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arXiv:2609.03650

Low-Frequency Charge Noise in Bilayer Graphene Quantum Dots

Jessica Richter, Max J. Ruckriegel, Jonas D. Gerber, Tijl Degroote, Christoph Adam, Markus Niese, Lara Ostertag, Clara Galante, Kenji Watanabe, Takashi Taniguchi, Petar Tomic, Artem O. Denisov, Hadrien Duprez, Klaus Ensslin, Thomas Ihn

cond-mat.mes-hallquant-phSubmitted Sep 3, 2026• Announced Sep 4, 2026
arXivHTMLPDF

Abstract

Bilayer graphene (BLG) quantum dots (QDs) are a promising platform for semiconductor qubits. However, the low-frequency charge noise that may ultimately limit coherence has remained largely unexplored. Here, we systematically characterize charge noise in gate-defined BLG QDs using transport-based noise spectroscopy. We extract a median amplitude of $ S_μ^{1/2} (1~\text{Hz}) = 1.16~μ\text{eV}/\sqrt{\text{Hz}}$, placing BLG well within the range reported for established semiconductor quantum-dot platforms. Across variations in charge occupation, confinement, source-drain bias, and charge-sensor operating conditions, neither the noise amplitude nor the spectral dependence shows a reproducible trend in electrostatic tuning, indicating that we extracted the intrinsic semiconductor noise. Consistent noise levels are further observed in double QDs and confirmed using an independent superconducting resonator-based dispersive readout. Extending the study to BLG devices incorporating transition metal dichalcogenide layers reveals no measurable charge noise increase in weakly proximitized QDs. These results validate BLG as a viable platform for coherent quantum information processing.

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Semiconductor quantum dots in which electrons or holes are isolated via electrostatic potentials generated by surface gates are promising building blocks for semiconductor-based quantum technology.Here, we investigate double-quantum-dot (DQD) charge qubits in GaAs capacitively coupled to highimpedance superconducting quantum interference device array and Josephson-junction array resonators.We tune the strength of the electric-dipole interaction between the qubit and the resonator in situ using surface gates.We characterize the qubit-resonator coupling strength, the qubit decoherence, and the detuning noise affecting the charge qubit for different electrostatic DQD configurations.We find all quantities to be systematically tunable over more than one order of magnitude, resulting in reproducible decoherence rates Γ 2 =2π < 5 MHz in the limit of high interdot capacitance.In the opposite limit, by reducing the interdot capacitance, we increase the DQD electric-dipole strength and, therefore, its coupling to the resonator.Employing a Josephson-junction array resonator with an impedance of approximately 4 kΩ and a resonance frequency of ω r =2π ∼ 5.6 GHz, we observe a coupling strength of g=2π ∼ 630 MHz, demonstrating the possibility to operate electrons hosted in a semiconductor DQD in the ultrastrong-coupling regime (USC).The presented results are essential for further increasing the coherence of quantum-dot-based qubits and investigating USC physics in semiconducting QDs.

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Bilayer graphene (BLG) quantum dots (QDs) are a promising platform for semiconductor qubits. However, the low-frequency charge noise that may ultimately limit coherence has remained largely unexplored. Here, we systematically characterize charge noise in gate-defined BLG QDs using transport-based noise spectroscopy. We extract a median amplitude of Sμ1/2(1 Hz)=1.16 μeV/Hz S_μ^{1/2} (1~\text{Hz}) = 1.16~μ\text{eV}/\sqrt{\text{Hz}}Sμ1/2​(1 Hz)=1.16 μeV/Hz​, placing BLG well within the range reported for established semiconductor quantum-dot platforms. Across variations in charge occupation, confinement, source-drain bias, and charge-sensor operating conditions, neither the noise amplitude nor the spectral dependence shows a reproducible trend in electrostatic tuning, indicating that we extracted the intrinsic semiconductor noise. Consistent noise levels are further observed in double QDs and confirmed using an independent superconducting resonator-based dispersive readout. Extending the study to BLG devices incorporating transition metal dichalcogenide layers reveals no measurable charge noise increase in weakly proximitized QDs. These results validate BLG as a viable platform for coherent quantum information processing.
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-Stückelberg-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 SεS_\varepsilonSε​ on the order of 0.5-0.9 neV/Hz/\sqrt{\mathrm{Hz}}/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.
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 using 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.
We evaluate the charge noise acting on a GaAs/GaAlAs based semiconductor double quantum dot dipole-coupled to the voltage oscillations of a superconducting transmission line resonator. The in-phase (I) and the quadrature (Q) components of the microwave tone transmitted through the resonator are sensitive to charging events in the surrounding environment of the double dot with an optimum sensitivity of 8.5×10−5 e/Hz. A low frequency 1/f type noise spectrum combined with a white noise level of 6.6×10−6 e2/Hz above 1 Hz is extracted, consistent with previous results obtained with quantum point contact charge detectors on similar heterostructures. The slope of the 1/f noise allows to extract a lower bound for the double-dot charge qubit dephasing rate which we compare to the one extracted from a Jaynes-Cummings Hamiltonian approach. The two rates are found to be similar emphasizing that charge noise is the main source of dephasing in our system.
Discrete charge fluctuations, routinely observed in semiconductor quantum dot devices, may contribute significantly to device drift and errors resulting from qubit miscalibration. Understanding the nature and origins of these discrete charge fluctuations may provide insights into material improvements or means of mitigating charge noise in semiconductor quantum dot devices. In this work, we measure multi-level charge fluctuations present in a Si/SiGe double quantum dot device over a range of device operating voltages and temperatures. To characterize the parameter-dependent dynamics of the underlying fluctuating degrees of freedom, we perform a detailed analysis of the measured noise timeseries. We perform algorithmically assisted drift detection and change point detection to detrend the data and remove a slow fluctuator component, as a preprocessing step. We perform model comparison on the post-processed time series between different nnn-level fluctuator (nnnLF) factorial hidden Markov models (FHMMs), finding that although at most sweep values the independent pair of 2LFs model would be preferred, in a particular region of voltage space the 4LF model outperforms the other models, indicating a conditional rate dependence between the two fluctuators. By tracking fluctuator transition rates, biases, and weights over a range of different device configurations, we estimate gate voltage and conductivity sensitivity. In particular, we fit a phenomenological, detailed balance model to the extracted independent 2LFs rate data, yielding lever arm estimates in the range of −2μ-2 μ−2μeV/mV up to 4μ4 μ4μeV/mV between the two 2LFs and nearby gate electrodes. We expect that these characterization results may aid in subsequent spatial triangulation of the charge fluctuators.
High Resolution Image Download MS PowerPoint Slide We implement circuit quantum electrodynamics (cQED) with quantum dots in bilayer graphene, a maturing material platform that can host long-lived spin and valley states. Our device combines a high-impedance ( Z r ≈ 1 kΩ) superconducting microwave resonator with a double quantum dot electrostatically defined in a graphene-based van der Waals heterostructure. Electric dipole coupling between the subsystems allows the resonator to sense the electric susceptibility of the double quantum dot from which we reconstruct its charge stability diagram. We achieve sensitive and fast detection of the interdot transition with a signal-to-noise ratio of 3.5 within 1 μs integration time. The charge–photon interaction is quantified in the dispersive and resonant regimes by comparing the resonator response to input–output theory, yielding a coupling strength of g /2π = 49.7 MHz. Our results introduce cQED as a probe for quantum dots in van der Waals materials and indicate a path toward coherent charge–photon coupling with bilayer graphene quantum dots.
Semiconductor quantum dots in which electrons or holes are isolated via electrostatic potentials generated by surface gates are promising building blocks for semiconductor-based quantum technology.Here, we investigate double-quantum-dot (DQD) charge qubits in GaAs capacitively coupled to highimpedance superconducting quantum interference device array and Josephson-junction array resonators.We tune the strength of the electric-dipole interaction between the qubit and the resonator in situ using surface gates.We characterize the qubit-resonator coupling strength, the qubit decoherence, and the detuning noise affecting the charge qubit for different electrostatic DQD configurations.We find all quantities to be systematically tunable over more than one order of magnitude, resulting in reproducible decoherence rates Γ 2 =2π < 5 MHz in the limit of high interdot capacitance.In the opposite limit, by reducing the interdot capacitance, we increase the DQD electric-dipole strength and, therefore, its coupling to the resonator.Employing a Josephson-junction array resonator with an impedance of approximately 4 kΩ and a resonance frequency of ω r =2π ∼ 5.6 GHz, we observe a coupling strength of g=2π ∼ 630 MHz, demonstrating the possibility to operate electrons hosted in a semiconductor DQD in the ultrastrong-coupling regime (USC).The presented results are essential for further increasing the coherence of quantum-dot-based qubits and investigating USC physics in semiconducting QDs.