Unlike quantum computing, quantum cryptography is already fully developed and being used, mostly in the West and China by governments and military.
Quantum cryptography is a way of encrypting data so that the laws of physics make it impossible to hack.
It uses a phenomena called quantum superposition where one particle is in multiple states at the same time.
Quantum collapse is a key feature of quantum cryptography.
Quantum collapse is when a superposition is measured and it randomly reverts back to being in just one state, rather than multiple at once.
So quantum cryptography works like this: you encode your secret information in different parts of the non-binary superposition and only your intended receiver knows the algorithm for decoding it without collapsing the superposition into randomness.
Any spies will measure the encoded superposition in an arbitrary way so therefore they will destroy, or collapse, the information they intend to steal.
