating on social media thanks to the unscrupulous request of one of the referees and the authors' blunt response:

A lot of the comments I've seen about this example demonstrate a lack of understanding about how peer review works. 

It is never the reviewers who accept or reject papers - it is the editor who does so, based on advice provided by the referees. 

The editor knows the identity of the referees. 

The editor knows if a referee is asking for a bunch of irrelevant self-citations.

The editor knows not to base their decision to accept or reject the paper based on such self-serving comments.

While the authors' response in this case is amusing and made their paper go viral, it puts both the journal and the authors in a bad light. As one of my collaborators said once, "shitty referee reports will produce a stinky smell extending to our work."  Anyone can see here that the referees were more interested in boosting their citations than evaluating the scientific merits of the work, so the paper might as well be preprint that has not undergone peer review.

The correct response is to explain to the editor why the requested citations are irrelevant and leave them out of the revised manuscript. Don't cave in to blackmail.

Cargo cult science

Feynman coined the term "cargo cult science" during a commencement address. This term describing research that is aimed at confirming an assumed hypothesis became more widely known after the address was incorporated into the final chapter of his book Surely You're Joking, Mr. Feynman! Methods which superficially seem scientific will ultimately fail to deliver if researchers lack "utter honesty" - not just avoiding falsehoods, but bending over backwards to state all the possible flaws in your research. The latter is scientific integrity, the former is advertising.

Feynman argued adamantly against fooling the layman when talking about your research. He gives an example of an astronomer friend who asked what applications of his work he should mention in a radio interview. Feynman retorted "there aren't any" and the friend was dismayed because saying that would not attract continued funding support for his research.

This message remains relevant today, especially with increasing competition for grant funding and faculty positions, high impact journals with strict length limits, and big conferences with short talks. Even when we agree with being honest and discussing flaws in our research in principle, excuses inevitably come up:

"I don't have time to discuss limitations - I only have 10 minutes including questions."

"My peers who publish in Top Journal all start their papers this way - it's the only way to make it past the editor." 

"Unless I frame my proposal in terms of this Grand Challenge it will not be funded."

"I have to play this game until I get tenure, and then I will be free to do honest old-fashioned research."

"I just need this grant so I can extend my postdoc's contract..."

The end result: Paper introductions and grant applications written by large language models, because they can sell the science in a more exciting way (weasel words can be inserted to smooth over overt factual errors). Seminars where the speaker boldly claims application X in the introduction, only to backtrack when questioned after the talk (lucky there was an expert present to point out a key flaw known by specialists in the topic). Researchers wasting months on ideas that were already tried and didn't work (no rewards for publishing negative results).

It doesn't need to be this way.

 

If you think there is not enough scientific integrity nowadays, you can help by participating in peer review and questioning unsubstantiated claims and excessive hype in the right way.

You should be curious and respectful, not belligerent and dismissive. Recommending rejection on the basis of how the broader context of the results are sold (rather than the results themselves) rarely leads to a constructive outcome - either the authors will ask for your opinion to be dismissed, or they will publish the offending claims unaltered in another venue. Instead you could ask the authors to explain in more detail how approach X is expected to help goal Y and possible flaws to better put the work in context. 

The same approach is also useful for Q&A sessions after talks. Often, the speaker is well aware of certain gaps in the logic of the presentation but didn't have the time to elaborate on them.  Questions in this vein help them to better convey the important unanswered questions in their research topic and are valuable to both the speaker and the audience.

The system has too much inertia to change immediately, but by putting the broader context and salesmanship behind the research under closer scrutiny you can help to diminish the influence of cargo cult science.

Academic working conditions

Comments on a Comment published a few weeks ago in Nature Human Behaviour: Quality research needs good working conditions.

There is "a lack of permanent positions with dedicated research funding, leading to an overreliance on project-based funding with short-term research positions." Unless one lands a tenured position, the longest term of reliable employment one is likely to encounter is during the PhD studies (3+ years). Postdocs depend on periodic renewal of short-term 1 or 2-year contracts and face the prospect of probably needing to move to a different city or country if they need to take up a new position. It's hard.

The relation between turnover and research quality is nuanced. Yes, in certain circumstances pressure can foster creativity and productivity, but the threat of non-renewal is not the only form of pressure that can be applied. Internal project deadlines ("if we don't have a promising result by x, let's try a different line of research"). Performance bonuses. Conference submission deadlines. There are many possibilities.

On the flip side, there are many examples of stagnant research institutions dominated by faculty members nearing retirement with no incentives to undertake quality new research. The problem with research is that it isn't always successful. It is hard for an outsider to distinguish hard but unfruitful work from slacking off.

Unfortunately the terms of employment contracts are typically controlled by upper university management. Thus, even those tenured faculty who would prefer to have a more stable team composition have little power to effect change.

 

Students on strike

Graduate students in California have been on strike for three weeks, pushing for a livable wage.

The cost of living in California is amongst the highest in the USA, partially due to expenses for essentials including housing being pushed up by tech workers on much higher salaries. It's hard to carry out deep research if you are distracted by worrying about whether you will have enough food to last the week, or whether the next rent increase will leave you homeless.

Unfortunately universities have little incentive to increase the pay of junior researchers. The majority of graduate students are foreigners on temporary visas with little bargaining power; a few years in poverty can be a pathway to permanent residency, which opens up many more opportunities compared to their home countries. 

Moreover, salaries funded by research grants are often fixed by the funding agencies, with top-ups explicitly forbidden in some cases. Even when professors may be strongly in favour of paying their team members a livable wage, they have little power to effect change with salaries controlled by upper university management.

Despite these hurdles, the University of California system has now agreed to pay rises of up to 29% for postdocs and researchers. 

Will this lead to broader change within the broken academic system?

Meanwhile, in the headlines a few days ago Singapore and New York were tied as the world's most expensive cities. This comes amidst an absolutely insane rental market here, with monthly rents up by more than 70% in some cases.

Research funding in Korea

Earlier this month I had the pleasure of visiting former colleagues and collaborators in Korea. This was my first time delivering in-person seminars since covid and I had forgotten how invigorating and inspiring it is to present and discuss physics face-to-face.

One issue that I learned about during my trip was the lack of stability in science funding in Korea - research grants are typically reviewed (and funding levels adjusted) every year, and changes in government lead to dramatic shifts in funding priorities.

The Institute for Basic Science (IBS) was established in 2011 with the aim of providing a stable environment for carrying out long-term fundamental research.

After an initial 8-year grace period to give directors enough time to set up their centres, their performance is reviewed to determine whether funding should continue (see this 2020 perspective article for further background).

However, passing this review does give centres stability to continue to pursue their ambitious research goals. Subsequent performance reviews are planned every 3 years, with the potential for significant cuts in funding or even the entire centre shutting down.

A related issue is the puzzling combination of the centralisation of leadership while reducing the autonomy of the centre directors.

Presently tenure is limited to centre directors; if a director resigns, retires, or is hit by a bus the whole centre is shut down unless a suitable external replacement can be recruited. Meanwhile, team leaders on (on paper) tenure-track positions are not given the stability of tenure and the opportunity potentially replace directors reaching mandatory retirement age. Lasting institutions require strong base of staff at all different levels and clear avenues for career progression.

Despite directors being so essential to the continued operation of the research centres, government policy dictates that the hiring of research staff be delegated to an external committee. Moreover, candidates identities should be hidden from this committee, although publication lists can still be included in the "blinded" CVs! I understand this puzzling policy is not limited to IBS, but also applies to other government-funded research institutes.

It is remarkable that despite all these pressures and constraints researchers at IBS are still able to carry out world-class research!

More on the academic job market

Another perspective on academic jobs was published in Science a few weeks ago: As professors struggle to recruit postdocs, calls for structural change in academia intensify.

Finding suitably-qualified postdocs to hire is a challenge, especially amidst competition from quantum startups that can afford to offer significantly higher salaries. 

Grant funding rules often prevent professors from offering competitive salaries.

Overhead fees claimed by universities are growing faster than postdoc salaries (NUS's overhead costs increased from 20% to 30% last year, if I recall correctly).

Something has to change.

The great resignation in physics

Yesterday Nature published a feature article asking "Has the great resignation hit academia?" The article mostly focuses on experiences of researchers in the humanities and life sciences, but they are equally relevant to physics. Some snippets:

"Grievances include a lack of support, increased workloads, ..., and salaries that have not kept up with cost of living." 

Unofficially, it seems that the salaries of fresh postdocs in Singapore have not increased significantly since 2015, despite rising costs of living, especially rent. Frustratingly, professors seem to be powerless to address this due to postdoc salaries being fixed by upper management or funding agency rules. Consequently it is very hard to attract and retain junior researchers.

"A 2018 study predicted that higher education would lose half to two-thirds of its academic workforce to retirement, career burnout or job dissatisfaction within five years."

"By May 2021, one in five academic jobs in Australia had been cut."

The sacking of Australian research staff is particularly galling given that upper management and administration seem to be doing better than ever. With the boom in quantum technologies many Australian researchers are realizing they can keep doing the same physics under much better working conditions in spin-off companies including Q-CTRL, Quantum Brilliance, Nomad Atomics, and Diraq.