Friday, June 26, 2020

The Classics matter

Some people might expect me to be enthused that the Australian government recently announced that the tuition costs for university degrees in the humanities and social sciences would increase and the costs of undergraduate degrees in mathematics and sciences has decreased. This is based on three unquestioned assumptions and values. First, university is a job-training program. Second, all these extra mathematics and science graduates will get employment in the area that they study. Third, there is no need to address the massive other problems that Australian universities are facing, further accentuated by covid-19.

The central purpose of a university education is to learn to think.

Why study the classics? Recently, I read the following letter to The Economist written by Robert Machado, a PhD student in classics at Cambridge.
As a teacher and researcher in classics, I care profoundly about the subject’s purpose (Johnson, May 2nd). Too many of my colleagues rely on the guff that it teaches grammatical rigour or fall back onto vague assertions about the origins of Western civilisation. Although it is good to have a knowledge of ancient societies, the study of classics or indeed any ancient peoples offers one important transferable skill. When studying any ancient civilisation, one quickly brushes up against the reality that 99.9% of the information one would like to have is already lost. This forces any student or researcher to reflect hard on what data can be used. We must carefully analyse and argue over every scrap, while avoiding the temptation to come to conclusions that the data do not justify. In an age where we are faced with a glut of data, knowing what they can or cannot be used to say is vital.
Rodney Stark was a well-established sociology professor at the University of Washington when he made the bold move to work on the history of early Christianity, making use of methods and concepts from sociology. In the Preface to his book, The Rise of Christianity, he notes
my effort to reconstruct the rise of Christianity has been a cherished hobby - a justification for reading books and articles that now fill an entire wall of my study. It would be impossible to express adequately how much pleasure I have gained from these authors. I am convinced that the students of antiquity are on average the most careful researchers and the most graceful writers in the world of scholarship. 
Parenthetically, I note that Stark's work and attitude provides a model of how to successfully break into a new field.

Wednesday, June 24, 2020

Why Josephson matters

Reflecting on macroscopic quantum effects in condensed matter I have come to the view that Brian Josephson is a key figure. But, the observation of magnetic flux quantisation in superconducting cylinders is also a landmark.

The significance of Josephson is nicely laid out in a fascinating article published by in Physics Today in 2001 by Donald G. McDonald
John Bardeen, the leading condensed matter theorist of his day, was quite wrong when he dismissed a startling prediction by the unknown Brian Josephson. 

The article nicely lays out several important precursors to Josephson's work that all occurred after BCS theory in 1957.

1. The experimental (unanticipated) discovery by Ivar Giaever in 1960 of single-particle tunneling in SIS junctions [superconductor-insulator-superconductor sandwiches]. I-V curves clearly showed the structure of the BCS energy gap.
[Aside. This discovery was also laid the foundation for John Rowell's tunneling experiments that allowed a quantitative (strong-coupling BCS) analysis of the electron-phonon interaction responsible for superconductivity.]

2. The discovery by Hans Meissner [not the discoverer of the Meissner effect!] in 1960 of the proximity effect, where superconductivity is induced in a non-superconducting metal, by close proximity to a superconductor.

3. The discovery in 1961 by two independent experimental groups that the magnetic flux inside a cylinder was quantised in units of h/2e where h is Planck's constant and e is the electronic charge. This effect had been predicted by Fritz London in 1948, albeit without the factor of 2.
These experiments provided ``the first direct demonstration of a macroscopic quantum effect.''


The data above is from a 1971 paper, observing flux quantisation within one-half of a per cent.

A nice article on the history of the discovery is

 Aside. These experiments also clearly showed the physical nature of the magnetic vector potential, A, and illustrated the Aharonov-Bohm effect.

4. Josephson's attendance at a series of lectures ``Concepts in Solids" that Phil Anderson gave to graduate students at Cambridge in 1961-1962. In particular, at the end, Anderson introduced the concept of broken symmetry as an organising principle to describe ``condensed systems" such as antiferromagnets, superfluid 4He, ferroelectrics, and superconductors.

Distinctly quantum phenomena are tunneling, superposition (and the associated coherence and interference), and entanglement. Josephson junctions can be used to illustrate all of these at the macroscopic scale.

This is explored in a nice autobiographical article by Tony Leggett.
Because of the strong prejudice in the quantum foundations community that it would never be possible to demonstrate characteristically quantum-mechanical effects at the macroscopic level, this assertion made us [Leggett and Garg] the target of repeated critical comments over the next few years. Fortunately, our experimental colleagues were more open-minded, and several groups started working toward a meaningful experiment along the lines we had suggested, resulting in the first demonstrations (29, 30) of MQC [Macroscopic Quantum Coherence] in rf SQUIDs (by then rechristened flux qubits) at the turn of the century. However, it would not be until 2016 that an experiment along the lines we had suggested (actually using a rather simpler protocol than our original one) was carried out (31) and, to my mind, definitively refuted macrorealism at that level. I find it rather amusing that nowadays the younger generation of experimentalists in the superconducting qubit area blithely writes papers with words like “artificial atom” in their titles, apparently unconscious of how controversial that claim once was.

Thursday, June 18, 2020

The lecture Feynman really wanted to give to undergraduates

For Condensed Matter Physics: A Very Short Introduction, I have started writing a chapter on "Quantum matter". It is a challenge to decide what to include, particularly given how the content needs to be accessible to a general audience. The question, "What is quantum matter?" is an interesting one. Currently, I have decided to focus on how superconductors and superfluids can exhibit macroscopic quantum effects. More on that later. 

In the process, I was reminded of the last lecture in the celebrated Feynman Lectures on Physics. These are now available online, including photos.

The Schrödinger Equation in a Classical Context: A Seminar on Superconductivity



Here is Feynman's introduction to the lecture, given on June 4, 1964. This was the last lecture in a two-year ``introductory" physics course for Caltech undergraduates.
This lecture is only for entertainment. I would like to give the lecture in a somewhat different style—just to see how it works out. It’s not a part of the course—in the sense that it is not supposed to be a last minute effort to teach you something new. But, rather, I imagine that I’m giving a seminar or research report on the subject to a more advanced audience, to people who have already been educated in quantum mechanics.

All that aside, this is a subject I want to talk about. It is recent and modern and would be a perfectly legitimate talk to give at a research seminar. My subject is the Schrödinger equation in a classical setting—the case of superconductivity.
The lecture includes a description of the quantisation of magnetic flux, the Josephson effect, Shapiro steps, and a SQUID. All of these phenomena had only been discovered in the two years before the lecture. It is striking that Feynman clearly appreciated the significance of these recent discoveries, not just for condensed matter but also for quantum theory. He concludes the lecture as follows.
These then are some illustrations of things that are happening in modern times—the transistor, the laser, and now these junctions, whose ultimate practical applications are still not known. The quantum mechanics which was discovered in 1926 has had nearly 40 years of development, and rather suddenly it has begun to be exploited in many practical and real ways. We are really getting control of nature on a very delicate and beautiful level.

I am sorry to say, gentlemen, that to participate in this adventure it is absolutely imperative that you learn quantum mechanics as soon as possible. It was our hope that in this course we would find a way to make comprehensible to you at the earliest possible moment the mysteries of this part of physics.
 

Tuesday, June 16, 2020

Taking a break from it all

Covid-19 and the associated fallout marches on. Increasing attention is being given to the impact of social isolation (sheltering in place) on mental health. Finally, it caught up with me. This is in spite of my personal situation and that in Australia being relatively easy. Almost immediately when I moved my office to home I started having significant neck and back problems. I made six trips to the physiotherapist over the course of four weeks, carefully monitored my posture, did exercises, and limited my sitting time. I got better. But, I know wonder how much was psychosomatic. I pretty quickly got zoom fatigue. Then a few weeks ago I started to see other mental health warning signs, particularly being easily overstimulated and anxious. I was disappointed because I thought I was managing it relatively well. 

So I bit the bullet. I took 9 days off work and never looked at email.
Social distancing requirements are now relaxing in Australia and we are now allowed in-state travel. My wife and I (and Priya the dog) went to our favourite Queensland holiday destination Bribie Island for a week. (This is also the location of the photo from my blogger profile). It was wonderful. Here are a few photos. I also saw some dolphins really close to the shore!



I also had a phone appointment with my psychologist who challenged me to restart mindfulness exercises. I am also trying to keep on top of the basics (sleep, diet and healthy fluid intake, exercise, limited screen time, reducing stress, ...)
 
So, do not under-estimate the impact of covid-19 on your mental health. Once you get a chance take a break.

Feel free to share your own experiences and/or relevant articles.