The following is the key for the optical buffer using QCI mechanism:

1. bandwidth-delay-product (BDP): Hence, we need not only more delay, but also bigger bandwidth of the QCI (EIT, CPO, or whatever) window.
   
2. how about gaseous medium: too narrow bandwidth but the delay is very good. Storage is OK.
   
3. how about crystal medium: bandwidth is also narrow but the delay could be good. Storage is OK, at least in ultracold crystal.
   
4. How about semiconductor medium: bandwidth could be very large and the delay could be OK. Storage is not OK.

Let's think about the possible or potential applications of this.