Trapped ions beyond carrier and sideband interactions

Trapped ions driven by electromagnetic radiation constitute one of the most developed quantum technologies to date. The scenarios range from proof-of-principle experiments to on-chip integration for quantum information units. In most cases, these systems have operated in a regime where the magnitude of the ion-radiation coupling constant is much smaller than the trap and electronic transition frequencies. This regime allows the use of simple effective Hamiltonians based on the validity of the rotating-wave approximation. However, novel trap and cavity designs now permit regimes in which the trap frequency and the ion-radiation coupling constant are commensurate. This opens up new avenues for faster quantum gates and state transfers from the ion to a photon and other quantum operations. From the theoretical side, however, there is not yet much known in terms of models and applications that go beyond the weak-driving scenario. In this work, we present two main results in the scenario of stronger driving. First, we revisit a known protocol to reconstruct the motional Wigner function and expand it to stronger-driving lasers. This extension is not trivial because the original protocol makes use of effective Hamiltonians valid only for weak driving. The use of stronger fields or faster operations is desirable since experimental reconstruction methods of that kind are usually hindered by decoherence. We then present a model that allows the analytical treatment of stronger driving and that works well for nonresonant interactions, which are generally out of the reach of previous models.

Automated summary

Trapped ions driven by electromagnetic radiation are highly developed quantum technologies, ranging from proof-of-principle experiments to on-chip integration for quantum information units. With novel trap and cavity designs, faster quantum gates and state transfers become possible. However, there is currently limited knowledge on models and applications that go beyond the weak-driving scenario.