Richard Cleve Daniel Gottesman Michele Mosca Rolando D. Somma David L. Yonge-Mallo Efficient discrete-time simulations of continuous-time quantum query algorithms. 409-416 2009 STOC http://doi.acm.org/10.1145/1536414.1536471 conf/stoc/2009 db/conf/stoc/stoc2009.html#CleveGMSY09