Quantum logic operations between physically distinct qubits is an essential aspect of large-scale quantum information processing. We propose an approach to high-speed mixed-species entangling operations in trapped-ion quantum computers, based on mechanical excitation of spin-dependent ion motion by ultrafast pulsed lasers. We develop the theory and machine design of pulse sequences that realize megahertz-speed "fast gates" between a range of mixed-isotope and mixed-species ion pairings with experimentally realistic laser controls. We demonstrate the robustness of the gate mechanism against expected experimental errors, and identify errors in ultrafast single-qubit control as the primary technical limitation. The proposed mixed-species gate mechanism can be used for fast transfer of quantum information between specialized qubits and quantum memories, which we show enables the protection of matter-photon interfaces against rapid spin dephasing in optical networks of trapped-ion processors.

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• Quantum algorithms & computation
• Quantum communication, protocols & technology
• Quantum control
• Quantum gates
• Quantum networks
• Ultrafast optics