“Basically, you store an encryption key (1024 or 2048 bits) in a photon”
Basically? How do you store that many bits of info in a single photon?
A photon captures the “quantum state” of the electron that generated it. When the photon hits another electron, the target electron absorbs the quantum state of the source electron.
The quantum state is the magnetic field (expressed as a vector) generated by the source electron as it “spins” around a nucleus. The field vector has both an angle and a magnitude. It is information and can represent a set of bits.
The more accurately you can measure the field of an electron, the more bits you can reliably store in it and read from it. Right now, they can read up to 2k bits from a single electron.
If they are really using quantum entanglement, they don’t need the photon. Because the source and target electrons are entangled, changes in the field generated by the source instantly induce changes in the entangled target.
Entanglement is the only way you could do this from an earth station to a satellite. That’s what makes this article about the Chinese quantum satellite so very impressive.