Quantum cryptography is any cryptography that is based on the laws of quantum physics. The two most popular techniques used are quantum teleportation based systems (which is the direction China seems to be going), and quantum uncertainty based systems (which is the route the US seems to be going). Quantum teleportation uses entanglement to 'teleport' information from point A to point B, such that it never passes through any other points. The quantum uncertainty based systems transmit data from point A to point B such that it cannot be intercepted at any of the points in between without the interception being immediately detected by the people at point A and B. So with quantum teleportation you would teleport a symmetric key from point A to B and then use that to encrypt data which you transmit over the line as normal (or you might be able to teleport the entire plaintext), with quantum uncertainty based systems you would transmit the keying material and if you detect an interception you would generate new keying material and try again (perhaps after finding where the interception was carried out on the line, and capturing the enemy spies trying to steal your information). In either case you can do key exchange without the threat of interception, either because interception is impossible or because interception is impossible to do without it being immediately detected. There are probably other quantum encryption systems as well but these two are the most popular by far. Technically classical computers can do anything quantum computers can do, but it is only theoretically because you would need so many classical computers they would form a black hole before you got the power of a much smaller quantum computer. yeah pretty much