  Solid-state impurity spins with optical control are currently investigated
for quantum networks and repeaters. Among these, rare-earth-ion doped crystals
are promising as quantum memories for light, with potentially long storage
time, high multimode capacity, and high bandwidth. However, with spins there is
often a tradeoff between bandwidth, which favors electronic spin, and memory
time, which favors nuclear spins. Here, we present optical storage experiments
using highly hybridized electron-nuclear hyperfine states in
$^{171}$Yb$^{3+}$:Y$_2$SiO$_5$, where the hybridization can potentially offer
both long storage time and high bandwidth. We reach a storage time of 1.2 ms
and an optical storage bandwidth of 10 MHz that is currently only limited by
the Rabi frequency of the optical control pulses. The memory efficiency in this
proof-of-principle demonstration was about 3%. The experiment constitutes the
first optical storage using spin states in any rare-earth ion with electronic
spin. These results pave the way for rare-earth based quantum memories with
high bandwidth, long storage time and high multimode capacity, a key resource
for quantum repeaters.
