2004/03/31 by M. Sauerhoff, D. Sieling
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1016/j.tcs.2004.12.031
published as Theoretical Computer Science 334, pp. 177-225, 2005 · 45 pages, 3 Postscript figures. Proofs rearranged, typos corrected
arxiv created 2005/04/29 · arxiv updated 2009/12/01
In this paper, the space complexity of nonuniform quantum computations is investigated. The model chosen for this are quantum branching programs, which provide a graphic description of sequential quantum algorithms. In the first part of the paper, simulations between quantum branching programs and nonuniform quantum Turing machines are presented which allow to transfer lower and upper bound results between the two models. In the second part of the paper, different variants of quantum OBDDs are compared with their deterministic and randomized counterparts. In the third part, quantum branching programs are considered where the performed unitary operation may depend on the result of a previous measurement. For this model a simulation of randomized OBDDs and exponential lower bounds are presented.