Condensed concepts

This week at UQ there was a fascinating Quantum Science Seminar by Jorg Schmiedmayer, describing some beautiful ultra cold atom experiments.  Much of the talk is nicely discussed in a book chapter Does an isolated quantum system relax?  [Answer is yes]. Some of the most recent results are in a Science paper, Experimental observation of a generalised Gibbs ensemble that appeared this month. The experiments involve a one-dimensional Bose gas that can be described as a Luttinger liquid. This means that many properties, even non-equilibrium ones , can be calculated analytically and compared to experiment. This is a theorists dream! Here are a few things that stood out. Relaxation from a non-equilibrium state to the thermal equilibrium state occurs on several different time scales. First there is rapid relaxation to a "quasi-steady state" described by a Generalised Gibbs ensemble [This idea goes back to Jaynes] that involves an effective temperature [that one can even the

Take one if you can. A great privilege and opportunity of having a tenured faculty position is the possibility at most institutions of taking a sabbatical. Roughly one year away for every six years of service or one semester away every seventh semester. I am concerned that increasingly many faculty don't take sabbaticals and that some institutions or departments (at least in Australia) discourage them. I think they are particularly important for Australians because of our geographic isolation. [For some strange reason at UQ it is called a Special Studies Program]. There are many obstacles to taking sabbaticals: finance, family commitments, keeping a group running, inertia, .... For some US faculty they also have to come up with some of the salary.... I have actually only ever taken one sabbatical (Oxford in 2004). However, for the past 12 years I have had few teaching and admin. responsibilities and have had freedom to travel. I am actually in the process of applying for on

In Carl Caves recent UQ Quantum Science Seminar "Quantum metrology meets Quantum Information Science" as an aside he also made an important side point. People often erroneously assume that the converse of a statement is true (i.e.  A implies B means that B implies A). This came up because a few referees had said that some of the results he presented in the seminar were "obvious". Roughly speaking, this concerns the issue of trying to determine what input quantum state to an interferometer will produce a "physical" output state. He found that the input state had to be "physical" (by some well-defined technical criteria). Showing this is non-trivial. However, it is obvious a physical input state is sufficient to produce a physical output state. But, that does not mean it is necessary . Showing this turned out to be quite non-trivial. I can immediately think of two other cases where scientists made similar errors of conflating necessary and suf

On tuesday at UQ Carl Caves gave a Quantum Science Seminar "Quantum metrology meets Quantum Information Science". One side point he made was that just because quantum entanglement is glamorous and beloved by luxury journals does not mean that you actually always need it to optimise any and every task. A specific example is in this paper which states: The Heisenberg limit is thus achieved without any entanglement between the arms of the interferometer. In fact, Jiang, Lang, and Caves  [4]  showed that the state  ∣ ∣ ψ in ⟩ opt is the only nonclassical product state, i.e., not a coherent state, that produces no modal entanglement after a beam splitter. These results indicate that, as in Ref.  [18] , modal entanglement is not a crucial resource for quantum-enhanced interferometry.

Feynman said "The first principle is that you must not fool yourself and you are the easiest person to fool." Walter Kauzmann emphasised that people will often believe what they want to believe rather than what the evidence before them suggests they should believe. Students need to learn skepticism. Furthermore, it needs to be modelled to them by their advisors. In particular, students should not just believe something because - their advisor/supervisor believes it or tells them it is true - it has been published, especially if it is in a luxury journal - someone famous [or a group of famous people] claims it is true - it is an exciting idea. Basic but important questions to ask are: What is the evidence? How reliable is the evidence? Is there an alternative explanation, particularly a simpler one? Maybe I am just becoming a grumpy old man, but I think I do increasingly encounter students and young researchers who lack this basic skill. I fear that this is

I have just finished a paper with Bijyalaxmi Athokpam and Sai  Ramesh, Isotopic fractionation in proteins as a measure of hydrogen bond length If a deuterated molecule containing strong intramolecular hydrogen bonds is placed in a hydrogenated solvent it may preferentially exchange deuterium for hydrogen. This preference is due to the difference between the vibrational zero-point energy for hydrogen and deuterium.  It is found that the associated fractionation factor $\Phi$  is correlated with the strength of the intramolecular hydrogen bonds. This correlation has been used to determine the length of the H-bonds (donor-acceptor separation) in a diverse range of enzymes and has been argued to support the existence of short low-barrier H-bonds. Starting with a potential energy surface based on a simple diabatic state model for H-bonds we calculate $\Phi$ as a function of the proton donor-acceptor distance $R$.  For numerical results, we use a parameterization of the model for symmet

Universities (and their problems) are certainly increasingly in the news. Here are a few things I read recently and recommend. Unfortunately, a lot of it is discouraging. The Economist ran a cover story The World is Going to University (but is it worth it?)   and special report . It particularly documents the "massification" that is going on and the associated problems. Did you know China has hired almost 100,000 new faculty in the past few decades! UQ economist John Quiggin wrote an excellent piece Rank delusions  in the (USA) Chronicle of Higher Education. [If it is behind a pay-wall you can read it on his blog ]. Basically annual university rankings are a pointless exercise that just tell us what we already know. They are actually basically the same as 100 years ago! In contrast, the top 50 companies on the Dow Jones index are completely different. The eminent British literary critic Terry Eagleton has a biting piece The Slow Death of the University (also in th

This is the main point of a nice article by Roald Hoffmann , that I posted about in the early days of this blog. I experienced this a few weeks ago. I have been working on a paper with my postdoc Nandan Pakhira about the viscosity of strongly correlated fermion fluids, focussing on the Hubbard model. A basic issue I got quite confused about is the relation between the momentum, Bloch wave vector, and velocity of an electron in a Bloch state. Yet, I when I taught this to my solid state physics class I was reminded of the correct result.

I should too. Last week I was on vacation at Bribie Island with my family. [Aside: this is the location of my profile picture you can see to the right]. We stayed in a house with, thankfully, no internet access. I don't have a phone. I could have gone to the local library or to McDonalds to access the internet. But, why spoil a good holiday? I set up my email with an "out of office" auto-reply. When I came back to work 2 days ago I went through the 140 messages in about 20 minutes. This was incredibly efficient. Most were deleted. About a dozen were about science or some admin. tasks requiring action. I set up one delayed post on my blog during my absence. I survived. My colleagues survived. My students survived. My friends survived. My collaborators survived. Bureaucrats survived. Most things can wait. I benefited from not having the distraction or of thinking about things I would have to do when I got back. I find a greater challenge is turning off

The documentary The Ivory Tower is worth watching. It gives a broad balanced overview of the major challenges facing undergraduate education in the USA. The particular focus in on the sky-rocketing cost of tuition and student debt [now greater than $1 trillion]. It is alarming that since the 1970’s tuition has increased at a greater rate than any other “commodity”, even health care! The documentary highlights that major contributions to the increasing cost are increasing number of administrators, many of excessive salaries, and fancy buildings [gyms, swimming pools, cafes, luxury apartments, …. all with lots of glass and open space] designed to lure students. Rankings and status have played a perverse role leading to an unsustainable “arms race”. But it is not all about affordability; attention is given to the other two vertices of the iron triangle [although that term is not used]: quality and access. The hype and limited potential of MOOC ’s is discussed. They are no substi

Unfortunately, The Big Bang Theory TV show features little physics these days. It is often just like "Friends" except some of the characters happen to work at Caltech. However, a recent episode, "The Troll Manisfestation" centred on superfluid helium and also mentions co-authorship, the arXiv, and physics blogs. There is some commentary on the physics in the episode by string theorist, Lubos Motl.

I think one of the weakest aspects of my teaching is running tutorials. In Australia, for most upper level undergraduate courses there is a weekly one hour tutorial [problem solving session] that is run by the lecturer. Mostly I have run these tutorials according to a traditional format. There are a set of problems that the students are meant to attempt before the session. At the tutorial I then work through the solutions on the board. There are many problems with this approach. Students often don't attempt the problems beforehand because they are not assessed. It is just like a lecture. Students are hesitant to ask questions and just write down what you write on the board. It is somewhat boring. I am not sure the students get much out of it. Previously, I posted about a different approach that my colleague Joel Corney introduced for a large second year class we were co-teaching. I thought this was quite effective. But, it also required TA's (grad. student tutors) to help.

The primary point of this post is to raise a philosophical question, "What is definitive experimental evidence for the existence of quasi-particles and a Fermi surface in a metal?" Specifically, if one sees quantum oscillations, such as Shubnikov de Haas, or maps out the Fermi surface using Angle Dependent MagnetoResistance, has one "seen" the Fermi surface? The secondary point is an unfortunate one. It provides another concrete example of the perverse influence of luxury journals, particularly the Nature Publishing Group, on science. People make silly unjustified claims to get published. At first I was excited when I saw the Nature Communications paper Quasiparticles and Fermi liquid behaviour in an organic metal   T. Kiss, A. Chainani, H.M. Yamamoto, T. Miyazaki, T. Akimoto, T. Shimojima, K. Ishizaka, S. Watanabe, C.-T. Chen, A. Fukaya, R. Kato, S. Shin It reports Angle Resolved PhotoEmission Spectroscopy (ARPES) measurements on an organic metal. For the