Quantum Zero-Error Algorithms Cannot be Composed [article]

Harry Buhrman, Ronald de Wolf
2003 arXiv   pre-print
We exhibit two black-box problems, both of which have an efficient quantum algorithm with zero-error, yet whose composition does not have an efficient quantum algorithm with zero-error. This shows that quantum zero-error algorithms cannot be composed. In oracle terms, we give a relativized world where ZQP^ZQPZ̄QP, while classically we always have ZPP^ZPP=ZPP.
arXiv:quant-ph/0211029v2 fatcat:45ukmtw4dja7rd57p54h5hli5m