Room-temperature near-infrared optical readout of triplet spin states integrated in carbon nanotubes towards quantum sensing

Optically addressable electron spin qubits that function at room temperature and under ambient conditions are essential for advancing quantum sensing. Solid state defect platforms offer robust spin-photon interfaces but lack precise defect positioning and electronic tunability. Molecular spin qubits enable bottom up chemical design yet suffer from limited photostability. Here, we introduce para-halophenyl (-Cl, -Br and-I) quantum defects in (6,5) single wall carbon nanotubes that trap triplet excitons with a spin-photon interface that is operable under ambient, room temperature conditions. These defects were shown to emit in the near infrared within the biological transparency window, and their placement on the nanotube surface provides nanoscale proximity to target environments. The deep optical traps formed by the defects yield exceptional photostability. Here, we demonstrate optical initialization and readout of these triplet states at room temperature, provide proof of principle sensing of paramagnetic molecules, and highlight potential for on chip detection. Together, these results establish SWCNT defects as a promising new platform for future quantum sensing.