Tunable coupling scheme for flux qubits at the optimal point

Antti O. Niskanen, Yasunobu Nakamura, Jaw-Shen Tsai

Published 2005-12-12, updated 2006-01-24Version 2

We discuss a practical design for tunably coupling a pair of flux qubits via the quantum inductance of a third high-frequency qubit. The design is particularly well suited for realizing a recently proposed microwave-induced parametric coupling scheme. This is attractive because the qubits can always remain at their optimal points. Furthermore, we will show that the resulting coupling also has an optimal point where it is insensitive to low-frequency flux noise. This is an important feature for the coherence of coupled qubits. The presented scheme is an experimentally realistic way of carrying out two-qubit gates and should be easily extended to multiqubit systems.