Researchers directly measure quantum distance for the first time
Researchers at Yonsei University in South Korea have directly measured the quantum distance in a solid material, black phosphorus, for the first time, which has significant implications for quantum physics and the development of new technologies.
Quantum metric measurement
The quantum metric is a measure that helps determine electronic properties in solid-state materials, such as transport behaviour. While it has previously been measured in artificial systems, obtaining this quantity in real solids has proven to be a considerable challenge, until now.
The Yonsei University team, in collaboration with researchers from the USA and led by Keun Su Kim, Underwood Distinguished Professor of Physics and Director of the Centre for Bandstructure Engineering at Yonsei University, has reported the first experimental measurement of the quantum distance in black phosphorus. Their findings have been published in the journal Science.
The research brought together an experimental group from Yonsei University, including Yoonah Chung and Soobin Park, and a theory group from Seoul National University led by Professor Bohm-Jung Yang, with Sunje Kim and Yuting Qian.
Black phosphorus as a research candidate
Black phosphorus was selected by the theory group as an ideal material for investigating the quantum distance of electrons due to its structural simplicity. Using guidance from the theory team, the experimental group employed photoemission measurements, specifically, the angle-resolved photoemission spectroscopy technique and synchrotron radiation via the Advanced Light Source in the USA, to study black phosphorus.
"The theory group found that one of the elemental layered crystals, black phosphorus, is an ideal material to study the quantum distance of electrons owing to its structural simplicity. Based on this input, the experimental group measured the quantum distance of electrons in black phosphorus using the momentum space distribution of the pseudospin texture of the valence band from the polarization dependence of angle-resolved photoemission spectroscopy technique and synchrotron radiation via Advanced Light Source in the USA."
Implications for quantum science
The quantum distance measures the similarity between two quantum states. A distance of one means the states are the same, while a distance of zero means they are completely opposite. The concept has been present in theoretical physics for some time, but its experimental measurement in real materials has been a continuing target for researchers.
By successfully measuring the full quantum metric tensors of Bloch electrons in black phosphorus, the research has established a precedent for direct measurement in other solid-state systems. Prof. Kim highlighted the broader impact of this achievement, stating:
"Measuring the quantum distance is fundamentally important not only to understand anomalous quantum phenomena in solids, including special ones such as superconductors, but also to advance our quantum science and technologies. As an example, a precise measure of quantum distances would help develop fault-tolerant quantum computation technologies."
Advancements in technology
Understanding material behaviour at the quantum mechanical level is regarded as a critical foundation for advances in multiple fields. Measurement of the quantum distance enables comprehensive exploration of complex phenomena in solids and underpins progress in semiconductor technology, the development of higher transition-temperature superconductors, and quantum computing.
The methodologies demonstrated by the Yonsei University team are expected to inform future investigations of quantum geometric responses in a wide range of crystalline materials.
The study's outcomes are expected to contribute knowledge crucial for the development of advanced superconductors, next-generation semiconductors, and quantum computers that can surpass conventional technologies in reliability and power.
