Quantum decoherence dynamics of divacancy spins in silicon carbide

TL;DR

This study demonstrates that divacancy spins in silicon carbide exhibit exceptionally long coherence times of 1.3 ms, attributed to decoupling of nuclear spins and the crystal's binary structure, advancing solid-state qubit development.

Contribution

The paper provides the first combined experimental and theoretical analysis of long coherence times in divacancy spins in silicon carbide, highlighting the role of nuclear spin environment and crystal structure.

Findings

Achieved a 1.3 ms Hahn-echo T2 coherence time in SiC divacancy spins.

Decoupling of 29Si and 13C nuclear spins at moderate magnetic fields enhances coherence.

Binary crystal structure reduces strongly coupled nuclear spin pairs, prolonging T2.

Abstract

Long coherence times are key to the performance of quantum bits (qubits). Here, we experimentally and theoretically show that the Hahn-echo coherence time (T2) of electron spins associated with divacancy defects in 4H-SiC reaches 1.3 ms, one of the longest T2 times of an electron spin in a naturally isotopic crystal. Using a first-principles microscopic quantum-bath model, we find that two factors determine the unusually robust coherence. First, in the presence of moderate magnetic fields (300 G and above), the 29Si and 13C paramagnetic nuclear spin baths are decoupled. In addition, because SiC is a binary crystal, homo-nuclear spin pairs are both diluted and forbidden from forming strongly coupled, nearest-neighbor spin pairs. Longer neighbor distances result in fewer nuclear spin flip-flops, a less fluctuating intra-crystalline magnetic environment, and thus a longer T2 time. Our results point to polyatomic crystals as promising hosts for coherent qubits in the solid state.