Thursday, June 30, 2011

Time management in the academic circus

Believe it or not!
I was asked to give a talk with this title to a group of academics (a mixture of staff from universities and theological colleges). At first I thought the title a bit silly, but I eventually came around to the circus metaphor and built it into my talk. I used points such as
  • Choose your ringmaster
  • Choose your act
  • Choose your audience
  • Juggling less balls is an easier act
  • Plan your act
  • Many small acts can be built into a great act
  • Face it! Academia is a circus!
  • Tune out background noise to focus on your performance
  • A circus should be fun but not drive your crazy
I will leave you to flesh out the details for yourself.

Tuesday, June 28, 2011

Michael Tinkham (1928-2010)

I am a bit slow on news. I just learned that Michael Tinkham died late last year. There is a nice (but short) obituary in Nature by Malcolm Beasley. Let me know if you know of other obituaries.

I really only knew Tinkham through his classic book Introduction to Superconductivity. It is interesting that when I was in graduate school (1983-1988) the book was out of print but my advisor Jim Sauls taught a whole course based on the book and arranged for us to get reprints (of mediocre quality). However, high-Tc changed all that and there is now a Dover Edition.
[His book on Group Theory and Quantum Mechanics is also hard to surpass.]

I did finally meet Tinkham at Harvard in 1996. I asked him if we could talk about organic superconductors because I was starting to get interested in them. He replied something like, "I know nothing about them. Lets talk about something else."
I don't recall whether Tinkham's comment eventually made me more or less inclined to work on organic superconductors.

I think Tinkham then told me about some recent experiments in his lab measuring electronic excitations on single nanometre sized metallic grains. [They added electrons one by one to the metallic grain and saw the effect of the "superconducting" energy gap]. Only later I appreciated how amazing these experiments were when later (by circumstance) I moved to UQ and  collaborated with some mathematical physics colleagues on papers inspired by those experiments.

Monday, June 27, 2011

Seminar on interlayer magnetoresistance

Here are the slides  for a Quantum Sciences Seminar I gave today at UQ.

Communicating the sweetness of science

Finding and doing cool science demos to impress children is not hard. However, the problem is that it is easy to fall into the trap that they become more like a magic show and communicate little about science. A grand challenge is actually performing demos that teach school children to think scientifically and critically. Framing questions and investigating possible answers for oneself is completely different from saying "gee whiz! this is so cool!" and just learning scientific names and mantras.

There is a really nice article in the Journal of Chemical EducationThe Science of Chocolate: Interactive Activities on Phase Transitions, Emulsification, and Nucleation. It describes a series of demonstrations that can be done with children (and their parents). I am going to try this next week! (at a holiday kids club my church is running).

The demonstrations [described in the Supplementary material] focus on answering three questions:
  • Why does chocolate usually melt in my mouth, not my hand?
  • Why does chocolate feel smooth?
  • Why does chocolate snap when you break it and have sheen?
The demonstrations provide a nice way to see in a memorable manner how changes in material composition change material properties.

Saturday, June 25, 2011

Advancing science in Africa

Physics Today has in interesting article Raising the scientific level and networking in Africa by Tony Feder.
"Bringing top scientists to Africa has a greater impact than sending individual African scientists abroad."
It features the African School on Electronic Structure Methods and Applications (ASESMA) that was held for two weeks last year. [I am very happy my former student Elvis Shoko was able to attend]. The organisers have obtained funding to hold a similar school every two years through 2020. An excellent feature of the schools is that it is backed up by a year-round mentoring progam.
Nature Physics also had an article about ASESMA.

Aside: I only just received this January 2011 issue of Physics Today in the mail.

Facebook in the research university

First, I am not a real Facebook user. The little I know is that its uncritical and careless use can create all sorts of problems.

I think there is a significant issue here for both undergraduates and graduate students. Don't assume that what you post on Facebook is private. It is just like email. Don't write anything that you don't want to become public. Furthermore, Check and understand your Facebook privacy settings! You might be surprised what information people have access to.

You are welcome to your own private views about politics, religion, global warming, marriage, sex, the university, your advisor, ....
However, if your views are (or become) publicly available and you express your views with expletives, prejudice, in a disrespectful and uncivil manner, and an uncritical manner it may create doubt in the minds of faculty about your credibility and suitability as a (potential) scholar.

And, don't do Facebook at work!
Recently, I was receiving a tour of a world class lab and one of the grad students was busy on Facebook. He could not talk to me until he had finished what he was doing. This did not create a good impression!

On a lighter note, this clip from The Bang Theory mentions the issue.

Thursday, June 23, 2011

Tailoring your talk (and abstract) to your audience

Previously I posted about the challenge of writing an effective talk abstract. Next week I am giving the Quantum Sciences Seminar at UQ. This is meant for mostly theorists working in quantum optics, BECs, quantum information, and condensed matter. Note the diverse audience. Below, I offer up for critique my abstract.
You can decide whether I was at all successful in pitching the abstract to my audience rather than just recycling one I used for a different more specialised audience. I have not prepared the talk yet. I will aim for the talk to be a less technical and specialised version of this one. Suggestions on how to do that are welcome.

Interlayer magnetoresistance as a probe of quantum coherence in layered metals

Many of the most scientifically interesting and technologically important electronic materials discovered in the past two decades have two common features:
a layered crystal structure and strong interactions between electrons.
Examples include the high-Tc cuprate superconductors and organic charge transfer salts.
Two fundamental questions about such layered metals concern the quantum coherence of interlayer charge transport and  the coherence of excited states (quasi-particles) within the layers.

I will describe the theory needed to describe the dependence of the interlayer magnetoresistance on the direction of the applied magnetic field [angle dependent magnetoresistance (ADMR)] in a wide range of materials. ADMR can be understood as a semi-classical effect or in terms of the Aharonov-Bohm effect [1].
However, there is a diverse range of strongly correlated electron materials for which
this theory fails, even on a qualitative level: the angular dependence is the opposite to
that expected from the Lorentz force law [F = q v x B].

I will discuss how ADMR is sensitive to anisotropies around an intralayer Fermi surface. Consequently, it has been used to determine anisotropies in the Fermi surface, interlayer hopping, and quasi-particle scattering rate [2,3]. On the other hand, ADMR is not very sensitive to the quantum coherence of the interlayer transport [3,4].

This talk is aimed to be at a tutorial level with an emphasis on open problems rather than a detailed technical discussion of my own recent contributions.

[1] B.K. Cooper and V.M. Yakovenko, Phys. Rev. Lett. 96, 037001 (2006).
[2] M. Abdel-Jawad et al., Nature Physics 2, 821 (2006).
[3] M.P. Kennett and R. H. McKenzie, Phys. Rev. B 76, 054515 (2007).
[4] P. Moses and R.H. McKenzie, Phys. Rev. Lett. 81, 4492 (1998).

Finding two lost triplets

Previously I discussed the importance concept of twin states in chemical bonding and photophysics. In certain situations this needs to be extended to three states, particularly in molecules with close to triangular symmetry.

A nice paper, Towards experimental determination of conical intersection properties: a twin state based comparison with bound excited states  by Shmuel Zilberg and Yehuda Haas just appeared in PhysChemChemPhys.

The paper discusses how the lowest lying triplet state can be close in geometry and energy a conical intersection between the two lowest lying singlet states (S0/S1).

The paper focuses on the specific case of the organic molecule acepentalene shown below. Unfortunately, it has not be synthesized yet in its neutral form.  The molecule has three possible degenerate valence bond structures, all related by C3v symmetry.

All of the discussion is in the framework of the Born-Oppenheimer approximation. I note that the relevant vibrational frequencies (~2000 cm-1) mean that the zero point energies are comparable to the energy barriers (~ 6 kcal/mol ~ 2000 cm-1) between the three degenerate ground states.
The resonance energy which mixes the valence bond structures can been estimated to be about 3000 cm-1, from about one third of the gap between the S0/S1 intersection and the S2 state.
The fact that all these energy scales are comparable suggests vibronic effects may be important requiring a full quantum treatment of the combined electronic and vibrational degrees of freedom.

Wednesday, June 22, 2011

A mechanism to encourage lecture attendance

It is of increasing concern to me how few students actually attend lectures. For example, in the second year undergraduate course I taught recently, attendance was in the range 50-60%. This is not unusual.

I consider that attending the lectures is an integral part of the EDUCATION that a course is meant to provide. Contrary, to what many students believe education and passing assessment are not the same thing. I am also aware there is much more to a course than just attending lectures.

If all the students were at home reading the text and solving problems I would not mind. However, based on their performance on exams I am skeptical of this.
If lectures seem not to be helpful then students need to engage with the lecturer to trying and make them moreso, e.g., by asking relevant questions. Again, this is part of the education process. Students need to learn to make the system work for them.

So what should we do about it?
Here is one radical proposal to address the issue.
At the beginning of each lecture a head count is performed and recorded. This is then averaged over the whole semester. This number is then the maximum number of students that will be allowed to pass the course, regardless of what students score on the other assessment.

This mechanism will not only provide a significant incentive for students to attend but also to encourage other students in the class to attend.

I would not claim this is a perfect solution. However, I believe it is significantly better than the status quo. I welcome comments.

Tuesday, June 21, 2011

A simple test of student understanding?

This post may be obvious to some and it is probably something I should have learnt or done long ago. In setting and marking my recent set of exams I have stumbled upon an observation. I think it illustrates a few important points:
  • Too many students approach university exams in the same way they have been taught to approach high school ones. They study for "the exam" not study "the subject". This means memorising solutions to problems rather than actually learning to solve the problems.
  • Students actually learn and understand less than we want to admit.
  • Exams should test actual understanding.
Here is what I found. Take an old exam or assignment question (which students have seen before) and change it slightly in a manner which you might consider to fairly trivial (e.g., use different parameter values, replace a 1/4 filled energy band with a 3/4 filled band, ask them to sketch a simple graph that was not in the original question, make a sub-part simpler, change the order of the question sub-parts).

Then it appears that some students have actually memorised the solution to the question that they have encountered before. They can reproduce (regurgitate?) parts of the question they have seen before but not new parts, even when the new aspects of the question may be trivial. Sometimes they will even write out the solution to part (c) on the old exam, even though on the actual exam part (c) is a different question!

I realise that my observations need to take into account the stress of exam conditions. Sometimes, students may fail read to question carefully and realise it is different. But I still think there is still something here.

I am certainly going to be more diligent about not simply recycling questions. I also need to draw a harder line with students who just want me to tell them an answer to an old question, rather than actually helping them to think through how to solve it. This is a danger of running revision tutorials.

Saturday, June 18, 2011

Getting soft on students using software

I believe that advances in computer hardware and software are becoming a real mixed blessing in the education and training of graduate (and advanced undergraduate) students.

On the one hand it is wonderful that students can use commercial software and freeware to quickly plot graphs, do statistical analysis, do Monte Carlo simulations, perform quantum chemistry calculations, ....
In principle, this should lead to deeper and more sophisticated analysis and more time for reflection.
However, it seems to me sometimes the opposite is happening.
I increasingly encounter research students who seem to treat software as a magical "black box" and lack a basic understanding of the
  • physical principles and equations the software is based on
  • limitations and reliability of the software and the underlying equations
  • need to perform systematic checks and comparisons with analytical results in well understood limits 
But, some of this responsibility must ultimately rest with advisors and their expectations. If a student "fails" on any of the above accounts they need to be sent back to their desk until they have addressed them. Students should also not be allowed to speak in public about their work until they have addressed the above issues.
I once heard of a respected condensed matter theorist who made all his students write their own software from scratch. Perhaps, this is a bit extreme but I can see why he did it.

So should there be limitations on how much software undergraduate students use in research? Should they have to pass a test before they get a "drivers license"? What might that test look like?

Friday, June 17, 2011

A primer on unconventional superconductors

For the centenary of the discovery of superconductivity Science has a series of articles about superconductivity. One of the articles is The Challenge of Unconventional Superconductivity by Mike Norman. This a very nice succinct summary of the history, key physics, and open problems. This article will be a particularly good resource for introducing students and new workers to the field. Nevertheless, I also learnt a lot and enjoyed it.

Norman considers the main classes of unconventional superconductors
  • superfluid 3He
  • heavy fermions
  • cuprates
  • organics [at least BEDT-TTF based materials]
  • iron based pnictides
It is great the organics are mentioned and compared to these other materials, since they are often ignored in reviews and conferences on this topic.

I mention just a few important and/or curious things and/or quibbles that come up in the article.

First with regard to superfluid 3He
many factors contribute to the pair interaction, including density, spin, and transverse current interactions (12). Hence, it can be misleading to claim that one mechanism is the sole cause of pairing in unconventional superconductors.
In fact, although more than 30 years have elapsed since the discovery of heavy-fermion superconductors, the actual symmetry of the Cooper pairs of any of them has not yet been unambiguously determined.
[The cuprates] violated most if not all of the empirical search rules set down by Bernd Matthias; these rules were based on the previous record high Tmaterials, which were cubic transition metal alloys, 
[In 1987] a very different theory appeared that, for better or worse, would change the face of physics (34). Philip Anderson, the Nobel laureate, proposed instead that cuprates would exhibit a novel phase of matter where the spins formed a liquid of singlets—the so-called RVB (resonating valence bond) state 
As much as I love RVB theory (and PWA) surely this is overstated! I would not say RVB changed the face of physics. I would just say RVB changed the face of the physics of strongly correlated electron materials.

I don't follow the sentence below about the organics.
These materials were discovered well before the cuprates and were an equal surprise to the community; as Bernd Matthias once quipped, “there aren’t any!” Well, they are indeed real, 
Matthias died in 1980, and the first organic superconductor (TMTSF)2PF6 was discovered in 1979. So I presume this statement [quip?] was made before the discovery and was essentially that he did not believe organic superconductors would ever be found. [Little predicted them with erroneous arguments in 1964. Basically, he ignored the Peierls instability].
[For the iron pnictides] It has been speculated that the order parameter is a so-called s± state, where the Fermi surfaces around the Γ point of the Brillouin zone have an order parameter with one sign, and those around the M point of the zone the opposite sign (46).
I disagree with the use of the word "speculated". Mazin et al. suggested this order parameter based on a concrete RPA calculation using the band structure they obtained from LDA calculations. You can debate whether this calculation is reliable in the parameter regime of the actual materials. Surely, in the weakly coupling limit it is the correct result and involves no free parameters.

Now the punchline:
From a theoretical point of view, it has become increasingly obvious that unconventional superconductivity is a very tough problem. 
Anyway. Great article! Good way to celebrate the centenary. Thanks, Mike. 

Thursday, June 16, 2011

Telling a great scientific story is hard work

Even when you have exciting and important scientific results don't delude yourself that writing the paper or a grant application will be a breeze. This struggle to communicate a great story actually occurs in many areas of life, not just science. The sooner that we and students accept this the better off we will all be.

This past weekend I watched the movie Children of the Silk Road. This prompted an internet search for more background information.... An interesting article in The Times has the subheading "The bravery of George Hogg in leading a group of wartime Chinese children to safety from the Japanese has taken 22 years to reach the screen. Scriptwriter James MacManus recounts the saga."

Here are a few relevant extracts to illustrate my main point:

I got a call from Barry Spikings, the well-known Hollywood producer.... He was the first in a long cast of producers, agents and directors who fell in love with the Hogg story . . . but never got round to making the film. Spikings .... gave me the name of Linda Seifert. “The best script agent either side of the Atlantic,” he opined....                                                    If George Hogg is the true hero of the film then Linda should be its heroine. She did not believe that a journalist could begin to write a film but she did, and still does, believe that Hogg’s extraordinary story will make a great film. She gave me a pile of old scripts and a book on screen-writing. I presented a first draft three weeks later. The title was The Bitter Sea, from an old Chinese saying. 
Linda was a hard task-mistress. She made me write the script again and again. Each new draft came back with a demand for a rewrite. Finally the script was sent out and the rewrites began again as production companies paid for options and demanded their own version. Needless to say, nothing of my script - not even the original title - has survived four different writers and the many film companies that have developed the film over the years. What has survived is Hogg’s story...
So even if you have a great scientific story expect to work very hard to get the scientific audience that it deserves.
An earlier post with a similar point is Writing IS Hard Work.

Wednesday, June 15, 2011

Ubiquitous conical intersections

What happens after a large molecule absorbs a photon? Will it emit light, undergo a conformational change, dissociate into two or more smaller molecules, or relax to its original ground state geometry? This is photochemistry.

Potential Energy Surface Crossings in Organic Photochemistry is a nice introductory review article from 1996 by Bernardi, Olivucci, and Robb. It is particularly helpful because it was only at that time that both experimental and computational evidence that conical intersections are quite ubiquitous in large molecules and key to understanding mechanisms of non-radiative decay.
They stress how originally it was thought that photochemistry proceeded via coupling of vibrational states rather than via coupling of electronic states.

How do conical intersections arise? The review points out that often conical intersections occur when a molecule relaxes to a geometry that has a local triangular symmetry (i.e. there is an equal coupling between three electronic states). This means there is a C_3 symmetry and the two degenerate eigenstates belong to the two-dimensional E representation.

I find very helpful a J. Phys. Chem. A paper Locating Electronic Degeneracies of Polyatomic Molecules: A General Method for Nonsymmetric Molecules by Zilberg and Haas. A paragraph is below
It is not clearly stated, but the matrix has a C_3 symmetry and the eigenstates are in the A and E representations. The latter are two-fold degenerate.
The figure above is taken from a review by Klessinger.

Tuesday, June 14, 2011

Grant applications should not contain equations

This is the advice I was given at the beginning of my career and I have followed it strictly since. For better or worse, there will be people reading the application who don't really understand the equations and including them will tend to put them off.
Feeling a need to include equations may also be a sign that the application is getting too technical and too detailed.
As a reviewer I can't say I have ever encountered an application without equations that I think needed them. I have certainly encountered applications with equations that I think could have done without them.
Most reviewers are asking big picture questions:
  • Is the project important and worthwhile and realistic? 
  • Does the applicant have a track record that suggests they will succeed?
  • Is there a concrete plan?
But how does one avoid generic statements which may suggest you actually don't have a concrete and specific plan? e.g., "we will calculate the temperature dependence of the interlayer resistance for a layered metal".
This is where references come in.
Also, you can refer to equations by name (the un-informed will not be put off and the informed will know what you are talking about).
Hence, you can write "our calculations will use the Kubo formula for the conductivity with an electronic self energy calculated by Dynamical Mean-Field Theory (in a manner similar to reference 11)." This is a lot less off-putting and takes up much less space than writing down the relevant equations and defining all the notation.

Having said the above it highlights to me the struggle of writing a good application. There is a hard balance to find between being too generic and being too detailed.

My thanks to Tony Wright for asking me the question.

Monday, June 13, 2011

Deconstructing interlayer resistance

This posts presents a major theoretical challenge for the theory of strongly correlated electron materials. 
The graph below shows the temperature dependence of the interlayer and intralayer resistance of strontium ruthenate (Sr2RuO4). The inset shows that below 30 K both have the quadratic temperature dependence characteristic of a Fermi liquid. However, over a broader temperature range the interlayer resistance has a non-monotonic temperature dependence.   
The figure is taken from a 1998 PRB by Nigel Hussey and collaborators.
Although, there have been various "hand waving" explanations of this data, I am unaware of any actual calculation that reproduces it.

I see two possible alternative explanations which could be backed up by concrete calculations. (There are other alternatives but here I focus on the two least exotic and most doable theoretical scenarios).

1. The anisotropy may arises partly due to the presence of multiple bands at the Fermi energy and different coherence temperatures associated with them. Based on the interlayer hoppings deduced from LDA calculations and angle-dependent magnetoresistance oscillations [see this review by Bergemann et al.] the interlayer conductivity is dominated by the beta band [composed of d_xz and d_yz orbitals]. It needs to be checked if the following two conditions hold:
  • the interlayer conductivity is dominated by a different band [because the corresponding Fermi velocity is much larger] than beta 
  • if the beta band has a much lower coherence temperature [above which the crossover from a Fermi liquid to a bad metal occurs] than the other bands
If these conditions hold then I can conceive that one may find temperature dependences like that shown above. The relevant calculation would be a natural extension of the LDA+DMFT calculations described here.

2.  The anisotropic temperature dependence may arise for similar reasons as in the cuprates (see this post). The interlayer hopping integral vanishes in certain directions (along the zone diagonals) due to the crystal structure [see the Bergemann review], whereas the intra-layer Fermi velocity does not. Consequently, the interlayer conductivity is biased towards certain parts of the Fermi surface. If there is an anisotropic pseudogap or a very anisotropic scattering rate over the Fermi surface this may produce the desired anisotropy. This would require a Cluster DMFT type calculation on a realistic multiband model.

Minimum requirements for graduating physics majors

To me there are certain minimum core skills and knowledge that a student must have if they are to be allowed to graduate. What might be good way to measure this? Different professions (accounting, medicine, law, ...) have quite strict standards and administer national (or international) exams with quite high failure rates, leading to people taking the exam several times before they pass.

One simple, but far from perfect, way to test basic physics knowledge and skills may be via the GRE Physics exam, which is required to be taken by all applicants to graduate programs in Physics and Astronomy in North America. Significant advantages of this approach is:
  • it is internationally bench marked
  • it tests basic knowledge of first and second year undergraduate physics
  • some one else designs, administers, and marks the test. (This reduces faculty workloads, and also reduces the chance of prejudice and/or favortism towards individual students).
Disadvantages to the test include it is multiple choice and largely tests speed of problem solving. It also needs to be acknowledged that high marks on the exam are widely acknowledged as not a good predictor of success at graduate school. But, that is not the goal here. It is simply to test basic knowledge and problem solving ability.

To me the primary benefit is it will stop students from graduating who have benefited from soft marking (or too much group work), who have forgotten most of what they learnt (or never learnt) in the first 2 years of their degrees, or do not integrate knowledge across subjects.

But what should be a minimum score required for students to graduate?
Searching the net I have struggled to find measures of "good" and "bad" scores. One reference point I found is that at Carnegie-Mellon the middle 70% of students admitted into the Ph.D program obtained scores in the range 665 to 980 (out of 1000). This placed them in the 47-94% percentile of those who took the exam.
Hence, I would think that a reasonable proposal is that a physics major should not be allowed to graduate until they obtain a score of at least 500.

I welcome comments, particularly people from North American universities who are more familiar with the exam.

I also welcome alternative proposals on minimum graduation standards.

Saturday, June 11, 2011

Benchmarks for excellent teaching

I recently received in the mail a catalogue from The Great Courses. It took me a while to realise that this is the Australian incarnation of what used to be called The Teaching Company. I first encountered the latter at the recommendation of my father-in-law. The company sells DVDs, and CDs of some of the best undergraduate lecture courses from (mostly) US universities. I previously had my department buy a copy of The Joy of Science, 60 lectures on science for non-science majors. Just watching a few lectures challenged the clarity and simplicity of my own lectures.
On the personal side, I have really enjoyed listening to CD's of most of the series How to listen to and understand great music. I was challenged to make my teaching more interesting.
Don't balk at the prices because they often have 70% off sales. For example, right now the Chaos course by Steven Strogatz and the Quantum Mechanics course by Ben Schumacher are on sale.

Friday, June 10, 2011

Limited information

A good week for me is where I understand something knew, even if this is just clarifying some mis-understanding about something I should have "known". Here is what I learnt this week. It will be obvious to people who have mastered their linear algebra and quantum information, but for some reason I was confused.

Consider a state |psi> in a composite Hilbert space A+B of dimension 2 x n where n >2. Then the reduced density matrix rho_A (which traces over B) is a 2 x 2 matrix and rho_B is an n x n matrix. The former has 2 eigenvalues [say x and 1-x] and rho_B has n eigenvalues. For some mistaken reason I thought that it might be possible that rho_B has many non-zero eigenvalues (after all if n is large it will be a large matrix!). But this is not the case, it only has two [x and 1-x]. In other words, rho_A and rho_B has the same rank (i.e, number of non-zero eigenvalues).

This is actually "obvious" if |psi> is written according to the Schmidt decomposition. It can only contain at most 2 terms.

This was all motivated by trying to quantify entanglement between electronic and nuclear degrees of freedom in molecules. I will post more about that later...
I thank Jeff Reimers for correcting my misunderstanding.

Thursday, June 9, 2011

The basic goal of physics

I believe that in all its branches, physics is still an experimental science. Even in theoretical physics, most of the great advances have been conceptual rather than mathematical. The basic goal of physics is not mathematical elegance or even the achievement of tenure, but learning the truth about the world around us. 
P.W. Anderson, Some thoughtful words (not mine) on research strategy for theorists
This whole article (just one page) is worth reading in full and contemplating.

Entangled doctor-patient relations

I believe in quantum pharmacology but certainly not quantum pharmacy! Drugs involve chemical or physical bonding at very specific sites in specific proteins. Quantum physics is integral to that function. However, anything beyond that is classical.

But, yesterday, I stumbled across this incredible paper which just leaves me speechless! This is part of a long series of papers by the author, claiming homeopathy is based in quantum physics.

Evid Based Complement Alternat Med. 2007 Mar;4(1):7-16. Epub 2006 Sep 14.

Journeys in the country of the blind: entanglement theory and the effects of blinding on trials of homeopathy and homeopathic provings.


Department of Chemistry, Imperial College London SW7 2AZ, UK.


The idea of quantum entanglement is borrowed from physics and developed into an algebraic argument to explain how double-blinding randomized controlled trials could lead to failure to provide unequivocal evidence for the efficacy of homeopathy, and inability to distinguish proving and placebo groups in homeopathic pathogenic trials. By analogy with the famous double-slit experiment of quantum physics, and more modern notions of quantum information processing, these failings are understood as blinding causing information loss resulting from a kind of quantum superposition between the remedy and placebo.

Tuesday, June 7, 2011

Ferromagnetism is not a spontaneously broken symmetry

Spontaneous symmetry breaking is one of the most important concepts to emerge [no pun intended!] from theoretical physics in the twentieth symmetry.
Ferromagnetism is sometimes given as an example of broken symmetry. However, it should be stressed that is the different from spontaneous symmetry breaking which:
  • is a strictly quantum effect
  • only exists in the thermodynamic limit
In a letter to Physics Today Phil Anderson wrote:
In ferromagnetism, specifically, the ground state is an eigenstate of the relevant continuous symmetry, and as a result the symmetry is unbroken and the low-energy excitations have no new properties. Broken symmetry proper occurs when the ground state is not an eigenstate of the original group, as in antiferromagnetism or superconductivity; only then does one have the concepts of quasidegeneracy and of Goldstone bosons and the "Higgs" phenomenon.
It is also worth reading the ensuing exchange between Anderson and Rudolf Peierls on the subject. I thank John Fjaerestad for making me aware of this correspondence.
Note added: Peierls discussed his point of view in more detail in his 1992 Dirac Memorial lecture at Cambridge, published here.
Also, Piers Coleman told me that in the early 90's Peierls came to Princeton specifically to have a public debate with Anderson about the issue. The large audience, including some famous theorists, was divided about who was correct.

Sunday, June 5, 2011

What motivated Feynman?

There is nice book of essays by Richard Feynman, The Pleasure of Finding Things Out, that is worth reading. The title piece is the transcript of an interview with the BBC in 1981. Here is an extract:
 I won't have anything to do with the Nobel Prize... it's a pain in the... I don't like honours. I appreciate it for the work that I did, and for people who appreciate it, and I know there's a lot of physicists who use my work, I don't need anything else. I don't see that it makes any point that someone in the Swedish Academy decides that this work is noble enough to receive a prize - I've already got the prize. The prize is the pleasure of finding the thing out, the kick in the discovery, the observation that other people use it - those are the real things, the honours are unreal to me. I don't believe in honours, it bothers me, honours bother, honours is epaulettes, honours is uniforms, my papa brought me up this way. I can't stand it, it hurts me.

Saturday, June 4, 2011

Teaching and assessing high school students

I recently learned something that greatly concerned me about high school education in Queensland. It seems teachers are not allowed to mark exams and assignments in the same manner we do at university. i.e. one gains or loses specific marks for specific actions such as getting the correct answer, including units in the calculation, stating what law or principle or equation one is using, drawing a relevant diagram. Instead, assessment is "criteria based". This means students get credit if teachers can tick off certain broadly based and pre-determined criteria, which seem to rarely get more specific than "using adequate quantitative reasoning". This significantly muddies the waters about right and wrong answers. Marking becomes a much more complicated exercise and more subjective.

I talked two physics and maths teacher about this and they agreed that it is ridiculous, but their hands are tied by the state government education bureaucracy.

I found learning this quite helpful because it may explain why increasingly I encounter students at university who cannot solve problems (especially in exam situations)  in the manner I expect.

To me this underscores the value of the International Baccalaureate as an alternative. There are now high schools in Brisbane (both public and private) which offer this as an option. I like it because it is internationally bench-marked and not subject to local political fashions.

Friday, June 3, 2011

What do you conclude from this graph?

The graph below (taken from a paper Environment assisted quantum transport by Patrick Rebentrost, Masoud Mohseni, Ivan Kassal, Seth Lloyd and Alán Aspuru-Guzik) shows the calculated efficiency of transport (blue curve) of an exciton through at network in the presence of a dissipative and dephasing environment. The horizontal scale is the magnitude of the dephasing rate. n.b. it is a logarithmic scale and spans 10 orders of magnitude. The vertical line is the estimated dephasing rate at room temperature. 
To me the curve shows that the efficiency is quite insensitive to the environment, i.e. it is greater than 80 per cent for dephasing rates varying by eight orders of magnitude! In terms of biological functionality I would say that the environment matters little to the efficiency, except when the system couples very strongly to the environment.

However, other people interpret this graph in a very different way. In a 2010 paper in PNAS,  Long-lived quantum coherence in photosynthetic complexes at physiological temperature, the authors (led by Greg Engel from University of Chicago) state
theoretical studies incorporating both incoherent and coherent transfer as well as thermal dephasing predict that environmentally assisted quantum transfer efficiency peaks near physiological temperature
we ... observe quantum coherence lasting beyond 300 fs, showing that evolution has had the opportunity to exploit the theorized environmentally assisted quantum transport (EnAQT) mechanism for biological function. 
What do you think?

Thursday, June 2, 2011

Colloquium on quantum biology

Here are my slides for the UQ Physics Colloquium. I have tried to build it around 5 key ideas:

1. Truly quantum dynamics requires phase coherence.

2. We can quantify quantum decoherence of excited states of optically active biomolecules. (Decoherence arises due to dielectric relaxation of the surrounding protein and water.)

3. Quantum dynamics is determined by competition between system timescale [which creates superposition state] and time scales of the environment.

4. There are significant scientific reasons to be skeptical about these claims of “quantum biology”.

5. The real scientific challenges for understanding are defining and solving realistic effective Hamiltonians for specific functional processes.

The key reference is a 2008 Review article I wrote with Joel Gilmore.

Overall I feel there is too much material, some of it is too technical, ...
I welcome feedback.