Yet there is some solid reasoning that this ‘counterfactual communication’ may not only be plausible, but depending on how it works, may reveal fundamental aspects of reality that have been hidden from view until now.
Counterfactual physics is not a new thing in itself, describing a way to infer activity in the absence of something. In a way, it’s pretty straightforward. If your dog barks at strangers and you hear silence when the front door is opened, you have received information that a familiar person has entered your house despite the absence of sound.
Yet in recent years the question of a quantum version of this type of transfer has arisen, with physicists exploring the possibility that quantum information can be transported without a particle being exchanged.
The concept is not just theoretical. Ghost imaging uses a separated pair of entangled photons to infer information about an object without it absorbing and transmitting any of the particles.
A leading researcher in the field has proposed an experimental plan to test the physics behind a kind of exchange-free communication, a method he calls contraportation.
As you might expect given the nature of the physics involved, quantum computing plays a role. The proposal uses qubits – the probabilistic versions of classical binary information carriers – to transfer information from one place to another without ever interacting.
Salih’s previous research involves light being separated through complex arrays of splitters and detectors, showing a non-intuitive result of information arriving at a destination despite there being no particle to carry it.
What the physicist proposes is a new calculation scheme based on his previous theoretical protocol published in 2013.
“While counterportation achieves the ultimate goal of teleportation, namely liberated transport, it remarkably does so without any detectable carriers of information traveling across,” says physicist Hatim Salih, of the University of Bristol in the UK.
“If counterporting is to be realized, an entirely new type of quantum computer must be built: an exchange-free one, where communicating parties do not exchange particles.”
Teleportation is a well-established means of transferring a quantum state from one place to another. Although the details are complex, it involves entangling multiple objects and then separating them by an arbitrary distance before carefully measuring the entangled objects somewhere in a very specific way. Only when the separated object is also measured in relation to the results, communicated via old-fashioned methods, is the teleportation realized.
The end result is not the transfer of a solid object, as such, but rather a very specific quantum state. Completing the measurements on the original object effectively destroys it, meaning the state has effectively jumped from one place to another.
Counterportation is a quantum form of counterfactual communication that results in the transfer of quantum information, just like teleportation (only without the added hassle).
The obvious question is how. This is where a particular type of Einstein-Rosen (ER) bridge or wormhole comes in, a hypothesis representing the overlap or connection between entangled objects.
According to Salih, this kind of local wormhole could act as the medium through which netting occurs.
While wormholes have been theorized in terms of black holes, it is possible that they also describe entangled phenomena on smaller scales. If wormholes do exist, their description could help fill in gaps in our knowledge of the fundamental nature of matter.
“The goal in the near future is to physically build such a wormhole in the laboratory, which can then be used as a test bed for rival physical theories, even those of quantum gravity,” says Salih.
“Our hope is to ultimately provide remote access to local wormholes for physicists, physics hobbyists and enthusiasts to explore fundamental questions about the universe, including the existence of higher dimensions.”
We should note that this is all theoretical for now—and based on grounds that not all scientists agree on—but it adds another layer of intrigue to the scientific discussion going on about quantum counterfactual communication and its potential role in research.
“This is a milestone we’ve been working towards for a lot of years,” says Salih. “It provides a theoretical as well as a practical framework for exploring new enduring puzzles about the universe, such as the true nature of spacetime.”
The research is published in Quantum Science and Technology.