Quantum Interference Effect for Two Atoms Radiating a Single Photon

We present experimental evidence for a modulation in the time-resolved atomic fluorescence light following the photodissociation of ${\mathrm{Ca}}_2$ molecules by a pulsed laser. This modulation is due to an interference effect involving two atoms recoiling in opposite directions, while only one photon is emitted. The period of the modulation is equal to the time for the interatomic distance to increase by an optical wavelength.