Quasi-Continuous Cooling of a Microwave Mode on a Benchtop using Hyperpolarized NV$^-$ Diamond

TL;DR

This paper demonstrates continuous microwave mode cooling using optically pumped NV$^-$ diamond at zero magnetic field, achieving a noise temperature of 188 K and outperforming pentacene-doped para-terphenyl in efficiency and immediacy.

Contribution

It introduces a novel method of microwave mode cooling with NV$^-$ diamond that operates continuously at low optical power without prior preparation.

Findings

Achieved microwave mode cooling to 188 K noise temperature.

NV$^-$ diamond cools immediately upon optical excitation.

Outperforms pentacene-doped para-terphenyl in efficiency.

Abstract

We demonstrate the cooling of a microwave mode at 2872 MHz through its interaction with optically spin-polarized NV$^-$ centers in diamond at zero applied magnetic field, removing thermal photons from the mode. By photo-exciting (pumping) a brilliant-cut red diamond jewel with a continuous-wave 532-nm laser, outputting 2 W, the microwave mode is cooled down to a noise temperature of 188 K. This noise temperature can be preserved continuously for as long as the diamond is optically excited and kept cool. The latter requirement restricted operation out to 10 ms in our preliminary setup. The mode-cooling performance of NV$^-$ diamond is directly compared against that of pentacene-doped para-terphenyl, where we find that the former affords the advantages of cooling immediately upon light excitation without needing to mase beforehand (or at all) and being able to cool continuously at substantially lower optical pump power.