Relaxation of a transmon qubit from unconfined states and resurgence of coherence

A transmon qubit coupled to a circuit cavity is an extensively studied system, which has also been used to realize a wide variety of hybrid devices, such as with the cavity electromechanical systems. However, often the large power requirements for optomechanical systems render the c-QED setup incompatible. Motivated from this aspect, we investigate the relaxation of a transmon qubit after driving it to unconfined states with large power. We measure the resurgence time corresponding to the relaxation of qubit back to the ground state. After re-initializing transmon to its ground state, we create single photon states in the cavity by rapidly tuning the qubit frequency and swapping the single excitation to the cavity.