Laser-induced charging of microfabricated ion traps

TL;DR

This study investigates how laser-induced photoelectric charging affects microfabricated ion traps used in quantum computing, revealing wavelength and material dependencies at cryogenic temperatures.

Contribution

It provides the first detailed analysis of laser wavelength and material effects on charging in microfabricated ion traps at 6 K.

Findings

Lower wavelength lasers cause more charging.

Aluminum traps charge more than copper or gold.

Charging dynamics follow a rate equation model.

Abstract

Electrical charging of metal surfaces due to photoelectric generation of carriers is of concern in trapped ion quantum computation systems, due to the high sensitivity of the ions' motional quantum states to deformation of the trapping potential. The charging induced by typical laser frequencies involved in doppler cooling and quantum control is studied here, with microfabricated surface electrode traps made of aluminum, copper, and gold, operated at 6 K with a single Sr$^+$ ion trapped 100 $\mu$m above the trap surface. The lasers used are at 370, 405, 460, and 674 nm, and the typical photon flux at the trap is 10$^{14}$ photons/cm$^2$/sec. Charging is detected by monitoring the ion's micromotion signal, which is related to the number of charges created on the trap. A wavelength and material dependence of the charging behavior is observed: lasers at lower wavelengths cause more charging, and aluminum exhibits more charging than copper or gold. We describe the charging dynamic based on a rate equation approach.