ZZ freedom in two qubit gates*

Achieving high fidelity two qubit gates requires elimination of unwanted interactions among qubits. Weakly anharmonic superconducting qubits in the absence of external driving exhibit an always-on phase error mainly due to a sub-MHz repulsion between computational and non-computational energy levels, the so-called static ZZ interaction. Here we present that in general there are two theoretical ways for eliminating fundamental ZZ error: 1) static ZZ freedom by combining qubits with opposite sign anharmonicity 2) dynamic ZZ freedom in driven qubits with a microwave pulse, which can be universally realized by combining qubits with any anharmonicity signs. Scaling up the number of such qubits can mitigate high fidelity gate operation.

Reference

1. Xuexin, Xu, and M. H. Ansari. "ZZ freedom in two qubit gates." arXiv:2009.00485 (2020).
2. Ku, Jaseung, et al. "Suppression of Unwanted ZZ Interactions in a Hybrid Two-Qubit System." arXiv:2003.02775 (2020)