50 years of Physical Review A

In the beginning, there was the Physical Review, and it was good. So good in fact that it soon started to grow exponentially. At an event celebrating the 100th anniversary of the Physical Review in 1993, one unnamed physicist quipped that “The theory of relativity states that nothing can expand faster than the speed of light, unless it conveys no information. This accounts for the astonishing expansion rate of The Physical Review” (New York Times, April 20, 1993). (At the risk of sounding like Sheldon Cooper, if this physics joke went over your head, this post is probably not for you.) As a result of the rapid growth of the Physical Review, in 1970, it was split into four journals, Physical Review A, B, C and D. One factor that drove this split was that many scientists had personal subscriptions to print journals at that time. (I still have one, although not to a member of the Physical Review family.) In its last year, the old Physical Review published 60 issues averaging over 400 pages each. That’s another 400-page issue roughly every 6 days. Most of the material in each issue would have been completely irrelevant to any given reader. You can imagine the printing and shipping costs, the problem of storing these journals in a professor’s office, not to mention the time needed to identify the few items of interest in these rapidly accumulating issues. So splitting the Physical Review, which in some sense had started in 1958 when Physical Review Letters became a standalone journal, was perhaps inevitable.

The new journals spun out of the Physical Review were to be “more narrowly focused”, which is, of course, a relative thing. Four journals were still to cover the entire breadth of physics. Each of the sections was correspondingly broad: PRB covered solid-state physics, C covered nuclear physics, D covered particles and fields, and Phys. Rev. A covered… everything else: the official subtitle of PRA at the time was “General Physics”, which included atomic and molecular physics, optics, mathematical physics, statistical mechanics, and so on.

Physical Review A, now describes itself as “covering atomic, molecular, and optical physics and quantum information”, other topics having over time been moved out to other journals. Physical Review E in particular was split out from PRA in 1993 to cover “Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics”. (That description has changed over the years as well, as the process of splitting and redefining journal subject matter continues. PRE is now said to cover “statistical, nonlinear, biological, and soft matter physics”. Physical Review Fluids was born in 2016 to pick up some of the material that would formerly have been in PRE.) Despite the evolution of PRA, one thing that hasn’t changed is that it has been an important journal for chemical physics right from the day it was born. This year marking the 50th anniversary of Physical Review A, and given that I trained in chemical physics at Queen’s and at the University of Toronto, I thought it would be a good time for me to write a few words about this journal. As with all of my blog posts, this will be a highly idiosyncratic and personal history.

I thought it would be fun to start by looking at the contents of the very first issue of PRA. Atomic and molecular physics featured prominently in this issue, with several papers either reporting on the results of theoretical calculations, or on the development of computational methods for atomic and molecular physics. Interestingly, the entire issue contained just one experimental paper. I suspect that this is an artifact of the period of time in which this first issue appeared. The atomic and molecular spectroscopy experiments that could be done using conventional light sources had mostly been done, and lasers, which would revolutionize much of chemical physics in the decades to follow, were not yet widely available in physics and chemistry laboratories.

One of the things that struck me on looking at this first issue is how short papers were in 1970. Excluding comments and corrections, the first issue contained 27 papers in 206 pages, so the average length of a paper in this issue was just under 8 pages. The papers in the first issue ranged from just 2 pages to 16. Eleven of these papers ran to four pages or less. And remember, Physical Review Letters was spun out more than two decades earlier, so there was already a venue for short, high-priority communications. Other than in letters journals like PRL, we don’t see many short papers anymore, and even in PRL, two- or three-page papers are a rarity. The “least publishable quantum” has grown over time, and the ease with which graphics can be generated has resulted in an explosion of figures in modern papers. I suspect, too, that concise writing isn’t as highly valued now as it was in 1970.

As is often the case in anniversary years, Phys. Rev. A has created a list of milestone papers. This list includes several classic papers on laser-cooling of atoms, a technique for obtaining ultra-cold atoms in atom traps, i.e. atoms very close to their zero-point energy within the trap. Because this almost entirely eliminates thermal noise, this technique allows for very high precision spectroscopic measurements, and therefore for very sharp tests of physical theories. Interestingly, in ion traps, the mutual repulsion of the ions causes them to crystallize when they are sufficiently cooled, which was the topic of one of my two papers in Phys. Rev. A.

The list of milestone papers also includes Axel Becke’s classic paper on exchange functionals with correct asymptotic behaviour. I have mentioned Becke’s work in this blog before, in my post on the 100 most-cited papers of all time, a list on which two of his papers appear. And as I mentioned there, Axel Becke was the supervisor of my undergraduate senior research project, resulting in my first publication, which also appeared in Phys. Rev. A. If you pay any attention at all to lists of influential papers and people, Axel’s name keeps popping up, and not without reason. He has been one of the most creative people working in density-functional theory for some decades now. Interestingly, Axel has only published three times in PRA, and I’ve just mentioned two of those papers. (Axel’s favourite publication venue by far has been The Journal of Chemical Physics.) His only other paper in PRA, published in 1986, was on fully numerical local-density-approximation calculations in diatomic molecules.

Many beautiful papers in nonlinear dynamics were published in Phys. Rev. A before the launch of Phys. Rev. E. I will mention just one of the many, many great papers I could pick, namely a very early paper on chaotic synchronization by Pecora and Carroll. Chaotic synchronization, which has potential applications in encrypted communication, became a bit of a cottage industry after the publication of this paper. I believe that the Pecora and Carroll paper was the first to introduce conditional Lyapunov exponents, which measure the extent to which the response to chaotic driving is predictable.

Currently, my favourite Phys. Rev. A paper is a little-known paper on radiation damping by William L. Burke, from volume 2 of the journal. This is a wonderful study in the correct application of singular perturbation theory that also contains a nice lesson about what happens when the theory is applied incorrectly. If you teach singular perturbation theory, this might be a very fruitful case study to introduce to your students.

I could go on, but perhaps this is a good place to stop. PRA has been a central journal for chemical physics throughout its 50 years. While PRE picked up many topics of interest to chemical physicists, PRA remains a key journal in our field. Until the Physical Review is reconfigured again, I think it’s safe to say that PRA will continue to be a central journal in chemical physics.