-Functionalization of Single-Walled Carbon Nanotubes Creates Localized Spins

Chemical functionalization-introduced quantum defects in single-walled carbon nanotubes (SWCNTs) have shown compelling optical properties for their potential applications in quantum information science and bioimaging. Here, we utilize temperature- and power-dependent electron spin resonance measurements to study the fundamental spin properties of SWCNTs functionalized with well-controlled densities of quantum defects. Signatures of isolated spins that are highly localized at the defect sites are observed, which we further confirm with density functional theory calculations. Applying temperature-dependent line width analysis and power-saturation measurements, we estimate the spin-lattice relaxation time and spin dephasing time to be around 9 μs and 40 ns, respectively. These findings of the localized spin states that are associated with the quantum defects not only deepen our understanding of the molecular structures of the quantum defects but could also have strong implications for their applications in quantum information science.