Light from engineered quantum structures

Light from engineered quantum structures
by Robert Schreiber
Berlin, Germany (SPX) Mar 06, 2025

Quantum physics often deals with entities so small that specialized microscopes are needed to observe them. However, researchers at the Institute for Atomic and Subatomic Physics at TU Wien are working with quantum structures large enough to be seen with the naked eye-albeit with some effort. These superconducting circuits, which can span hundreds of micrometers, function as artificial atoms with tunable properties, allowing precise control over quantum phenomena.

Unlike natural atoms, which possess fixed energy characteristics, these engineered structures can be customized to exhibit desired quantum behaviors. By coupling them in a controlled manner, scientists have demonstrated the ability to store and retrieve light-a critical advancement for future quantum experiments. This research, conducted by Johannes Fink's group at ISTA in collaboration with Stefan Rotter from TU Wien's Institute for Theoretical Physics, has been published in 'Physical Review Letters'.

Configurable Quantum States

A fundamental feature of quantum mechanics is that energy levels in atoms are quantized-an electron can exist in discrete energy states but not in between. "For natural atoms, these energy levels are predetermined by nature," explains lead author Elena Redchenko. "In contrast, with our artificial atoms, we can precisely define the allowable energy values and the spacing between them."

By directing microwaves through a metal wire resonator positioned near the superconducting artificial atoms, researchers were able to manipulate the interaction between the microwaves and the artificial atoms. This process allows photons from the microwaves to transition into and out of the artificial atoms in a highly controllable manner.

"Our findings demonstrate that photons exchange predictably between the microwaves in the wire and the artificial atoms," says Redchenko. "Because we can engineer these artificial atoms to fit exact specifications, we can explore phenomena that would be impossible with natural atoms or other conventional quantum systems."

Generating Quantum Light and Storing Photons

With the right configuration, artificial atoms can be used to generate precise sequences of quantum light pulses. "We start by sending a short classical microwave pulse into the wire," Redchenko explains. "However, due to the interaction with the artificial atoms, the system can produce a series of quantum light pulses at precisely defined time intervals-essentially functioning as an on-chip quantum timer."

Redchenko highlights the system's adaptability for various quantum experiments. "This platform allows us to generate individual photons on demand, which is crucial for many quantum applications. Additionally, we can use it to store photons temporarily and release them when needed-an essential capability for quantum memory."

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