Figure 2
From: Photonic ququart logic assisted by the cavity-QED system
Schematic circuit of elementary ququart gates.
(a) Schematic hybrid controlled not (CNOT) gate on a ququart-qubit photon system. (b) Schematic controlled phase C[Z4(π)] on a two-ququart photon system. CPSj represent polarizing beamsplitters in the circular basis, which transmit 
and reflect 
. Wj represent the Hadamard operations 
on the excess electron spins ej. Hj represent half-wave plates (HWP) to perform the Hadamard operation 
on the polarization DOF of a photon.
