Tunable coupling between three qubits as a building block for a superconducting quantum computer
Peter Groszkowski, Austin G. Fowler, Felix Motzoi, Frank K. Wilhelm · Physical Review B · 2011
Large-scale quantum computers will consist of many interacting qubits. In this paper we expand the two flux qubit coupling scheme first devised by P. Plourde et al. [Phys. Rev. B 70, 140501 (2004)] and realized by T. Hime et al. [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 terms of the couplers' dimensions. We explore two cases: the ``on-state'' where the interaction energy between two nearest-neighbor qubits is high, and the ``off-state'' where it is turned off. In both situations we study the undesirable crosstalk with the third qubit. Finally, we use the grape algorithm to find efficient pulse sequences for two-qubit gates subject to our calculated physical constraints on the coupling strength.