Figure 5
From: Photonic ququart logic assisted by the cavity-QED system
Schematic hyperentanglement-assisted quantum code.
Blue lines are a hyperentangled state 
. The input photon A is in the state 
. The encoding circuit consists of one controlled-phase gate C[Z(Ï€)]. The polarization-error may be derived in a noisy environment or noisy quantum channel for quantum super-dense coding. The joint measurement is completed with a hyper-Bell state analysis to determine the error syndrome. The recovery operations R is dependent of the measurement outcomes shown in Table 1.
