Two-atom superradiance is studied for atoms having a $J=0$ ground state and a $J=1$ excited state. The atoms lie on either the $x$ or $z$ axis and are excited by a ${\sigma }_{+}$ polarized laser pulse propagating in the $z$ direction. We show quite generally that, for atoms on the $z$ axis, the internal angular momentum lost by the atoms as they decay is fully transferred to the angular momentum of the fields radiated by the atoms. For atoms on the $x$ axis, however, some of the internal angular momentum is converted to orbital angular momentum of the two-atom system. We use a state vector approach that allows us to calculate the angular momentum in the field at all times. A key component of the calculation is the role played by the vacuum field induced excitation exchange between the two atoms. For atoms on the $x$ axis, we first neglect retardation associated with this excitation exchange and use a molecular state basis to calculate the angular momentum dynamics of the atoms and the fields. To illustrate the modification of the early time dynamics produced by retardation, we then use a bare atom state basis to calculate the angular momentum in the atoms and the fields for times $t<2R_{21}/c$, where $R_{21}$ is the separation of the atoms.

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• Angular momentum of light
• Collective effects in atomic physics
• Quantum optics
• Spontaneous emission
• van der Waals interaction