# Quantum hardware simulating four-dimensional inelastic neutron scattering

## Abstract

Magnetic molecules, modelled as finite-size spin systems, are test-beds for quantum phenomena1 and could constitute key elements in future spintronics devices2,3,4,5, long-lasting nanoscale memories6 or noise-resilient quantum computing platforms7,8,9,10. Inelastic neutron scattering is the technique of choice to probe them, characterizing molecular eigenstates on atomic scales11,12,13,14. However, although large magnetic molecules can be controllably synthesized15,16,17,18, simulating their dynamics and interpreting spectroscopic measurements is challenging because of the exponential scaling of the required resources on a classical computer. Here, we show that quantum computers19,20,21,22 have the potential to efficiently extract dynamical correlations and the associated magnetic neutron cross-section by simulating prototypical spin systems on a quantum hardware22. We identify the main gate errors and show the potential scalability of our approach. The synergy between developments in neutron scattering and quantum processors will help design spin clusters for future applications.

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## Code availability

The custom Python scripts for the quantum har-dware and original codes are available from the corresponding author upon reasonable request.

## Data availability

The data that support the plots and other findings of this study are available from the corresponding author upon reasonable request.

## References

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## Acknowledgements

This work was partly funded by the Italian Ministry of Education and Research (MIUR) through PRIN Project 2015 HYFSRT, ‘Quantum Coherence in Nanostructures of Molecular Spin Qubits’. The authors also acknowledge useful discussions with G. Amoretti and G. Prando.

## Author information

A.C., F.T. and M.G. used the IBM chips to implement gate sequences. Analysis of the experimental results was carried out by A.C., F.T., D.G., I.T. and S.C. Numerical calculations were performed by A.C. and F.T. P.S., I.T., D.G. and S.C. conceived the work and discussed the results with other co-authors. A.C. and S.C. wrote the manuscript with input from all co-authors.

Correspondence to S. Carretta.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Journal Peer Review Information: Nature Physics thanks Emilio Lorenzo, David Tennant and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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## Supplementary information

### Supplementary Information

Supplementary Figures 1–27, Supplementary Tables 1–6 and Supplementary References 1–9.

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• #### DOI

https://doi.org/10.1038/s41567-019-0437-4

• ### Studies of Spinons, Majoranas, and Monopoles in Spin Liquid and Quantum Critical Magnets with Neutrons

• David Alan Tennant

Journal of the Physical Society of Japan (2019)

• ### First-principles many-body models for electron transport through molecular nanomagnets

• A. Chiesa
• , E. Macaluso
• , P. Santini
• , S. Carretta
•  & E. Pavarini

Physical Review B (2019)