Over recent years, the gap between theoretical security of quantum crytography and practical implementation has provided plenty of fun for super-geniuses the world over.
Yes, quantum cryptography is supposed to be unbreakable. After all, if anybody even observes the state of a qubit that Alice has prepared, entangled with another and sent to Bob, the entanglement is destroyed, and Bob will know something’s wrong.
However, practical implementations of quantum cryptography left various possible attack vectors. To close these attacks (described in more detail below), the quantum crypto community proposed a new protocol, MDI-QKD (measurement device independent quantum key distribution), and now, two research groups working independently have verified that MDI-QKD gets a long way towards a provably-secure quantum crypto scheme.