Improved cooling and direct temperature measurement of in-plane motion in a 2D ion crystal in a Penning trap

Quantum simulation and sensing demonstrations in two-dimensional ion crystals in Penning traps rely on the shared axial motional modes of the ions. While the in-plane motion is not directly utilized, elevated in-plane temperatures impact the stability of the axial modes, limiting the implementation of quantum information protocols. Previous work used only standard Doppler laser cooling, which is ineffective for the low-frequency magnetron modes. We present a novel experimental technique that enables efficient cooling of the magnetron motion. Our approach relies on resonantly coupling the poorly cooled magnetron modes with the well cooled high-frequency planar (cyclotron) modes. We also discuss new experimental efforts to estimate the temperatures of these in-plane modes. We utilize a deformable mirror to imprint AC Stark shift (ACSS) patterns in the rotating frame of the ions. This results in an effective modulation of the ACSS experienced by each ion as it moves in the crystal plane, causing spin dephasing that is directly proportional to the size of the thermal fluctuations. Measurements of the spin dephasing allow quantitative determination of the temperatures associated with the planar modes of the ion crystals.