Posted in 2011
Hans Schumacher
from Physikalisch-Technische Bundesanstalt Braunschweig, German metrology center, gave a talk today. The main direction of his research is to make a practical electric-current standard that uses electron counting in Coulomb blockade regime. Many teams, including that in Delft, have attempted this 20-15 years ago but have to stop. Hans Schumacher boldly took the road that has considered to be a dead end and has demonstrated to us a significant progress as well as a hope for even further progress. I like his strive very much and wish him best sucsess.
That was positive and encouraging part of the talk. There was also a negative and dissapoinig part. It appears that the physical factor that stopped the research 15 years ago – undesired co-tunneling processes – has been completely forgotten today. At least the speaker could not give correct esimations of the precision limitations owing to this factor, and I suspect that people helping him did not think about it too. Find this outrageous since the factor has been discussed in the literature in quite some detail and presents common knowledge in quantum transport. I suggest that the authors, invoved editors and especially anonymous referees of
Phys. Rev. Lett. 104, 186805 (2010)should immediately attend my master course in quantum transport. This seems the only way to restore the continuity of scientific progress:)
Exam Quantum Transport: results
I will leave for vacations soon. In order not to dissappoint the sudents with the delay of the marks, I had to check the exam papers of quantum transport quickly. I’ve worked over the weekend and finally done the job today.
The exam consisted of two parts: the problem and multiple-choice questions (mcq). Roughly, problem checks the attendance of problem-solving sessions, while mcq check if a student has re-read the lecture material before the exam:) The mcq are very accurate tool: in many cases, I can see at which lecture a student stopped re-reading of the lecture material.
The distribution of the answers to mcq was rather standart, perhaps with the maximum slightly larger than expected. However, there was a problem with the problem.
Let me explain the problem without formulas. There are two ways to solve scattering problems considered in the course. Way 1 employes summation of elementary scattering trajectories, is easy and constructive for elementary setups, but is too complicated for just a bit more complex situations. Way 2 is more formal: it requires to make a system of linear equations for amplitudes of reflected and transmitted waves that has to be solved subsequently. Both ways, the difference between them and their formal mathematical similarity have been explicitly explained in course of the lectures and problem sessions. The formulation of the exam problem clearly suggested: do it in way 2.
Oh. Vast majority of the students did it in way 1. The success to follow the way has been varying while the suffering remained rather invariant. Now I understand why the students looked so gloomy. Now it’s my turn to look so: I’ve so carefully paved way 2 to lead to examination sucsess, and almost nobody took it.
Besides a point in the problem that we regarded as ultimately trivial appeared to be an almost universal stumbling block for both strong and weak. Oh. These apparent misunderstandings made the evaluation a complicated and painful procedure. The results could be better, but, after all, they are not so bad.
Exam Quantum Transport: as an event
The exam took place today, again in that quasi-infinite building of Civil Engineering. For a change, it was one floor higher than the previous exam. So we steadily increase the exercise challenge
The weather is funny today, it tries to be hot and humid, but only reaches warm and suffocating. I felt the students are unhappy even before the examination: must be weather. There were rather many enlisted for the examination. However, I got several messages from people who could not prepare on time, and several just did not show up. Finally, I have ten exam papers to check.
My audience this year was different from what I used to have. They showed more interest and perhaps more motivation. However, they are decisively less nerdy. From a quick look at questionairs, I recognize that many have found the exam difficult. Well, that must be this funny weather…
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Topological excitations
will become a part of the book on Advanced Quantum Mechanics I write with Jeroen Danon. I’m currently squeezing the material to a chapter devoted to superfluidity. It’s a difficult piece of writting: yet I dream it will be a good one.
The trick to implement the concept is to consider the superfluid in lower dimensions where vortices have finite energy and can be regarded as elementary excitations. I also hope to be able to say something about Feynmann’s roton variational function: a gem almost forgotten in modern education.
Exam Advanced Statistical Mechanics: results
I’ve finished checking the exam papers today. Good news is everybody has passed (the examination). Though a minority had to struggle for this. The distribution of the marks is pretty standard (otherwise). The fact the students made presentations was undoubtedly helpful.
However, I was dissapointed with the following. There were three groups of students: some obviously prtefer the lectures, some attended the problem-solving sessions only, some tried to combine both. Each of the three groups have exhibited distinct weak points in course of examination… While this is natural for the first two groups, and has a very straightforward workaround, I’m puzzled with the third group. The results of those were good but can easily be better.
Another point of dissapointment are the marks the students gave to our course (there is a questionaire to fill after the examination, a remedy for post-examination stress). It’s 7 in average, could be better giving amount of energy I gave..
Few skeletons in every genome
Today we have had another Kavli Colloquium. Actually, my day was busy and nervous, and I thought I could skip “this bio stuff” and concentrate at work at hand. I’ve changed the decision at the last moment and have not regretted: in fact, I think it was one of the best colloquia I ever attended.
Though there was hardly any physics. Stephen Quake, prof Bioingenering from Stanford and enterpreneur, has neatly and skilfully tuned the presentation to the perception and level of general physical audience, I appreciate much his effort to get us following. The talk did not sound any “biological” though it was.
It was about reading genomes of individual humans by means of single-molecule DNA sequencing. Stephen Quake is a leading palyer in the field. Three years ago he read his own genome for $ 50,000 cost. According to his projections, this cost can drop to $ 500 whithin years. The reading of someone’s genome can become as usual as a blood test. And perhaps will become compulsory as a drug test (in order to descrease costs of medical aid by early detection of potential gene-related medical problems). The positive sides of it are clear (though, as was stressed in the talk, less obvious than we’d like them to be). With a bit of imagination, one can picture negative sides of it (don’t want to do this here, leave it as an exercise for the reader).
When I was a kid, I read stories about scientists whose work reshapes the world within years. I think today I finally came reasonably close to seeing one. Stephen Quake looks very human, more human than most profs of science (me including). That’s why I sympathize with him and wish him to never regret the opportunities his research may unleash…
No Coulomb Blockade of Majorana Fermions
you, dear reader, and all modern society will have to live without spectacular achievements in this research direction.
My research proposal described in this post has been rejected in the course of our national competition, FOM Projectruimte. In comparison with the last year competition I invested more time to the writting, have brought more original and more experimentally relevant ideas, have discussed proposal with many and incorporated their feedback.
The result of these actions was evident and imminent: the proposal has been rejected faster and with worse mark. A modern referee does not have time to read the proposal, and expects to see the things expected. Any unexpected creativity is punished immediately, at the level of instinct.
Yet the creativity was certainly present in the marks I get. The referees suppose to give three marks: “scientific quality”, “risky character”, “total assesment” that supposed to summarize the two. Only the third one counts, while the first two are given for fun. In that case, the fun was all mine: 3.0 “scientific quality”, 3.2 “risky character”, 3.5 “total assesment”. Surprised, I asked the FOM functioneers for a comment. Got nothing except “such things happen”. They happen indeed!
Fritz and Hans: an attempt at phenomenological understanding
This is a title of my contribution to the last Kavli Newsletter. I’ve written it a while ago and almost forgotten about, yet Huub Salemink was as kind as to remind me today. Here it goes:
The immediate motive to write this column is evident: J.E. Mooij was awarded the Fritz London prize. And though he has to wait for half a year to get his hands on it, we are all glad, consider it as our common achievement, and congratulate him from the depth of our common heart. Yet here I’d like to attempt a deeper study that, for the absence of exact microscopic theory, is bound to be phenomenological. By virtue of this approach, I have to disregard any personal detail however important it might seem.
The phenomenon of Fritz London is evident and lies within penetration depth. Foreign experience cannot be underestimated: it took only a year for this 1933 refugee to come up with a seminal theoretical contribution to superconductivity theory, long before this theory came into existence. It was a gem of phenomenology and implied a professorship. But how could an émigré penetrate the hearts of Duke colleagues so deeply as to make Fritz into a prize? When John Bardeen got this prize he did not hide it in his pocket; after a while, he returned back an amount 10 times greater to the prize fund, and that was no grant money. While we do not know what attracted him that strongly, it is well established that superconductivity, and thus research thereupon, requires attractive interactions.
The phenomenon of Hans Mooij is perhaps more complicated and certainly less explored. Why would a successful Shell employee run back to science? And if really looking for science, why would he run to a place where leading professors were not burdened with Ph.D. titles and published only once every two years in a local journal? And, if adjusted to such an environment, why work persistently at changing it into a Nature-publishing collective where almost any Ph.D. is a professor? Why, upon coining your own scientific reputation, would you care about, promote, and defend the research in fields so different from your own? Being successful in all that, why still look for new topics to investigate? Well, it is clear that the usual assumption of local, or contact, attractive interaction does not work here. The interaction must be global and arise from a kind of unbroken symmetry where your individual research and success is equivalent to those of others.
I wonder if we can comprehend this unusual symmetry in more exact terms. Actually, I do not care if we cannot. The point would be to accept its existence at the phenomenological level, understand the possible (and perhaps impossible) experimental consequences, and utilize the phenomenon.
The author is indebted to J. E. Mooij for numerous manifestations.
Exam Advanced Statistical Mechanics: as an event
has taken place today in one of the rooms of nearly-infinite building of Civil Engineering. Me and Alina made two levels upstairs and two hunderd meters in horizonal direction to reach the room. The latter appeared closed, the students confusingly flocking around. Being a responsible person, I marched the way back, got the key and marched forth. So I was already tired to start with. Fortunately, Alina has performed most of exam supervision.
Seven students have shown up. Most of them made presentation and got a bit easier version of the exam. Only one international student has decided to do a fuller version.
The impression is the exam was doable for most students. I still have to check the results and their responses on the questionaire.
Julia Meyer
has been visiting tuesday-wednesday this week. She’s a faculty in Grenoble now, after being in Germany and a loong time in US. I like very much her serious, thorough and ingenious approach to theoretical physics: something rarely seen in her generation/our field.
She gave a talk about various aspects of 1d interacting electrons. I especially liked the last part devoted to ordering of classical electrons in 1d confining potential. It’s a beautiful and context-rich problem that I also touched many years ago.