To determine an object’s quantum properties, you may only need to measure how it exchanges heat with its environment, without touching the object itself.
Everything radiates heat, but when quantum objects do it, they can reveal properties that would otherwise be difficult to detect without being destroyed in the process. This means we can diagnose an object’s quantumness by observing how it warms up or cools down.
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| Heat can reveal whether something has quantum properties SkillUp/Shutterstock |
Thermodynamics, the study of how heat flows between objects, was developed to better understand engines, but Patryk Lipka-Bartosik at the University of Geneva in Switzerland and his colleagues wanted to apply it to tiny objects in the quantum realm.
They devised a method to determine whether a quantum object had either of two quantum properties: entanglement – a special correlation between quantum objects – and coherence, which quantifies how wave-like a quantum object is. They set up a theoretical model where an object with one or none of these properties is in contact with another, and heat flows from the warmer into the colder of the two.
Their calculations showed that studying this heat flow was enough to diagnose whether the first object was quantum and had coherence or entanglement. For instance, the largest amount of heat that could be transferred in this process was greater when the first object was quantum than when it did not have quantum properties, says Alexssandre de Oliveira Junior at the Technical University of Denmark, who worked on the study. Practically, this means that there are heat flows that a classical object could simply never sustain, so if those were measured, the team’s work would imply that the object had to be quantum.
“This might in principle lead to some concrete device. Think of it as a smart thermometer, which doesn’t just measure temperature or dissipated heat, but also gives away structural information on the quantum system,” says Gerardo Adesso at the University of Nottingham in the UK. This means that we could infer how wave-like – how quantum – a particle is based on the heat it is naturally losing due to being in contact with its environment, which may have previously been written off as an inevitable but not necessarily useful process, he says.
Though their mathematical recipe for making such a thermometer is very general, the researchers tried adapting their equations for two experimentally feasible quantum systems. Specifically, they outlined a protocol for detecting entanglement in a system of two quantum bits, like those in a quantum computer, and certifying the coherence of several particles that have spin, like those in a magnet.
Jonatan Bohr Brask at the Technical University of Denmark, who was also part of the project, says this work could allow us to better understand and use quantum heat engines in the future. Such tiny machines could play a role in cooling other quantum devices, like computers, which need to be cold to work well.
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