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The pairing of electrons is ubiquitous in electronic systems featuring attractive inter-electron interactions, as exemplified in superconductors. Counterintuitively, it can also be mediated in certain circumstances by the repulsive Coulomb interaction alone. Quantum Hall (QH) Fabry-Pérot interferometers (FPIs) tailored in a two-dimensional electron gas under a perpendicular magnetic field have been argued to exhibit such an unusual electron pairing, seemingly without attractive interactions. Here, we show evidence in graphene QH FPIs, revealing not only a similar electron pairing at bulk filling factor ν B  = 2, but also an unforeseen emergence of electron tripling characterized by a fractional Aharonov-Bohm flux period of h/3e (h is the Planck constant and e the electron charge) at ν B  = 3. Leveraging plunger-gate spectroscopy, we demonstrate that electron pairing (tripling) involves correlated charge transport on two (three) entangled QH edge channels. This spectroscopy indicates a quantum interference flux periodicity determined by the sum of the phases acquired by the distinct QH edge channels having slightly different interfering areas. Phase jumps observed in the pajama maps can be accounted for by the frequency beating between pairing/tripling modes and the outer interfering edge., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Hybridizing superconductivity with the quantum Hall (QH) effect has notable potential for designing circuits capable of inducing and manipulating non-Abelian states for topological quantum computation 1-3 . However, despite recent experimental progress towards this hybridization 4-15 , concrete evidence for a chiral QH Josephson junction 16 -the elemental building block for coherent superconducting QH circuits-is still lacking. Its expected signature is an unusual chiral supercurrent flowing in QH edge channels, which oscillates with a specific 2ϕ 0 magnetic flux periodicity 16-19 (ϕ 0  = h/2e is the superconducting flux quantum, where h is the Planck constant and e is the electron charge). Here we show that ultra-narrow Josephson junctions defined in encapsulated graphene nanoribbons exhibit a chiral supercurrent, visible up to 8 T and carried by the spin-degenerate edge channel of the QH plateau of resistance h/2e 2  ≈ 12.9 kΩ. We observe reproducible 2ϕ 0 -periodic oscillations of the supercurrent, which emerge at a constant filling factor when the area of the loop formed by the QH edge channel is constant, within a magnetic-length correction that we resolve in the data. Furthermore, by varying the junction geometry, we show that reducing the superconductor/normal interface length is crucial in obtaining a measurable supercurrent on QH plateaus, in agreement with theories predicting dephasing along the superconducting interface 19-22 . Our findings are important for the exploration of correlated and fractional QH-based superconducting devices that host non-Abelian Majorana and parafermion zero modes 23-32 ., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)