Rogue Rubidium Leads to Atomic Anomaly

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The team looked to causes of broadening typically encountered in the lab, such as short-range interactions between atoms or imperfections in laser beams, to explain what they were seeing. But nothing captured the magnitude of the effect.

Although the experiment did not provide direct evidence for the cause, the team suspects that a small fraction of atoms in other Rydberg levels contaminated the excitation process by interacting with clean atoms and broadening their transitions. The first few contaminants, created by stray photons in the environment, led to additional excited atoms and more contaminants, a process that quickly leads to many more excited atoms.

It’s as if the atoms are sampling different shifts to their energy levels because of the changing configuration of these unavoidable contaminants, Goldschmidt says. This causes atoms that wouldn’t otherwise get excited to absorb photons and hop up to the higher energy level, creating more Rydberg atoms.

Such broadening is a challenge for some Rydberg atom-based proposals. Many proposals call for using Rydberg atoms trapped in a lattice to create quantum computers or general purpose quantum simulators that could be programmed to mimic complex physics ordinarily too hard to study in a lab. Rydberg atoms are a favorite platform because they have strong interactions and they don’t need to be right next to each other to interact.

But the broadening discovered here prompts a closer look at these proposals. Some that don’t use Rydberg states directly, but instead use weakly excited Rydberg states to gain some of their advantages and avoid some drawbacks, could also face challenges. “Even with weak lasers that barely excite to the Rydberg state, you still get these contaminants,” Goldschmidt says. “A better understanding of this broadening is important for trying to build Rydberg-based devices for quantum information processing.”

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