Researchers at Friedrich Schiller University Jena and the University of Regensburg have demonstrated a new optical technique for quantifying Berry curvature, a quantum property influencing electron behavior, within a single atomic layer of tungsten diselenide. The team used ultrashort laser pulses to measure the curvature, a feat previously accomplished only through complex experimental methods.
“We wanted to make a quantum property accessible that has so far been difficult to determine experimentally,” says lead author Nele Tornow of the University of Jena’s Institute of Solid State Physics. Published in the latest issue of Nature Photonics, the method combines optical measurements with an analytical model to reveal these subtle quantum geometric properties.
Nonlinear Circular Dichroism Reveals Quantum Geometric Properties
Researchers directed ultrashort laser pulses at this material, demonstrating the technique’s capability at an extremely small scale and opening a new avenue for investigating quantum geometry. The measurement relies on a two-pulse sequence; the first alters the material’s electronic states for a minuscule fraction of a second, while the second detects this change optically. This interaction generates light at twice the frequency of the initial laser, and the polarisation of this emitted light reveals information about the Berry curvature.
The entire process occurs within a few hundred femtoseconds, a unit of time representing one millionth of a billionth of a second, highlighting the speed at which these quantum properties can be probed. Changing the rotation direction of the initial laser pulse reverses the sign of the measured signal, providing a clear indicator of the curvature.
The team’s approach provides a specific value for the Berry curvature, a significant improvement over previous methods that primarily relied on theoretical calculations or complex experimental setups. The measured Berry curvature aligned with theoretical calculations, validating the accuracy of the new optical technique and its analytical model.
Giancarlo Soavi from the Institute of Solid State Physics and the Abbe Centre of Photonics at the University of Jena explains that this optical method allows investigation of these properties on extremely short timescales. The team states that the fundamental principles of their method are applicable to other materials, suggesting a broader potential for mapping quantum geometric properties, and the analytical model, developed in collaboration with researchers from the University of Regensburg, is designed to be adaptable, further expanding the technique’s reach.
The first pulse alters the electronic states of the material for a tiny fraction of a second.
See today’s quantum computing news on Quantum Zeitgeist for the latest breakthroughs in qubits, hardware, algorithms, and industry deals.
