Sub-Doppler cooling of a trapped ion in a phase-stable polarization gradient*

A major challenge in the scalability of trapped-ion platforms used in quantum computing and sensing is interfacing the optical systems needed for atomic control with an increasing number of qubits. Contained in this scalability challenge is the issue of quickly and efficiently preparing trapped ions in their motional ground states. One potential technology that may provide robust and scalable optical systems and simultaneously address this state preparation challenge is photonic integrated circuits or PICs. PICs have already been integrated in trapped-ion platforms for some applications but have not yet been used for polarization sensitive fast cooling. Here we focus on one type of polarization sensitive cooling, polarization gradient cooling or PGC. PGC appears to be a natural choice for situations where many motional modes need to be cooled in parallel, which is the case for ion-based quantum computers where many physical qubits are needed. PICs are well suited to implement PGC because a single laser split on chip guarantees optical phase stability. Furthermore, the stable beam paths precisely indexed to the trap location that are available with PICs eliminates vibration and beam pointing issues present in many large-scale trapped ion systems. This phase stability provided has enabled us to study polarization gradient cooling in a phase stable gradient, which we believe is the first time this has been demonstrated. In this talk I will begin by describing PICs and how they can be integrated into an ion trap. Then I will describe the basis of polarization gradient cooling and describe how our system differs from the standard picture. Finally, I will present measurements of phase-stable polarization gradient cooling and discuss next steps for these experiments.