On-chip optical quantum memory using erbium ions

Rare earth ion doped crystals provide an excellent solid state platform for optical quantum memories, which will enable long distance quantum communication and modular quantum computing. Among rare earths, erbium is appealing due to its long lived telecom wavelength resonance, allowing integration with silicon and with existing optical communication technology and infrastructure.
We present an on-chip all-optical quantum memory at telecom wavelengths using the atomic frequency comb protocol. By working at dilution fridge temperatures, we access a regime where the erbium ions have long optical coherence times and good spectral holeburning properties using only a moderate magnetic field, applied with permanent magnets. A nanobeam photonic crystal cavity etched directly in erbium-167 doped yttrium orthosilicate is used to enhance coupling to the ions. We store coherent pulses for memory times as long as 10 µs, albeit with limited efficiency. The memory has a high fidelity (>90%) and can be multiplexed in frequency and time. Ongoing work towards a higher efficiency device is discussed.