title: Computational multiqubit tunnelling in programmable quantum annealers.
abstract: Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Boixo
authors.affiliation: Google, Venice, California 90291, USA.|NASA Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: Vadim N
authors.initials: VN
authors.lastname: Smelyanskiy
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Alireza
authors.initials: A
authors.lastname: Shabani
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Isakov
authors.affiliation: Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Dykman
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Vasil S
authors.initials: VS
authors.lastname: Denchev
authors.affiliation: D-Wave Systems Inc., Burnaby, British Columbia, Canada V5C 6G9.|Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6.
authors.forename: Mohammad H
authors.initials: MH
authors.lastname: Amin
authors.affiliation: D-Wave Systems Inc., Burnaby, British Columbia, Canada V5C 6G9.
authors.forename: Anatoly Yu
authors.initials: AY
authors.lastname: Smirnov
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Masoud
authors.initials: M
authors.lastname: Mohseni
authors.affiliation: Google, Venice, California 90291, USA.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Neven