Transmon Hamiltonian H = 4E_C(n̂−n_g)² − E_J·cos(φ̂); charge-basis Schur triangulation

Transmon Hamiltonian charge-basis Schur triangulation. Setup: a transmon qubit is a Josephson junction shunted by a large capacitance, giving Hamiltonian H = 4E_C·(n̂ − n_g)² − E_J·cos(φ̂) with E_J / E_C ≈ 50–200 placing the qubit in the…