  We demonstrate a dual-rail optical Raman memory inside a polarization
interferometer; this enables us to store polarization-encoded information at
GHz bandwidths in a room-temperature atomic ensemble. By performing full
process tomography on the system we measure up to 97\pm1% process fidelity for
the storage and retrieval process. At longer storage times, the process
fidelity remains high, despite a loss of efficiency. The fidelity is 86\pm4%
for 1.5 \mu s storage time, which is 5,000 times the pulse duration. Hence high
fidelity is combined with a large time-bandwidth product. This high
performance, with an experimentally simple setup, demonstrates the suitability
of the Raman memory for integration into large-scale quantum networks.
