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Slowing laser light in the undergraduate laboratory

FEB 17, 2023
An experiment involving electromagnetically induced transparency gives students the opportunity to explore quantum applications of lasers.
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Slow light is a phenomenon that has captured the attention of both scientists and the public for decades. Through a handful of methods, the speed of light can be dramatically reduced, and, in certain cases, light can be stopped entirely. In one such method, electromagnetically induced transparency (EIT), a laser beam splits and recombines inside an atomic vapor, where quantum effects occur within a narrow frequency range and the refractive index increases quickly. This results in a proportional decrease in the group velocity of the light.

DeRose et al. describe an experimental setup to observe slow light using EIT in warm rubidium vapor. Their setup can reach speeds lower than 400 meters per second and is ideal for undergraduate or graduate study.

When building the experimental setup, students must learn to manipulate every aspect of a laser beam, including the intensity, frequency, polarization, and phase. Running the experiment provides exposure to advanced optics and the manipulation of magnetic fields. The theory behind EIT involves practical applications of the physics taught in the classroom and is relevant to cutting-edge research in quantum computing.

“EIT and slow light are central topics of research in the fields of quantum information and quantum technology,” said author Samir Bali. “The physics are within the wheelhouse of undergraduate seniors and first- or second-year graduate students, who are often interested in knowing about concrete quantum applications of lasers.”

The authors envision improvements to their experimental design to reduce signal degradation and enhance the power of the laser, with the aim of exploring other quantum effects, such as squeezed states of light.

Source: “Producing slow light in warm alkali vapor using electromagnetically induced transparency,” by Kenneth DeRose, Kefeng Jiang, Jianqiao Li, Macbeth Julius, Linzhao Zhuo, Scott Wenner, and Samir Bali, American Journal of Physics (2022). The article can be accessed at https://doi.org/10.1119/5.0128967 .

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