Physical Review A 57, 120 (1998); preprint cond-mat/9701055. Section II develops coupled single-electron spin qubits and electrically controlled exchange.
Verified section 3.2, equations (3.6)–(3.15): diagonal/off-diagonal decomposition and second-order projected Hamiltonian. Section 1.1 records the Anderson-to-Kondo application. The wiki two-level example is derived independently.