Parallel entangling gates in trapped-ion chains using orthogonal motional modes*

Parallel operations are important for both near-term quantum computers and larger-scale fault-tolerant machines because they reduce execution time and qubit idling. We present a pairwise-parallel gate scheme on a trapped-ion quantum computer where entangling gates are driven simultaneously on different sets of orthogonal motional modes in a trapped-ion chain. We demonstrate the utility of this scheme by creating a high-fidelity GHZ state in one step using parallel gates with one overlapping qubit and show its advantage for long circuits by running a digital quantum simulation of a transverse-field Ising model. With essentially no overhead apart from additional initial cooling, this method effectively extends the available gate depth by up to a factor of two. We use ground-level qubits in ¹⁷¹ Yb+ driven by Raman lasers in this demonstration, but this scheme can be easily applied to other types of trapped-ion qubits and addressed gate schemes, broadly enhancing the capabilities of trapped-ion quantum computers.