Figure 2: Quantum memory.
From: A multiplexed light-matter interface for fibre-based quantum networks
(a) Simplified level scheme of Er3+ in silica glass. Frequency-selective optical pumping from the 4I15/2 electronic ground state (|g〉) via the 4I13/2 excited state (|e〉) into an auxiliary (spin) state (|s〉) allows spectral tailoring. (b) Inhomogeneous broadening and AFC structure. The inhomogeneously broadened optical absorption line of erbium ions in silica fibre at 1 K extends roughly from 1,500 to 1,540 nm wavelength. A 2-GHz-wide section of a 16-GHz-wide comb at 1,532.5 nm with teeth spacing Δ=200 MHz is shown.
