Stimulated measurement of spontaneous four-wave mixing from a warm atomic ensemble

Photon-pair sources from atomic ensembles are considered essential to the development of quantum science and technology based on atom-photon interfaces. The measurement of spectral-temporal biphoton wave forms is important for the characterization of frequency-time entangled photon pairs. Here, we demonstrate a stimulated measurement of the biphoton spectral wave form (BSW) of narrow-band photon pairs emitted from a Doppler-broadened cascade-type atomic ensemble. A BSW with submegahertz resolution is obtained as a function of the absolute optical frequency determined by atomic transitions, which reveals a spectral shift of approximately 510 MHz from the expected resonance frequency of the 5P(3/2) - 5D(5/2) and 5S(1/2) - 5P(3/2) transitions of Rb-87 atoms.