  We present a proof-of-concept demonstration of free-space quantum key
distribution (QKD) with single photons generated from an isolated defect in
hexagonal boron nitride (hBN). The source, operating at room temperature with a
10% brightness, is integrated into a B92 protocol and a secure key rate (SKR)
of 238 bps and a quantum bit error rate (QBER) of 8.95% are achieved with 1 MHz
clock rate. The effect of temporal filtering of detected photons on the
performance of QKD parameters is also studied. We believe that our results will
accelerate the work on improving the performance of optically active defects in
hBN and their use in high-performance practical QKD systems.
