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Congratulations, you have just (re-)discovered quantum cryptography :-)

(Note that while you can use this to securely establish a shared secret, you can't use it to transmit information faster than light.)

Quantum... blockchain?

Kind of but not really.

https://www.technologyreview.com/2019/02/14/103409/what-is-q...

Yes, this is a big part of quantum telecommunication. But you always need a classical side-channel. You can even copy a quantum state using 2 entangled qubits and a classical channel. This is called quantum teleportation.