New Technique Can Study Individual Atoms That Are Too Close To Distinguish

Artist's rendering of the new technique. Rachel Davidowitz

Researchers from Princeton University have developed a new technique that can distinguish individual atoms even when they are too close to be discerned by optical microscopes. This approach allows them to measure and control these atoms, something that could be useful in future applications such as quantum computing. The breakthrough is reported in the journal Science.

The team used a finely tuned laser to excite a group of closely spaced erbium atoms inside a crystal. There were six tightly packed atoms in this crystal and, thanks to the excitation response, they were able to measure the behavior of these atoms.

The team were particularly interested in the particle spin of the atoms. This property is unique to the quantum world and is of notable interest for quantum computing. The spin can be “up” or “down”, akin to the zeros and ones of the binary codes of regular computers. However, quantum mechanics allows for states to be in superposition, where they are up and down at the same time.

This unusual property is key to the expected power of computing. By taking advantage of quantum superposition, a handful of quantum bits (qubits) can outperform the most powerful supercomputers. But before we can have such a device, there are many obstacles to overcome. This technique is a novel approach to solve one of them.

The team is especially interested in creating a quantum logic gate. In computing, a logic gate is used to perform certain operations. Switching the spin from up to down is key to performing computations and making the atoms really close to each other. This allows researchers to create superposition combinations between the different spins. The laser comes in by delicately exciting the atoms, providing the researchers a measurement of the spin without disrupting it.

"The strength of the interaction is related to the distance between the two spins," Dr Songtao Chen, one of the paper's two lead authors, said in a statement. "We want to make them close so we can have this mutual interaction, and use this interaction to create a quantum logic gate."

Although erbium is not commonly used in quantum processors, the team highlighted the advantages of this element. In particular, the light emitted can be used through a silicon device and optical fibers, among the main components of the current telecommunication infrastructure.

The erbium atoms were placed in the gaps between the atoms of a crystal. The team believes that thousands of atoms can be assessed with this technique and plan to investigate this idea further.

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