Milli-Kelvin Platform for Quantum Many-Body Dynamics with Solid State Spin Defects

The relaxation dynamics of solid-state spin defects provide a unique window into many-body quantum systems. We are developing a milli-Kelvin experimental platform that leverages a hybrid system of nitrogen-vacancy (NV) and P1 centers in diamond to investigate spin relaxation and noise in disordered dipolar environments. Our setup integrates a scanning confocal microscope into a Bluefors LD-400 dilution refrigerator (full temperature tunnability from 10 mK to 300 K), equipped with a 6,1,1 Tesla vector magnet and microwave control for both NV and P1 spins. The possibility to thermally polarize optically dark P1 centers at low temperatures provides a new degree of experimental tunability, allowing us to control and probe spin dynamics in an effectively dual-species spin system. 

A central focus of our current study is the anomalous plateau observed in ensemble NV's T₁ relaxation times at low temperatures, which remains poorly understood. We hypothesize that the dense P1 spin bath is the dominant source of decoherence, generating magnetic noise that influences NV relaxation dynamics. By using NV's T₁ measurements as a probe, we aim to extract the noise spectrum of the P1 ensemble and study its dependence on temperature, external fields, and Floquet-engineered interactions. Additionally, we are exploring possibilities of cavity-assisted initialization and readout of NV and P1 spin states. These capabilities allow us to shed new light into disorder-driven quantum phases and lay the foundation for hybrid quantum technologies utilizing defect spins in diamond at milli-kelvin temperature.