# Approach to Dark Spin Cooling in a Diamond Nanocrystal

## TL;DR

This paper demonstrates a rapid spin polarization transfer from an NV center to a diamond nanocrystal's paramagnetic defects, indicating potential for spin bath cooling and enhanced magnetometry.

## Contribution

It introduces a fast, efficient method for spin bath cooling in diamond nanocrystals using a Hartman-Hahn protocol, with detailed numerical analysis of polarization distribution.

## Key findings

- Spin transfer occurs on microsecond timescale.
- Strong polarization transfer blockade observed.
- Non-uniform spin bath polarization with up to 25% near NV.

## Abstract

Using a Hartman-Hahn protocol, we demonstrate spin polarization transfer from a single, optically-polarized nitrogen-vacancy (NV) center to the ensemble of paramagnetic defects hosted by an individual diamond nanocrystal. Owing to the strong NV-bath coupling, the transfer takes place on a short, microsecond time scale. Upon fast repetition of the pulse sequence we observe strong polarization transfer blockade, which we interpret as an indication of spin bath cooling. Numerical simulations indicate that the spin bath polarization is non-uniform throughout the nanoparticle averaging approximately 5% over the crystal volume, but reaching up to 25% in the immediate vicinity of the NV. These observations may prove relevant to the planning of future bath-assisted magnetometry tests.

---
Source: https://tomesphere.com/paper/1703.03988