  Engineering multiphoton resources is of importance in quantum metrology,
quantum lithography, and biological sensing. Here we propose a concept of
dynamical emission of $N$ strongly-correlated photons. This is realized in a
circuit quantum electrodynamical system driven by two Gaussian-pulse sequences.
The underlying physical mechanism relies on the stimulated Raman adiabatic
passage that allows efficient and selective preparation of target multiphoton
states. Assisted by the photon decay, a highly pure $N$-photon bundle emission
takes place in this system. In particular, the dynamical $N$-photon bundle
emission can be tuned by controlling the time interval between consecutive
pulses so that the device behaves as an $N$-photon gun, which can be triggered
on demand. Our work opens up a route to achieve multiphoton source devices,
which have wide potential applications in quantum information processing and
quantum metrology.
