Light-Powered “Electron Lighthouse” Steers Current with Laser Light

Physicists at the University of Michigan (U-M) have built a semiconductor device that emits a directed beam of electrons without applying an external electric field. By overlapping two infrared laser pulses of different wavelengths, the researchers can rotate the electron beam’s direction simply by changing the light’s polarization. The resulting current is “ballistic,” meaning the electrons travel along trajectories set by their initial launch velocity rather than diffusing through the material.

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The experiment, conducted in U-M’s Lurie Nanofabrication Facility (LNF), required a custom fabrication process to avoid stray electric fields that could confound the measurements. Two laser beams intersect within the semiconductor; their quantum-interference pattern supplies the energy that launches electrons. Adjusting the polarization of the light changes the interference condition, thereby steering the electron beam much like a lighthouse rotates its light. The team confirmed that the generated currents are detectable with electrodes integrated into the device.

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Yiming Gong, a machine-learning scientist now at Grainger and the study’s first author, led the development of the fabrication recipe. Senior author Steven Cundiff, an experimental physicist at U-M, oversaw the optical design. The work builds on a theoretical prediction by John Sipe of the University of Toronto, who foresaw that quantum interference could produce a voltage-free electron beam. Funding was provided by the U.S. National Science Foundation.

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Cundiff emphasized that the approach differs from conventional electron transport, which relies on applied electric fields, and highlighted the surprise of detecting the ballistic currents with their own measurement apparatus. Gong described the lack of established methods for creating a field-free setup as the primary technical hurdle his team overcame.

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• “Probably the most surprising thing is that the currents produced by this process are even detectable using the device we made,” — Steven Cundiff, an experimental physicist at U-M, as well as the study's senior author

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• “That was the biggest puzzle to solve for me, because there isn't a standard way to do that,” — Yiming Gong, a machine learning scientist now at Grainger and the study's first author

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• “Actually, this project is kind of interesting, because I started working on [its predecessor] many years ago as a way to make a phase-sensitive detector for use in stabilizing frequency combs,” — Steven Cundiff, an experimental physicist at U-M, as well as the study's senior author

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The authors suggest that mastering light-controlled electron flow could advance quantum-sensing techniques, improve high-speed imaging and telecommunications, and potentially accelerate quantum-computing algorithms by exploiting interference-driven probability amplification.

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