Applicability of IBM's projected 50-qubit quantum computer Q to cryptanalysis? IBM announced Q, a project for a 50-qubit universal quantum computer, according to the press realease. Here is more PR spin, and the research sub-page.

What would be the applicability of that to cryptanalysis?
What would be the applicability of that to cryptanalysis?


It wouldn't appear to have any direct applicability to cryptanalysis, for two reasons:


50 Qbits is just not enough to attack any cryptographical problem; to apply either Shor's or Grover's algorithm against any realistic problem, you'll end up needing thousands.
It doesn't appear that they're addressing the decoherence issue.  That is, in a quantum computer, you'll end up getting random perturbations to the running state.  Cryptographical computations take quite a long time (far longer than we can go without expecting such a random event to occur), and are quite sensitive to such perturbations.  What they'll need to do is run error correction logic (which has multiple physical qbits stand for the one logical one, and has logic to detect such a perturbation on one of the physical qbits, and correct it).


Now, I'm not saying that what IBM is trying to build is useless; for one, it would appear that the computations that Chemical modeling requires fits nicely into what they have.

And, while this isn't immediately useful for cryptography, it is another step towards a Real Quantum Computer (where "Real" means "can actually solve an interesting cryptographical problem).