Researchers at the ArQuS Laboratory of the University of Trieste (Italy) and the National Institute of Optics of the Italian National Research Council (CNR-INO) have achieved the first imaging of individual trapped cold atoms in Italy, introducing techniques that push single-atom detection into new performance regimes. By combining intense, microsecond-scale fluorescence pulses with fast re-cooling, the team demonstrated record-speed, low-loss imaging of individual ytterbium atoms—capturing clear single-atom signals in just a few microseconds while keeping more than 99.5% of the atoms trapped and immediately reusable.
This approach allows researchers to distinguish multiple atoms within a single optical tweezer without significant blurring, enabling precise onsite atom counting rather than the binary "zero-or-one" detection typical of existing methods. This capability is key for scaling neutral-atom quantum computers, advancing next-generation atomic clocks, and enhancing quantum simulators that probe complex many-body physics.
"To photograph extremely faint light sources—whether distant astronomical bodies or individual atoms—long exposures are typically required, to collect enough photons to isolate them out from background noise," explains Francesco Scazza, associate professor at the University of Trieste and head of the ArQuS Laboratory. "In our work we adopted a different strategy, analogous to using a camera flash: by illuminating the atoms intensely for a very short time, we can gather enough signal to distinguish each atom clearly while drastically reducing the imaging duration."
The method's ultrafast fluorescence pulses are complemented by rapid cooling steps. "Our technique relies on the fact that atoms gain energy during the imaging process, but not enough to escape the optical traps," adds Alessandro Muzi Falconi, PhD candidate in Physics at the University of Trieste. "With short, intense fluorescence pulses, we can detect atoms without losses in just a few millionths of a second—about a thousand times faster than typical acquisition times. Fast cooling pulses then remove the excess energy, allowing us to re-image the same atoms repeatedly."
The team also reports the first single-atom imaging of the fermionic isotope ytterbium-173, which features six internal ground-state levels. This opens pathways toward quantum circuits based on qudits rather than qubits, enabling more efficient storage and processing of quantum information.
The results, published in Quantum Science and Technology and Physical Review Letters, mark a significant advance for neutral-atom platforms. Founded in 2022 through a collaboration between the University of Trieste and the CNR and supported by a €1.4-million ERC Starting Grant, the ArQuS Laboratory continues to develop next-generation tools for quantum science and technology.
