Tunable Coupling Scheme for Implementing High-Fidelity Two-Qubit Gates

Superconducting qubits now offer coherence times exceeding 100 s and single-qubit gate fidelities above 99. 9%, but realizing a large-scale quantum computer is still impeded by the quality of two-qubit gates, with typical fidelities of 95--99%. Here a simple, broadly applicable scheme to improve two-qubit gates using a tunable coupler is proposed. It simplifies the coupling scheme, and reduces unwanted interactions typically present in schemes in which the interactions are always on. Numerical simulations show that this approach should allow two-qubit gate fidelities greater than 99. 9%, when implemented using state-of-the-art superconducting qubits.