Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2610.38476

Coherent Electronic Lensing in Proximitized Graphene

Ivan Villani, Samuele Fracassi, Niccolò Traverso Ziani, Maura Sassetti, Matteo Carrega, Vaidotas Mišeikis, Camilla Coletti, Fabio Beltram, Kenji Watanabe, Takashi Taniguchi, Sergio Pezzini, Stefan Heun

cond-mat.mes-hallcond-mat.supr-conquant-phSubmitted Oct 28, 2026• Announced Oct 29, 2026
arXivHTMLPDF

Abstract

Spatially resolved control of coherent electron transport offers a route to understanding and engineering interference phenomena in hybrid superconducting devices. Here, we use Scanning Gate Microscopy (SGM) to investigate Fabry-Pérot (FP) interference in the n-p-n cavity of a ballistic graphene Josephson junction. Spatial maps of the superconducting switching current and normal-state conductance reveal circular interference fringes arising from two distinct effects of the SGM tip potential. A global shift of the Fermi wave vector modulates the FP resonances of the cavity, while a local perturbation produces additional oscillations that persist at fixed Fermi wave vector as the tip bias is varied. An analytical model identifies the origin of this local response with coherent electron lensing, in which the tip modifies the phase accumulated along interfering trajectories. The measured fringe patterns in the switching current indicate that this mechanism affects superconducting transport, consistent with tip-induced shifts of the resonance conditions for Andreev bound states. These results establish SGM as a tunable local lens for controlling interference in superconducting ballistic graphene devices.

AI Summary

The paper asks how a local electrostatic perturbation modifies Fabry–Pérot (FP) interference and superconducting transport in a ballistic graphene Josephson junction. Scanning gate microscopy is performed at $300$ mK on an hBN-encapsulated graphene device with Nb contacts, length $600$ nm and width $3\,\mu$m. Contact-induced electron doping creates an n–p–n cavity when the channel is hole-doped; a biased tip scans $100$ nm above the graphene. Spatial maps show intersecting circular fringes in both switching current and dissipative conductance, with aligned maxima and minima. One representative fringe changes the switching current from $193$ to $225$ nA. Combined back-gate and tip-bias sweeps distinguish a global effective doping shift from additional oscillations that persist at fixed effective Fermi wave vector. Fourier analysis gives a cavity length of $460\pm25$ nm, with little variation across a $20$ V tip-bias range, arguing against cavity-length changes as their origin. A semiclassical scattering model attributes the residual response to an impact-parameter-dependent phase shift from the local tip potential, termed coherent lensing. It reproduces selected conductance traces; normal-state tight-binding simulations also reproduce spatial fringe patterns. Correlated switching-current fringes are interpreted as evidence that the perturbation shifts Andreev-bound-state resonance conditions. The analytical treatment assumes smooth potentials, near-normal transmission and a perturbative local tip contribution. Conductance extracted from low-voltage dissipative branches is explicitly only a proxy for normal-state conductance because of excess current. The superconducting interpretation rests on transport correlations rather than direct Andreev-level measurements.

Little sign of AI-generated textIncrementalOverclaims

Error found: The analytical tip-potential decomposition defines its global component as the spatial average but uses a non-zero-average Lorentzian residual, leaving the claimed global/local phase separation internally inconsistent. The analytical line-cut fits reach a nominal perturbation-to-Fermi-energy ratio of one despite relying on a weak-perturbation derivation, without directly validating those line cuts beyond that approximation. The analytical fit uses a 530 nm cavity length, inconsistent with the reported Fourier estimates of 460 ± 25 nm and 427 ± 30 nm, without explaining why the same parameter can still set the unperturbed Fabry–Pérot phase.

Written by gpt-6.1-sol from the paper's full text. Automated: it can be wrong.

Related papers

High-field Josephson effect enabled by a moiré Hofstadter spectrum

A. Díez-Carlón, M. Cárdenes Wuttig, N. Wei +7 more

Magnetic fields generally suppress phase-coherent Josephson transport, limiting superconducting interferometry to relatively low fields. Here we show that moiré-engineered graphene Josephson junctions can overcome this constraint. Using ballistic graphene/hBN junctions, we establish phase-coherent Andreev transport through Fabry-Pérot oscillations and Fraunhofer interference that persist across both the primary Dirac cone and reconstructed moiré minibands. We then demonstrate phase-coherent Josephson interference up to 6 T in the fractal Hofstadter-butterfly regime, well beyond the range expected for conventional ballistic graphene junctions. Comparison with Hofstadter-spectrum calculations reveals that superconductivity survives where the moiré potential transforms Landau levels with quenched group velocity into dispersive magnetic Bloch bands with finite quasiparticle group velocity, enabling extended electron-hole Andreev trajectories across the junction. Our results show that Hofstadter minibands can stabilize phase-coherent superconductivity deep into the parameter domain conventionally associated with the quantum Hall regime, establishing a new platform for high-field superconducting interferometry.

cond-mat.mes-hallCross-listedarXiv:2607.11721•Jul 14, 2026

Superconducting quantum interference devices with graphene junctions.

Michael D. Thompson, Jonathan R. Prance, R. P. Haley +7 more

We present measurements of DC superconducting quantum interference devices based on Nb/graphene/Nb Josephson junctions. The superconducting proximity effect in graphene can be used to build Josephson junctions whose critical current can be controlled by field-effect gates. These junctions combine the tunability of semiconductor Josephson junctions with the high critical currents and low contact resistances of metal SNS junctions. By using local gates, the SQUID junction critical currents can be modified individually and this allows the sensitivity and symmetry of the SQUID to be controlled in-situ. We compare the critical current of the SQUID with simulations that include a non-sinusoidal current phase relation in the junctions, as expected for ballistic graphene junctions. We also investigate the transfer function of the device in both symmetric and asymmetric configurations and find a highest transfer function of 300 μV/Φ0. Graphene Josephson junctions have the potential to add functionality to existing technologies; for example, to make SQUID magnetometers with tunable sensitivity or superconducting qubits with fast electrical control.

Bulletin of the American Physical Society•Mar 17, 2017•0 citations

Phase-dependent microwave response of a graphene Josephson junction

R. Haller, Gergő Fülöp, David I. Indolese +10 more

Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing a radio frequency SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss, and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we estimate lifetimes on the order of $\ensuremath{\sim}10$ ps for nonequilibrium populations.

arXiv:2108.00989•Physical Review Research•Mar 14, 2022•29 citations

The Superconducting Talbot Effect in Phased-Array Josephson Junctions

Hechen Ren, Ziying Li

We introduce the superconducting Talbot effect---a macroscopic quantum self-imaging phenomenon occurring when proximitized Cooper pairs propagate through a ballistic two-dimensional electron gas. By configuring periodic superconducting leads into a phased-array Josephson junction with programmable phase differences, we demonstrate active steering of the resulting superconducting Talbot carpet. To overcome transport resolution limits, we design a Vernier-scale collector array that performs sub-wavelength sampling of the fractional Talbot pattern. This approach maps real-space quantum interference with high robustness to disorder, enabling direct extraction of Fermi wavelengths across helical, spin-degenerate, and spin-orbit-split Fermi surfaces. Tight-binding numerical calculations on a square lattice validate the real-space interference patterns. Our results establish a versatile framework for coherent wavefront engineering and quantum materials diagnostics in superconducting optics.

cond-mat.mes-hallCross-listedarXiv:2609.24572•Sep 22, 2026

A ballistic graphene superconducting microwave circuit

Felix E. Schmidt, Mark D. Jenkins, Kenji Watanabe +2 more

Josephson junctions (JJ) are a fundamental component of microwave quantum circuits, such as tunable cavities, qubits, and parametric amplifiers. Recently developed encapsulated graphene JJs, with supercurrents extending over micron distance scales, have exciting potential applications as a new building block for quantum circuits. Despite this, the microwave performance of this technology has not been explored. Here, we demonstrate a microwave circuit based on a ballistic graphene JJ embedded in a superconducting cavity. We directly observe a gate-tunable Josephson inductance through the resonance frequency of the device and, using a detailed RF model, we extract this inductance quantitatively. We also observe the microwave losses of the device, and translate this into sub-gap resistances of the junction at μeV energy scales, not accessible in DC measurements. The microwave performance we observe here suggests that graphene Josephson junctions are a feasible platform for implementing coherent quantum circuits.

arXiv:1806.11389•Nature Communications•Sep 28, 2018•66 citations

Gate-Tunable Spectrum and Charge Dispersion Mitigation in a Graphene Superconducting Qubit

Nicolás Aparicio, Simon Messelot, Edgar Bonet +5 more

Controlling the energy spectrum of quantum-coherent superconducting circuits, i.e., the energies of excited states, the circuit anharmonicity, and the states' charge dispersion, is essential for designing performant qubits. This control is usually achieved by adjusting the circuit's geometry. In situ control is traditionally obtained via an external magnetic field, in the case of tunnel Josephson junctions. More recently, semiconductor-weak-links-based Josephson junctions have emerged as an alternative building block with the advantage of tunability via the electric-field effect. Gate-tunable Josephson junctions have been succesfully integrated in superconducting circuits using, for instance, semiconducting nanowires or two-dimensional electron gases. In this Letter we demonstrate, in a graphene superconducting circuit, a large gate tunability of qubit properties: frequency, anharmonicity, and charge dispersion. We rationalize these features using a model considering the transmission of Cooper pairs through Andreev bound states. Noticeably, we show that the high transmission of Cooper pairs in such weak link strongly suppresses the charge dispersion. Our Letter illustrates the potential for graphene-based qubits as versatile building blocks in advanced quantum circuits.

arXiv:2506.04959•Physical Review Letters•Nov 20, 2025•2 citations
Spatially resolved control of coherent electron transport offers a route to understanding and engineering interference phenomena in hybrid superconducting devices. Here, we use Scanning Gate Microscopy (SGM) to investigate Fabry-Pérot (FP) interference in the n-p-n cavity of a ballistic graphene Josephson junction. Spatial maps of the superconducting switching current and normal-state conductance reveal circular interference fringes arising from two distinct effects of the SGM tip potential. A global shift of the Fermi wave vector modulates the FP resonances of the cavity, while a local perturbation produces additional oscillations that persist at fixed Fermi wave vector as the tip bias is varied. An analytical model identifies the origin of this local response with coherent electron lensing, in which the tip modifies the phase accumulated along interfering trajectories. The measured fringe patterns in the switching current indicate that this mechanism affects superconducting transport, consistent with tip-induced shifts of the resonance conditions for Andreev bound states. These results establish SGM as a tunable local lens for controlling interference in superconducting ballistic graphene devices.
The paper asks how a local electrostatic perturbation modifies Fabry–Pérot (FP) interference and superconducting transport in a ballistic graphene Josephson junction. Scanning gate microscopy is performed at 300300300 mK on an hBN-encapsulated graphene device with Nb contacts, length 600600600 nm and width 3 μ3\,\mu3μm. Contact-induced electron doping creates an n–p–n cavity when the channel is hole-doped; a biased tip scans 100100100 nm above the graphene.
Spatial maps show intersecting circular fringes in both switching current and dissipative conductance, with aligned maxima and minima. One representative fringe changes the switching current from 193193193 to 225225225 nA. Combined back-gate and tip-bias sweeps distinguish a global effective doping shift from additional oscillations that persist at fixed effective Fermi wave vector. Fourier analysis gives a cavity length of 460±25460\pm25460±25 nm, with little variation across a 202020 V tip-bias range, arguing against cavity-length changes as their origin.
A semiclassical scattering model attributes the residual response to an impact-parameter-dependent phase shift from the local tip potential, termed coherent lensing. It reproduces selected conductance traces; normal-state tight-binding simulations also reproduce spatial fringe patterns. Correlated switching-current fringes are interpreted as evidence that the perturbation shifts Andreev-bound-state resonance conditions.
The analytical treatment assumes smooth potentials, near-normal transmission and a perturbative local tip contribution. Conductance extracted from low-voltage dissipative branches is explicitly only a proxy for normal-state conductance because of excess current. The superconducting interpretation rests on transport correlations rather than direct Andreev-level measurements.
Magnetic fields generally suppress phase-coherent Josephson transport, limiting superconducting interferometry to relatively low fields. Here we show that moiré-engineered graphene Josephson junctions can overcome this constraint. Using ballistic graphene/hBN junctions, we establish phase-coherent Andreev transport through Fabry-Pérot oscillations and Fraunhofer interference that persist across both the primary Dirac cone and reconstructed moiré minibands. We then demonstrate phase-coherent Josephson interference up to 6 T in the fractal Hofstadter-butterfly regime, well beyond the range expected for conventional ballistic graphene junctions. Comparison with Hofstadter-spectrum calculations reveals that superconductivity survives where the moiré potential transforms Landau levels with quenched group velocity into dispersive magnetic Bloch bands with finite quasiparticle group velocity, enabling extended electron-hole Andreev trajectories across the junction. Our results show that Hofstadter minibands can stabilize phase-coherent superconductivity deep into the parameter domain conventionally associated with the quantum Hall regime, establishing a new platform for high-field superconducting interferometry.
We present measurements of DC superconducting quantum interference devices based on Nb/graphene/Nb Josephson junctions. The superconducting proximity effect in graphene can be used to build Josephson junctions whose critical current can be controlled by field-effect gates. These junctions combine the tunability of semiconductor Josephson junctions with the high critical currents and low contact resistances of metal SNS junctions. By using local gates, the SQUID junction critical currents can be modified individually and this allows the sensitivity and symmetry of the SQUID to be controlled in-situ. We compare the critical current of the SQUID with simulations that include a non-sinusoidal current phase relation in the junctions, as expected for ballistic graphene junctions. We also investigate the transfer function of the device in both symmetric and asymmetric configurations and find a highest transfer function of 300 μV/Φ0. Graphene Josephson junctions have the potential to add functionality to existing technologies; for example, to make SQUID magnetometers with tunable sensitivity or superconducting qubits with fast electrical control.
Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing a radio frequency SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss, and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we estimate lifetimes on the order of $\ensuremath{\sim}10$ ps for nonequilibrium populations.
We introduce the superconducting Talbot effect---a macroscopic quantum self-imaging phenomenon occurring when proximitized Cooper pairs propagate through a ballistic two-dimensional electron gas. By configuring periodic superconducting leads into a phased-array Josephson junction with programmable phase differences, we demonstrate active steering of the resulting superconducting Talbot carpet. To overcome transport resolution limits, we design a Vernier-scale collector array that performs sub-wavelength sampling of the fractional Talbot pattern. This approach maps real-space quantum interference with high robustness to disorder, enabling direct extraction of Fermi wavelengths across helical, spin-degenerate, and spin-orbit-split Fermi surfaces. Tight-binding numerical calculations on a square lattice validate the real-space interference patterns. Our results establish a versatile framework for coherent wavefront engineering and quantum materials diagnostics in superconducting optics.
Josephson junctions (JJ) are a fundamental component of microwave quantum circuits, such as tunable cavities, qubits, and parametric amplifiers. Recently developed encapsulated graphene JJs, with supercurrents extending over micron distance scales, have exciting potential applications as a new building block for quantum circuits. Despite this, the microwave performance of this technology has not been explored. Here, we demonstrate a microwave circuit based on a ballistic graphene JJ embedded in a superconducting cavity. We directly observe a gate-tunable Josephson inductance through the resonance frequency of the device and, using a detailed RF model, we extract this inductance quantitatively. We also observe the microwave losses of the device, and translate this into sub-gap resistances of the junction at μeV energy scales, not accessible in DC measurements. The microwave performance we observe here suggests that graphene Josephson junctions are a feasible platform for implementing coherent quantum circuits.
Controlling the energy spectrum of quantum-coherent superconducting circuits, i.e., the energies of excited states, the circuit anharmonicity, and the states' charge dispersion, is essential for designing performant qubits. This control is usually achieved by adjusting the circuit's geometry. In situ control is traditionally obtained via an external magnetic field, in the case of tunnel Josephson junctions. More recently, semiconductor-weak-links-based Josephson junctions have emerged as an alternative building block with the advantage of tunability via the electric-field effect. Gate-tunable Josephson junctions have been succesfully integrated in superconducting circuits using, for instance, semiconducting nanowires or two-dimensional electron gases. In this Letter we demonstrate, in a graphene superconducting circuit, a large gate tunability of qubit properties: frequency, anharmonicity, and charge dispersion. We rationalize these features using a model considering the transmission of Cooper pairs through Andreev bound states. Noticeably, we show that the high transmission of Cooper pairs in such weak link strongly suppresses the charge dispersion. Our Letter illustrates the potential for graphene-based qubits as versatile building blocks in advanced quantum circuits.