Learning Inhomogeneous Heisenberg Hamiltonians in Nanographene Spin Chains
Authors:
Greta Lupi,
Saketh Ravuri,
Chenxiao Zhao,
Weidan Zhang,
Cesare Roncaglia,
Renxiang Liu,
Xinliang Feng,
Daniele Passerone,
Pascal Ruffieux,
Roman Fasel,
Jose L. Lado,
Gonçalo Catarina
Abstract:
Inferring microscopic Hamiltonians from experimental data is a central challenge in quantum materials and quantum simulation. In low-dimensional spin systems, exchange interactions are often assumed to be spatially uniform, despite structural and environmental inhomogeneities that can locally modify the coupling. Here, we leverage a local, length-independent machine learning methodology to reconst…
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Inferring microscopic Hamiltonians from experimental data is a central challenge in quantum materials and quantum simulation. In low-dimensional spin systems, exchange interactions are often assumed to be spatially uniform, despite structural and environmental inhomogeneities that can locally modify the coupling. Here, we leverage a local, length-independent machine learning methodology to reconstruct spatially modulated exchange interactions directly from inelastic scanning tunneling spectroscopy maps. We demonstrate this approach with nanographene spin chains, identifying both near-uniform and inhomogeneous regimes across the synthesized magnets. The reconstructed models quantitatively reproduce the experimental spectra and recover the correct scaling of the excitation gap with system size. Our results establish a general strategy to bridge local spectroscopic measurements with effective many-body Hamiltonians.
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Submitted 28 June, 2026;
originally announced June 2026.
Radio-frequency charge detection on graphene electron-hole double quantum dots
Authors:
Katrin Hecker,
Samuel Möller,
Hubert Dulisch,
Şiyar Duman,
Leon Stecher,
Lucca Valerius,
Tobias Deußen,
Saketh Ravuri,
Kenji Watanabe,
Takashi Taniguchi,
Florian Libisch,
Christian Volk,
Christoph Stampfer
Abstract:
High-fidelity detection of charge transitions in quantum dots (QDs) is a key ingredient in solid state quantum computation. We demonstrate high-bandwidth radio-frequency charge detection in bilayer graphene quantum dots (QDs) using a capacitively coupled quantum point contact (QPC). The device design suppresses screening effects and enables sensitive QPC-based charge readout. The QPC is arranged t…
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High-fidelity detection of charge transitions in quantum dots (QDs) is a key ingredient in solid state quantum computation. We demonstrate high-bandwidth radio-frequency charge detection in bilayer graphene quantum dots (QDs) using a capacitively coupled quantum point contact (QPC). The device design suppresses screening effects and enables sensitive QPC-based charge readout. The QPC is arranged to maximize the readout contrast between two neighboring, coupled electron and hole QDs. We apply the readout scheme to a single-particle electron-hole double QD and demonstrate time-resolved detection of charge states as well as magnetic field dependent tunneling rates. This promises a high-fidelity readout scheme for individual spin and valley states, which is important for the operation of spin, valley or spin-valley qubits in bilayer graphene.
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Submitted 1 December, 2025; v1 submitted 15 September, 2025;
originally announced September 2025.