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Researchers Find Deep Link Between Quantum Entanglement and Thermalization

At Trinity College Dublin, theoretical physicists have discovered an in-depth connection between quantum entanglement—one of the most remarkable features of quantum mechanics—and thermalization. Thermalization is the process where something enters into thermal equilibrium with its surroundings.

The study outcomes were recently reported in Physical Review Letters, a renowned journal.

Thermalization is a familiar process—consider how a cup of coffee reaches room temperature as time passes. By contrast, quantum entanglement is a different phenomenon.

However, a study conducted by Marlon Brenes, PhD Candidate, and Professor John Goold from Trinity, along with Silvia Pappalardi and Professor Alessandro Silva at SISSA in Italy, reveals how the two are inseparably associated with each other.

Professor Goold, leader of Trinity’s QuSys group, explained the significance of the discovery: “Quantum entanglement is a counterintuitive feature of quantum mechanics, which allows particles that have interacted with each other at some point in time to become correlated in a way which is not possible classically. Measurements on one particle affect the outcomes of measurements of the other—even if they are light years apart. Einstein called this effect ‘spooky action at a distance’.”

It turns out that entanglement is not just spooky but actually ubiquitous and in fact what is even more amazing is that we live in an age where technology is starting to exploit this feature to perform feats which were thought to be impossible just a number of years go. These quantum technologies are being developed rapidly in the private sector with companies such as Google and IBM leading the race.

John Goold, Professor and Leader, QuSys group, Trinity College Dublin

But how are these things linked to cold coffee?

When you prepare a cup of coffee and leave it for a while it will cool down until it reaches the temperature of its surroundings. This is thermalisation. In physics we say that the process is irreversible—as we know, our once-warm coffee won’t cool down and then magically warm back up,” described Professor Goold.

How irreversibility and thermal behaviour emerges in physical systems is something which fascinates me as a scientist as it applies on scales as small as atoms, to cups of coffee, and even to the evolution of the universe itself,” he continued

Professor Goold added, “In physics, statistical mechanics is the theory which aims at understanding this process from a microscopic perspective. For quantum systems the emergence of thermalisation is notoriously tricky and is a central focus of this current research.”

So how is this connected to entanglement and what do the results have to say?

In statistical mechanics there are various different ways, known as ensembles, in which you can describe how a system thermalizes, all of which are believed to be equivalent when you have a large system (roughly on scales of 10^23 atoms).

John Goold, Professor and Leader, QuSys group, Trinity College Dublin

However, what we show in our work is that not only is entanglement present in the process, but its structure is very different depending on which way you choose to describe your system. So, it gives us a way to test foundational questions in statistical mechanics. The idea is general and can be applied to a range of systems as small as a few atoms and as large as black holes,” explains Professor Goold.

Super-computers were used by Marlon Brenes, PhD candidate at Trinity and first author of the paper, to simulate quantum systems to test the concept.

The numerical simulations for this project that I performed are at the limit of what can currently be done at the level of high-performance computing. To run the code I used the national facility, ICHEC, and the new Kay machine there.

Marlon Brenes, PhD candidate, Trinity College Dublin

Brenes added, “So, as well as being a nice fundamental result the work helped us really push the boundaries of this type of computational approach and establish that our codes and the national architecture are performing at the cutting edge.”

Professor Goold’s study is financially supported by an SFI-Royal Society University Research Fellowship and a European Council Starting Grant.


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