Newly observed effect makes atoms transparent to certain frequencies of light

At certain frequencies, a phenomenon recently identified as "collectively induced transparency" (CIT) causes groups of atoms to abruptly stop reflecting light.

By trapping ytterbium atoms inside an optical cavity—basically a small cage for light—and firing a laser at them, CIT was discovered. As the frequency of the light is changed, a transparency window forms in which the light simply travels through the cavity unhindered, even though the laser's light would initially bounce off the atoms up to a point.

"We never knew this transparency window existed," says Andrei Faraon (BS '04), a professor of applied physics and electrical engineering at Caltech and co-corresponding author of an article on the finding that appeared in the journal Nature on April 26. "Our research has largely evolved into a quest to understand why,"

Analysis of the transparency window suggests that interactions between groupings of atoms and light in the cavity are what caused it. Destructive interference is a phenomena where waves from two or more sources can cancel one another out. The groupings of atoms continuously absorb and reemit light, which often causes the laser's light to be reflected. At the CIT frequency, however, a balance is established by the light that each atom in a group reemits, which causes a decrease in reflection.

A graduate student at Caltech named Mi Lei is the co-lead author and co-opinionated on the study. "An ensemble of atoms strongly coupled to the same optical field can lead to unexpected results," she adds.

The optical resonator, which has features smaller than 1 micron in size and is just 20 microns long, was created at the Kavli Nanoscience Institute at Caltech.

A graduate student named Rikuto Fukumori is the paper's co-lead author. "Through conventional quantum optics measurement techniques, we found that our system had reached an unexplored regime, revealing new physics," he adds.

In addition to the transparency phenomena, the researchers also noticed that depending on the laser's strength, a group of atoms may absorb and emit light from the laser either considerably quicker or much slower than a single atom. Because there are so many interacting quantum particles, the physics underpinning these processes, known as superradiance and subradiance, is still not well understood.

"We were able to monitor and control quantum mechanical light-matter interactions at the nanoscale," explains co-corresponding author Joonhee Choi, a former postdoctoral fellow at Caltech who is currently an assistant professor at Stanford University.

This discovery has the potential to one day help pave the road to more effective quantum memory in which information is stored in an ensemble of highly linked atoms, even though the study is essentially foundational and increases our comprehension of the enigmatic realm of quantum effects. Faraon has also experimented with controlling the interactions between several vanadium atoms to provide quantum storage.

In addition to memory, these experimental systems offer crucial insight into future links between quantum computers, according to co-author and physics professor Manuel Endres, a Rosenberg Scholar.