Scientists Have Finally Achieved Direct Counterfactual Quantum Communication

FIONA MACDONALD 4 MAY 2019

Quantum communication is a strange beast, but one of the weirdest proposed forms of it is called counterfactual communication - a type of quantum communication where no particles travel between two recipients.

Theoretical physicists have long proposed that such a form of communication would be possible, but in 2017, for the first time, researchers were able to experimentally achieve it - transferring a black and white bitmap image from one location to another without sending any physical particles.

If that sounds a little too out-there for you, don't worry, this is quantum mechanics, after all. It's meant to be complicated. But once you break it down, counterfactual quantum communication actually isn't as bizarre as it sounds.

First up, let's talk about how this differs from regular quantum communication, also known as quantum teleportation, because isn't that also a form of particle-less information transfer?

Well, not quite. Regular quantum teleportation is based on the principle of entanglement - two particles that become inextricably linked so that whatever happens to one will automatically affect the other, no matter how far apart they are.

This is what Einstein referred to as "spooky action at a distance", and scientists have already used it to send messages over vast distances.

But that form of quantum teleportation still relies on particle transmission in some form or another. The two particles usually need to be together when they're entangled before being sent to the people on either end of the message (so, they start in one place, and need to be transmitted to another before communication can occur between them).

Alternatively, particles can be entangled at a distance, but it usually requires another particle, such as photons (particles of light), to travel between the two.

Direct counterfactual quantum communication on the other hands relies on something other than quantum entanglement. Instead, it uses a phenomenon called the quantum Zeno effect.

Very simply, the quantum Zeno effect occurs when an unstable quantum system is repeatedly measured.

In the quantum world, whenever you look at a system, or measure it, the system changes. And in this case, unstable particles can never decay while they're being measured (just like the proverbial watched kettle that will never boil), so the quantum Zeno effect creates a system that's effectively frozen with a very high probability.

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https://www.sciencealert.com/scientists-have-finally-achieved-direct-counterfactual-quantum-communication