NIST researchers develop miniature lens to sequester atoms

It is notoriously difficult to control atoms. They are zigzagging like fireflies, sprouting from the strongest of containers and vibrating even at temperatures close to absolute zero.

However, scientists need to hunt down and manipulate single atoms for quantum devices, such as atomic clocks or quantum computers, to function properly. If individual atoms can be grouped and controlled into large matrices, they can act as quantum bits, or qubits – discrete small units of information whose state or direction can eventually be used to perform calculations at speeds much greater than the fastest supercomputer.

Researchers at the National Institute of Standards and Technology (NIST), along with collaborators from JILA – a joint institute between the University of Colorado and NIST at Boulder – have shown for the first time that they can hunt single atoms using a new miniature version of "optical tweezers" – a system that catches atoms. Using the laser beam as eating sticks.


Illustration of focused light using a flat glass surface studded with millions of nanotubes (referred to as metalens) forming optical tweezers. (a) The cross-section of the device depicts plane light waves that are focused by secondary waves generated by nanobeams of varying sizes. (b) The same metallic is used to capture and photograph the single rubidium atoms.

attributed to him:

Sean Kelly/Nest

Usually, optical tweezers are obtained 2018 Nobel Prize in Physics, characterized by massive centimeter-sized lenses or microscopic targets outside of a vacuum that hold individual atoms. NIST and JILA have previously used this technology with great success to create an atomic clock.

In the new design, instead of typical lenses, the NIST team used unconventional optics — a square glass wafer about 4 mm long printed with millions of pillars a few hundred nanometers (billionths of a meter) high that collectively act as very small. lenses. These printed surfaces, dubbed metasurfaces, focus laser light to trap, manipulate, and image individual atoms within a vapor. The metasurfaces can operate in the vacuum where the trapped cloud of atoms is, unlike regular optical tweezers.

The process includes several steps. First, incoming light of a particularly simple shape, known as a plane wave, strikes groups of tiny nanopillars. (Planar waves are like moving parallel plates of light that have a uniform wave front, or phase, whose vibrations remain synchronized with each other and do not diverge or converge as they travel.) Wavelets, each slightly out of sync with its neighbor. As a result, neighboring waves reach their peaks at slightly different times.

These waves combine, or "interfer" with each other, causing them to focus all their energy in a specific position – the location of the atom that will be trapped.

Depending on the angle at which the incoming planar light waves strike the nanopillars, the small waves are focused in slightly different places, allowing the optical system to trap a series of individual atoms located in slightly different locations from each other.

Because the miniature flat lenses can operate inside a vacuum chamber and require no moving parts, atoms can be trapped without having to build and manipulate a complex optical system, said NIST researcher Amit Agrawal. Other researchers at NIST and JILA have previously used conventional optical tweezers with great success in designing atomic clocks.

In the new study, Agrawal and two other NIST scientists, Scott Papp and Wenqi Zhu, along with collaborators from JILA’s Cindy Regal Group, designed, manufactured and tested the surfactants and conducted single-atom trapping experiments.

In a paper published today in Quantum PRX, the researchers reported that they separately trapped nine single rubidium atoms. Agrawal said the same technology, which has been scaled up using multiple metasurfaces or one with a large field of view, should be able to trap hundreds of single atoms, and could routinely lead the way to trapping an array of atoms with a wafer-scale optical system. .

The system held the atoms in place for about 10 seconds, long enough to study the quantum mechanical properties of particles and use them to store quantum information. (Quantum experiments run on time scales from ten millionths to one thousandth of a second.)

To prove that they had captured rubidium atoms, the researchers lit them with a separate light source, causing them to shine. Then the piercing surfaces played a second crucial role. At first, they formed and focused the incoming light that trapped the rubidium atoms. Now, the metasurfaces have captured and focused the fluorescent light emitted by these same atoms, and the fluorescent radiation is redirected to the camera in order to image the atoms.

Superficial metasurfaces can do more than confine single atoms. By focusing light with pinpoint precision, metasurfaces can coax individual atoms into special quantum states, designed for specific atom-trapping experiments.

For example, polarized light directed by tiny lenses can cause an atom — a similar quantum property of the Earth spinning on its axis — to spin to point in a specific direction. These interactions between focused light and single atoms are useful for many types of atom-scale experiments and devices, including future quantum computers.

Paper: T.-W. Hsu, W. Zhu, T. Thiele, M. O. Brown, S. B. Papp, A. Agrawal and CA Regal. Trapping a single atom in the optical forceps of the surface lens. Quantum PRX. Posted online August 1, 2022. DOI: 10.1103/PRXQuantum.3.030316.