  Quantum memories capable of storing single photons are essential building
blocks for quantum information processing, enabling the storage and transfer of
quantum information over long distances. Devices operating at room temperature
can be deployed on a large scale and integrated into existing photonic
networks, but so far warm quantum memories have been susceptible to noise at
the single photon level. This problem is circumvented in cold atomic ensembles,
but these are bulky and technically complex. Here we demonstrate controllable,
broadband and efficient storage and retrieval of weak coherent light pulses at
the single-photon level in warm atomic caesium vapour using the far
off-resonant Raman memory scheme. The unconditional noise floor is found to be
low enough to operate the memory in the quantum regime at room temperature.
