Transform-Limited Photon Emission from a Lead-Vacancy Center in Diamond above 10 K

Transform -limited photon emission from quantum emitters is essential for high-fidelity entanglement generation. In this Letter, we report the coherent optical property of a single negatively charged leadvacancy (PbV) center in diamond. Photoluminescence excitation measurements reveal stable fluorescence with a linewidth of 39 MHz at 6 K, close to the transform limit estimated from the lifetime measurement. We observe 4 orders of magnitude different linewidths of the two zero -phonon lines, and find that the phonon -induced relaxation in the ground state contributes to this huge difference in the linewidth. Because of the suppressed phonon absorption in the PbV center, we observe nearly transformlimited photon emission up to 16 K, demonstrating its high temperature robustness compared to other color centers in diamond.