Strongly regular quantum Hamiltonian ($|E_j-E_k|\ne |E_r-E_s|$ for distinct transitions)

A drift Quantum Hamiltonian is strongly regular when its energy levels are nondegenerate and distinct unordered transitions have distinct absolute nonzero Bohr frequencies. Sometimes regularity is required only on the graph of allowed control transitions. This lets polynomials in the squared drift adjoint action separate different coupling quadratures and permits frequency-selective resonant quantum control. This notion is unrelated to a strongly regular graph.