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Study shows how parts of electrons move at different speeds in one dimension

16 June 2022
An international collaboration observes spin-charge separation with ultracold atoms

A quantum simulator at Rice University is giving physicists a clear look at spin-charge separation, the quantum world’s version of the magician’s illusion of sawing a person in half. Published this week in Science, the study also involved SISSA researcher Feng He as well as theoretical physicists in USA, China and Australia. The research has implications for quantum computing and electronics with atom-scale wires.

Electrons are minuscule, subatomic particles that cannot be divided. Despite this, quantum mechanics dictates that two of their attributes — spin and charge — travel at different speeds in one-dimensional wires. Rice physicists built an ultracold venue where they could repeatedly view and photograph a pristine version of this quantum spectacle, theoretically formulated by physicists Shinichiro Tomonaga and Joaquin Luttinger about 60 years ago.

“People have observed spin-charge separation in solid-state materials, but they've not seen it in a very clean or quantitative way,” said Randy Hulet, Rice's Fayez Sarofim Professor of Physics and a member of the Rice Quantum Initiative. “Our experiment is really the first to deliver quantifiable measurements that can be compared with a nearly exact theory.”

SISSA’s young researcher Feng He, previously at Wuhan Institute of Physics and Mathematics (WIPM, Chinese Academy of Science) was part of the team of theoretical physicists who took part in the research. “Under inspiring discussion with Xiwen Guan of WIPM and Han Pu of Rice University, my co-worker Sheng Wang in WIPM and I carried-out the modeling of the experimental data and the theoretical analysis. We extracted the information of spin and charge velocities building from the data and explained them by means of “Thermodynamics Bethe ansatz” method - a technique wildly applied in a bunch of integrable models to determinate their equilibrium properties in the thermodynamic limit,” said He. “We spent a lot of effort on this theoretical analysis as there are a lot of subtle details which are tricky. Eventually, the experimental data closely matched predictions from our theoretical calculations,” concluded the physicist. 

The research has implications for quantum computing and electronics with atom-scale wires: “As integrated circuits become smaller, chipmakers have to start worrying about dimensionality,” Hulet said. “Their circuits eventually become a one-dimensional system that has to conduct and transport electrons in the same way as the one-dimensional wires we've been talking about.” The study could also aid the development of technology for topological quantum computers that would encode information in qubits that are free from the decoherence that plagues today’s quantum computers.

Original paper