  Quantum memories for quantum communication need to be able to store photons
for an extended time and then to release them on demand. This can be achieved
in atomic frequency comb ensemble based quantum memories by control pulses that
transfer the excitation to and from long-lived spin states. However, such
pulses can give rise to coherent and incoherent noise due to their interaction
with the memory ensemble. In this article, we experimentally demonstrate the
ability to switch off the coherent noise from such control pulses during the
echo emission in a spin-wave quantum memory, using the linear Stark effect in
rare-earth-ion doped crystals. By applying an electric field pulse, the echo
emission was coherently switched off prior to the first spin transfer pulse,
and the stored data pulse was restored only when both an optical recall pulse
and a re-phasing electrical pulse were applied, giving a high degree of control
of both desired and undesired emissions. We estimate the effectiveness of this
technique by turning off the free induction decay of a narrow ensemble of ions.
This technique can thus improve the noise performance of spin-wave storage at
the single photon level by quenching coherent optical radiation created by the
strong control pulses. The method demonstrated here represents a
proof-of-principle that the spin-wave storage scheme can be combined with Stark
control. The combined scheme serves as an addition to the toolbox of techniques
that can be used to realize a full version of a quantum repeater.
