Cooling by Heating of a ¹³⁸Ba⁺ Ion with Sunlight

Cooling in atomic systems is typically done using a low-entropy, ‘cold’ laser or by coupling to a cold bath. However, in some schemes, cooling can be performed by heating a given mode, known as ‘cooling by heating’. We discuss how to cool a trapped ion to its motional ground state using sunlight to drive the cooling and provide estimates of achievable cooling rates with this implementation. We measure the spectrum of sunlight coupled into a single mode fiber for delivery to the ion and compare it to the spectrum of a blackbody in quasi-one-dimension. Finally, we report deshelving and cooling of the internal states of ¹³⁸Ba⁺ with sunlight, a form of internal cooling by heating.