Quantum entanglement has now been directly observed at the macroscopic scale

Quantum entanglement has now been directly observed at the macroscopic scale

Quantum entanglement is the bonding of two particles or objects, even though they may be far apart – their respective properties are linked in a way that is not possible under the rules of classical physics.

It’s a strange phenomenon that Einstein described as “frightening action at a distance”, but its strangeness is what makes it so fascinating to scientists. In a 2021 study, quantum entanglement was directly observed and recorded at the macroscopic scale – a much larger scale than the subatomic particles normally associated with entanglement.

The dimensions involved are still very small from our point of view – the experiments involved two tiny aluminum drums one-fifth the width of a human hair – but in the realm of quantum physics they are absolutely enormous.

Two metal drums
Macroscopic mechanical drums. (J.Teufel/NIST)

“If you independently analyze position and momentum data from the two drums, they each look hot,” physicist John Teufel of the National Institute of Standards and Technology (NIST) in the United States said last year. United.

“But looking at them together, we can see that what looks like random movement of one drum is strongly correlated with the other, in a way that’s only possible through quantum entanglement.”

Although there is nothing to say that quantum entanglement cannot occur with macroscopic objects, it was previously thought that the effects were not noticeable at larger scales – or perhaps the macroscopic scale was governed by a another set of rules.

Recent research suggests that is not the case. In fact, the same quantum rules apply here too and can also be observed. The researchers vibrated the drum’s tiny membranes using microwave photons and kept them in a synchronized state in terms of position and speed.

To avoid outside interference, a common problem with quantum states, the drums were cooled, entangled and measured in separate stages inside a cryogenically cooled enclosure. The drum states are then encoded in a reflected microwave field that works similarly to radar.

Previous studies had also reported on macroscopic quantum entanglement, but the 2021 research went further: all the necessary measurements were recorded rather than inferred, and the entanglement was generated deterministically and not randomly.

In a series of related but separate experiments, researchers also working with macroscopic drums (or oscillators) in a state of quantum entanglement showed how it is possible to measure the position and momentum of both drumheads at the same time. time.

“In our work, the drumheads exhibit collective quantum motion,” said physicist Laure Mercier de Lepinay, from Aalto University in Finland. “The drums vibrate in opposite phase to each other, so that when one of them is in an end position of the vibration cycle, the other is in the opposite position at the same time.”

“In this situation, the quantum uncertainty of the movement of the drums is canceled if the two drums are treated as a single quantum mechanical entity.”

What’s making headlines is that it circumvents Heisenberg’s uncertainty principle – the idea that position and momentum can’t be perfectly measured at the same time. The principle states that the recording of either measurement will interfere with the other through a process called quantum feedback action.

In addition to supporting the other study by demonstrating macroscopic quantum entanglement, this particular research uses this entanglement to avoid quantum feedback action – essentially studying the line between classical physics (where the uncertainty principle applies ) and quantum physics (where it doesn’t seem).

One of the potential future applications of both sets of findings relates to quantum networks – being able to manipulate and entangle objects on a macroscopic scale so that they can power next-generation communication networks.

“Apart from practical applications, these experiments examine how far into the macroscopic realm experiments can push the observation of distinctly quantum phenomena,” write physicists Hoi-Kwan Lau and Aashish Clerk, who were not involved in the studies, in a commentary on the research published at the time.

The first and second studies were published in Science.

A version of this article was first published in May 2021.

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