Crosstalk Suppression in Individually Addressed Two-Qubit Gates in a Trapped-Ion Quantum Computer

Crosstalk between target and neighboring spectator qubits due to spillover of control signals represents a major error source limiting the fidelity of two-qubit entangling gates in quantum computers. We show that in our laser-driven trapped-ion system coherent crosstalk error can be modeled as residual X sigma phi interaction and can be actively canceled by single-qubit echoing pulses. We propose and demonstrate a crosstalk suppression scheme that eliminates all first-order crosstalk utilizing only local control of target qubits, as opposed to an existing scheme which requires control over all neighboring qubits. We report a two-qubit Bell state fidelity of 99.52(6)% with the echoing pulses applied after collective gates and 99.37(5)% with the echoing pulses applied to each gate in a five-ion chain. This scheme is widely applicable to other platforms with analogous interaction Hamiltonians.

Automated summary

In quantum computers, crosstalk between the target and neighboring spectator qubits due to the spillover of control signals is a major error source limiting the fidelity of two-qubit entangling gates. This study proposes a crosstalk suppression scheme that eliminates all first-order crosstalk using only local control of the target qubits, as opposed to existing schemes. Experimental results in a laser-driven trapped-ion system show high fidelity for the two-qubit Bell state, indicating the potential applicability of this scheme to other platforms with analogous interaction Hamiltonians.