Vortex formation in neutron-irradiated superfluid 3He as an analogue of cosmological defect formation
V. M. H. Ruutu · V. B. Eltsov · A. J. Gill · T. W. B. Kibble · M. Krusius · Yu. G. Makhlin · B. Plaçais · G. E. Volovik · Wen Xu
Abstract and summary · read the original at the source
In one page
Cosmology says the early universe cooled through phase transitions so fast that the new order could not agree with itself everywhere, and the disagreements froze in as defects. That is a hard idea to test on a universe you only get one of. The Helsinki group with Tom Kibble, Grisha Volovik and their colleagues built a version you can run all afternoon. They rotate a cylinder of superfluid helium-3 and fire thermal neutrons at it. Each neutron that lands splits a helium nucleus, and the fragments dump their energy as heat, boiling a cigar-shaped pocket back to ordinary liquid. The pocket recools through the superfluid transition in about a microsecond, and a tangle of quantized vortices freezes into it. Rings above a critical size then expand in the rotating flow and are counted one at a time by nuclear magnetic resonance, as steps on a chart. The count follows a clean cubic law in flow speed — the same law the frozen-tangle picture predicts.
Why it matters hereChapter 5 reads the vacuum as a quantum fluid, and this is where that reading stops being a metaphor: the same equations that describe defect freezing in the early universe are tested here on a liquid, one defect at a time. Chapter 13 needs experiments that connect condensed matter to cosmology, and this is the cleanest of them.
What it claims
01Absorbing a thermal neutron in superfluid helium-3 runs the reaction that turns a neutron and a helium-3 nucleus into a proton, a triton and 0.76 MeV, and the 573 keV proton and 191 keV triton lay down ionisation tracks 70 and 10 micrometres long whose recombination heats a cigar-shaped pocket of the liquid back above the superfluid transition temperature.Abstract; Introduction, third paragraph; Figure 1 caption, panels b and c
Published and peer-reviewed02That pocket recools by quasiparticle diffusion in a characteristic time of about one microsecond, and the resulting rapid transition freezes in a random network of quantized vortices with an initial defect spacing of order one micrometre — the mechanism Kibble formulated and Zurek refined.Equations 1 and 2 and the two paragraphs following them
Published and peer-reviewed03Vortex loops larger than a critical radius set by the superflow velocity expand under the Magnus force, reach the container wall as rectilinear lines and are counted individually by nuclear magnetic resonance, each absorption event appearing as a distinct step in the absorption record whose height is the number of lines nucleated.Paragraph beginning ’The number of the vortex lines is monitored with NMR’; Figure 2 insert caption
Published and peer-reviewed04The nucleation rate vanishes below a threshold superflow velocity and above it follows a cubic law in the velocity normalised to that threshold, fitted at 1.37 plus or minus 0.03 vortex lines per minute in one data set and 1.46 plus or minus 0.12 in another, against a theoretical estimate of about 2.Figure 2 main frame caption; Figure 4 caption; Equation 5
Published and peer-reviewed05The threshold velocity varies with temperature as the cube root of the reduced temperature, a different exponent from the fourth root followed by the spontaneous critical velocity measured without the neutron source, and once results are plotted against that threshold the dependence on temperature, pressure and magnetic field disappears into a single parameter.Equation 4 and the paragraph following it; Figure 3 caption; Figure 4 caption
Published and peer-reviewed06The authors put the analogy plainly: many direct parallels and formal analogies connect superfluid helium-3 theory with the field theories used to describe the physical vacuum, gauge fields and fermionic elementary particles, and they suggest the vortex nucleation seen during the rapid cool-down is similar to defect formation during cosmological phase transitions in the early universe.Abstract, final sentence; Introduction, second paragraph, citing Volovik reference 7
What to watch
Read it · abstract
Abstract
We report the observation of vortex formation upon the absorption of a thermal neutron in a rotating container of superfluid 3He-B. The nuclear reaction n + 3He = p + 3H + 0.76 MeV heats a cigar shaped region of the superfluid into the normal phase. The subsequent cooling of this region back through the superfluid transition results in the nucleation of quantized vortices. Depending on the superflow velocity, sufficiently large vortex rings grow under the influence of the Magnus force and escape into the container volume where they are detected individually with nuclear magnetic resonance. The larger the superflow velocity the smaller the rings which can expand. Thus it is possible to obtain information about the morphology of the initial defect network. We suggest that the nucleation of vortices during the rapid cool-down into the superfluid phase is similar to the formation of defects during cosmological phase transitions in the early universe.
V. M. H. Ruutu, V. B. Eltsov, A. J. Gill, T. W. B. Kibble, M. Krusius, Yu. G. Makhlin, B. Plaçais, G. E. Volovik and Wen Xu. Nature 382, 334–336 (1996); author version arXiv:cond-mat/9512117, 15 December 1995.
Authors and affiliations. Low Temperature Laboratory, Helsinki University of Technology, Espoo, Finland; Kapitza Institute for Physical Problems, Moscow; Blackett Laboratory, Imperial College, London; T-6 Theoretical Division, Los Alamos National Laboratory; Landau Institute for Theoretical Physics, Moscow; Laboratoire de Physique de la Matière Condensée de l'École Normale Supérieure, Paris. The collaboration was carried out under the EU Human Capital and Mobility Programme.
(Abstract only. The full author version is free to read on arXiv as cond-mat/9512117 — see the rights note above for why the text is not reproduced here.)
The way in
https://doi.org/10.1038/382334a0Published in Nature 382, 334 (1996). The author version was posted to arXiv as cond-mat/9512117 on 15 December 1995 under the arXiv.org perpetual non-exclusive licence rather than a Creative Commons licence, so this page carries the summary, the claims and the authors’ own abstract, and sends the reader to the source. The abstract below is the one on the arXiv version, which is titled ’Big bang simulation in superfluid 3He-B — Vortex nucleation in neutron-irradiated superflow’. The claims are located against that version’s equations and figure captions.
How to cite it
V. M. H. Ruutu, V. B. Eltsov, A. J. Gill, T. W. B. Kibble, M. Krusius, Yu. G. Makhlin, B. Plaçais, G. E. Volovik, Wen Xu (1996) Vortex formation in neutron-irradiated superfluid 3He as an analogue of cosmological defect formation. doi:10.1038/382334a0
Where it sits in the curriculum
The vacuum as a quantum fluidThe unified pictureWhat the vacuum is