Entanglement is one of the most valuable resources in the quantum realm – for instance, it is the powerhouse behind quantum encryption – and in theory, it may be possible to extract an infinite amount of it from the universe.
Interacting with a quantum field usually changes its state, but at Leibniz University Hannover in Germany was looking for cases when this can be avoided. This led him to the idea of “quantum embezzlement” where a person equipped with a quantum device could extract a resource from the field’s state without it ever noticing. It’s similar to mining for a kind of fuel, which the device could then use for a task like sending an encoded message.
Wilming and his colleagues focused on quantum entanglement – an inextricable link between quantum objects – which is a necessary resource for many quantum computing and quantum communication schemes. They found that embezzling entanglement from relativistic quantum fields could be surprisingly fruitful.
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The researchers mathematically analysed a scenario where two people, Alice and Bob, want to extract and share entanglement from a low-energy state of a relativistic quantum field – a quantum object that extends through all space. Their calculations showed that Alice and Bob do not have to coordinate their actions by communicating with each other to do so. Even if the two only quietly interact with the field near their own location, the mathematical structure of that field allows them to embezzle as much quantum entanglement as they want.
, also at Leibniz University Hannover and who worked on the project, says the field is like an “entanglement bank” and Alice and Bob are trying to surreptitiously extract its funds. Across the cosmos, there is infinite entanglement, which would remain the case even if Alice and Bob undertook a quantum heist.
“Since the bank is in the same state before and after the embezzlement, that means that no one can detect it. It’s the perfect crime,” he says.
However, the researchers’ calculations do not offer a recipe for what actions Alice and Bob should specifically perform to make this a reality – they only prove that it is possible. Because of this, their result may not have an impact on practical quantum devices, says at the University of Oxford. Contemporary researchers know how to create quantum entanglement in other ways that are more accessible and concrete than starting with a relativistic quantum field, he says.
Team member at Leibniz University Hannover says that relativistic quantum fields are infinite in a way that has no counterpart among experimentally accessible quantum objects. But learning that these fields are so suitable for entanglement embezzlement may help pinpoint more practical objects that are similar enough to be, if not great for embezzling, then at least very good.
Additionally, the new work offers a way to classify infinite objects like quantum fields based on their entanglement content, says Wilming. His team’s calculations revealed that there can be different types of entanglement contained in different fields, and they could be ranked in terms of how easy it is to embezzle from them.
“What happens with relativistic quantum fields is probably the craziest case,” says van Luijk, of the infinite embezzlement. That’s due to the fact that relativistic quantum fields are everywhere and can give rise to particles that can be almost as fast as the speed of light – a type of infinite freedom of existence and motion that is hard to deplete.
Journal reference:
Physical Review Letters,
