"Bell Test for Entangled Qubits" by Manwesulimo2004 / CC BY 3.0

This Is an Image of Quantum Entanglement… Sort Of

Jul 23, 2019

By Ryan F. Mandelbaum

A new quantum mechanics experiment shows the field’s spookiest concept, entanglement, in a whole new way. But, of course, it’s not as simple as that.

Lots of other news outlets have covered what they’ve described as the first-ever image, or even a “photo,” of entanglement, sometimes called spooky action at a distance. The picture does sort of show entanglement, but it’s not the two lobes of the image that are entangled—it’s the photons in this image and other photons elsewhere. Additionally, the experiment doesn’t overcome some of the loopholes that other scientists have required and gone great lengths to overcome, for tests like these. It’s not that the physicists are doing anything wrong; it’s that entanglement is a hard topic to cover in easy-to-understand terms without handwaving. So, let’s try.

Before we get to the image, you’ll need a crash course in quantum mechanics. Quantum mechanics are the mathematical rules devised to explain the weird behavior of the smallest particles. These particles’ properties, like their energy, are “quantized,” meaning they can only assume values from a set of options. At the same time, particles can take on a superposition of states, meaning they assume several of these values simultaneously when you’re not looking at them. Those values are accompanied by amplitudes, which you might think of as signal strengths. An equation called the “wave function” describes all the possible values with their amplitudes.

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