Solid-state spin coherence time approaching the physical limit

Abstract

Extending the coherence time of quantum systems to their physical limit is a long-standing pursuit and critical for developing quantum science and technology. By characterizing all the microscopic noise sources of the electronic spin [nitrogen-vacancy (NV) center] in diamonds using complete noise spectroscopy, we observe a previously unforeseen noise spectrum manifested as the empirical limit ($T_2\approx \frac{1}{2}{T}_1$) that has puzzled researchers for decades in various solid-state systems. By implementing a corresponding dynamical decoupling strategy, we are able to surpass the empirical limit and approach the upper physical limit T₂ = 2T₁ for NVs, from room temperature down to 220 kelvin. Our observations, including the independence across different spatial sites and its dependence on temperature in the same way as spin-lattice relaxation, suggest an emerging decoherence mechanism dominated by spin-lattice interaction. These results provide a unified and universal strategy for characterizing and controlling microscopic noises, thereby paving the way for achieving the physical limit in various solid-state systems.