arXiv subjects

Reyhaneh Ghassemizadeh

Publications and source records attributed to Reyhaneh Ghassemizadeh.

4 recordsLinked to original sources

arXiv2025

Spin coherence in strongly coupled spin baths in quasi-two-dimensional layers

We investigate the spin-coherence decay of NV$^-$-spins interacting with the strongly-coupled bath of nitrogen defects in diamond layers. For thin diamond layers, we demonstrate that the spin-coherence times exceed those of bulk diamond, thus allowing to surpass the limit imposed by high defect concentrations in bulk. We show that the stretched-exponential parameter for the short-time spin-coherence decay is governed by the hyperfine interaction in the bath, thereby constraining random-noise models. We introduce a novel method based on the cluster-correlation expansion applied to strongly-interacting bath partitions. Our results facilitate material development for quantum-technology devices.

quant-ph↗

arXiv2024

Coherence properties of NV-center ensembles in diamond coupled to an electron-spin bath

We investigate nitrogen-vacancy center (NV) ensembles in diamond under the influence of strongly-correlated electron-spin baths. We thoroughly calculate the decoherence properties of the NV central spin for bath concentrations of 0.1-100 ppm using the cluster-correlation expansion (CCE) method. We systematically analyze possible origins of the significant deviations in the values of the $T_2$ coherence time reported in literature. We demonstrate that significant variations can originate from the choice of averaging and fitting procedures used for the ensemble average and we point out the respective aspects that need to be considered, when comparing the various theoretical studies. Our study may ease readers to perform reliable and fast simulations on the central spin problem. It provides an understanding and interpretation of the outcome parameters describing the dynamics of the local bath spins.

quant-ph↗

arXiv2022

Stability and electronic structure of NV centers at dislocation cores in diamond

We present a density functional theory analysis of the negatively charged nitrogen-vacancy (NV) defect complex located at or close to the core of 30$^\circ$ and 90$^\circ$ partial glide dislocations in diamond. Formation energies, electronic densities of states, structural deformations, hyperfine structure and zero-field splitting parameters of NV centers in such structurally distorted environments are analyzed. The formation energies of the NV centers are up to 3 eV lower at the dislocation cores compared to the bulk values of crystalline diamond. We found that the lowest energy configuration of the NV center at the core of a 30$^\circ$ partial glide dislocation is realized when the axis of the NV center is oriented parallel to the dislocation line. This special configuration has a stable triplet ground state. Its hyperfine constants and zero field splitting parameters deviate by only 3% from values of the bulk NV center. Hence, this is an interesting candidate for a self-assembly of a linear array of NV centers along the dislocation line.

cond-mat.mtrl-sci↗

arXiv2022

Influence of (N,H)-terminated surfaces on stability, hyperfine structure, and zero-field splitting of NV centers in diamond

We present a density functional theory analysis of the negatively charged nitrogen-vacancy (NV$^-$) defect complex in diamond located in the vicinity of (111)- or (100)-oriented surfaces with mixed (N,H)-terminations. We assess the stability and electronic properties of the NV$^-$ center and study their dependence on the H:N ratio of the surface termination. The formation energy, the electronic density of states, the hyperfine structure and zero-field splitting parameters of an NV$^-$ center are analyzed as function of its distance and orientation to the surface. We find stable NV$^-$ centers with bulk-like properties at distances of at least $\sim8$ Angstroem from the surface provided that the surface termination consists of at least 25\% substitutional nitrogen atoms. Our results indicate that axial NV centers near a flat 100\% N-terminated (111) surface are the optimal choice for NV-based quantum sensing applications as they are the least influenced by the proximity of the surface.

cond-mat.mtrl-sci↗