Circuit design for multi-body interactions in superconducting quantum annealing systems with applications to a scalable architecture

Abstract

Quantum annealing provides a way of solving optimization problems by encoding them as Ising spin models which are implemented using physical qubits. The solution of the optimization problem then corresponds to the ground state of the system. Quantum tunneling is harnessed to enable the system to move to the ground state in a potentially high non-convex energy landscape. A major difficulty in encoding optimization problems in physical quantum annealing devices is the fact that many real world optimization problems require interactions of higher connectivity, as well as multi-body terms beyond the limitations of the physical hardware. In this work we address the question of how to implement multi-body interactions using hardware which natively only provides two-body interactions. The main result is an efficient circuit design of such multi-body terms using superconducting flux qubits in which effective N-body interactions are implemented using N ancilla qubits and only two inductive couplers. It is then shown how this circuit can be used as the unit cell of a scalable architecture by applying it to a recently proposed embedding technique for constructing an architecture of logical qubits with arbitrary connectivity using physical qubits which have nearest-neighbor four-body interactions. It is further shown that this design is robust to non-linear effects in the coupling loops, as well as mismatches in some of the circuit parameters.Quantum computing: Superconducting multi-qubit interaction circuitsA new method to build devices which implement interactions between more than two qubits in quantum annealing systems similar to those produced by D-Wave Systems has been proposed by a collaboration from UCL, Durham University, and the University of Oxford led by Paul Warburton. Such interactions occur naturally in many real world optimization problems. They demonstrate that constructing these circuits is experimentally feasible in the near term, and discuss how additional degrees of freedom included in their technique could help solve problems more efficiently. This new coupler design opens up a wide array of new architectural possibilities for these devices, as well as new ways in which they could solve problems, potentially leading to a new generation of more efficient quantum annealers.