Delta axis spectroscopy: a method to measure excited state tunnel couplings

We propose and experimentally implement a new method to measure excited state tunnel couplings in quantum dot qubits: delta axis spectroscopy. In this method, pulsed gate voltages shift the energy levels of a double quantum dot perpendicular to the detuning axis on the stability diagram. This method can therefore be viewed as similar to DAPS [1], except that the gate voltage pulses move the double quantum dot chemical potentials in the same direction rather than in opposite directions. Delta axis spectroscopy enables the measurement of the double quantum dot energy spectrum as a function of detuning, using only low frequency (baseband) pulsed gate voltages. By fitting this spectrum, we extract not only energy splittings but also ground and excited state tunnel couplings. We demonstrate this method on a 3-qubit Tunnel Falls device [2].



[1] Edward H. Chen et al. Detuning Axis Pulsed Spectroscopy of Valley-Orbital States in Si/Si-Ge Quantum Dots, Phys. Rev. Applied 15 044033 (2021)

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