Quantum entanglement has now been observed directly at the macroscopic scale

Quantum entanglement is the joining of two particles or objects together, even though they may be far apart – the properties of each are related in a way that is not possible under the rules of classical physics.

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

The dimensions involved are still quite small from our perspective – the experiments involved two aluminum barrels as small as a fifth of the width of a human hair – but in the world of quantum physics, they’re pretty massive.

Macroscopic mechanical cylinders. (GT Theophile/Nest)

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

“But looking at them together, we can see that what looks like the random motion of one drum is closely related to the other, in a way that can only be achieved through quantum entanglement.”

While there is no telling that quantum entanglement cannot occur with macroscopic objects, before then it was thought that the effects were not noticeable at larger scales – or perhaps that the macroscopic scale is governed by another set of rules.

Recent research indicates that this is not the case. In fact, the same quantitative rules apply here as well, and they can be seen as well. The researchers vibrated the membranes of the small cylinder using microwave photons and kept them in synchrony in terms of their position and velocities.

To prevent external interference, a common problem with quantum cases, the drums were cooled, interlocked, and measured in separate phases while inside a refrigerated container. The states of the barrels are then encoded into a reflex microwave field that operates in a manner similar to radar.

Previous studies have also reported macroscopic quantum entanglement, but the 2021 paper goes further: all necessary measurements were recorded rather than inferred, and the entanglement was generated in a deterministic, non-random manner.

In a series of related but separate experiments, researchers also working with macroscopic drums (or oscillators) in quantum entanglement have shown how the position and momentum of both ends of the drums can be measured simultaneously.

“In our work, drum machines show collective quantum motion,” said physicist Laure Mercier de Lipinay, of Aalto University in Finland. “The barrels vibrate in a phase opposite to each other, so that when one is in the final position of the vibration cycle, the other is in the opposite position at the same time.”

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

What makes this major news is that it wraps around the Heisenberg Uncertainty Principle – the idea that position and momentum cannot be perfectly measured at the same time. The principle states that recording any one of the measurements will overlap the other through a process called quantitative back procedure.

In addition to supporting the other study in demonstrating macroscopic quantum entanglement, this particular research uses this entanglement to avoid quantum background action—essentially investigating the line between classical physics (where the uncertainty principle applies) and quantum physics (where it now doesn’t seem to be).

One potential future application of the two sets of results is in quantum networks – the ability to manipulate and entangle objects on a microscopic scale so that they can power next-generation communications networks.

Physicists Hoi-Kwan Lau and Aashish Clerk, who were not involved in the studies, wrote in a commentary on research published at the time.

Both the first and second studies were published in Sciences.

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

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