Ion Imaging via Long-Range Interaction with Rydberg Atoms

Christian Gross, Thibault Vogt, and Wenhui Li

Phys. Rev. Lett. 124, 053401 – Published 4 February 2020

Abstract

We demonstrate imaging of ions in an atomic gas with ion–Rydberg-atom interaction induced absorption. This is made possible by utilizing a multiphoton electromagnetically induced transparency (EIT) scheme and the extremely large electric polarizability of a Rydberg state with high orbital angular momentum. We process the acquired images to obtain the distribution of ion clouds and to spectroscopically investigate the effect of the ions on the EIT resonance. Furthermore, we show that our method can be employed to image the dynamics of ions in a time resolved way. As an example, we map out the avalanche ionization of a gas of Rydberg atoms. The minimal disruption and the flexibility offered by this imaging technique make it ideally suited for the investigation of cold hybrid ion-atom systems.

Received 18 October 2019
Accepted 7 January 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.053401

Physics Subject Headings (PhySH)

Electromagnetically induced transparency Long-range interactions

Atoms Ions Rydberg atoms & molecules

Imaging & optical processing

Atomic, Molecular & Optical

Authors & Affiliations

Christian Gross^1,†, Thibault Vogt ^1,2,†, and Wenhui Li ^1,3,*

¹Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543
²MajuLab, CNRS-UCA-SU-NUS-NTU International Joint Research Unit, Singapore 117543
³Department of Physics, National University of Singapore, Singapore 117542

^*wenhui.li@nus.edu.sg
^†These two authors contributed equally to this work.

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Vol. 124, Iss. 5 — 7 February 2020

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Images

Figure 1
(a) Concept of the ion–Rydberg-atom interaction induced absorption. (b) Plots of $C_{4}$ coefficients of the interaction $V_{IR} (R)$ between a ${}^{87}{Rb}^{+}$ ion and a ${}^{87}{Rb}$ Rydberg atom in the $| n G_{9 / 2}, m_{J} = 9 / 2 ⟩$ state (green diamonds), the $| n D_{5 / 2}, m_{J} = 5 / 2 ⟩$ state (blue squares), and the $| n S_{1 / 2}, m_{J} = 1 / 2 ⟩$ state (red dots) [22]. (c) Photoionization and multiphoton Rydberg EIT detection schemes. (d) Sketch of the experimental setup. A bias $B$ field along $z$ defines the quantization axis. The 479 nm ionization beam is aligned along $x$ with the axial axis of the atomic ensemble. The 780 nm ionization beam passes through a pattern of one or more slits, which is imaged onto the atomic cloud using a $1.8 ∶ 1$ relay telescope (not shown). The detection fields include a 780 nm probe laser, a 482 nm laser beam counterpropagating with the 479 nm beam, and two microwave fields with wave vectors in the $x - y$ plane. The probe light is scattered inside the Rydberg blockade spheres (green balls) around the ions (black dots), which cast shadows on an electron-multiplying charge-coupled-device (EMCCD) camera.
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Figure 2
Imaging of ion clouds. (a) EIT image $T_{0}$ acquired without ions. (b) EIT image $T_{i}$ acquired in the presence of three ion clouds. (c) Image of the relative transmission $T_{i} / T_{0}$ . Each of the images (a) and (b) is the average of about 220 preprocessed images. The dashed lines delimit the areas where the atoms are exposed to the photoionization 780 nm laser beam. About 11 ions are created in each of the three exposed areas.
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Figure 3
(a),(b) EIT spectra showing mean probe transmissions ${\bar{T}}_{i}$ and ${\bar{T}}_{0}$ vs probe field detuning $Δ_{P}$ using the Rydberg state $| 27 G_{9 / 2}, m_{J} = 9 / 2 ⟩$ in (a) and $| 28 D_{5 / 2}, m_{J} = 5 / 2 ⟩$ in (b). The data markers correspond to experimental spectra recorded without ions (red circles) and with ions (blue diamonds). The EIT image $T_{i}$ shown in the inset is the average of 22 preprocessed images. (c) Relative absorption $A = 1 - {\bar{T}}_{i} / {\bar{T}}_{0}$ recorded for $Δ_{P} = 2 π \times 8 MHz$ as a function of $f_{e}$ and $N_{i}$ . The dashed lines are three-level EIT fits, and the solid lines are the result of a theoretical model as detailed in the text. The error bars are the standard error over more than 20 imaging realizations.
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Figure 4
Avalanche ionization. Interaction induced images of the space charges after an excitation duration $t_{e} = 0.14 μ s$ (a), $3 μ s$ (b), $5 μ s$ (c), $7 μ s$ (d), and $10 μ s$ (e). Corresponding absorption images of ground-state atoms acquired after $t_{e} = 5 μ s$ (f) and $10 μ s$ (g). (h) Relative transmission ( ${\bar{T}}_{i} / {\bar{T}}_{0}$ ) extracted from the ion images at the position just outside the excitation region (red squares) and transmission ( $\bar{T}$ ) of the absorption images at the center of the excitation region (black dots) vs $t_{e}$ . The boxes on (c) and (f) indicate the areas for extracting ${\bar{T}}_{i} / {\bar{T}}_{0}$ and $\bar{T}$ , respectively.
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