Prior to that, Arnold was the project manager and a co-investigator on the Simons Array project, the cutting-edge cosmic microwave background (CMB) polarization experiment currently deploying to the Chilean Atacama Desert. He received his Ph.D. at the University of California, Berkeley, working on the precursor to the Simons Array — POLARBEAR — which produced the first non-zero measurement of B-mode polarization in the CMB using CMB data alone.