Independent labs confirm e/4 charge in gallium arsenide

Two independent experiments have measured quasiparticles carrying approximately one-quarter of an electron's charge in the ν = 1/2 fractional quantum Hall state in gallium arsenide. The measured charge values are 0.250 ± 0.013 and 0.249 ± 0.018 times the electron charge, both matching one-quarter of an electron's charge, or e/4.

Method and verification

The charge was measured using shot noise in quantum point contacts. The researchers studied electrons confined within a 70-nanometer-wide layer of gallium arsenide. Each device contained a narrow constriction, a quantum point contact, built using a distinctive etching method and fine-tuned with metal gates to control current flow.

They tested two nearly identical devices in two different laboratories. The independent verification was done by Mitali Banerjee’s group at EPFL and Moty Heiblum’s group at the Weizmann Institute of Science. The technique was first validated by measuring known states with charges of a full electron and two-thirds of an electron before proceeding to the e/4 measurement.

Significance

The observed e/4 charge supports the existence of non-Abelian anyons in this state. Non-Abelian anyons are predicted to enable topological quantum computers, providing immunity from local structural defects or noise. Moving such particles around each other can create error-free quantum computers. The ν = 1/2 quantum Hall state survives up to a few degrees Kelvin.

Mitali Banerjee noted the state's practical potential. This is important because the quantum Hall state that was studied here is special as it survives up to a few kelvins, and is thought to be only the second known state in gallium arsenide to possess special non-Abelian properties that can eventually enable a topological quantum computer, she said. She added that non-Abelian states store information in the global geometry, ensuring protection from local noise.

Context

This marks the first time two different research groups have obtained consistent fractional charge measurements in this field. "For the first time in the history of this field, two different groups have measured the same values of fractional charge," stated Mitali Banerjee. The research was conducted by scientists from the groups of Mitali Banerjee at EPFL, Moty Heiblum at the Weizmann Institute of Science, and Mansour Shayegan at Princeton University.

The study focused on the ν = 1/2 fractional quantum Hall state in a wide gallium arsenade quantum well. The measurements were made at temperatures just above absolute zero. The research was published in Physical Review Letters in a paper titled 'Observation of e/4 Charge at ν = 1/2 in a Wide GaAs Quantum Well' by Tomer Alkalay et al. The result supports progress toward fault-tolerant quantum computation by confirming a key signature of non-Abelian quasiparticles in a material system compatible with semiconductor fabrication.