Computational Advantage from Quantum-Controlled Ordering of Gates

Mateus Araújo, Fabio Costa, Časlav Brukner
2014 Physical Review Letters  
It is usually assumed that a quantum computation is performed by applying gates in a specific order. One can relax this assumption by allowing a control quantum system to switch the order in which the gates are applied. This provides a more general kind of quantum computing, that allows transformations on blackbox quantum gates that are impossible in a circuit with fixed order. Here we show that this model of quantum computing is physically realizable, by proposing an interferometric setup that
more » ... rometric setup that can implement such a quantum control of the order between the gates. We show that this new resource provides a reduction in computational complexity: we propose a problem that can be solved using O(n) blackbox queries, whereas the best known quantum algorithm with fixed order between the gates requires O(n^2) queries. Furthermore, we conjecture that solving this problem in a classical computer takes exponential time, which may be of independent interest.
doi:10.1103/physrevlett.113.250402 pmid:25554864 fatcat:brd5pikcujdqvbimi4p2cosh6q