Harry Buhrman Richard Cleve Monique Laurent Noah Linden Alexander Schrijver Falk Unger New Limits on Fault-Tolerant Quantum Computation. 411-419 2006 conf/focs/2006 FOCS http://doi.ieeecomputersociety.org/10.1109/FOCS.2006.50 db/conf/focs/focs2006.html#BuhrmanCLLSU06