Quantum cryptography has had a bad couple of years. For a decade or so, we were promised the capability to send messages with absolute secrecy guaranteed by the laws of physics. At least in theory. In practice, however, things turned out a little differently. In 2010, a team at the University of Toronto in Canada announced that they had successfully hacked a commercial quantum cryptography system. The problem was not the theory but the practical limitations of the equipment used to carry out this kind of communication and the loopholes this introduces.
Then, earlier this year, a UK-based team showed that these kinds of practical limitations can never be overcome entirely since there is no way to prove beyond doubt that any machine is not compromised (unless it is used only once and then thrown away). So rather than being perfect, quantum cryptography turns out to be just 'pretty good', a standard that is perfectly acceptable for most people and one that very much looked as if it was the best we ever can hope for.