Simulating High-Fidelity Two-Qubit Gates with Singlet-Triplet Qubits Generated by Capacitive Coupling and Interqubit Exchange Interaction

Two-qubit gates in singlet-triplet qubits can be generated via capacitive coupling or interqubit exchange interaction. Both methods suffer considerably from charge noise and nearly all approaches to mitigate this effect rely on the fact that the noise is slow compared to the gate time. We show that in the strictly capacitive case where gate times are much slower, maximally entangling gates with fidelities above 99% are achievable by operating the qubit in a sweet spot regime that is predicted by a Hund-Mulliken model [1]. The advantage of this control method is that it naturally suppresses two-qubit errors regardless of the noise-frequency profile. In addition, we find comparable fidelities when both interqubit exchange and capacitive interactions are simultaneously used to generate entanglement. We compare these theoretical results with gates that are found using an optimization technique that numerically searches for high-fidelity two-qubit gates using a full-noise and control error model [2].

[1] Wolfe et al., arXiv:1709.09165 [cond-mat.mes-hall] (2017)
[2] Cerfontaine et al., PRL 113, 150501 (2014)