  Long-lived quantum memories are essential components of a long-standing goal
of remote distribution of entanglement in quantum networks. These can be
realized by storing the quantum states of light as single-spin excitations in
atomic ensembles. However, spin states are often subjected to different
dephasing processes that limit the storage time, which in principle could be
overcome using spin-echo techniques. Theoretical studies have suggested this to
be challenging due to unavoidable spontaneous emission noise in ensemble-based
quantum memories. Here we demonstrate spin-echo manipulation of a mean spin
excitation of 1 in a large solid-state ensemble, generated through storage of a
weak optical pulse. After a storage time of about 1 ms we optically read out
the spin excitation with a high signal-to-noise ratio. Our results pave the way
for long-duration optical quantum storage using spin-echo techniques for any
ensemble-based memory.
