Single anyons and anyon binding in a quantum Hall dot
Marco Valentini, Will Wang, Amir Shapour Mohammadi, Noah Samuelson, Chengxuan Li, Liam Cohen, Mark Zakharyan, Jiechao Feng
First convincing single-anyon trapping with controlled depletion to the last e/3 quasiparticle plus a provocative anyon-binding observation, backed by serious DMRG; tempered by indirect charge calibration and single-device evidence for binding.
Abstract
Anyons are particles with quantized fractional statistics. In theory, a single anyon can be stabilized as a localized fractional charge within the bulk of a topologically ordered two-dimensional insulator. However, experiments to date have focused on probing anyons in structures in which many anyonic excitations coexist and interact. Here, we demonstrate the trapping of a single anyon in a device consisting of a graphene-based quantum point contact with an embedded tunable quantum Hall dot. Benchmarking our device at v = 1, we demonstrate backscattering between Fermi liquid edge states mediated by the whole-electron Coulomb blockade of the dot. The cleanliness and control available in our device allow depletion of the dot to the last quasihole, and we observe spin blockade for transitions to the opposite-spin Landau level. At v = 1/3 and 2/3, we observe backscattering resonances with three times the frequency, consistent with resonant transmission of e/3 charges via a single anyon transistor. We demonstrate controlled depletion to the last quasiparticle to form a single anyon quantum dot. Tracing the charge addition spectrum for quasiparticle number Nqp = 1-5, we observe highly irregular addition energies, consistent with DMRG modeling showing a complex orbital shell-filling behavior. At higher Nqp = 10-20, the addition energies show a striking pattern: quasiholes at 1/3 (and quasiparticles at 2/3) show a regular addition spectrum while quasiparticles at 1/3 (and quasiholes at 2/3) do not. We trace the origin of this irregularity to an attractive component of the inter-anyon interaction: by experimentally tuning the confining energy, we observe complete suppression of alternating charge sectors, after which the dot charges in increments of twice the fundamental charge. This observation indicates the emergence of an anyon binding energy as large as the charging energy.
AI Impact Assessments
(1 model)Core Contribution
The paper reports a graphene-based quantum point contact with an embedded, gate-tunable 90 nm quantum Hall dot. This device is used to trap and count individual anyons, down to the last e/3 quasiparticle at ν=1/3 and 2/3. Three results stand out.
1. At ν=1, the device acts as a single-electron/hole dot. It shows a spin blockade for opposite-spin quasi-electrons, which is lifted by magnon-assisted tunneling at bias above the Zeeman energy. This provides an absolute charge calibration (Nqp=0). The authors also report 0.3–0.8 meV excited-state spacings and very low charge noise (~10⁻³ e/√Hz at 10 mHz).
2. At fractional filling, the Coulomb-blockade periodicity is 3× shorter, consistent with e/3 charge. The Nqp=0 point is transferred from ν=1 at B=4.5 T to ν=1/3 at 13.5 T via a quantum-capacitance calibration. The authors then study the addition spectrum from Nqp=1 to 5. It is irregular, and DMRG on the Haldane sphere, with electrostatics, RPA screening and composite-fermion (Λ-level) analysis, reproduces the irregularity.
3. At larger |Nqp| (about 10–20), the authors see a particle-hole-related asymmetry. The 1/3 quasihole and 2/3 quasiparticle spectra are regular, while 1/3 quasiparticles and 2/3 quasiholes show even-odd alternation. Tuning the confinement makes the weak charge sectors disappear, so charge enters in steps of 2e/3. The authors interpret this as an anyon binding energy that reaches or exceeds the charging energy.
Single-anyon trapping with controlled depletion to the final quasiparticle is a real milestone. Earlier work, including bilayer-graphene and GaAs dots and Fabry-Perot interferometers, probed many-anyon ensembles. Reaching the single-anyon limit and demonstrating a "single anyon transistor" is the natural first step toward anyon-based topological qubits, where precision control of individual non-Abelian anyons is needed.
Methodological Rigor
Strengths:
Weaknesses:
Potential Impact
The impact is high for the mesoscopic FQH and quantum Hall interferometry communities. It matters especially for non-Abelian anyon platforms, since the authors expect to confine a single non-Abelian anyon with similar techniques, and for topological quantum computing roadmaps. The reported figures of merit are directly relevant: excitation gaps, charge stability, and charge noise among the best of any solid-state dot. The anyon-binding result reinterprets several previously puzzling observations, such as 2e/3 charge and pairing-like behavior in interferometers and shot noise. It is also relevant to theoretical proposals of anyon superconductivity. The device can be extended to fractional charge pumps for metrology. Adjacent fields include quantum Hall theory, graphene devices, and strongly correlated numerics (DMRG, composite fermions).
Timeliness
This is very timely. Anyon braiding in graphene and GaAs interferometers, and in STM-based experiments, has recently had many results. The single-anyon limit is the obvious next frontier. The paper is also part of a wave of competing reports (e/4 in bilayer graphene, Di Luca et al., and other graphene groups), so priority is shared, but the depth here (single-anyon limit, spin-blockade calibration, binding) is distinctive.
Strengths and Limitations
Strengths: a genuine experimental milestone; a clean demonstration of the ν=1 limit; combined theory-experiment in the few-anyon regime; a new phenomenology (anyon binding) that could redirect theory; and detailed methods and supplementary data.
Limitations: indirect Nqp calibration at fractional filling; single-device evidence; an ambiguous microscopic origin of binding; the lack of a signature of anyonic statistics or braiding; the abelian-only demonstration; and limited reproducibility because no code or data availability statement is given. The DMRG is also sensitive to phenomenological electrostatics.
Overall
A high-impact experimental paper, likely to be widely cited as the first single-anyon dot. The binding claim is provocative and may be contested, but it adds substantial interest. Because it does not yet demonstrate braiding or non-Abelian anyons, it is a precursor to the major future result rather than the endpoint.
Generated Oct 14, 2026
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First convincing single-anyon trapping with controlled depletion to the last e/3 quasiparticle plus a provocative anyon-binding observation, backed by serious DMRG; tempered by indirect charge calibration and single-device evidence for binding.