  We introduce a scheme for the parallel storage of frequency separated signals
in an optical memory and demonstrate that this dual-rail storage is a suitable
memory for high fidelity frequency qubits. The two signals are stored
simultaneously in the Zeeman-split Raman absorption lines of a cold atom
ensemble using gradient echo memory techniques. Analysis of the split-Zeeman
storage shows that the memory can be configured to preserve the relative
amplitude and phase of the frequency separated signals. In an experimental
demonstration dual-frequency pulses are recalled with 35% efficiency, 82%
interference fringe visibility, and 6 degrees phase stability. The fidelity of
the frequency-qubit memory is limited by frequency-dependent polarisation
rotation and ambient magnetic field fluctuations, our analysis describes how
these can be addressed in an alternative configuration.
