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The quantum world can be quite a strange one. Particles at opposite ends of a galaxy can instantaneously react to each other, and can exist in more than one place simultaneously. It now seems this world may be even more complicated, allowing communication to occur without a physical medium.
It's called counter-factual communication, and a group of researchers from Saudi Arabia's King Abdulaziz City of Science and Technology (KACST) and Texas A&M University in the US, have just published a paper in Physical Review Letters demonstrating it – at least in principle.
Imagine a communication channel between Alice and Bob, across which, normally something has to pass for communication to occur. But suppose Alice releases a photon – through an array of beam-splitters and mirrors – that Bob can choose to either block or not block.
What he does will rouse different detectors at Alice's end. In this way, Alice can infer Bob's action by checking her own detectors. But here is where it gets stranger: the photon didn't even have to leave Alice's side of the communication channel in order for her to know about Bob's choice.
One of the authors of the paper, Hatim Salih, a physicist at KACST, notes that, "unlike most communication protocols, in ours it is Bob who sends a message to Alice, not the other way round."
"This is a bit like Alice and Bob using pigeons to communicate – except that the pigeons never have to leave," says Zhenghong Li, one of the paper's authors.
As Salih says: "I believe the question of how information gets from Bob to Alice is a deep one speaking to the heart of the debate about the reality of the quantum state: if physical particles did not carry information between sender and receiver, what did?"
The wave-function is real but nonphysical: A view from counterfactual quantum cryptography
Counterfactual quantum cryptography, based on the idea of interaction-free measurement, allows Bob to securely transmit information to Alice without the physical transmission of a particle. From local causality, we argue that the fact of his communication entails the reality of the quantum wave packet she transmits to him. On the other hand, the travel was not physical, because were it, then a detection necessarily follows, which does not happen in the counterfactual communication. On this basis, we argue that the particle's wave function is real, but nonphysical. In the classical world, the reality and physicality of objects coincide, whereas for quantum phenomena, the former is strictly weaker. Since classical cryptography is insecure, the security of quantum counterfactual cryptography implies the nonphysical reality of the wave function.
Semi-counterfactual quantum cryptography: Alice inputs a single-photon into a beam-splitter via an optical circulator
C, which is split along arm a (internal) and b (to Bob). Each person applies either operation F (reflect) or A (absorb) randomly.
If Alice detects the photon in D0 , she knows that her and Bob’s inputs are anti-correlated. Further, if her input was F , then
Bob’s was A, making the communication of this bit counterfactual.
In contradistinction to other recent approaches to the question of the reality of the wave function, based on studying
the relationship between the wave function and an ontic space, we consider reality as contrasted from physicality,
both of which are operationally defined. Classical intuition encourages us to conflate these two concepts, which may
explain the difficulty in interpreting ψ, in spite of the successful quantitative applications of quantum theory. Our
approach shows that the wave function in counterfactual quantum cryptography is real, but non-physical. Further,
we have argued that the security of counterfactual cryptography entails non-physicality, thereby giving a concrete role
to the abstract concepts involved.
Our main idea is implicit in IFM and counterfactual computation. Invoking cryptography dramatizes the situation
by turning it into a communication scenario where physicality is linked with the issue of security. The conclusion
drawn here for the onticity of the wave function arguably strains the “peaceful co-existence” of relativity and quantum
nonlocality [20]. However, as evident from Figure 2, there is no overt contradiction with relativistic causality, because
our definition of reality is based on local causality.
originally posted by: Kashai
a reply to: ImaFungi
I have often heard that if something like telepathy were to be proven. It would deal a sever blow to efficacy of the current laws of physics.
So it would not mean the Universe was fake.
originally posted by: neoholographic
This is a boon for idealism and yet another crushing blow from Quantum Mechanics to materialism. You add in some of the recent studies from Psi that show human intention can have an effect on random systems and idealism is looking like it controls the material world that we "see and experience."
originally posted by: ImaFungi
I dont see why telepathy would be impossible. How do you think it would work though, a brain creating radio waves, or high pitch sound waves in audible, that register with another brain, exact words or images in their brain?
What he does will rouse different detectors at Alice's end. In this way, Alice can infer Bob's action by checking her own detectors. But here is where it gets stranger: the photon didn't even have to leave Alice's side of the communication channel in order for her to know about Bob's choice.