Tunable coupling between three qubits as a building block for a superconducting quantum computer
Centre for Quantum Computer Technology, University of Melbourne, Victoria, AustraliaLarge scale quantum computers will consist of many interacting qubits. In this paper we expandthe two ﬂux qubit coupling scheme ﬁrst devised in [Phys. Rev. B 70, 140501 (2004)] and realizedin [Science 314, 1427 (2006)] to a three-qubit, two-coupler scenario. We study L-shaped and line-shaped coupler geometries, and show how the interaction strength between qubits changes in termsof the couplers’ dimensions. We explore two cases: the “on-state” where the interaction energybetween two nearest-neighbor qubits is high, and the “oﬀ-state” where it is turned oﬀ. In bothsituations we study the undesirable crosstalk with the third qubit. Finally, we use the GRAPEalgorithm to ﬁnd eﬃcient pulse sequences for two-qubit gates subject to our calculated physicalconstraints on the coupling strength.I. INTRODUCTION