Isotope purification induced reduction of spin relaxation and spin coherence times in semiconductors

TL;DR

This study reveals that excessive isotope purification in semiconductors can paradoxically reduce spin coherence times by increasing coupling to paramagnetic defects, challenging the conventional approach of nuclear spin depletion for qubit enhancement.

Contribution

It demonstrates through numerical modeling that isotope purification beyond an optimal point can enhance defect coupling and decrease spin coherence, providing new insights into qubit material optimization.

Findings

Isotope purification can increase coupling to paramagnetic defects.

Enhanced defect coupling shortens spin relaxation times.

Optimal isotope purification level exists for maximizing coherence.

Abstract

Paramagnetic defects and nuclear spins are often the major sources of decoherence and spin relaxation in solid-state qubits realized by optically addressable point defect spins in semiconductors. It is commonly accepted that a high degree of depletion of nuclear spins can enhance the coherence time by reducing magnetic noise. Here we show that the isotope purification beyond a certain optimal level becomes contra-productive, when both electron and nuclear spins are present in the vicinity of the qubits. Using state-of-the-art numerical tools and considering the silicon vacancy qubit in various spin environments, we demonstrate that the coupling to spin-1/2 point defects in the lattice can be significantly enhanced by isotope purification. The enhanced coupling shortens the spin relaxation time that in turn may limit the the coherence time of spin qubits. Our results can be straightforwardly generalized to triplet point defect qubits, such as the NV center in diamond and the divacancy in SiC.