  Quantum memories integrated into nanophotonic silicon devices are a promising
platform for large quantum networks and scalable photonic quantum computers. In
this context, erbium dopants are particularly attractive, as they combine
optical transitions in the telecommunications frequency band with the potential
for second-long coherence time. Here we show that these emitters can be
reliably integrated into commercially fabricated low-loss waveguides. We
investigate several integration procedures and obtain ensembles of many
emitters with an inhomogeneous broadening of < 2 GHz and a homogeneous
linewidth of < 30 kHz. We further observe the splitting of the electronic spin
states in a magnetic field up to 9 T that freezes paramagnetic impurities. Our
findings are an important step towards long-lived quantum memories that can be
fabricated on a wafer-scale using CMOS technology.
