Direct measurement of the energy spectrum of a quantum dot qubit

TL;DR

This paper introduces delta-axis spectroscopy (DAXS), a new technique for directly measuring the energy spectrum of a quantum dot qubit across a wide range, improving understanding of the full Hamiltonian.

Contribution

The authors develop and demonstrate a Hamiltonian-agnostic method, DAXS, for comprehensive energy spectrum measurement of double quantum dots, surpassing existing techniques.

Findings

Successfully measured the energy spectrum of a Si/SiGe double quantum dot.

Extracted diagonal and off-diagonal couplings of a 15-level Hamiltonian.

Achieved good agreement between measured spectrum and theoretical model.

Abstract

The mapping between gate voltages applied to a double quantum dot, and the parameters of a Hubbard-like Hamiltonian, is of utmost importance for understanding and operating spin qubits. State-of-the-art techniques for measuring Hamiltonian parameters (e.g., detuning axis pulsed spectroscopy, DAPS) provide details about energy levels; however, tunnel coupling estimates typically reveal only a small portion of the full Hamiltonian. Here, we demonstrate a Hamiltonian-agnostic technique for measuring the double dot energy spectrum over a wide energy range, at every value of the detuning, called delta-axis spectroscopy (DAXS). We apply the DAXS method to obtain the energy spectrum of a Si/SiGe double quantum dot and use this data to extract the diagonal and off-diagonal couplings of a 15-level Hubbard-like Hamiltonian, demonstrating very good agreement with the experimental measurements.