Figure 7
Schematic quantum superdense coding using the hyperentanglement in the Eq. (24).
PS, BS and H are defined in the Fig. 1. Xp, Xs, CNOT1 and CNOT2 are defined in the Fig. 6. Zp = |H〉 〈H| − |V〉 〈V| and Zs = |r1〉 〈r1| − |r2〉 〈r2| denote the Pauli flip and Pauli phase flip on the spatial DoF {r1, r2} of one photon. 
, 
, 
and 
. 
are single photon detectors. The feed-forward operations of Bob are only single photon operations.
