Figure 2: Mapping spontaneous decay.

(a) The experimental sequence prepares the emitter in an initial state, then homodyne detection is used to record the emitted radiation. Following a variable period of time, further rotations are applied to the emitter before state readout to perform quantum state tomography. To enhance the readout contrast, a pulse is applied to transfer the excited state population to a higher state of the system. (b) The level structure of the system and frequencies of the three microwave drives. The emitter is given by the lowest two energy levels. (c) We average the state tomography to determine , and conditioned on the outcome of the homodyne measurement. These correlated tomography results are displayed on the X–Z plane of the Bloch sphere for three different initial states: −z (d) +x (e) and + y (f). The colour scale indicates the relative occurrence of each measurement value. Note the different back-action dynamics between e and f, a result of phase-sensitive amplification.