Penning trap ExB mode temperature considerations for quantum information science*

Two dimensional crystals of hundreds of ions in a Penning trap have demonstrated numerous promising results in quantum simulation and sensing. One recent result was the demonstration of electric field sensing of 240 ± 10 nV/m in 1 second, with sensitivity to motional displacements 8.8 ± 0.4 dB below the standard quantum limit. A fundamental limitation was 40 Hz fluctuations of the axial center of mass mode, believed to be in part caused by elevated in-plane ExB  mode temperatures of order 10 mK, compared to the doppler limit of ~0.5 mK.

We present a description of how these elevated ExB modes affect our axial drumhead mode spectrum and its consequences in implementing our quantum simulation and sensing experiments. We then present a new experimental protocol to directly measure the in-plane temperature in the rotating frame of the ion crystal in a mode resolved way. Finally, we summarize ideas for improving the cooling of the in-plane modes.