Figure 4. Exploring the energy level structure for the coupled defect system.

(a) Level scheme of the resonantly coupled defect system for an applied strain near the right avoided level crossing of Fig. 3 at V_p≈7 V. Energy splitting and offset of the entangled states are determined by transversal and longitudinal coupling strengths and , respectively. (b) Pulse sequence used to map out the complete energy level structure. For the upper panel in c, the qubit was measured after the first swap operation at varying frequencies in order to calibrate the entangled states energies. The lower panel was obtained using the complete sequence: preparation of one of the entangled states or in a first swap, followed by a second qubit excitation and variation of the second swap frequency to reveal the transitions between the entangled states to the fully excited state . The colour maps were chosen according to the coloured arrows that indicate the corresponding transitions in a. Lines in c are calculated from theory.