Automating the Tuning of Magneto-Optical Trap Lasers for Use in Neutral Atom Quantum Computing*

Neutral atom quantum computers use atoms trapped by light as quantum bits. Our group focuses on computationally exploring light patterns useful for quantum computing [1-3] and investigating their properties experimentally. To hold atoms in light patterns, they must first be cooled to sub-mK temperatures using a magneto-optical trap (MOT). The MOT requires two lasers (trap and repump) tuned to the correct hyperfine transitions of the atom to within 1:100,000,000.

We developed Python code to automate the time-consuming process of tuning each of our grating-tuned near-infrared diode lasers. It performs the following steps: First, the hyperfine energy level structure of the ⁸⁷Rb atoms within the peaks of the Doppler-broadened spectrum is exposed using saturated absorption. Next, the conversion factor between grating voltage and laser frequency is determined using the signal from a 300MHz free spectral range Fabry-Perot interferometer to identify the trap and repump transitions. Lastly, the necessary voltage adjustment to place the zero of the optoelectronic feedback signal at the correct laser frequency is obtained. Then the laser is manually locked and the light traps are ready to be loaded.

[1] G. D. Gillen, et al., Phys. Rev. A 73, 013409 (2006), [2] K. Gillen-Christandl, et al., Phys. Rev. A 82, 063420 (2010), [3] K. Gillen-Christandl, et al., Phys. Rev. A 83, 023408 (2011).