Periodic Reporting for period 2 - FLATS (Flat Bands for Quantum Metrology)
Reporting period: 2024-04-01 to 2025-09-30
The fundamental limit of measurement accuracy is dictated by quantum mechanics, offering potential beyond classical approaches in metrology and sensing.
However, practical implementation of quantum standards and sensors faces challenges due to inherent incompatibilities in operating conditions,
such as magnetic fields and superconductivity, which restricts their accessibility and hinders the advancement of accurate quantum technologies.
In FLATS, we envision leveraging twisted bilayer graphene as a versatile platform to pioneer electrical quantum metrology standards operating under compatible conditions,
thus unlocking new possibilities for metrological sensors that transcend the limitations of the International System of Units (SI).
By uniting these endeavors on a common platform, we aim to create a unified, on-chip quantum laboratory capable of supporting multiple applications.
Our strategy involves establishing a European twistronics platform to achieve unprecedented control over the relative angular alignment of graphene and hexagonal boron nitride (hBN) layers.
Through this platform, we will develop innovative quantum electrical standards using twisted heterostructures,
laying the foundation for a novel on-chip metrological quantum laboratory.
This initiative marks a pivotal step toward implementing quantum-enhanced measurements for transformative metrological applications.
However, practical implementation of quantum standards and sensors faces challenges due to inherent incompatibilities in operating conditions,
such as magnetic fields and superconductivity, which restricts their accessibility and hinders the advancement of accurate quantum technologies.
In FLATS, we envision leveraging twisted bilayer graphene as a versatile platform to pioneer electrical quantum metrology standards operating under compatible conditions,
thus unlocking new possibilities for metrological sensors that transcend the limitations of the International System of Units (SI).
By uniting these endeavors on a common platform, we aim to create a unified, on-chip quantum laboratory capable of supporting multiple applications.
Our strategy involves establishing a European twistronics platform to achieve unprecedented control over the relative angular alignment of graphene and hexagonal boron nitride (hBN) layers.
Through this platform, we will develop innovative quantum electrical standards using twisted heterostructures,
laying the foundation for a novel on-chip metrological quantum laboratory.
This initiative marks a pivotal step toward implementing quantum-enhanced measurements for transformative metrological applications.
During the initial phase of FLATS, the consortium has achieved substantial progress toward establishing twistronics as a foundation for next-generation quantum metrology. A major milestone has been the deployment of the open twistronics platform, which now serves as a shared resource for fabrication protocols, simulation tools, and collaborative development across the consortium. Numerical simulations are converging toward the optimal twist angles for magic-angle bilayer graphene, guiding experimental design and advancing our understanding of correlated flat-band regimes. Experimentally, twisted bilayer graphene has proven to be a versatile platform: we have demonstrated proximity-induced superconductivity across dispersive and flat-band regimes, revealing that superconducting correlations persist even as the bandwidth narrows and that the critical current departs from normal-state scaling in the flat-band limit. These signatures point to interaction-driven contributions to the supercurrent and highlight the increasing influence of quantum geometry and multiband pairing. Building on this foundation, Josephson junctions and single-photon detectors have been successfully realized in MATBG, enabling further exploration of symmetry-broken effects such as the Josephson diode behavior and preparing the ground for future device arrays to be delivered to LNE. Parallel efforts on quantum electronic interferometry have led to significant improvements of the graphite Mach–Zehnder interferometer, which now exhibits tunable coherence well-suited for upcoming QAHE-based experiments. In addition, key metrological protocols—including Hong–Ou–Mandel interference and single-electron tomography—have been demonstrated within the Quantum Hall regime, establishing a solid basis for future operation at zero magnetic field once QAHE is achieved. MATBG-based single-photon detection has reached impressive sensitivities, and development of the THz detection platform continues to progress, despite an anticipated delay of approximately one year for this particularly ambitious milestone. Altogether, the consortium’s accomplishments illustrate rapid scientific momentum and a clear trajectory toward the ambitious goals of FLATS, reinforcing the central role of twistronics in advancing quantum materials and metrological technologies.
Exceptional coherence demonstrated in our Quantum Hall experiments establishes our platform as a powerful tool for quantum information processing. We achieved full quantum state tomography of a 2e Leviton by colliding it with a weak fermionic field and reconstructing its Wigner distribution from shot-noise measurements. This accomplishment represents one of the most advanced demonstrations of electron-optics-based quantum state reconstruction and will serve as the basis for extending the protocol to the Quantum Anomalous Hall regime. In parallel, we significantly improved the graphite Mach–Zehnder interferometer, enabling independent control of multiple edge channels, an essential capability for QAHE systems with higher Chern numbers. Experiments performed in the (νN = 2, νP = –2) configuration revealed the evolution of dual interference patterns and provided direct insights into how coherence and visibility respond to gate-controlled interferometer size. Beyond electron interferometry, we fabricated ultra-clean Josephson junctions in twisted bilayer graphene and systematically explored proximity-induced superconductivity from the dispersive to the flat-band limit. These measurements revealed that superconducting correlations remain unexpectedly robust even in the narrowest bands, with critical currents showing dome-shaped filling dependence and clear signatures of strong correlations and quantum geometry. Moving toward quantum sensing applications, we demonstrated that MATBG absorbs single infrared photons with enough efficiency to fully suppress superconductivity in micrometer-scale devices. Finally, by operating these junctions near their critical current, we achieved single-photon detection with Poissonian statistics, establishing MATBG as a promising platform for next-generation quantum sensors and photonic applications.