Various approximations can be achieved by setting different blocks of Eq. 142 to zero. The usual Tamm-Dancoff Approximation (TDA) can be achieved by setting B = 0, while other QED Hamiltonians (in their many-state generalizations) can also achieved. For example, setting g = 0 is the generalized RWA, while also setting the DSE term to zero (∆ = 0), one arrives at an analogue of the JC Hamiltonian. These various choices have been extensively discussed in Ref. 93, and is schematically depicted in Fig. .