Internal state cooling of an atom with thermal light

TL;DR

This paper demonstrates a novel optical cooling method that reduces an atom's internal state entropy using broadband thermal light, showcasing a counterintuitive cooling-by-heating phenomenon with practical sunlight.

Contribution

It introduces a new cooling technique employing thermal light, contrasting traditional laser cooling, and experimentally shows entropy reduction in a single atom using broadband sunlight.

Findings

Internal state entropy of a single atom is reduced more than twofold.

Cooling power increases with higher thermal occupation of the light source.

Demonstrates cooling using broadband sunlight instead of coherent laser light.

Abstract

A near-minimal instance of optical cooling is experimentally presented wherein the internal-state entropy of a single atom is reduced more than twofold by illuminating it with broadband, incoherent light. Since the rate of optical pumping by a thermal state increases monotonically with its temperature, the cooling power in this scenario increases with higher thermal occupation, an example of a phenomenon known as cooling by heating. In contrast to optical pumping by coherent, narrow-band laser light, here we perform the same task with fiber-coupled, broadband sunlight, the brightest laboratory-accessible source of continuous blackbody radiation.