  Interfaced single-photon sources and quantum memories for photons together
form a foundational component of quantum technology. Achieving compatibility
between heterogeneous, state-of-the-art devices is a long-standing challenge.
We built and successfully interfaced a heralded single-photon source based on
cavity-enhanced spontaneous parametric down-conversion in ppKTP and a matched
memory based on electromagnetically induced transparency in warm $^{87}$Rb
vapor. The bandwidth of the photons emitted by the source is 370 MHz, placing
its speed in the technologically relevant regime while remaining well within
the acceptance bandwidth of the memory. Simultaneously, the experimental
complexity is kept low, with all components operating at or above room
temperature. Read-out noise of the memory is considerably reduced by exploiting
polarization selection rules in the hyperfine structure of spin-polarized
atoms. For the first time, we demonstrate single-photon storage and retrieval
in a ground-state vapor cell memory, with $g_{c,\text{ret}}^{(2)}=0.177(23)$
demonstrating the single-photon character of the retrieved light. Our platform
of single-photon source and atomic memory is attractive for future experiments
on room-temperature quantum networks operating at high bandwidth.
