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Single-Atom Resolved Collective Spectroscopy of a One-Dimensional Atomic Array

Britton Hofer*, Damien Bloch*, Giulio Biagioni, Nathan Bonvalet, Antoine Browaeys, and Igor Ferrier-Barbut†

  • *These authors contributed equally.
  • †Contact author: igor.ferrier-barbut@institutoptique.fr
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PRX Quantum 6, 030364 – Published 26 September, 2025

DOI: https://doi.org/10.1103/xf8r-ymrj

Abstract

Ordered atomic arrays feature an enhanced collective optical response compared to random atomic ensembles due to constructive interference in resonant dipole-dipole interactions. One consequence of this is the existence of a large shift of the transition with respect to the bare atomic frequency. In the linear optics regime (low light intensity), one observes a spectroscopic shift of the Lorentzian atomic line often called the collective Lamb shift. For stronger driving, many excitations are present in the system rendering the calculation of this shift theoretically challenging, but its understanding is important for instance when performing Ramsey spectroscopy in optical clocks. Here we report on the study of the collective optical response of a one-dimensional array of 30 dysprosium atoms. We drive the atoms on the narrow intercombination transition isolating a two-level system, and measure the atomic state with single-shot state readout using a broad transition. In the linear optics regime, we measure the shift of the resonance in steady state due to dipole interactions, and measure how this shift depends on the interatomic distance. We further resolve at the single atom level how the excitation is distributed over the array. Then, on the same transition we perform Ramsey spectroscopy i.e., away from the linear regime. We observe a time-dependent shift, that allows us to draw the connection between the collective Lamb shift observed in the linear optics regime and in the large-excitation case.

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Popular Summary

The response of a single atom to an excitation with laser light resonant with an atomic transition is well understood. However, when many atoms are present, an atom is subject not only to the laser field but also to the field radiated by other dipoles, making the calculation of the response a hard many-body problem. This is expected to be particularly the case when the atoms are ordered in space because of constructive interference. Probing the collective response of an atomic array with single-atom precision is extremely challenging but necessary to understand the response and test many-body models.

In this paper we report on probing the collective response of an atomic array, down to the single atom on an optical tweezer array experimental platform. We are able to measure in a single shot the state of each individual atom. We observe how each single atom responds to the light excitation and observe a shift of the atomic line due to collective effects. We measure how this shift depends on the distance between the atoms. In addition, we perform Ramsey spectroscopy in which many atoms are excited at the same time. This regime is hard to describe theoretically. This shift is important to understand because it can cause a systematic uncertainty in the most precise optical atomic clocks. We show on the experiment how the shift in Ramsey spectroscopy and its evolution in time can be understood from simple calculations, demonstrating the usefulness of the single-atom tweezer platform to understand the collective optical response of atomic arrays.

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PRX Quantum 6, 030364– Published 26 September, 2025
  • Received 3 December 2024
  • Revised 5 June 2025
  • Accepted 7 August 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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