Hi all,
Lawrence Ioannou from Cambridge will be giving an additional talk tomorrow 5pm in HIT J51 (sorry, I don't know why they gave us J floor instead of K). Title and abstract below.
Cheers, Roger
Universal quantum computation in a hidden basis
Suppose we are given several copies of a state |psi> that is promised to be orthogonal to |0>, but is otherwise unknown. We consider the quantum-information-theoretic tasks of state preparation and universal quantum computation with respect to the "hidden basis" {|0>,e^{i \theta}|psi>}^{\otimes l}, of an l-logical-qubit system, for a random \theta. We give an exact algorithm for state preparation, and give an efficient approximation algorithm for universal computation. We apply our results to quantum-public-key authentication protocols, by showing that a class of digital signature schemes is insecure.