First-principles theory of extending the spin qubit coherence time in hexagonal boron nitride

TL;DR

This paper presents a first-principles theoretical study demonstrating that isotopic enrichment and strain engineering can significantly extend the spin coherence time of boron vacancy qubits in hexagonal boron nitride, enhancing their quantum application potential.

Contribution

The study introduces two novel materials engineering methods—isotopic enrichment and strain induction—to substantially increase the spin coherence time of VB- in h-BN, supported by quantum many-body computations.

Findings

Isotopic enrichment with 10B triples the coherence time.

Strain-induced curvature enhances T2 by 1.3 times.

Combined methods yield T2 of over 200 microseconds.

Abstract

Negatively charged boron vacancies (VB-) in hexagonal boron nitride (h-BN) are a rapidly developing qubit platform in two-dimensional materials for solid-state quantum applications. However, their spin coherence time (T2) is very short, limited to a few microseconds owing to the inherently dense nuclear spin bath of the h-BN host. As the coherence time is one of the most fundamental properties of spin qubits, the short T2 time of VB- could significantly limit its potential as a promising spin qubit candidate. In this study, we theoretically proposed two materials engineering methods, which can substantially extend the T2 time of the VB- spin by four times more than its intrinsic T2. We performed quantum many-body computations by combining density functional theory and cluster correlation expansion and showed that replacing all the boron atoms in h-BN with the 10B isotope leads to the coherence enhancement of the VB- spin by a factor of three. In addition, the T2 time of the VB- can be enhanced by a factor of 1.3 by inducing a curvature around VB-. Herein, we elucidate that the curvature-induced inhomogeneous strain creates spatially varying quadrupole nuclear interactions, which effectively suppress the nuclear spin flip-flop dynamics in the bath. Importantly, we find that the combination of isotopic enrichment and strain engineering can maximize the VB- T2, yielding 207.2 and 161.9 {\mu}s for single- and multi-layer h-10BN, respectively. Furthermore, our results can be applied to any spin qubit in h-BN, strengthening their potential as material platforms to realize high-precision quantum sensors, quantum spin registers, and atomically thin quantum magnets.