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Microwave Spectroscopy of Few-Carrier States in Bilayer Graphene Quantum Dots

Max J. Ruckriegel1, Christoph Adam1, Rebecca Bolt1, Chuyao Tong1, David Kealhofer1, Artem O. Denisov1, Mohsen Bahrami Panah1,2, Kenji Watanabe3, Takashi Taniguchi4 et al.

Thomas Ihn1,2 and Klaus Ensslin1,2

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PRX Quantum 7, 033037 – Published 24 August, 2026

DOI: https://doi.org/10.1103/j1ts-9nys

Abstract

Bilayer graphene is a maturing material platform for gate-defined quantum dots that hosts long-lived spin and valley states. Implementing solid-state qubits in bilayer graphene requires a fundamental understanding of such confined electronic systems. In particular, states of two and three carriers, for which the exchange interaction between particles plays a crucial role, are a cornerstone for qubit readout and manipulation. Here we report on the spectroscopy of few-carrier states in bilayer graphene quantum dots, using circuit quantum electrodynamics (cQED) techniques that offer substantially improved energy resolution compared to standard transport techniques. Measurements of a superconducting high-impedance resonator capacitively coupled to the double quantum dot reveal dispersive features of two- and three-electron states, enabling the detection of Pauli spin and valley blockade and the characterization of the spin-orbit gap at zero magnetic field. The results deepen our understanding of few-carrier spin and valley states in bilayer graphene quantum dots and demonstrate that cQED techniques are a powerful state-selective probe for semiconductor nanostructures.

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Popular Summary

Confined electrons in two-dimensional crystals, specifically in bilayer graphene, can host robust quantum states, making them a promising platform for solid-state qubits. However, conventional measurement techniques have so far limited the characterization of these intricate quantum states. To better understand few-carrier states in graphene, we have developed a measurement scheme that provides high energy resolution of electronics states at zero or low magnetic field. We achieve the improvements by coupling confined charges in bilayer graphene to a superconducting microwave circuit that detects the electrons’ energy states with greater precision than other methods. The new approach works even at zero magnetic field, where subtle energy differences were previously blurred, giving scientists a much clearer picture of how electrons interact in this environment. The technique points toward faster, more reliable ways to read information from future graphene qubits and offers a versatile tool for exploring quantum materials at their smallest scales.

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PRX Quantum 7, 033037– Published 24 August, 2026
  • Received 25 November 2025
  • Accepted 21 May 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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