Interband transitions and interference effects in superconducting qubits

We investigate phase-sensitive interference effects in a periodically sin(2 pi f (rf) t)-driven, artificial two-state system connected to a microwave resonator at f (LC) a parts per thousand integral 800 MHz. We observe two kinds of multiphoton transitions in the two-state system, accompanied by: (1) Several quanta from the drive at f (rf) and (2) one quantum at f (rf) and several at f (LC) . The former are described using phase-sensitive Landau-Zener transitions, while the latter are discussed in terms of vibronic transitions in diatomic molecules. Interference effects in the vibronic transitions governed by Franck-Condon coefficients are also considered.