Professor Geun-Soo Kim from Yonsei University and Professor Beom-Jeong Yang from Seoul National University, as part of a joint research team, have succeeded for the first time in the world in directly measuring the quantum distance of electrons within a solid material. The research findings were published in the international academic journal Science on June 6 (local time, June 5 at 2 PM Seoul time).
The quantum distance is a physical quantity that numerically expresses the similarity of quantum states between particles in the microscopic world. The closer the two particles are to being identical, the closer the value is to 0, and the more different they are, the closer it is to 1. Measuring quantum distance is used in the field of quantum technologies, such as quantum computing and quantum sensing, for verifying computational accuracy and tracking states.
Previously, the quantum distance of electrons in solids was either calculated theoretically or measured indirectly. This study distinguishes itself by measuring quantum distance directly.
The joint research team focused on black phosphorus, a material with a simple structure, as their subject. Professor Yang’s team from Seoul National University theoretically revealed that the quantum distance of electrons in black phosphorus is determined by the phase difference of electron waves. Professor Kim’s team at Yonsei University measured the phase differences between electron waves through angle-resolved photoemission spectroscopy (ARPES) experiments and calculated the quantum distance based on this.
Angle-resolved photoemission spectroscopy is an experimental technique that analyzes the energy and momentum of electrons emitted from a material’s surface when light is shone on it. The research team utilized polarized light in this technique to confirm the difference in signal intensity according to the phase difference between electrons, extracting the quantum distance with precision.
This study was achieved by combining theoretical developments by Professor Yang’s team over the past decade with experimental execution by Professor Kim’s team. Both teams have previously published research outcomes on related topics in Science, Nature, and Nature Physics.
The research was conducted with support from the Basic Research Program and Leading Research Center funded by the Ministry of Science and ICT. The paper is titled “Direct measurement of the quantum metric tensor in solids.”