Electron Lighthouse Uses Laser Light to Steer Quantum Current

From Theoretical Prediction to Physical Device

The concept of an "electron lighthouse" was originally predicted by J.E. Sipe of the University of Toronto, who had collaborated with the U-M researchers on earlier work. The idea remained theoretical until Yiming Gong, then a doctoral student in the U-M Department of Physics, took on the challenge of fabricating a working device at the university's Lurie Nanofabrication Facility.

Earlier studies had already established that light alone could cause electrons to move through a material. The new experiment advances that finding by producing a narrow, directional stream of electrons whose precise path can be controlled, rather than a diffuse, undirected current.

The Physics Behind the Beam

The effect relies on quantum interference. When the semiconductor absorbs incoming light through two different pathways simultaneously, the two absorption processes can either reinforce or cancel each other out depending on the direction of electron travel. Cundiff likened the phenomenon to overlapping ripples: for electrons moving in one direction, the ripples align and amplify each other; for those traveling in other directions, they cancel out. The result is a current concentrated into a specific direction rather than spreading evenly.

Gong described the fabrication process as painstaking, noting that the biggest challenge was melding the device's materials without introducing any extraneous electric fields. "I worked with the LNF staff to play around with different recipes and temperatures to come up with a manufacturing process," he said. Preventing unwanted fields was essential to confirm that the electron flow came entirely from the light.

What Comes Next

Gong has since earned his doctorate from U-M and now works as a machine learning scientist in Chicago, applying the quantitative skills developed during his physics research. Kai Wang, a former postdoctoral scientist with Cundiff who is now a professor at Sun Yat-Sen University in China, also contributed guidance to the project. While the device was built primarily to explore fundamental physics, its ability to measure different aspects of light suggests potential future applications in optoelectronic technologies.