Monday, June 5, 2023

A newly discovered phenomenon makes atoms transparent

We never knew this transparency window existed.

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Many earlier experimental cQED studies concentrated on regimes where a few identical emitters interact with a weak external drive, allowing the system to be described by a few efficient, simple models. Despite its significance and potential in quantum applications, the dynamics of a disordered, many-body quantum system subject to a powerful drive still need to be thoroughly investigated.

A new study explored how a large, inhomogeneously broadened ensemble of solid-state emitters coupled with high cooperativity to a nanophotonic resonator behaves under strong excitation. By confining ytterbium atoms inside an optical cavity and blasting them with a laser, scientists at Caltech have discovered a phenomenon called ‘collectively induced transparency’ (CIT) that makes atoms transparent at specific frequencies. This phenomenon causes groups of atoms to stop reflecting light abruptly.

Caltech’s Andrei Faraon (BS ’04), William L. Valentine, Professor of Applied Physics and Electrical Engineering, and co-corresponding author of a paper said, “We never knew this transparency window existed. Our research has primarily become a journey to find out why.”

As the frequency of the light is changed, a transparency window appears in which the light passes through the cavity unhindered, even though the laser’s light will initially bounce off the atoms up to a point.

Analysis of the transparency window suggests that it results from interactions between atom groups and light in the cavity. This effect is similar to destructive interference, in which waves from two or more sources can cancel one another out. The groupings of atoms continuously absorb and reemit light, which typically 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.

Co-lead author Mi Lei, a graduate student at Caltech, said, “An ensemble of atoms strongly coupled to the same optical field can lead to unexpected results.”

Scientists also fabricated an optical resonator measuring just 20 microns in length. It includes features smaller than 1 micron.

Using conventional quantum optics measurement techniques, scientists found that their system had reached a new regime, revealing new physics.

Aside from the newly discovered phenomenon that causes atoms to become transparent, scientists have also found that a group of atoms can absorb and emit light from a laser much faster or slower than a single atom depending on the laser’s intensity. Because there are so many interacting quantum particles, the physics underlying these processes, known as superradiance and subradiance, still needs to be better understood.

Scientists could monitor and control quantum mechanical light–matter interactions at nanoscale.

The study could offer new insights into the mysterious world of quantum effects. It could lead to more efficient quantum memories storing information in an ensemble of strongly coupled atoms.

Journal Reference:

  1. Lei, M., Fukumori, R., Rochman, J. et al. Many-body cavity quantum electrodynamics with driven inhomogeneous emitters. Nature (2023). DOI: 10.1038/s41586-023-05884-1
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