Category Archives: Academic advices

Physics and the bumper sticker

In the remote preparation for my Coursera on randomness, I read Nate Silver‘s The signal and the noise. I am not sure how much of it will enter my course, since I don’t plan to enter into the topics he deals with (politics, the stock market, climate change, prevention of terrorism, baseball and poker). But the conclusion struck a cord.

The author lists seven approximations to describe the “efficient market hypothesis”, which run: 1. No investor can beat the stock market, 2. No investor can beat the stock market over the long run, and so on until approximation 7 which a is five lines long sentence. Then he adds (emphasis is mine):

“The first approximation — the unqualified statement that no investor can beat the stock market — seems to be extremely powerful. By the time we get to the last one, which is full of expressions of uncertainty, we have nothing that would fit on a bumper sticker. But it is also a more complete description of the objective world.”

Sounds familiar? Let’s give it a try:

Example 1:

  • Bumper sticker: No extension of quantum theory can have improved predictive power
  • Expression full of uncertainty: the authors work under the assumption of no-signaling (so, if you are Bohmian, don’t worry, our result does not concern you).  Then they assume a lot of quantum physics, but not all of it, otherwise the claim would be tautological. Beyond the case of the maximally entangled state, which had been settled in a previous paper, they prove something that I honestly have not fully understood. Indeed, so many other colleagues have misunderstood this work, that the authors prepared a page of FAQs (extremely rare for a scientific paper) and a later, clearer version.
  • Comment: the statement “Colbeck and Renner have proved that quantum theory cannot be extended” is amazingly frequent in papers, referee reports and discussions. Often, it comes in the version: “why are people still working on [whatever], since Colbeck and Renner have conclusively proved…?” It is pretty obvious however that many colleagues making that statement are not aware of the “details” of what Colbeck and Renner have proved: they have simply memorized the bumper sticker statement. I really don’t have a problem with Colbeck and Renner summarizing their work in a catchy title; what is worrisome is other experts repeat the catchy title and base decisions solely on it.

Example 2:

  • Bumper sticker: The quantum state cannot be interpreted statistically [Yes, I know that the title of the final version is different, but this is the title that sparked the curiosity of the media]
  • Expression full of uncertainty: the authors work with a formalization of the notions of “ontic” and “epistemic” that is accepted by many people, though not by Chris Fuchs and some of his friends. They add a couple of other reasonable assumptions, where by “reasonable” I mean that I would probably have used them in a first attempt to construct an epistemic model. Then they prove that such an epistemic model is inconsistent.
  • Comment: too many people have commented on this paper. The latest contrary claim has been posted online today, I have not read it because I am really not following the debate, but for those who are interested, here it is.

Example 3:

  • Bumper sticker: either our world is fully deterministic or there exist in nature events that are fully random [the use of “either-or” makes it too elaborated for a real bumper sticker, but for someone who browses these papers, the sentence is basic enough]
  • Expression full of uncertainty: the authors consider a very weak source of randomness, something like a very biased coin; in fact, it can be more perverse than that, because it can have correlation over various tosses. But it cannot be completely perverse: the authors make an assumption about its structure (technically known as “Santha-Vazirani” by the names of the first two persons who proposed it). Then they prove that, if this source is used as seed for a specific quantum experiment, the outcomes of the experiment are guaranteed to be much more random. In the limiting case of an experiment lasting infinitely long time, and whose results do not deviate by any amount from the optimal result allowed by quantum physics, the source can contain almost no randomness, while the final list will be almost fully random.
  • Comment: in a paper just published, we studied what happens if we remove the Santha-Vazirani assumption, so that the source can be as perverse as you wish. Not surprisingly, the conclusions become more pessimistic: now, one would need a fair amount of initial randomness in order for the quantum step to produce further randomness. Nothing wrong at all: some guys get a good result with an assumption, others test the limit of the assumption, this is the normal course of science. But read again the bumper-sticker statement: taken in itself, out of the paper where it belongs, that statement has not been “scientifically proved” — it even sounds closer to being impossible to prove, without the crucial assumption

Scientific madeleines

The two conferences I attended these last weeks (CEQIP and Vaxjo) were pretty good in science, food, drink, location and atmosphere. For me, they were also full of Proustian madeleines: I have met again so many colleagues and realized how they have actually shaped my life, even when the interaction had been short.

  • Mario Ziman is one of the organizers of CEQIP. I met him in my very first conference in quantum information, in the castle of Budmerice near Bratislava, back in 2001. He was doing his PhD under the supervision of Vladimir Buzek, I had recently started my post-doc with Nicolas Gisin. As an outcome of those discussions, Mario and I (and Nicolas and Vlado and another student called Peter) worked in two papers about entanglement and thermalization. At that time, it was a rather unusual topic; now it is a big one, only in CEQIP we had at least three presentations. None of the young authors was probably even aware of our old works, but Mario and I knew better than struggling for recognition: we simply sat there in the back, enjoying the progress of the field and exchanging nods.
  • I have had fewer interactions with the other organizer, Jan Bouda; but I cannot forget a funny moment when he was visiting Singapore, probably in 2007. In the old big office of was to become CQT, Andreas Winter, Nicolas Brunner and I asked him to explain his research. He started out: “I don’t know if you are familiar with quantum cryptography”… This time, I discovered that Jan is very familiar with Moravian wines and their weaker and stronger relatives.
  • Another Slovak in CEQIP: Martin Plesch. He is presently working in Brno and has picked up the topic of randomness. In the conference in Budmerice in 2001, he was an undergrad. He had been tasked to drive Nicolas Gisin and me to Vienna airport on the last day. It was raining, we were a bit late, and Martin was going rather fast on those country roads, keeping really, really close to the car in front.
  • In Vaxjo I met again Hans-Thomas Elze, a German working in Pisa, who is the organizer of a series of conferences in Tuscany. When I went in 2004, it was held in Piombino. At that time, Hans-Thomas was still working in Brazil: as a result, the proceedings of that conference were published in Brazilian Journal of Physics. My paper dealt with an unconventional question and (as you can imagine from the journal) was forgotten until the group of Stefan Wolf made a great progress in 2011. The final solution of the problem appeared in Nature Physics. In Vaxjo, Hans-Thomas invited me to attend his next conference in September 2014. I don’t think there is an Etruscan Journal of Physics, but we’ll see…
  • Since a few years, I coincide with Mauro D’Ariano at least once per year and we always have good conversations. In the middle of complaints about bureaucracy, punctuated by the typical Italian word –zz-, he keeps an exemplary scientific drive. A few years ago, we were having fast food lunch in the March Meeting in Boston. He was telling me that, in his maturity, he wanted to start tackling “really serious” problems. Concretely, he had been reading a lot about field theory, cosmology, relativity… and was declaring his disappointment in finding gaps in the usual arguments. He had decided to try and reconstruct physics from scratch… well, from some quantum form of scratch. Normally, I tend to dismiss beginners who find problems in what others have devoted their lives too — but here, and with Mauro, I could only agree. A few years have passed: his attempt of reconstructing all that we know from basic quantum building blocks has not hit the wall: on the contrary, he and his collaborators are deriving more and more results, and even the “experts” start taking them quite seriously. Thanks Mauro for showing what serious and constant work can do!

Why am I writing all this? For no special reason other than to record minute events and people who are part of my life of a physicist.

The decline of impact factors

The influence of the impact factor is declining, according to a statistical survey which I reached starting from a blog post in Physics Today.

Many, including myself, shall certainly welcome a scientific world in which it won’t be true any longer that “a research published in Nature is, by the very fact, of the highest quality” and that “a young scientist who has published in Nature has far higher chances of getting a job“. But we don’t have to forget that the issue is deeper.

In the past, careers in science were supposedly determined by a panel of wise men (I would like to add “and women”, but it would be an anachronism): as well known, oligarchy is fair only in the eyes of those who share the same wisdom as the oligarchs. Presently, the panel of wise persons is still required for hiring, promotions etc, but there is a request of control by an independent, supposedly neutral authority. This motivates the demand of metrics, may reduce the influence of the whims of some people but introduces other problems. I fear that we won’t hit the perfect system.

Back to the statistical survey: figures 4 and 5 are really intriguing: they indicate that only few of the most cited papers are published in the most cited journals, and the percent is declining since around the year 1990. I am not sure if this is an instance of Simpson paradox… What is even more intriguing is that each figure has two graphs, and it seems to me that, by the definitions used, the two graphs should add up to 100%; but they don’t. So either something is wrong with me, or with this analysis: better finish this post and go back to work.

It will not backfire

Yesterday I was talking with a colleague about some sloppy papers published in the (supposedly) best journals — don’t try to find out which papers: you won’t guess, the sample is too big. At some point, my friend said about the authors: “It will backfire on them”. He said it with a point of sadness, because he has sincere concern for those people. I have thought it myself many times. But… will it really?

How many people are prisoners of their lust and commit horrible crimes! Many, probably most, go unpunished, even by their own conscience that they have managed to silence. Why should anything happen to people who are just prisoners of their mathematics, whose only mistake consists in not noticing that their definitions do not describe reality?

How many people commit financial crimes and injustices that ruin lives, and live without worries other than that of being one day stolen of their riches by poor fellows who will be called “criminals”! Why should some scientists, very decent fellows, be the victims of unfailing divine wrath just because they embellish (I am not speaking of faking) their results in order to get additional 5k$ per year of travel money?

No, I don’t think it will backfire: I don’t think we will see those sloppy works denounced and their authors forced to make amends. When the lobbying that keeps them going comes to an end, they will probably just be forgotten… but so will most of the works that one can consider “serious”: time is quite blind in erasing stuff.

If you want to uphold supposedly high standards, you must find other motives than the mere fear of being criticized one day.

Complacency in science

I have finally read Galbraith’s Short history of financial euphoria, which Alain Aspect suggested to me during a random dinner chat a few months ago. It’s nice: it’s the first time I understand something about finance. And it triggered a concern about academia.

In finance as well as in academia, people often fall into euphoria over something that is, by all rational standards, rather worthless. In my field of research, for instance, the latest craze is the following process:

  1. Write down a new version of some criterion that tests that “something is quantum” (a new Bell inequality, a new test of contextuality, a version of Leggett-Garg…); the simpler — the more trivial — the better, because of point 2.
  2. Find a couple of friends to do an experiment for you. Better if they have been running their setup for ages and have exhausted all the serious science that could possibly be done with it, because they will be more than happy to learn that their old machinery can still be used to perform “fundamental tests”. Moreover, since your test is simple and simple quantum physics has been tested to exhaustion, you have no doubt that the experimental results will uphold your theory.
  3. If you can, present it as “the first step towards [a big goal]”. Never mind that it is rather the last use of a setup that has made its time (I refrained to use “swan’s song”, because the last song of the swan is supposed to be the most beautiful; the last concert of an 80 years old pop star would be more appropriate a metaphor). If you can’t invoke the future, present it as “the conclusive proof of [some quantum claim]”. Never mind that the claim is usually always the same, namely, that results of measurements are not pre-established, that there is intrinsic randomness, or however you want to phrase it. Also never mind the fact that there cannot be a “conclusive claim” every month.

The euphoria mechanism is entertained as follows:

  • The big journals (Nature at the forefront) prefer to publish tons of poor science rather than risking and losing a single real breakthrough. So, if someone claims to have solved “the mystery of the quantum” (the general readership of Nature finds quantum physics mysterious), better take them seriously.
  • In turn, people notice that “if you do that, you publish in Nature”. Since “that” is not that difficult after all, it’s worth while going for it.
  • Once you have published in Nature (or Science or…), you are hailed as a hero by the head of your Department, by the communication office of your university, by the agencies that granted you the funds.
  • Put yourself now at the other end, namely in the place of the one who would like to raise a dissenting voice and reveal the triviality of the result. All the legitimate instances (peer reviewed journals, heads of prestigious Departments, grant agencies, even popular magazines and newspapers!) are against you. Isn’t it “obvious” then that you are only venting your jealousy, the jealousy of the loser?

So far, the analogy with financial euphoria is clear. I guess (though I have not studied the statistics) that the speed of the crash is also analogously fast: it happens when some of the editors of the main journals take a conscious decision of having “no more of that”, because they realize that there is really nothing to gain. The rumor spreads that “refereeing has become tough”; the journals are accused of having become irrational since “if they accepted the previous paper, why they refuse this one” (while it’s one of their few moments of rationality).

And the consequences? The same too, but fortunately without criminal pursuits, despair and suicides. The very big fish get out unscathed: either their science is really serious (that is, they have invested only a small amount of their scientific capital in the euphoric topic); or their power is really big (that is, they have invested only a small amount of their political power in backing the euphoria). The opportunists will try to follow the wind as they should, and will be forgotten as it should. Those who face uncertain destiny are the young fellows, who were doing serious science when the euphoria caught them at the right time and the right place. Because of this, they have been raised to prominence. Somehow, all their capital is invested in that topic. Will they be able to find their way out and continue doing serious science? Or will they end up teaming with their buddies, set up a specialized journal for themselves and publishing there until their old age? If one day you find me as the founder of a journal called “Nonlocality”, please wake me up.

Happy Easter!

Map your project

“I live in a house with garden in North America”. What is preposterous about this sentence? If you speak about your garden, you would not expect the whole of North America as a location. You’d expect something like “I live in a house with garden in the District D, Town T, Canada”.

Well, that is the level of introduction that you get in many papers and scientific presentations: let me make up one. “Quantum computers will have capacities beyond those of any classical computer. Here, we study how a bi-exciton decays in the quantum dots that our group has been trying to fabricate for 10 years with moderate success” (the last half is usually phrased differently, but everyone knows what that means). The point I am making here is: there is a world between the grand dreams of the field and the specific research topic one is dealing with. Following up on a point of a previous post: it is very useful to take some minutes to locate your project on the map of science, with a gradual zoom:

Continent – Nation – Town – Street – House

or, if you prefer:

Grand field – Big challenge within the field – Approach to the challenge – Specific technique [here is “the specifics of my boss”] – My project


Quantum computing – Experimental quantum coherence – Artificial atoms, Quantum dots – Self-assembled GaAs quantum dots – decay of the bi-exciton

Once you have established this map, here is my advice on how to structure a 20 minutes (10 slides) presentation, according to the circumstances. Take it with flexibility of course 🙂

  • Undergrad project: 1-1-3-2-3 [your project is probably an incremental step in your supervisor’s field, so it’s better to take a close focus; but two or three slides on the bigger picture are necessary]
  • PhD Thesis defense: 1-2-2-1-4 [your project is more relevant, so it should contribute at least a bit to the “big challenge”, if not to the grand field]
  • Generic conference: 1-3-3-2-1 [people should remember that “you work in that challenge”, they will forget the details]
  • Conference of your grand field: 0-2-3-3-2
  • Conference of your big challenge: 0-1-2-3-4
  • Specialized workshop: 0-0-1-3-6 [here is where people really care about your technicalities]
  • Grant defense: 5-3-0-0-2 [fine print will be lost, but you have to show that you are doing everyday progress]

A last word: contrary to geography, starting from your project you may zoom out in different ways. For instance, a study on quantum dots may also be seen as belonging to material science, or to quantum optics, rather than to quantum computing… Some people like to bring up all those maps at once: it’s a dangerous option, because it may confuse the audience on your motivation and also give the impression that you are trying to “play up”. The safe option consists in choosing one of the possible maps (the one that your public may like most) and stick to it.

Theorists collaborating with experimentalists: a tentative guide

This post is triggered by some of my students. I could give them my own advice directly, but I prefer to write it here because they may benefit from other valuable feedback. The issue at stake is pretty specific: the role of theorists collaborating with experimentalists. The background is my own, limited experience, the classification is as crude as it gets, the analysis proposed here is not the only possible one and is not even always suitable — so, let’s start!

It seems to me that theorist can contribute in four ways to experiments:

  1. Vision: come up with a new concept. It can be very general (say, quantum optics; quantum computing; quantum cryptography) or more specific (say, squeezed states; measurement-based quantum computing; quantum repeaters), but in any case it opens paths that were unexpected before. You won’t find these ideas planned in research proposals: they “happen”. I don’t suggest you base your career on the hope of having such a flash of genius (though you should be ready to recognize it, if it comes).
  2. Tools: develop the necessary theoretical understanding. To continue with the examples above: develop the formalism of quantum optics; invent fault-tolerant architectures; provide the formalism to do security proofs.
  3. Proposals: suggest that a given experimental setup can be used to observe some interesting effect, and do a rough first feasibility study.
  4. Specific description: take a real experiment and describe the physics, to the point where your theory matches the data.

As you can understand, these categories are not tight: for instance, some proposals make it directly into an experiment (nowadays, this is the route of choice to publish your proposal in Nature).

OK, now: here you come and have to decide in which direction to go. You may want absolutely to study a type of experiment: then you need to know what people in that field would appreciate. Or you may want to spend your life (say) inventing proposals: then you need to assess which experimental field is ripe for those. In both cases, the crucial insight for me is: there is a strong correlation between the role of a theorist and the stage of development of the experimental field:

  • At the beginning of a field, proposals are really important; they are also the fast way to celebrity (example: Cirac-Zoller first proposal of a logic gate in quantum computing). If you are up for a longer-term investment, go for tools even at this stage: your effort will be appreciated with a lag, but when the moment comes, you are seen as a pioneer and you are among the few of can really make a difference (example: the work of Norbert Lutkenhaus on unconditional security of quantum cryptography).
  • Once the field is mature, proposals must become really relevant (some physics journals can be seen as a cemetery of irrelevant proposals). Rule of thumb: if no experimentalist cares about your proposals, with overwhelming probability you are not the misunderstood genius, but just the delayed fellow (though, of course, exceptions are possible). At this stage, tools are the most appreciated contribution of theorists: if you develop them, you can choose to keep contact with the labs, or you can take the way of mathematical physics and develop them for their own sake. Both ways are serious; my advice is, but whichever you take, keep an eye on the other.
  • When a field is so mature that even the tools are fully developed, there is little left to do other than specific descriptions (this is the case, for instance, of quantum optics per se, i.e. aside from possible applications in quantum information). Specific descriptions of experiments are tricky. First, you need to check if the experimental group “needs your service”: some groups, for instance, have developed their tools so well, that their experiments are “textbook experiments”, which means that anyone who can follow a textbook can do the theory. Now, if your help is welcome, it is normally very welcome. Since there few people able to do that (compared to the mass of people contributing to the cemetery of proposals), you will be noticed among the experimentalists and may be asked for various collaborations. This is great for a PhD and, if you have such competence, you would do well in keeping it alive for the rest of your career. But you have to do something else as well, if you want to get a position: you need to show that you are also capable of original work (see why in a previous post).

Peer review

Recently, I have submitted four papers to a conference with different co-authors. After the peer review process, one was accepted for a talk, the three others for a poster. I do not copy all the reports here because it would be boring, but just the marks we received to the question “is this worth a talk”, ranging from +3 to -3. You will see a pattern emerge.

Paper 1 (the one that was accepted) had three reviewers: marks 3, 2 and 1

Paper 2 had three reviewers: 2, 0, -2

Paper 3 had two reviewers: 1, -2

Paper 4 had two reviewers: -3, 2 (the first reviewer, having noticed a few typos, mentioned “poor right up” [sic] as one of the reasons not to consider our submission).

Do you see the pattern? No? Look more closely… YES, you have got it: peer reviewing is random number generation 😉

Technical corollaries:

(1) With little post-processing, any correlation with the content of the paper can be removed for papers 2-4.

(2) Paper 1 is special, not because there is no spread, but because the average is not centered around 0. This bias is robust and can be eliminated only by suppressing buzzwords.

How to convey the wrong message

Last week, two undergraduates I know managed to convey the wrong impression about themselves and their work in a remarkably instructive way. They have learned from their (ultimately harmless) mistakes. Maybe someone else can learn too.

Case 1: a student presents the progress in his project. He starts by stressing that the title has changed because the initial project proved too ambitious. The rest of the talk is a review of some schemes for atom cooling: nice and clear, but covering pretty well known material and leaving important schemes aside. You are listening to him. What do you conclude?

Here is a pretty reasonable analysis: the student did not match the expectations of the supervisor, so the initial ambitious project was tuned down to something hardly more than a review of literature.

Here is the truth: the incompetent fellow, if anyone, is the supervisor (myself), who did not evaluate correctly the difficulty of the initial project. The student is doing very well, he has done much more than a simple review in terms of calculations and simulations. The review was simple because I asked him to use graphs and pictures instead of equations; it was incomplete because the goal is to describe a real ongoing experiment, not to review the whole field of atom cooling!

Where did the student fail? Here are some hints:

  1. Opening the talk by stressing that the focus of the project has changed was the wrong thing to do: it conveys the message that something has gone wrong. Incidentally, the initial topic was pretty similar and nobody would have noticed the change.
  2. The student embarked in the usual idiotic “atom cooling is a fundamental whatever-not in modern physics, interesting both for our understanding of nature and for applications” and failed to mention the REAL motivation, which is the description of an experiment which is really happening two floors below.
  3. The talk was too simple. One must be clear of course, but if it is a research project, one must devote one or two slides to show off — I mean, to convey what has been done.

Case 2: after a few months of research under the direction of a post-doc, a student is asked in the office of the professor (a Singaporean Chinese, which matters for what follows). The professor starts by asking “What have you learned of this field so far?” and the student replies “Nothing much really”.

Here, you don’t have to be a professor to guess the rest. What is more astonishing is the background story.

The truth is that the student had learned a lot and was aware of it. But she feigned ignorance in order to give the professor the chance to explain things from the beginning and learn from his insight! She thought that, by acting this way, she would show how eager to learn she is and how much she appreciates the wisdom of the professor.

This attitude, to this extreme, can only be found in students who have been formed in the Confucian style. But a milder form happens everywhere: for instance, when a professor asks in a lecture “Do you know this or do you need a reminder?”, almost always the students ask for the reminder (maybe there it’s also a trick to slow down the pace and trick the professor into not covering too much new material). In the context of master-to-disciple relationships, it may have its value (though I personally hate it). But if you are going into research, you have to show what you know and admit what you really don’t know: both false humility and false confidence will be detected and signal the end of your application.

A tale of 2011

Many things happened in 2011, of which I can only be thankful. I wanted to consign one to record, which may otherwise be missed, because it is about a “failure” — or better said: a beautiful reaction to a disappointing realization.

Starting in August 2010, a student of mine, Thinh, had been studying a new class of protocols for quantum cryptography, inspired by a previous work. By April, he had managed to define the key mathematical objects to very general scenarios. This was his Final Year Project (FYP), which was awarded as “Outstanding” by the university. A few months later, together with Lana (post-doc), we prepared a paper and submitted to Physical Review Letters (PRL; for the unaware: one of the most prestigious journals for physics).

When the referee report came, the tone was expected: “good work but not of enough broad interest” — very common nowadays for quantum cryptography. The referee stressed how he/she liked very much our generalization, i.e. Thinh’s result. With a few modifications, we could have had the paper published in Physical Review A (PRA; a very good journal still, edited by the same society; a Tier 1 journal in NUS, for the sake of the bureaucrats who care about these classifications).

However, one of the small comments of the referee caught our attention: we realized that the family of protocols we had considered was uninteresting! In a nutshell, these protocols collect a lot of information, but then discard much of it and rely on the rest. Why should one do so?? In other words, all that we did was correct and even elegant, but the object of our study was sort of pointless.

Now you see the alternatives we were facing: (1) skip this awareness under the carpet, do the modifications suggested by the referees and submit to PRA, with quasi-certainty of being accepted; (2) forget about this paper and write rather a technical note, explaining why these protocols are not interesting, to be sent to a very specialized (i.e. less visible) journal. For me, there was no doubt that (2) was the correct course, but I let Thinh and Lana decide — and I am very proud to say that they took the right decision 🙂 The paper has duly been re-written and is under consideration in a specialized journal of our field.

Now comes the scary part of it. I told this story to several friends working in the academic world, over coffees or lunches or other informal meetings. Many of them, especially the younger one, were astonished: “Wow, you guys are so honest! I know many who would never had dropped the chance of publishing in a Tier 1 journal”. For myself, I am sure that Thinh and Lana have made a bigger step in their career by choosing the right course: if you keep your standards high, Tier 1 publications will come.

Happy New Year!