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Bettering the Odds for Quantum Interaction With 4Pi Microscopy

Photonics.com
Nov 2017
SINGAPORE, Nov. 1, 2017 — Researchers used a superresolution imaging technique to strengthen photon-atom interaction, revealing a way to boost interaction between photons and a single atom that could be useful in quantum computing and metrology.

Using a lens to focus photons onto an atom has so far been limited by diffraction; but according to researchers, high-resolution imaging offers ways to exceed the diffraction limit. Researchers adapted 4Pi microscopy, a superresolution imaging technique, to efficiently couple light to a single atom.

In its experiment, a research team from the National University of Singapore fired a red laser at a trapped Rubidium atom. Researchers compared the amount of scattering that occurred when light came from one direction with the amount of scattering that took place when light came from two directions.

Atomic interaction with photons, National University of Singapore.

I
n the copper-encircled chamber at the center of this setup, photons bounce off a single atom. Controlling such interactions is important for quantum computing and metrology. Courtesy of Center for Quantum Technologies, National University of Singapore.

Next, the team split the laser beam, sending one half of the beam around the front and one half around the back of the atom. At the back of the atom, the laser beam passed through a strongly focusing lens to reach the atom. This double-lens configuration is known as 4Pi microscopy.

With light coming at it from both sides, the atom scattered around two in every five photons — double what it was seen to scatter with just one lens.

Atomic interaction with photons, National University of Singapore.

An imaging technique called 4Pi microscopy boosts resolution by sandwiching the sample between two strongly focusing lenses. Quantum researchers have shown that borrowing this lens trick can boost interactions between photons and a single atom. Courtesy of Ale Cere/Center for Quantum Technologies, National University of Singapore.

The atom not only changed the direction of the photons, but also their spacing. Researchers observed 36.6(3) percent extinction of the incident field, and a modified photon statistics of the transmitted field, indicating nonlinear interaction at the single-photon level.

Results of the experiment could lead to ways to implement effective interactions between photons with tightly focused free space modes and single atoms. Strongly interacting photons could find application in imaging, metrology, quantum computing and cryptography, and constitute a novel platform to study many-body physics.

In the future, the team expects that by using higher numerical aperture lenses, the 4Pi arrangement could enable the efficient conversion of a coherent beam into single photons. The team believes that even stronger interactions are technically within reach.

“There’s a lot of physics to investigate in nonlinear interactions with photons,” said researcher Chin Yue Sum. The team noted that quantum interaction is crucial for processing information stored in light, such as in optical quantum computing.

The research was published in Nature Communications (doi:10.1038/s41467-017-01495-3). 

GLOSSARY
quantum optics
The area of optics in which quantum theory is used to describe light in discrete units or ‘quanta’ of energy known as photons. First observed by Albert Einstein’s photoelectric effect, this particle description of light is the foundation for describing the transfer of energy (i.e. absorption and emission) in light matter interaction.
Research & TechnologyeducationAsia-Pacificopticsquantum opticsfree space opticslensesatomic interactions with photonsnonlinear optics

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