Scientists discover quantum mechanical 'hurricanes' form spontaneously

October 16, 2008

University of Arizona scientists experimenting with some of the coldest gases in the universe have discovered that when atoms in the gas get cold enough, they can spontaneously spin up into what might be described as quantum mechanical twisters or hurricanes.

The surprising experimental results agree with independent numerical simulations produced by collaborating scientists at the University of Queensland in Australia. The Arizona and Queensland researchers are reporting the results of the research in today's issue (Oct. 16) of the journal Nature.

The results are of great interest because they reveal something fundamentally new about certain kinds of "phase transitions," and nature is replete with phase transitions.

Common phase transitions include liquid water freezing to ice, or liquid water boiling to steam. Another common phase transition occurs in proteins when raw eggs are cooked. More exotic examples of phase transitions include the cooling of materials until they become superconductors, and, on the scale of the universe, the phase transition that transformed the early universe from a hot, dense system born from the Big Bang into the universe with protons, electrons, structure and forces observed today.

A group of UA scientists headed by optical sciences associate professor Brian P. Anderson uses lasers and magnetic fields to trap gases of rubidium atoms and cool them to temperatures of about 50 billionths of a degree Kelvin, which is close to minus 460 degrees Fahrenheit. This temperature is about as close as scientists have ever been to reaching absolute zero, the hypothetical temperature at which all molecular activity ceases.

By first creating such a cold gas in their UA campus laboratory, and then lowering the temperature of the system just a little bit more, some atoms in the gas still behave much as they do in classical physics, bouncing around at random. However, this additional cooling induces a phase transition where other atoms of the gas become a new form of matter called a Bose-Einstein condensate, a tiny droplet of superfluid which behaves according to quantum physics.

Bose-Einstein condensates, or BECs, were first produced in Nobel Prize-winning experiments in 1995. Since then, theoretical and experimental researchers have studied BECs intensely, using BECs as valuable new tools for probing a wide range of fundamental physics. The UA experimental team, and the University of Queensland theoretical team headed by physicist Matthew Davis, paired up to push the limits of what is known about how BECs actually form.

"Scientists understand a lot more about BECs after over ten years of work, but there are still some great surprises," said Anderson.

Their work lends additional support to the idea that spontaneous "topological defect" formation in phase transitions is a widespread phenomenon, even at temperatures near absolute zero. "Defect" in this sense means that a discontinuity has appeared in the background superfluid of the BEC.

"In our experiments, we found that when we cool an already very cold gas through the BEC phase transition, the BEC can spontaneously begin to rotate, creating something like a microscopic quantum mechanical hurricane where atoms rotate as a fluid around a vortex core where there is no fluid," Anderson said.

"The idea of spontaneous formation of vortices in BECs had been lightly discussed as theoretically possible before, but had not been observed in experiments," he added.

Ironically, showing that BECs could be spun up into a rotating state to form vortices was a hot research topic just a few years ago. Anderson was a postdoc on the team that was the first to create a vortex in a BEC. They used creative but relatively difficult techniques. Other groups have now used a variety of techniques to successfully create BECs with many vortices.

"What was so surprising about our work is that we saw these things just appear by themselves. You just make your condensate, and they sometimes appear. You don't have to somehow manipulate your system, all you have to do is cool through the phase transition."

" I think what we've done, for the first time, is link experimental observations of defect formation in a phase transition with a theoretical model and numerical simulations that are built on some pretty rigid foundations of quantum mechanics," Anderson said.

"By collaborating with our colleagues in Australia, who are doing the theoretical research, we can back out details of the physical process that causes these vortices to spontaneously form. It will help us understand more about how superfluids develop, and perhaps more about universal phase transition dynamics in general, including the kind of phase transition that occurred in the early universe."

The experimental research was supported by grants from the National Science Foundation and the Army Research Office. The theoretical work was supported by the Australian Research Council and the University of Queensland.

The UA and University of Queensland science results agree with an important theoretical model called the "Kibble-Zurek mechanism" that concerns how defects can form in a phase transition. The model says that the faster a system undergoes a phase transition, the more defects -- in this case, the vortices -- naturally and spontaneously form. Conversely, the slower the system is cooled, the smoother the phase transition into a new state will be and the fewer defects will appear.

Farther into the future, Anderson said, BECs may become useful in devices in ways similar to laser light. Rotation sensors, accelerometers or interferometers based on the coherence properties of Bose-Einstein condensates are among the envisioned possible applications, he said.

But for now, perhaps most exciting use for BECs is as a tool for exploring the fundamental ideas of physics in ways that couldn't be explored before.

University of Arizona

---

---

	Phase Transitions (Primers in Complex Systems) by Ricard V. Solé (Author) Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation of diverse ecosystems, the book illustrates the power of simple models to reveal how phase transitions occur.Introductory chapters provide the critical concepts and the simplest mathematical techniques...
	Statistical Mechanics of Phase Transitions (Oxford Science Publications) by J. M. Yeomans (Author) Recent developments have led to a good understanding of universality: why phase transitions in systems as diverse as magnets, fluids, liquid crystals, and superconductors can be brought under the same theoretical umbrella and accurately described by simple models. This book describes the physics underlying universality and then lays out the theoretical approaches now available for studying phase transitions. Traditional techniques, mean-field theory, series expansions, and the transfer matrix, are described; the Monte Carlo method is covered; and two chapters are devoted to the renormalization group which led to a breakthrough in the field. The book will be useful as a textbook for a course in phase transitions, as an introduction for graduate students undertaking research in related...
	Elements of Phase Transitions and Critical Phenomena (Oxford Graduate Texts) by Hidetoshi Nishimori (Author), Gerardo Ortiz (Author) As an introductory account of the theory of phase transitions and critical phenomena, Elements of Phase Transitions and Critical Phenomena reflects lectures given by the authors to graduate students at their departments and is thus classroom-tested to help beginners enter the field. Most parts are written as self-contained units and every new concept or calculation is explained in detail without assuming prior knowledge of the subject. The book significantly enhances and revises a Japanese version which is a bestseller in the Japanese market and is considered a standard textbook in the field. It contains new pedagogical presentations of field theory methods, including a chapter on conformal field theory, and various modern developments hard to find in a single textbook on phase...
	Lectures On Phase Transitions And The Renormalization Group (Frontiers in Physics) by Nigel Goldenfeld (Author) Covering the elementary aspects of the physics of phases transitions and the renormalization group, this popular book is widely used both for core graduate statistical mechanics courses as well as for more specialized courses. Emphasizing understanding and clarity rather than technical manipulation, these lectures de-mystify the subject and show precisely "how things work." Goldenfeld keeps in mind a reader who wants to understand why things are done, what the results are, and what in principle can go wrong. The book reaches both experimentalists and theorists, students and even active researchers, and assumes only a prior knowledge of statistical mechanics at the introductory graduate level.Advanced, never-before-printed topics on the applications of renormalization group far from...
	Quantum Phase Transitions by Subir Sachdev (Author) Describing the physical properties of quantum materials near critical points with long-range many-body quantum entanglement, this book introduces readers to the basic theory of quantum phases, their phase transitions and their observable properties. This second edition begins with a new section suitable for an introductory course on quantum phase transitions, assuming no prior knowledge of quantum field theory. It also contains several new chapters to cover important recent advances, such as the Fermi gas near unitarity, Dirac fermions, Fermi liquids and their phase transitions, quantum magnetism, and solvable models obtained from string theory. After introducing the basic theory, it moves on to a detailed description of the canonical quantum-critical phase diagram at non-zero...
	Understanding Quantum Phase Transitions (Condensed Matter Physics) by Lincoln D. Carr (Editor) Quantum phase transitions (QPTs) offer wonderful examples of the radical macroscopic effects inherent in quantum physics: phase changes between different forms of matter driven by quantum rather than thermal fluctuations, typically at very low temperatures. QPTs provide new insight into outstanding problems such as high-temperature superconductivity and display fundamental aspects of quantum theory, such as strong correlations and entanglement. Over the last two decades, our understanding of QPTs has increased tremendously due to a plethora of experimental examples, powerful new numerical methods, and novel theoretical understanding of previously intractable quantum many-body problems. Understanding Quantum Phase Transitions organizes our current understanding of QPTs with an emphasis on...
	Index, Volume 20 (Phase Transitions and Critical Phenomena) by Cyril Domb (Series Editor) The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. It has moved into a central place in condensed matter studies. Statistical physics, and more specifically, the theory of transitions between states of matter, more or less defines what we know about 'everyday' matter and its transformations. The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable information on important recent developments.
	Conductor Insulator Quantum Phase Transitions by Vladimir Dobrosavljevic (Author), Nandini Trivedi (Author), James M. Valles Jr. (Author) Quantum phase transitions describe the violent rearrangement of electrons or atoms as they evolve from well defined excitations in one phase to a completely different set of excitations in another. The chapters in this book give insights into how a coherent metallic or superconducting state can be driven into an incoherent insulating state by increasing disorder, magnetic field, carrier concentration and inter-electron interactions. The problem necessarily involves many interacting particles and therein lies the challenge to develop a multi-faceted theory. Experiments probing microscopic structure, transport, charge and spin dynamics provide important clues. What sets this book apart is a strong dialog between experiment and theory that has the potential to solve some major issues in...
	Hysteresis and Phase Transitions (Applied Mathematical Sciences) by Martin Brokate (Author), Jürgen Sprekels (Author) This book presents a mathematical analysis of hysteretic phenomena, where two complementary viewpoints are taken: at first, scalar rate independent hysteresis is studied in a general setting that is based on the interplay between a discrete diagram-oriented and a function space approach: later, the connections between the occurrence of hysteresis and physical mechanisms like energy dissipation and phase transitions are discussed. The exposition ranges from the thermodynamic foundation of phenomenological theories of phase transitions over the variational formulation of the resulting initial-boundary value problems to the rigorous proof of results concerning existence, uniqueness and numerical approximation.
	Introduction to Phase Transitions and Critical Phenomena (International Series of Monographs on Physics) by H. Eugene Stanley (Author) First published in 1971, this highly popular text is devoted to the interdisciplinary area of critical phenomena, with an emphasis on liquid-gas and ferromagnetic transitions. Advanced undergraduate and graduate students in thermodynamics, statistical mechanics, and solid state physics, as well as researchers in physics, mathematics, chemistry, and materials science, will welcome this paperback edition of Stanley's acclaimed text.