  Photon emission and absorption by an individual qubit are essential elements
for the quantum manipulation of light. Here we demonstrate the controllability
of spontaneous emission of a qubit in various electromagnetic environments. The
parameter regimes that allow for exible control of the qubit emission routes
are comprehensively discussed. By properly tuning the system couplings and
decay rates, the spontaneous emission rate of the qubit can undergo Purcell
enhancement and inhibition. Particularly, when the cavity is prepared in the
excited state, the spontaneous emission rate of the qubit can be significantly
suppressed. We also demonstrate a spectral filter effect which can be realised
by controlling the steady-state emission spectra of qubits.
