A quantum device like an atomic clock or quantum computer cannot function properly unless single atoms can be captured and manipulated.
Physicists have developed new optical tweezers that grab individual atoms for the first time.
There is no doubt that atoms are difficult to control. However, scientists must trap and manipulate individual atoms to operate quantum devices, such as quantum computers and clocks.
But atoms don’t like to play along. They love their freedom. As a result, atoms are tough to handle, and they can escape from the most robust containers and jitter even at temperatures near absolute zero. Essentially, they are pretty rebellious, which explains a lot since humans are too, and atmos make up everything.
According to Northwestern University, atoms are the universe’s building blocks, except for energy. In the past, it was believed that atoms were the tiniest things in the universe that couldn’t be divided. The term “atom” comes from the Greek word for indivisible. As we now know, atoms consist of three subatomic particles: protons, neutrons, and electrons – all of which contain even smaller particles called quarks.
The possibility of corralling and controlling individual atoms in large arrays can enable us to use them as quantum bits – tiny discrete units of information that can eventually be used to run calculations faster than the fastest supercomputers.
So controlling the jittery atoms is something scientists must accomplish.
For the first time, researchers from NIST and JILA — the joint institute of the University of Colorado and NIST in Boulder — have demonstrated that atoms can be trapped using a novel miniaturized version of optical tweezers — a system that grabs atoms with laser beams as chopsticks.
A common feature of optical tweezers, which received the Nobel Prize in Physics in 2018, is the large, centimeter-sized lenses or microscope objectives that separate individual atoms from the vacuum holding them.
NIST and JILA have previously employed the technique with remarkable success.
The NIST team used an unconventional optic instead of lenses – a square glass wafer imprinted with millions of pillars just a few hundred nanometers in height that collectively function as tiny lenses. Using these metasurfaces, laser light is focused into a vapor, enabling individual atoms to be trapped, manipulated, and imaged.
As opposed to ordinary optical tweezers, metasurfaces can operate in a vacuum where trapped atoms are located.
Several steps are involved in the process. Initially, plane waves of light strike groups of nanopillars that have a particularly simple form.
Essentially, plane waves behave like a series of parallel sheets of light with a uniform wavefront or phase.
Their oscillations remain in sync as they travel and do not diverge or converge. However, in the presence of nanopillars, the plane waves are transformed into wavelets, each slightly out of sync with the next. The result is that adjacent wavelets reach their peaks slightly at different times.
As these wavelets combine or interfere with one another, all their energy is concentrated at one point – the trapped atom’s position.
A series of independent atoms can be trapped depending on the angle at which plane waves of light strike the nanopillars. This enables the optical system to capture atoms located at slightly different locations in the nanopillars.
According to NIST researcher Amit Agrawal, the mini flat lenses enable atoms to be trapped without having to construct and manipulate a complex optical system because they operate in a vacuum chamber and use no moving parts. Conventional optical tweezers have previously been used to design atomic clocks by other researchers at NIST and JILA.
The new paper described the process involved in designing, fabricating, and testing the metasurfaces and performing single-atom trapping experiments.
Researchers reported in PRX Quantum that they trapped nine individual rubidium atoms in separate containers. Hundreds of single atoms could be contained by scaling up the technique and using multiple metasurfaces or an optical system with a large field of view. This could pave the way for routinely trapping an array of atoms.
For about 10 seconds, the atoms were held in place, which allowed for testing their quantum mechanical properties and storing quantum information in them.
Using a separate light source, the researchers illuminated the rubidium atoms to demonstrate that they had captured them. In addition, metasurfaces played a crucial role in the process. Their initial step was to shape and focus on incoming light, which trapped the rubidium atoms. Next, the fluorescent light emitted by these same atoms is captured and focused using these metasurfaces. In contrast, the fluorescent radiation is redirected into a camera.
A metasurface is capable of more than just containing single atoms. Metasurfaces are capable of coaxing individual atoms into special quantum states by focusing light with pinpoint accuracy.
Through these tiny lenses, polarized light can be directed to cause the spin of an atom to point one way or another. The interaction between focused light and single atoms is helpful for a wide variety of experiments and devices at the atom-scale, including quantum computers in the future.
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