Quantum querying based on multicontrolled Toffoli gates for causal Feynman loop configurations and directed acyclic graphs

Abstract: Quantum algorithms are a promising framework for a proper treatment of Feynman loop integrals due to the existence of a manifestly causal representation scenario. Particularly, unfolding causal configurations of multiloop Feynman diagrams is understood as querying \textit{directed acyclic graph} (DAG) configurations of undirected graphs in graph theory. In this paper we present a quantum algorithm for querying causality of multiloop Feynman diagrams using an ingenious change in the logic of the design of the oracle operator. The construction of the quantum oracle is surprisingly based exclusively on multicontrolled Toffoli gates and XNOT gates. The efficiency of the algorithm is evaluated performing a comparison with a quantum algorithm based on binary clauses. Additionally, we explicitly analise several three-, four- and five-eloop topologies, which have not been previously explored due to their higher complexity.