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  • Open Access

Generation of Large Coherent-State Superpositions in Free-Space Optical Pulses

Lucas Caron, Hector Simon, Hugo Basset, Romaric Journet, and Rosa Tualle-Brouri*

  • *Contact author: rosa.tualle-brouri@institutoptique.fr
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Phys. Rev. X 16, 031047 – Published 21 August, 2026

DOI: https://doi.org/10.1103/q2h3-58pz

Abstract

The generation of non-Gaussian quantum states is a key requirement for universal continuous-variable quantum information processing. We report the experimental generation of large-amplitude squeezed coherent-state superpositions (squeezed cat states) on free-space optical pulses, reaching an amplitude of α=2.47, which, to our knowledge, exceeds all previously reported values. Our protocol relies on the controlled mixing of the Fock states |1⟩ and |2⟩ through a tunable beam splitter, followed by heralding via homodyne detection. The resulting state displays three well-resolved negative regions in its Wigner function and achieves a fidelity of 0.53 with the target state ∝S^(z)(|α⟩−|−α⟩), with α=2.47 and squeezing parameter z=0.56. These results constitute a significant milestone for temporal breeding protocols and for the iterative generation of optical Gottesman-Kitaev-Preskill states, opening perspectives for scalable and fault-tolerant photonic quantum architectures.

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Popular Summary

Generating large-amplitude non-Gaussian states of light in free space remains a major hurdle for fault-tolerant photonic quantum computing. We overcome this limitation by experimentally generating squeezed coherent-state superpositions in free-space optical pulses that reach an amplitude of α=2.47. Our approach relies on mixing single- and two-photon Fock states on a tunable beam splitter, controlled using a fast Pockels cell and a quantum memory cavity, followed by heralding via homodyne detection. The reconstructed Wigner functions display three distinct negative regions, maintaining high fidelity even after storage inside our cavity. These results provide a crucial resource for iterative breeding protocols and bring scalable optical Gottesman-Kitaev-Preskill state generation closer to practical implementation.

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Phys. Rev. X 16, 031047– Published 21 August, 2026
  • Received 24 December 2025
  • Revised 30 April 2026
  • Accepted 20 July 2026
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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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