Researchers measured excitations in a fractional quantum Hall state whose inferred charge is consistent with one quarter of an electron’s charge. They did not split an electron: the result concerns quasiparticles that emerge from a collective quantum state in a gallium arsenide layer.
What the researchers measured
The team studied the ν = 1/2 fractional quantum Hall state in a 70-nanometre-wide gallium arsenide (GaAs) layer. In this state, the relevant excitations are quasiparticles—collective features of the many-electron system, not pieces of individual electrons.
To ask “what charge do its quasiparticles carry?”, researchers measured shot noise: electrical fluctuations produced as carriers pass through a constriction. Each device had an etched quantum point contact, where quasiparticles could be partially scattered. The team first checked the measurement method on quantum Hall states with known quasiparticle charges of one electron and two-thirds of an electron. EPFL’s account of the experiment describes the setup and results.
Two devices gave estimates consistent with e/4
EPFL reported measurements from two nearly identical devices tested in separate laboratories—one at EPFL and one at the Weizmann Institute of Science. The reported fitted charges were:
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| Experimental setup | Reported charge estimate | Interpretation |
|---|---|---|
| EPFL device, measured at EPFL | 0.250 ± 0.013 times the electron charge | Consistent with e/4 |
| Weizmann device, measured at Weizmann | 0.249 ± 0.018 times the electron charge | Consistent with e/4 |
The uncertainties matter: these are measured estimates, not exact values. Their agreement across the two experimental setups supports the conclusion that the excitations carry a charge consistent with one quarter of the electron charge. The figures and device comparison are from EPFL’s 2026 account; they describe two devices, not a population-wide statistic.
Why fractional charge does not mean an electron was cut apart
An electron remains an electron. In a fractional quantum Hall state, many electrons interact under strong magnetic fields, and the system can support collective excitations with a fraction of the electron’s charge. The experiment inferred the charge carried by those quasiparticles from their noise at the constriction; it did not physically divide an electron.
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What the result says—and does not say—about non-Abelian anyons
Even-denominator quantum Hall states such as ν = 1/2 attract interest because some theories predict they may host non-Abelian anyons. These are quasiparticles whose exchange behavior could encode information in a way relevant to topological quantum computing. Measuring a charge consistent with e/4 is an important characterization of the state, but charge alone does not establish non-Abelian exchange statistics.
EPFL researcher Mitali Banerjee described the significance this way: “This is important because the quantum Hall state that was studied here is special as it survives till a few degrees Kelvin, and is supposed to be only a second such known state in gallium arsenide to possess special non-Abelian properties that can eventually enable a topological quantum computer,” EPFL reports. The conditional wording is important: the charge measurement does not itself demonstrate those properties, build a quantum computer, or show fault-tolerant computation.
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Paper behind the measurement
The results were reported by Tomer Alkalai and colleagues in “Observation of e/4 charge at ν = 1/2 in GaAs,” published in Physical Review Letters on 22 September 2026, according to EPFL’s paper listing. The paper’s DOI record identifies the publication.
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