  Plenty of quantum information protocols are enabled by manipulation and
detection of photonic spectro-temporal degrees of freedom via light-matter
interfaces. While present implementations are well suited for high-bandwidth
photon sources such as quantum dots, they lack the high resolution required for
intrinsically narrow-band light-atom interactions. Here, we demonstrate
far-field temporal imaging based on ac-Stark spatial spin-wave phase
manipulation in a multimode gradient echo memory. We achieve spectral
resolution of 20 kHz with MHz-level bandwidth and ultra-low noise equivalent to
0.023 photons, enabling operation in the single-quantum regime.
