Single-atom resolved collective spectroscopy of a one-dimensional atomic array

TL;DR

This paper investigates the collective optical response of a one-dimensional atomic array, measuring the shift of resonance due to dipole interactions in both linear and non-linear regimes, with single-atom resolution and Ramsey spectroscopy.

Contribution

It provides the first detailed experimental study connecting the collective Lamb shift in linear and large-excitation regimes in a 1D atomic array.

Findings

Measured the dipole interaction-induced shift in steady state.

Resolved excitation distribution at the single atom level.

Observed a time-dependent shift in Ramsey spectroscopy.

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 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 2-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 \emph{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.