Probing charge noise in bilayer graphene quantum dots by Landau-Zener-St\"uckelberg-Majorana spectroscopy

TL;DR

This study uses LZSM spectroscopy to measure high-frequency charge noise in bilayer graphene quantum dots, revealing noise levels comparable to other semiconductor platforms and identifying thermal and phonon effects as dominant noise sources.

Contribution

It is the first to quantify high-frequency charge noise in BLG quantum dots and identify its main sources using LZSM interference spectroscopy.

Findings

Charge noise spectral density is 0.5-0.9 neV/√Hz.

Charge noise levels are comparable to III-V and silicon platforms.

Thermal and phonon effects dominate over two-level fluctuators.

Abstract

Charge noise is an important factor limiting qubit coherence and relaxation in solid-state devices. In bilayer graphene (BLG) quantum dots, recently established as a promising platform for spin- and valley-based qubits, both the origin and magnitude of charge noise remain largely unexplored. Here, we investigate high-frequency charge noise using Landau-Zener-St\"uckelberg-Majorana (LZSM) interference spectroscopy. We study a single-particle charge qubit formed in a BLG double quantum dot at frequencies between 5 and 10 GHz and extract a noise spectral density $S_\varepsilon$ on the order of 0.5-0.9 neV$/\sqrt{\mathrm{Hz}}$. This is comparable to values reported for III-V semiconductor platforms and silicon. From the temperature and frequency dependence of the charge qubit decoherence, we conclude that thermal (Johnson) noise or electron-phonon coupling dominates over two-level fluctuators.