  Future quantum photonic networks require coherent optical memories for
synchronizing quantum sources and gates of probabilistic nature. We demonstrate
a fast ladder memory (FLAME) mapping the optical field onto the superposition
between electronic orbitals of rubidium vapor. Employing a ladder level-system
of orbital transitions with nearly degenerate frequencies simultaneously
enables high bandwidth, low noise, and long memory lifetime. We store and
retrieve 1.7-ns-long pulses, containing 0.5 photons on average, and observe
short-time external efficiency of 25%, memory lifetime (${1/e}$) of 86 ns, and
below ${10^{-4}}$ added noise photons. Consequently, coupling this memory to a
probabilistic source would enhance the on-demand photon generation probability
by a factor of 12, the highest number yet reported for a noise-free,
room-temperature memory. This paves the way towards the controlled production
of large quantum states of light from probabilistic photon sources.
