New electron spin theory to aid quantum devices

Electrons – those tiny subatomic particles that help make up the atoms in our bodies and the electricity that currently flows through your phone or computer – have properties such as mass and charge that will be familiar to anyone who has followed a high school physics class. But electrons also have a more abstract property called spin, which describes how they interact with magnetic fields.

Electronic spin is of particular importance to a research area called spintronics, which aims to develop quantum electronic devices that use spin in memory storage and information processing. Spin is also at the heart of qubits, the basic unit of information used in quantum computing.

The problem with using spin in these quantum devices is that its quantum states can be easily perturbed. To be used in a device, the spins of the electrons must maintain their quantum state as long as possible to avoid the loss of information. It’s called spin coherence, and it’s so delicate that even the tiny vibrations of the atoms that make up the device can erase the spin state irreversibly.

In a new article published in the journal Physical examination letters, Marco Bernardi, Professor of Applied Physics, Physics and Materials Science; and Jinsoo Park, associate postdoctoral researcher in applied physics and materials science, developed a new theory and numerical calculations to predict spin decoherence in materials with high accuracy.

Bernardi explains: “Existing theories of spin relaxation and decoherence focus on simple models and qualitative understanding. After years of systematic effort, my group has developed computational tools to quantitatively study how electrons interact and move through materials.

“This new paper took our work one step further: we adapted an electrical transport theory to study spin, and discovered that this method can capture two main mechanisms governing spin decoherence in materials: spin scattering by atomic vibrations and spin precession modified by atomic vibrations.This unified treatment allows us to study the behavior of electronic spin in a wide range of materials and devices essential for future quantum technologies.

“It is almost surprising that in some cases we can predict spin decoherence times with an accuracy of a few percent of the measured values ​​- down to a billionth of a second – and access microscopic details of spin motion out of scope of experiments. Ironically, our research tools – computers and quantum mechanics – can now be used to develop new computers that use quantum mechanics.”

The article describing the research, titled “Predicting Phonon-Induced Spin Decoherence from First Principles: Colossal Spin Renormalization in Condensed Matter”, appears in the November 2 issue of Physical examination letters.

His companion paper describing the theory in detail, titled “Many-body theory of phonon-induced relaxation and spin decoherence”, appears in issue 17 of Physical examination B as editor’s suggestion.