Fig. 4: Verification of the coherent nature of the memory.
From: One-hour coherent optical storage in an atomic frequency comb memory
a Experimental sequence of the AFC echo interference, where e and l represent the earlier and the later, respectively. The interval of the two input pulses and that of the two read out pulses (π/2) should be the same in order to overlap the echoes (el+le) of the two inputs. b Visibility versus the storage time. The left inset shows an interference pattern after 5 min storage, generated by recording the intensity of the echo in the middle while varying the relative phase Δφ between the two input pulses. Each data point is averaged four times, and the error bars indicate one standard deviation of the echo area. After a storage time of 5, 30, and 60 min, the coherence is well maintained with a visibility of 93.0 ± 5.5%, 95.3 ± 4.2%, and 92.9 ± 4.9%, respectively. Single-shot oscilloscope traces of the signals after the 60 min storage are presented in the right inset. Constructive and destructive interference are observed at Δφ = 0° and 180°, respectively.
