In this talk, I will focus on our two recent experiments. In the first one, we propose and experimentally demonstrate a unique two-fold quantum delayed-choice experiment where wave or particle nature of a superconducting interfering device can be post-selected twice after the interferometer. This experiment is enabled by a quantum which-path detector implemented through a superconducting cavity, showing an unprecedented controllability to test of wave-particle complementarity through the peculiar quantum delayed-choice measurements. In the second experiment, we demonstrate a new method to generate arbitrary Fock-state superpositions in a superconducting circuit. As examples, we generate high-fidelity phase eigenstates under various Hilbert-space dimensions and squeezed states, which are useful for quantum walk and high-precision measurements.