  We explore applications of nonlinear circuit QED with a charge qubit
inductively coupled to a microwave LC resonator in the photonic engineering and
ultrastrong-coupling multiphoton quantum optics. Simply sweeping the
gate-voltage bias achieves arbitrary Fock-state pulsed maser, where the single
qubit plays the role of artificial gain medium. Resonantly pumping the
parametric qubit-resonator interface leads to the squeezing of resonator field,
which is utilizable to the quantum-limited microwave amplification. Moreover,
upwards and downwards multiphoton quantum jumps may be observed in the steady
state of the driving-free system.

Quantum Physics