Orders of Magnitude Improvement in Coherence of Silicon-Vacancy Ensembles in Isotopically Purified 4 H-SiC

Abstract

For solid-state spin systems, unwanted interactions with surrounding spin baths and inhomogeneity are ubiquitous challenges. In defect spin systems, part of this challenge is that the process of generating the desired defect often involves creating numerous unwanted defects that induce dephasing. Here we show that many of these issues can be alleviated with the silicon vacancy in silicon carbide (SiC), which is a simple defect to produce as it does not require the introduction of impurity atoms into the crystal. Previous measurements of the inhomogeneous dephasing time T2-of silicon-vacancy ensembles have thus far been limited to a few 100 ns due to the nuclear spin bath. We perform isotopic purification to minimize the influence of nuclear spins, leading to an order of magnitude improvement in the T2-at room temperature. Further improvements emerge by suppressing the effects of strain inhomogeneity via an informed choice of basis in the spin quartet. Combining these techniques leads to about a factor 50 improvement in the T2-of the defect ensemble even at high defect densities.