Solid-state single photon source with Fourier transform limited lines at room temperature

Solid-state single photon sources with Fourier transform (FT) limited lines are among the most crucial constituents of photonic quantum technologies and have been accordingly the focus of intensive research over the last several decades. However, so far, solid-state systems have only exhibited FT limited lines at cryogenic temperatures due to strong interactions with the thermal bath of lattice phonons. In this Rapid Communication, we report a solid-state source that exhibits FT limited lines measured in photoluminescence excitation (sub-100-MHz linewidths) from 3 to 300 K. The studied source is a color center in the two-dimensional hexagonal boron nitride and we propose that the center's decoupling from phonons is a fundamental consequence of the material's low dimensionality. While the center's luminescence lines exhibit spectral diffusion, we identify the likely source of the diffusion and propose to mitigate it via dynamic spectral tuning. The discovery of FT limited lines at room temperature, which once the spectral diffusion is controlled, will also yield FT limited emission. Our work motivates a significant advance towards room-temperature photonic quantum technologies and a different research direction in the remarkable fundamental properties of two-dimensional materials.