Making Quantum Computers a Reality: Unique Majorana Particles Found in a Magnetic Material, Shows CAU

SEOUL, South Korea, Feb. 16, 2021 /PRNewswire/ -- Recently, Google announced a breakthrough in the field of quantum computing with the invention of Sycamore, the "world's fastest computer," which could solve a highly complex problems in mere seconds. And although the prospect of making quantum computers that could be useful in the real world is exciting, it is still a few steps away. They are extremely challenging to stabilize, with the slightest disruption affecting their quantum behavior. Now, solid-state physicists have a plan to get around this problem.

According to recent theories, unique particles called "Majorana fermions" can protect their quantum states against external perturbations and thus could be used to build stable quantum computers, provided these particles can be achieved in solid materials. Thus, physicists have been looking for materials that emulate a "Kitaev honeycomb" (solid-state model known to birth Majorana fermions in magnetic fields). And, they have now succeeded—A study published in Nature Communications, led by Prof. Kwang-Yong Choi from Chung-Ang University, Korea, unveiled the existence of Majorana fermions in α-RuCl₃, a graphene-like quantum magnetic material closely resembling a Kitaev honeycomb in a magnetic field. Prof. Choi says, "If we can realize perfect Majorana fermions in solid materials, a stable quantum computer is not far away!"

The properties of α-RuCl₃ are such that at low magnetic fields, it exhibits a zigzag ordering of "spins"—an essential quantum property influencing the ordering of electrons in atoms and molecules. While in high magnetic fields, it exhibits a "spin polarized state," with all its spins oriented along the field. For intermediate fields, however, an interesting phase emerges. Prof. Choi explains, "Based on experimental and theoretical considerations, two opposing viewpoints exist for the intermediate field phase, one invoking conventional multi-particle magnetic excitations and the other Majorana fermionic excitations. Our aim was to characterize excitations emerging in the intermediate-to-high field phase."

In their study, the physicists excited α-RuCl₃ with polarized light and then mapped the behavior of the generated particles over wide ranges of magnetic fields and temperatures. Their findings showed multiple intensity peaks corresponding to bound states of multiple magnons (traveling "spin" waves). Moreover, they observed an additional low-energy peak at 2 K at intermediate field strength (8 T), which revealed itself to be a "Majorana bound state" (a bound system of itinerant Majorana fermions). Interestingly, the peak disappeared gradually with an increase in temperature. The physicists attributed this peculiar observation to the Majorana bound state's sensitivity to experiment parameters like scattering geometry and magnetic field direction.

These findings corroborate the viewpoint that the intermediate field phase in α-RuCl₃ is due to Majorana fermionic excitations, establishing it as a Kitaev honeycomb material. Prof Choi is excited about the implications of their findings, as he concludes, "We are close to achieving an ideal Majorana fermion through deconfinement of bound Majorana particles by strain engineering. We will now attempt to fine-tune magnetic parameters and stabilize the fragile Majorana fermions through interface engineering. In addition, we will test their statistics as a first step towards building quantum bits!"

Hopefully, we're only a few steps away from making quantum computers a practical reality!

Reference

Title of original paper: Magnon bound states versus anyonic Majorana excitations in the Kitaev honeycomb magnet α-RuCl₃

Journal: Nature Communications

DOI: 10.1038/s41467-020-15370-1

Chung-Ang University

Website: https://neweng.cau.ac.kr/index.do 

About Prof. Kwang-Yong Choi

Dr. Kwang-Yong Choi is a Professor of Physics at Chung-Ang University and the corresponding author of this study.

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SOURCE Chung-Ang University