Polarization-encoded quantum key distribution with a room-temperature telecom single-photon emitter

Single-photon sources (SPSs) are directly applicable in quantum key distribution (QKD) because they allow the implementation of the canonical BB84 protocol. To date, QKD implementations using SPSs are not widespread because of the need for cryogenic operation, or frequency conversion to a wavelength efficiently transmitted over telecommunication fibers. We report an observation of polarization-encoded QKD using a room-temperature telecom SPS based on a GaN defect. A field test over 3.5 km of deployed fiber with 4.0-dB loss yielded a quantum bit error rate (QBER) of 5.0% and a secure key rate of 585.9 bps. Further testing in a 32.5-km fiber spool (attenuation of 11.2 dB), which exhibited substantially lower polarization mode dispersion, yielded a QBER of 3.2% and a secure key rate of 50.4 bps. These results illustrate the potential of the GaN defects for supporting polarization-encoded quantum communication.