We have demonstrated the first two species maser. Ensembles of ${}^3\mathrm{He}$ and ${}^{129}\mathrm{Xe}$ gas, co-located in a double-chamber glass cell, performed simultaneous maser oscillations on their nuclear spin- $\frac{1}{2}$ Zeeman transitions. This new device may be used for experiments requiring precision magnetometry combined with frequency measurement of a second free-running species operating in the same volume. For example, the ${}^3\mathrm{He}$ maser may serve as a magnetometer, while the ${}^{129}\mathrm{Xe}$ maser may be used to search for a permanent electric dipole moment of the ${}^{129}\mathrm{Xe}$ atom as a test of time reversal symmetry.

• Received 23 July 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.3971