Direct measurement and fit of the energy spectrum of a quantum dot artificial molecule

We use delta axis spectroscopy (DAXS) to measure and fit the energy spectrum and tunnel couplings of a double quantum dot artificial molecule in a Tunnel Falls qubit device [1,2]. Double dots are critical components of quantum dot processors, and their energy spectrum and tunnel couplings are critical parameters for operating qubits. DAXS extends pulsed-gate spectroscopy, utilizing access to reservoirs on both sides of a double dot to measure the energy states of the system as a function of detuning. From a DAXS measurement, the energy level splittings and tunnel coupling values are determined by simultaneously fitting the eigenstates of the relevant Hamiltonian to the measured resonances. As a result, DAXS also allows for a more accurate determination of the ground state tunnel coupling than conventional approaches. We report the dependence of the various ground and excited state tunnel couplings on the center barrier gate voltage, and we also demonstrate how the energy states of the dots can be differentiated from resonances in the adjacent electron reservoirs.

 

[1] Samuel Neyens et al. Probing Single Electrons across 300-mm Spin Qubit Wafers, Nature 629, 80-85 (2024).

[2] H. C. George et al., 12-Spin-Qubit Arrays Fabricated on a 300 mm Semiconductor Manufacturing Line, Nano Lett. 25, 793 (2025).