Particles behaving as if they carry just one quarter of an electron’s charge have been measured by researchers at EPFL, Princeton, and the Weizmann Institute of Science. The finding, published in Physical Review Letters, represents a step toward understanding a rare quantum state potentially useful for building more stable quantum computers.
Scientists studied the ν = 1/2 fractional quantum Hall state formed in a layer of gallium arsenide, using a technique to measure the “shot noise” created by scattered quasiparticles. “For the first time in the history of this field, two different groups (Weizmann and EPFL) have measured the same values of fractional charge,” says Mitali Banerjee of EPFL, bolstering confidence in the existence of these unusual particles.
Gallium Arsenide Layer Reveals Fractional Quantum Hall Effect
The measured charge of quasiparticles within a gallium arsenide layer closely matches one quarter of an electron’s charge, specifically 0.250 ± 0.013 and 0.249 ± 0.013. This precision is notable given the experimental challenges of isolating and characterizing these fleeting, collective electron behaviors at temperatures just above absolute zero. The consistency between the two groups strengthens confidence in the observed fractional charge and the underlying physics at play.
This confirmation carries implications for the development of topological quantum computers, a promising architecture for building error-resistant machines. “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,” explains Mitali Banerjee of EPFL.
Non-Abelian anyons, potentially hosted within this quantum Hall state, offer a unique approach to quantum information storage; their quantum properties encode information in the global geometry of the system, protecting it from local disturbances and noise. The ability to reliably create and measure these fractional charges in gallium arsenide is a key step toward harnessing non-Abelian anyons for practical quantum computation. EPFL researchers contribute to quantum algorithms, quantum hardware, and quantum networks, with a particular focus on photonic quantum computing.
The university’s Center for Quantum Science and Engineering supports this research, aiming to sustain Swiss leadership in quantum photonics and information science. The independent verification of these findings by two distinct teams, Banerjee’s group at EPFL and Moty Heiblum’s group at the Weizmann Institute, is a significant result in this field, and validates the existence of these unusual quasiparticles.
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.
Mitali Banerjee, EPFL
Quantum Point Contact Measures e/4 Quasiparticle Charge
The precise measurement relied on analyzing “shot noise” generated as quasiparticles passed through a 70-nanometer-wide constriction etched into a layer of gallium arsenide, revealing the discrete nature of charge transfer at the quantum level. The technique first validated its accuracy by successfully measuring quasiparticles carrying full and two-thirds electron charges before focusing on the more elusive e/4 state.
The significance of this finding extends beyond simply confirming a theoretical prediction; the ν = 1/2 quantum Hall state is notable for its resilience at relatively high temperatures, surviving up to a few degrees Kelvin, and its potential to host “non-Abelian” quasiparticles. This work, alongside the independent verification from the Weizmann Institute, strengthens confidence in the existence of these fractional charges and the underlying physics governing their behavior, a crucial step toward realizing fault-tolerant quantum computation.
For the first time in the history of this field, two different groups (Weizmann and EPFL) have measured same values of fractional charge.
Mitali Banerjee, EPFL
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