Physicists force atoms into state of quantum 'hyper-entanglement' using tweezers made of laser light

Using optical tweezers composed of laser light, researchers have developed a novel way to manipulate individual atoms and create a state of hyper-entanglement.

This breakthrough could lead to new forms of quantum computing and advances in quantum simulations designed to answer fundamental questions about physics.

Caltech scientists have been using optical tweezers to control individual atoms for several decades, leading to a number of advances, including quantum error correction and a method for creating the world's most accurate clocks.

One persistent issue in the process, however, has been the natural motion of atoms, which can introduce noise (and errors) into a quantum system. But in the breakthrough study, published in the journal Science, that weakness has been transformed.

"We show that atomic motion, which is typically treated as a source of unwanted noise in quantum systems, can be turned into a strength," said Adam Shaw in a statement on Caltech's website, a postdoctoral researcher and first author on the study.

Instead of a disruptive influence, Shaw and colleagues have harnessed that movement to create hyper-entangled sets of atoms. Hyper-entanglement is distinct from traditional quantum entanglement, which describes two or more particles that are in-sync and share a property across vast distances. Hyper-entangled atoms, by contrast, can share multiple properties at the same time.

In the experiment, the Caltech team was able to link both the states of motion and electronic states (a measure of an atom's internal energy level) in a pair of atoms at the same time.

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This achievement is an important step in terms of both volume and efficiency, according to Manuel Endres, a professor of physics at Caltech and co-lead author of the study. "This allows us to encode more quantum information per atom," he said in the statement. "You get more entanglement with fewer resources."

To achieve that state of hyper-entanglement, the team first had to cool an alkaline earth atom with no charge using a novel method that Endres said involved "detection and subsequent active correction of thermal motional excitations." By deploying this method, the team was able to almost completely freeze the atom's motion.

The next step was to cause atoms to oscillate like a pendulum on a tiny scale in two different directions simultaneously, creating a state of superposition — when a particle exhibits opposite properties at the same time. These oscillating atoms were then entangled with partners that matched their motion, and finally hyper-entangled to also mirror their electronic states.

According to Endres, the point of the experiment was to find the limit of control they could exercise over the atoms. "We are essentially building a toolbox," he said. "We knew how to control the electrons within an atom, and we now learned how to control the external motion of the atom as a whole — it's like an atom toy that you have fully mastered."

One of the most exciting facets of this discovery is the implication that even more states or properties could be entangled, which Endres said could lead to a number of potential applications.

"Motional states could become a powerful resource for quantum technology, from computing to simulation to precision measurements."