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arXiv:2506.05123 · Physical Review Research

Light-assisted collisions in tweezer-trapped lanthanides

D. S. Grün, L. Bellinato Giacomelli, Arina Tashchilina, R. Donofrio, F. Borchers, Thomas Bland, Manfred J. Mark, Francesca Ferlaino

Published Feb 26, 2026• 3 citations
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Abstract

We present a quantitative investigation of one- and two-body light-mediated processes that occur to few erbium atoms in an optical tweezer, when exposed to near-resonant light. In order to study the intertwined effects of recoil heating, cooling, and light-assisted collisions, we develop a first-principles Monte Carlo algorithm that solves the coupled dynamics of both the internal and external degrees of freedom of the atoms. After validating our theoretical model against experimental data, we use the predictive power of our code to guide our experiment and, in particular, we explore the performance of different transitions of erbium for light-assisted collisions in terms of their efficiency and fidelity for single-atom preparation.

DOI
10.1103/rkn3-8rc9

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We present a quantitative investigation of one- and two-body light-mediated processes that occur to few erbium atoms in an optical tweezer, when exposed to near-resonant light. In order to study the intertwined effects of recoil heating, cooling, and light-assisted collisions, we develop a first-principles Monte Carlo algorithm that solves the coupled dynamics of both the internal and external degrees of freedom of the atoms. After validating our theoretical model against experimental data, we use the predictive power of our code to guide our experiment and, in particular, we explore the performance of different transitions of erbium for light-assisted collisions in terms of their efficiency and fidelity for single-atom preparation.
We present the first successful trapping of single erbium atoms in an array of optical tweezers. Using a single narrow-line optical transition, we achieve deep cooling for direct tweezer loading, pairwise ejection, and continuous imaging without additional recoil suppression techniques. Our tweezer wavelength choice enables us to reach the magic trapping condition by tuning the ellipticity of the trapping light. Additionally, we implement an ultrafast high-fidelity fluorescence imaging scheme using a broad transition, allowing time-resolved study of the tweezer population dynamics from many to single atoms during light-assisted collisions. In particular, we extract a pair-ejection rate that qualitatively agrees with the semiclassical predictions by the Gallagher-Pritchard model. This Letter represents a promising starting point for the exploration of erbium as a powerful resource for quantum simulation in optical tweezers.
In the past, light-assisted cold collisions between laser cooled atoms have been widely studied in magneto-optical atom traps (MOTs). We describe here theoretical studies of dynamical interactions, specifically cold collisions, between atoms trapped in near-resonant, dissipative optical lattices. The developed quantum-mechanical model is based on Monte Carlo wave-function simulations and combines atomic cooling and collision dynamics in a single framework. It turns out, that the radiative heating mechanism affects the dynamics of atomic cloud in a red-detuned lattice in a way that is not directly expected from the MOT studies. The optical lattice and position dependent light-matter coupling introduces selectivity of collision partners. Atoms, which are most mobile and energetic, are strongly favored to participate in collisions, and are more often ejected from the lattice, than the slow ones in the laser parameter region selected for study. For blue-detuned lattices, we study how optical shielding emerges as a natural part of the lattice and look for ways to optimize the effect. The simulations are computationally very demanding and would obviously benefit from the simplification schemes. We present some steps to this direction by showing how it is possible to calculate collision rates in near-resonant lattices in a fairly simple way.
We study the dynamics of atoms in optical traps when exposed to laser cooling light that induces light-assisted collisions. We experimentally prepare individual atom pairs and observe their evolution. Due to the simplicity of the system (just two atoms in a microtrap) we can directly simulate the pair's dynamics, thereby revealing detailed insight into it. We find that often only one of the collision partners gets expelled, similar to when using blue detuned light for inducing the collisions. This enhances schemes for using light-assisted collisions to prepare individual atoms and affects other applications as well.
In this thesis, we present our methods and results towards the development of deterministic preparation of single neutral atoms with a known quantum state in a single trap potential. Firstly, we experimentally study the dynamics of two atoms that undergo light-assisted collisions, where we can quantify different two-atom loss channels. We find that a combination of repulsive light-assisted collisions and in-trap laser cooling can result in only one of the two colliding atoms escaping the trap with near unity probability. This forms the essential basis in our single atom preparation method. With optimized repulsive light-assisted collisions and laser cooling parameters, we can prepare single neutral atoms with a preparation efficiency of 91%. When similar methods are applied in collisional blockade loading of single atoms in a tight trap, the preparation efficiency can be enhanced from the previously observed limit of around 50% to 80%. In a separate experiment, we also demonstrate an in-trap fluorescence detection method to count the number of atoms in a high density trap from 1 to more than 100 atoms with sub-Poissonian precision. Finally, we perform Raman sideband cooling on the prepared single atom with a single pair of Raman transition beams that couples both of the radial vibrational dimensions of the trapped atom. We show that the atom occupies the vibrational ground state in the two radial dimensions with a probability of 84%. This gives a 69% fidelity for the preparation of a pure atomic quantum state for a 2-D system.
We perform narrowline cooling of single dysprosium atoms trapped in a 1D optical tweezers array, employing the narrow single-photon transition at 741 nm. At the trapping wavelength of 532 nm, the excited state is less trapped than the ground state. To obtain efficient cooling performances, we chirp the frequency of the cooling beam to subsequently address the red sidebands of different motional states. We demonstrate the effectiveness of the cooling protocol through Raman thermometry, which we characterize for our experimental conditions. We obtain an array of 75 atoms close to the motional ground state in the radial direction of the tweezers. Our results demonstrate the possibility to manipulate the motional degree of freedom of dysprosium in optical tweezers arrays, a key ingredient to exploit the potential of lanthanide-based tweezers platforms for quantum science.
The detailed control achieved over single optically trapped neutral atoms makes them candidates for applications in quantum metrology and quantum information processing. The last few decades have seen different methods developed to optimize the preparation efficiency of single atoms in optical traps. Here we review the near-deterministic preparation of single atoms based on light-assisted collisions and describe how this method can be implemented in different trap regimes. The simplicity and versatility of the method makes it feasible to be employed in future quantum technologies such as a quantum logic device.