They want to store the state of received photons on „quantum harddrives“, transport them to the same place, read the states out and let them interfere locally.
This is the mentioned paper from december 2020 about hour-long optical storage (by Chaun-Feng Li et al.):
The state (phase) of the received photon will depend on the position of the receiver. Even if you have a perfect quantum hard drive, you still need to maintain the position of your receivers to within a wavelength. That will be hard to do if they are separated by a long distance.