Researchers from the ArQuS Laboratory at the University of Trieste managed to trap and photograph individual ytterbium atoms for the first time in Italy. They extended imaging techniques to new regimens: by observing the light emitted with a microscope, the researchers were able to clearly distinguish each individual atom and accurately count the number contained in a single trap, a capability lacking in existing techniques, where measurements were so far limited to distinguishing only between zero and an atom.  

The results, published in the two prestigious international journals Quantum Science Technology and Physical Review Letters, offer important perspectives for the development of sciences and technologies based on quantum bits (or qubits), such as computers and quantum clocks: The ability to observe every single atom with great precision is, in fact, a fundamental element for the realisation of a system of atomic qubits.  

Francesco Scazza, associate professor of Physics of Matter at the University of Trieste and head of the ArQuS Laboratory, explains: ‘To photograph very dim light sources, such as celestial bodies or, indeed, individual atoms, long exposures are usually used in order to collect a fairly large signal (i.e. a large number of photons) and to be able to distinguish the objects photographed from the background. In our work we have used an alternative approach, similar to using a camera flash: by illuminating the atoms with a lot of light for a very short period of time, it is possible to obtain a signal sufficient to distinguish each atom very clearly, reducing the duration of the detection without compromising its performance.’ 

In the technique devised by the ArQuS Laboratory, the atoms, cooled to almost absolute zero (-273 °C) by a laser light and then captured in ‘optical tweezers’ are illuminated with a second laser, of which they absorb and re-emit part of the light thanks to the fluorescence phenomenon.  

Omar Abdel Karim, a researcher at the ArQuS Laboratory, explains: ‘One of the main challenges in observing individual atoms is not losing atoms during image acquisition. Because of the absorption and re-emission of light, atoms acquire energy and can escape the trap. We were able to compensate for this effect by using an additional laser to cool the atoms during the image’. 
 
This solution is based on a delicate balance between the fluorescence light and the cooling light to ensure that the atoms remain trapped, allowing them to clearly distinguish their presence and reuse them for subsequent experiments. Another important element of the measurements conducted is the speed of execution.  

Alessandro Muzi Falconi, researcher at the ArQuS Laboratory, comments: ‘In recent years, one of the industry’s goals has been to develop imaging techniques that can observe atoms faster and faster, and possibly without losing them during imaging. Thanks to a technique based on short and intense fluorescence pulses, we were able to observe the atoms, without inducing losses, in a few millionths of a second, about a thousand times faster than the typical acquisition times. Our technique is based on the fact that atoms acquire energy during the image, but not enough to escape from optical traps. In addition, by means of fast cooling pulses we can remove the excess energy after the image, and repeat the observation of the same atoms for dozens of images in succession’. 

Another important result of the research group is the first observation of individual atoms of the element ytterbium-173, a particular isotope (atom of an element that has different mass numbers and therefore different atomic mass) charactersed by six internal states at its fundamental level, which would allow the development of quantum circuits based on qudits and no longer just qubits, storing and exchanging information more efficiently.  

The ArQuS Laboratory was born in 2022 from a collaboration between the University of Trieste and the Italian National Research Council (CNR) and thanks to an ERC Starting Grant of €1.4 million granted by the European Commission. 

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Comprehensive study published in Quantum Science Technology 

Single-atom imaging of 173Yb in optical tweezers loaded by a five-beam magneto-optical trap 

O. Abdel Karim1,2,4, A. Muzi Falconi3,4, R. Panza3,1, W. Liu1,5 and F. Scazza3,1,∗ 

1. National Institute of Optics of the National Research Council (CNR-INO), 34149 Trieste, Italy 
2. Department of Physics, University of Naples Federico II, 80138 Naples, Italy 
3. Department of Physics, University of Trieste, 34127 Trieste, Italy 
4. These authors contributed equally to this work. 
5. Present address: Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, People’s Republic of China. 

∗ Author to whom any correspondence should be addressed. 

Comprehensive study published in Physical Review Letters 

Microsecond-Scale High-Survival and Number-Resolved Detection of Ytterbium Atom Arrays 

A. Muzi Falconi1, R. Panza1,2, S. Sbernardori1,2, R. Forti1,3, R. Klemt4, O. Abdel Karim2, M. Marinelli1,5, and F. Scazza1,2,* 

1. Department of Physics, University of Trieste, 34127 Trieste, Italy 
2. National Institute of Optics of the National Research Council (CNR-INO), 34149 Trieste, Italy 
3. Elettra Sincrotrone Trieste S.C.p.A., 34149 Trieste, Italy 
4. Physikalisches Institut and Center for Integrated Quantum Science and Technology, Universität Stuttgart, 70569 Stuttgart, Germany 
5. Institute of materials of the National Research Council (CNR-IOM), 34149 Trieste, Italy 

*Contact author: francesco.scazza@units.it