Robust Two-Qubit Gates for Exchange-Coupled Exchange-Only Qubits*

We show how to perform dynamically corrected two-qubit gates, with the leading hyperfine error term cancelled, for various geometries of an exchange-only qubit network. These sequences are designed to obey the realistic experimental constraint of strictly non-negative couplings. Moreover, we show that these corrected sequences lead to substantial improvement in the gate fidelity. Together with single-qubit dynamically corrected gates, our results facilitate universal and robust multi-qubit quantum operations and pave the way towards scalable fault-tolerant quantum computation on the exchange-only qubit platform.