Understanding and reliably measuring the geometric properties of quantum states can shed new light on the intricate underpinning of various physical phenomena. The quantum geometric tensor (QGT) is a mathematical object that provides a detailed description of how quantum states change in response to perturbations, thus offering insights about their underlying geometry.
While this mathematical object has been the focus of numerous theoretical studies, measuring it in experimental settings has proved more challenging. As a result, direct measurements of the QGT have so far been limited to artificial two-level systems.
Researchers at Massachusetts Institute of Technology, Seoul National University and other institutions recently devised a new approach to measure the QGT in crystalline solids. Their proposed method, introduced in a Nature Physics paper, relies on photoemission spectroscopy, a technique typically used to examine the electronic structure of materials.
"The work started as we were thinking about ways to probe the Berry curvature of electrons in solids," Riccardo Comin, senior author of the paper, told Phys.org. "We originally devised an experiment based on the relationship between orbital angular momentum (probed by circular dichroic ARPES) and Berry curvature."
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