Figure 5: Multimode quantum storage.

(a) Creation of AFCs. The total, currently addressable bandwidth of 18 GHz is divided into different spectral sections, each featuring an AFC with distinct peak spacing. Depicted is the case of four, 4.5-GHz-wide AFCs, created using two lasers operating at 1,532.50 and 1,532.70 nm. The AFCs feature peak spacings of 333, 200, 143 and 111 MHz, corresponding to storage times of 3, 5, 7 and 9 ns, respectively. For each AFC, only a 1.3-GHz-wide section is shown. (b) Storage and recall. When broadband heralded photons with 50 GHz bandwidth are mapped onto a two-section AFC, where each section extends over 9 GHz bandwidth and has a peak spacing of 333 and 200 MHz, respectively, they are stored in two spectral modes and retrieved in two spectro-temporal modes, as shown in the back trace. Decreasing the bandwidth per AFC allows increasing the number of AFCs (spectral modes), as demonstrated with the storage of four and six spectral modes in the middle and the front trace, respectively. The modes are labelled f_i. For each mode, is measured to be larger than 2 (see Table 1).