Researchers have tracked a looping fractional charge in ultrathin carbon and seen it return with a consistent interference rhythm.
The result strengthens the case for quantum particles whose collective state can retain a record of earlier exchanges.
A loop with consequences
That rhythmic signal came from a gate-defined loop reported in a recent paper, where resistance rose and fell predictably.
By keeping the device stable, Dr. Yuval Ronen, a condensed matter physicist, tested whether the looped charge stayed coherent.
His laboratory at the Weizmann Institute of Science (WIS) builds graphene circuits that let scientists steer quantum motion with electrodes.
Such steering matters because future quantum computers need information that survives local bumps, not just perfect isolation in a freezer.
When electrons become fractions
Extreme cold and intense magnetic fields can force electrons to organize into new patterns that carry charge in pieces.
The fractional quantum Hall effect, electrons behaving as smaller charges along edges, was first reported in 1982.
Physicists often call these fraction-like excitations anyons, particle-like bundles that appear only in two dimensions.
Even-denominator fractions are strong candidates for non-Abelian anyons, swaps that reshape a shared quantum state, rather than simple timing changes.
Reading quantum interference
Quantum particles also act as waves. A wave function, the math that tracks those possibilities, describes their state.
When the loop split a wave and later recombined it, the two paths either reinforced or canceled, changing resistance.
The Aharonov-Bohm effect, a timing offset caused by encircling magnetic flux, set the rhythm for resistance bands.
Because the pattern stayed coherent over many circuits, the signal carried clues about what kind of fractional charge traveled.
The half-charge surprise
One report captured the team’s turning point, when the interference closely matched an even-denominator fraction.
“In our experiment, we managed to measure a fractional electron with an even denominator,” said Ronen.
Instead of the expected one-quarter charge, the orbiting wave looked like half an electron, hinting at a paired traveler.
Ronen’s team linked that half-charge signal to two particles moving together, but they had not separated them.
Inside the charged island
Changing voltages on the device also let the researchers tune electron density inside the island that the loop enclosed.
As that density changed, interference lines tilted, implying that the trapped particles carried one-quarter of an electron’s charge.
Those internal charges interacted with the circling wave, and their presence altered the recombination timing that set resistance.
By matching that island charge with the earlier loop result, the evidence leaned toward non-Abelian behavior.
Memory stored in topology
Order matters for these particles because each swap can rewrite the system-wide topological pattern, protected by global structure rather than microscopic details.
“In non-Abelian anyons, the exchange of positions leaves an imprint on the shape of the wave function,” explains Ronen.
A classic review describes how a whole system can store exchange history without pinning information to one spot.
That nonlocal storage sets a high bar for stray defects or vibrations to erase the encoded order.
Why noise matters less
Most quantum computers build qubits, units of information in a quantum computer, from local states that readily drift.
Heat, stray fields, and tiny material defects can nudge those local states, which scrambles the stored information.
“In non-Abelian anyons, information about the order of exchanges is stored not locally but in the wave function of the entire system,” adds Ronen.
If experiments like this one can control those exchanges on demand, error correction may become simpler and less expensive.
What evidence still lacks
Interference patterns alone cannot prove a full non-Abelian identity, because several quantum states can mimic similar timing.
The main data fit either a half-charge circling once or a one-quarter charge looping twice before recombining.
Temperature effects and fluctuations inside the island can also blur the clearest signatures, especially when multiple particles interact.
Only a direct readout of exchange order, not just charge size, will settle whether the system truly remembers.
Next steps for braiding
Work at WIS now focuses on isolating the smallest charges and controlling how many sit inside the island.
“We’ve shown that bilayer graphene almost certainly hosts particles that are non-Abelian anyons,” concludes Ronen.
To test the promised memory, the team needs to swap particles in different orders and compare the system-wide wave function.
If those ordered swaps leave distinct interference signatures, engineers could start designing logic elements that resist local noise.
A cautious path forward
This bilayer graphene device kept its signal coherent long enough to hint at particles with both fractional charge and history.
Progress now depends on isolating single non-Abelian anyons. Researchers must also prove that their exchange order changes the whole system as predicted.
The study is published in Nature.
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