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# Quantum logic detection of collisions between single atom–ion pairs

## Abstract

Studies of interactions between a single pair of atoms in a quantum state are a corner-stone of quantum chemistry, yet the number of demonstrated techniques that enable the observation and control of the outcome of a single collision is still small. Here we demonstrate a technique to study interactions between an ultracold neutral atom and a cold ion using quantum logic. We measure the inelastic release of hyperfine energy in a collision between an ultracold rubidium atom and isotopes of singly ionized strontium that we do not have experimental control over. We detect the collision outcome and measure the inelastic rate of the chemistry ion by reading the motional state of a logic ion qubit in a single shot. Our work extends the toolbox for studying elastic, inelastic and reactive chemical processes with existing experimental tools, especially for atomic and molecular ions for which direct laser cooling and state detection are unavailable.

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## Data availability

Source data are provided with this paper. Other data that support the findings of this study are available from the corresponding author on reasonable request.

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## Acknowledgements

We thank Z. Meir for useful comments on the manuscript. This work was supported by the Israeli Science Foundation, the Israeli Ministry of Science, Technology and Space and the Minerva Stiftung.

## Author information

Authors

### Contributions

O.K., M.P., N.A. and R.O. contributed to the experimental design, construction, discussions and wrote the manuscript. O.K. collected the data and analysed the results. O.K. claims responsibility for all figures.

### Corresponding author

Correspondence to Or Katz.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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### Peer review information

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## Extended data

### Extended Data Fig. 1 Detection efficiency of electron shelving technique and its extension to additional configurations.

(a) The probability P(1) to measure the ion in the S, electronic ground-state, (bright) after a single shelving π-pulse of duration Tπ, following a single exothermic process releasing a total energy ΔE. For energetic processes (ΔEη2ω1z) and low beam power (ωz1Tπ 1) the detection of hot events approaches unity. Variation of the pulse duration Tπ implies simultaneous change of the Rabi frequency and pulse duration. (b) Detection efficiency of two pulses of electron shelving in the low beam power limit with the experimental parameters. A tilted beam (red) features sharper detection curve with respect to a beam co-linear with the trap axis (blue, denoted as the ‘base configuration’ in this analysis) that is sensitive to motion only along that axis. Black arrow marks the energy of hyperfine-changing collision studied in the experimental realization. (c)-(e) Extensions of the base configuration. (c) Variation of the the axial trap frequency enables detection of exothermic processes releasing energy below kB × (1 mK) at standard trap frequencies. (d) Configurations with unbalanced masses change the detection probability for exothermic process via scaling of the parameters ξz1, ξz2 [c.f. Eq. (5)-(6))]. Top: variation of the atom to chemistry-ion mass ratio for a fixed $${m}_{{{{\rm{i}}}}}^{L}={m}_{{{{\rm{i}}}}}^{c}$$. Bottom: variation of the chemistry-ion to logic-ion mass ratio for a fixed $${m}_{{{{\rm{i}}}}}^{L}$$ and $${m}_{{{{\rm{a}}}}}={m}_{{{{\rm{i}}}}}^{L}$$. (e). Detection of elastic and endothermic collisional processes. An atom with kinetic energy Ea and moving perpendicular to the beam direction can scatter and generate motion of the crystal along the axis detected by the shelving beam (light-blue curve) in the base configuration. An endothermic process which converts a kinetic energy ΔE into internal one can be detected efficiently by varying the kinetic energy of the atom near Ea = 2ΔE (brown curve). Data in (a)-(e) is calculated numerically.

## Supplementary information

### Supplementary Information

Supplementary Notes 1 and 2 and Fig. 1.

## Source data

### Source Data Fig. 2

Data for Fig. 2d.

Data for Fig. 3.

### Source Data Extended Data Fig. 1

Data for Extended Data Fig. 1.

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Katz, O., Pinkas, M., Akerman, N. et al. Quantum logic detection of collisions between single atom–ion pairs. Nat. Phys. 18, 533–537 (2022). https://doi.org/10.1038/s41567-022-01517-y

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• DOI: https://doi.org/10.1038/s41567-022-01517-y

• ### Collision detection with logic

• MichaÅ Tomza

Nature Physics (2022)