  Despite the recognition of two-dimensional (2D) systems as emerging and
scalable host materials of single photon emitters or spin qubits, uncontrolled
and undetermined chemical nature of these quantum defects has been a roadblock
to further development. Leveraging the design of extrinsic defects can
circumvent these persistent issues and provide an ultimate solution. Here we
established a complete theoretical framework to accurately and systematically
design quantum defects in wide-bandgap 2D systems. With this approach,
essential static and dynamical properties are equally considered for spin qubit
discovery. In particular, many-body interactions such as defect-exciton
couplings are vital for describing excited state properties of defects in
ultrathin 2D systems. Meanwhile, nonradiative processes such as phonon-assisted
decay and intersystem crossing rates require careful evaluation, which compete
together with radiative processes. From a thorough screening of defects based
on first-principles calculations, we identify promising single photon emitters
such as SiVV and spin qubits such as TiVV and MoVV in hexagonal boron nitride.
This work provided a complete first-principles theoretical framework for defect
design in 2D materials.
