Breaking the Entangling Gate Speed Limit for Trapped-Ion Qubits Using a Phase-Stable Standing Wave
S. Saner, O. Băzăvan, Mariella Minder, P. Drmota, D. J. Webb, G. Araneda, R. Srinivas, David Lucas, C. J. Ballance
Abstract
All laser-driven entangling operations for trapped-ion qubits have hitherto been performed without control of the optical phase of the light field, which precludes independent tuning of the carrier and motional coupling. By placing $^{88}{\mathrm{Sr}}^{+}$ ions in a $\ensuremath{\lambda}=674\text{ }\text{ }\mathrm{nm}$ standing wave, whose relative position is controlled to $\ensuremath{\approx}\ensuremath{\lambda}/100$, we suppress the carrier coupling by a factor of 18, while coherently enhancing the spin-motion coupling. We experimentally demonstrate that the off-resonant carrier coupling imposes a speed limit for conventional traveling-wave M\o{}lmer-S\o{}rensen gates; we use the standing wave to surpass this limit and achieve a gate duration of $15\text{ }\text{ }\mathrm{\ensuremath{\mu}}\mathrm{s}$, restricted by the available laser power.