Extended Data Fig. 1: Obtaining degeneracy on demand via excited state spectroscopy.
This is a protocol for tuning the energy spectrum of a new charge configuration to create a level degeneracy, resulting in a speed-up of the qubit Rabi frequency. The protocol utilises tunnel-rate-based excited state spectroscopy (see Methods). The voltage detuning between dots, ΔVP, is swept across an interdot charge transition to observe changes in the interdot tunnel rate associated with the resonant tunneling into excited states [43]. a, Top-view schematic layout of the device gates. b, Excited state spectroscopy where Voffset is stepped. The two right-most features are designated as states A and B, representing the ground and first excited states of the P1 dot, which we observe to be converging for decreasing Voffset. The relevant gate voltages are shown in the table. In c, VJ is swept to re-adjust the interdot tunnel rate so that the excited state transition is visible at the probe frequency of 477 Hz. In d, we again try to measure movement in the excited state energy, this time at a lower Voffset. In e we sweep VJ to adjust the tunnel rate, and to get an indication of the effect on the excited state energy. We observe that the excited state energy appears to be decreasing for increasing VJ. Finally, we take a PESOS map in this configuration, and observe a speed up of the Rabi frequency at the location of the red triangle marked in e. This PESOS map is shown in main text Fig. 2b.
