June 1, 2023

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Collectively Induced Transparency

Atoms become transparent to certain frequencies of light

Artist’s conception of atoms striking a laser in an optical cavity. Scientists have discovered a new phenomenon called “collectively induced transparency” (CIT) in which groups of atoms stop reflecting light at certain frequencies. The team found this effect by trapping ytterbium atoms in an optical cavity and exposing them to laser light. At certain frequencies, a transparent window appeared through which light bypassed the cavity unhindered. Credit: Ella Maru Studio

The newly observed effect makes the atoms transparent to certain frequencies of light

Researchers at the California Institute of Technology have discovered a new phenomenon, “collectively induced transparency” (CIT), in which light passes unimpeded through groups of atoms at certain frequencies. This discovery could lead to improvements in quantum memory systems.

A newly discovered phenomenon called collectively induced transparency (CIT) causes groups of atoms to suddenly stop reflecting light at certain frequencies.

CIT was discovered by confining ytterbium atoms inside a photocavity—essentially a small box of light—and blasting them with a laser. Although the laser light will bounce off the atoms to a point, as the light’s frequency is tuned, a transparent window appears in which the light simply passes through the cavity unobstructed.

Andrei Faraon of the California Institute of Technology (BS ’04) and William L. Professor of Applied Physics and Electrical Engineering tells the Journal nature. “Our research basically became a journey to find out why.”

Analysis of window transparency indicates that it is the result of interactions in the cavity between groups of atoms and light. This phenomenon is similar to destructive interference, whereby waves from two or more sources can cancel each other out. Clusters of atoms constantly absorb and re-emit light, which generally results in reflection of laser light. However, at the CIT frequency, there is an equilibrium caused by the light being re-emitted from each atom in an ensemble, which leads to a decrease in reflectance.

“A group of atoms that are strongly coupled to the same optical field can lead to unexpected results,” says co-lead author Mei Li, a graduate student at Caltech.

The optical resonator, which is only 20 μm in length and includes features smaller than 1 μm, was fabricated at the Kavli Institute for Nanoscience at Caltech.

“Through traditional quantum optics measurement techniques, we have found that our system has reached an unexplored regime, revealing new physics,” says graduate student Rikuto Fukumori, co-lead author of the paper.

Besides the phenomenon of transparency, the researchers also note that the group of atoms can absorb and emit light from the laser either much faster or much slower than on its own.[{” attribute=””>atom depending on the intensity of the laser. These processes, called superradiance and subradiance, and their underlying physics are still poorly understood because of the large number of interacting quantum particles.

“We were able to monitor and control quantum mechanical light–matter interactions at nanoscale,” says co-corresponding author Joonhee Choi, a former postdoctoral scholar at Caltech who is now an assistant professor at Stanford University.

Though the research is primarily fundamental and expands our understanding of the mysterious world of quantum effects, this discovery has the potential to one day help pave the way to more efficient quantum memories in which information is stored in an ensemble of strongly coupled atoms. Faraon has also worked on creating quantum storage by manipulating the interactions of multiple vanadium atoms.

“Besides memories, these experimental systems provide important insight about developing future connections between quantum computers,” says Manuel Endres, professor of physics and Rosenberg Scholar, who is a co-author of the study.

Reference: “Many-body cavity quantum electrodynamics with driven inhomogeneous emitters” by Mi Lei, Rikuto Fukumori, Jake Rochman, Bihui Zhu, Manuel Endres, Joonhee Choi and Andrei Faraon, 26 April 2023, Nature.
DOI: 10.1038/s41586-023-05884-1

Coauthors include Bihui Zhu of the University of Oklahoma and Jake Rochman (MS ’19, PhD ’22). This research was funded by the Department of Energy, the National Science Foundation, the Gordon and Betty Moore Foundation, and the Office of Naval Research.

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