Fig. 2: Experimental sequence and oscilloscope traces.
From: One-hour coherent optical storage in an atomic frequency comb memory
a The experimental sequence. The class-cleaning sequence containing six pump lights is used to pump away unwanted ions and select a single class of ions. The spin polarization sequence polarizes the population into the \({\left|3\right\rangle }_{{\rm{g}}}\) state. Then the AFC is prepared in the \({\left|3\right\rangle }_{{\rm{g}}}\) state while keeping the \({\left|4\right\rangle }_{{\rm{g}}}\) empty using the \({\left|4\right\rangle }_{{\rm{g}}}\,\leftrightarrow\, {\left|3\right\rangle }_{{\rm{e}}}\) pump light. After the input pulse (Gaussian profile, colored with red) is absorbed, a control pulse transfers the optical excitation into a spin-wave excitation for long-term storage. Dynamical decoupling is employed for protecting the spin coherence and finally the spin excitation is transferred back to the optical regime with another control pulse. Two kinds of dynamical decoupling sequences, CPMG and KDDx, are tested for spin coherence protection. b Oscilloscope traces of the spin-wave AFC storage with a CPMG sequence with τ = 100 ms, which consists of four π pulses. The black line shows the traces of transmission of the input mode and remaining two-level AFC echo, which are directly detected by the photodetector. The red line shows the trace of the spin-wave AFC echo after a storage of 400 ms, which is heterodyne detected. The traces are averaged four times. The dashed line indicates the position of the control pulses.
