Carbon defects engineering in hexagonal boron nitride for single photon emission and spin qubits

The common defects in ultrathin hexagonal boron nitride (h-BN) provide diverse color centers for quantum information applications. However, deterministic manipulation of h-BN defects spatially and spectrally remains a grand challenge. Understanding the principles for tuning the spin state, zero-phonon line (ZPL) energy, emission intensity, and linewidth is highly sought after. Here, we showcase that substitutional carbon defects, ubiquitous in synthetic h-BN, can be engineered facilely to possess quantum emission and spin-selective luminescence properties on-demand. Within the h-BN host lattice, single carbon dimers and carbon defect complexes exhibit strong ZPL emission with wavelength and vibrational structure tunable by the size of the defect complex. The carbon impurities can also form charge-neutral spin defects with high quantum yield and prolonged spin coherence time with regard to the widely reported boron vacancy defect VB−. The essential roles of exciton nature and electron–phonon coupling in the quantum optical performance are elucidated, providing useful guidance for the design of solid-state single photon emitters and spin qubits.