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Trinity QuSys Team Uncovers New Quantum Phenomena

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Reviewed by Danielle Ellis, B.Sc.Oct 9 2024

The Trinity QuSys team, under the direction of Professor John Goold from the School of Physics, described their breakthrough in comprehending the effect in the very different and highly complex field of quantum physics in a study published in Physical Review Letters.

Initially conducted out of pure curiosity, the discovery bridged the gap between Aristotle’s observations two millennia ago and modern-day understanding, opening the door to a slew of “cool” - and “cooling” - implications.

The Mpemba effect is best known as the perplexing phenomenon in which hot water freezes faster than cold water. The counterintuitive effect was first observed by Aristotle over 2,000 years ago when he observed that the Greeks of Pontus were exploiting it in their fishing practices.

René Descartes, Francis Bacon, and other brilliant minds throughout history have also been piqued by the Mpemba effect. Numerous broadsheet articles continue to discuss it, and it frequently appears as an odd focal point in a variety of contexts. For example, in the MasterChef cooking competition, competitors have attempted to use the effect to produce frozen treats faster than seems feasible in dessert challenges.

And now, researchers can say that this strange effect is far more common than previously thought.

The ‘Mpemba effect’ gets its name from Erasto Mpemba who, as a school kid in 1963, was making ice cream in his home economics class in Tanzania. Mpemba did not wait for his hot ice cream mixture to cool before putting it directly in the fridge and was unsurprisingly puzzled to find that it froze before all the colder samples of his classmates.

John Goold, Professor, School of Physics, Trinity College Dublin

Goold added, “He pointed this out to his teacher, who ridiculed him for not knowing his physics – Newton’s law of cooling, for example, tells us that the rate at which an object cools is proportional to the temperature difference between the object and its surroundings. However, Mpemba convinced a visiting professor – Denis Osoborne from the University of Dar es Salaam – to test what he had seen and the pair published a paper that indeed evidenced the strange effect.”

While the Mpemba effect is still not fully understood - its presence is hotly debated at the macroscopic scale—it is much more visible at the microscopic scale, where physicists describe nature using quantum mechanics theory.

Many questions remain, such as how the quantum effect relates to the original effect, despite the fact that the quantum Mpemba effect has recently gained popularity. Is it possible to develop a thermodynamic framework to gain a better understanding of the phenomenon?

Some of the important questions are addressed by the QuSys research group's breakthrough.

“We are experts in the interface between non-equilibrium thermodynamics and quantum theory and, as such, we have the right toolbox to tackle these questions. Our work essentially provides a recipe to generate the Mpemba effect in quantum systems, where a physical transformation that effectively ‘heats’ the quantum system can be performed. This transformation of the quantum system then paradoxically allows it to relax or ‘cool’ exponentially faster by exploiting unique features in quantum dynamics,” Goold further stated.

The team has successfully connected the dots between the current knowledge of quantum mechanics and Aristotle’s observations from two millennia ago using the toolkit of non-equilibrium quantum thermodynamics.

And it now raises numerous research and application-related questions.

Goold stated, “While we first took this project on out of intellectual curiosity it forced us to ask several fundamental questions about the relationship between the laws of thermodynamics that describe cooling, and the quantum mechanics, which describe reality at the fundamental level. We are currently developing a geometrical approach to the problem, which will hopefully allow us to understand different types of Mpemba effect in the same mathematical framework.”

“What you actually have in this really ‘cool’ Mpemba effect is a way to speed up cooling – and the cooling of quantum systems is absolutely vital for applications in quantum technologies. With that in mind I am sure some of the tools we are developing to investigate this fundamental effect will be of paramount importance for understanding things like heat flows, and how to minimize dissipation in future technologies,” Goold concluded.