Quantifying Charge Noise Sources in Quantum Dot Spin Qubits via Impedance Spectroscopy, DLTS, and C‐V Analysis

ABSTRACT The coherence and fidelity of quantum dot (QD) spin qubits are fundamentally limited by charge noise originating from electrically active trap states at oxide interfaces, heterostructure boundaries, and within the bulk semiconductor. These traps introduce electrostatic fluctuations that couple to the qubit via spin–orbit interactions or charge‐sensitive confinement potentials, leading to dephasing and gate errors. In this work, we present a general framework for identifying and quantifying the spectral signatures of these trap states using AC impedance spectroscopy, deep‐level transient spectroscopy (DLTS), and conventional capacitance‐voltage (C‐V) analysis. While demonstrated using strained Ge/SiGe quantum well heterostructures, the approach is broadly applicable to other qubit platforms. We show that oxide interface traps dominate low‐frequency conductance and Nyquist spectra, quantum well (QW) interface traps are best resolved via multi‐exponential decays in time‐domain response, and bulk traps affect high‐frequency admittance and leakage currents. By correlating each trap type to its characteristic time constant, spatial location, and frequency response, we offer a diagnostic toolset for disentangling material‐induced noise sources that limit qubit performance. This unified methodology connects traditional semiconductor defect metrology with emerging qubit noise analysis and provides actionable guidance for material and process optimization in scalable quantum information technologies.