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

TL;DR

This paper reports the experimental creation of large-amplitude non-Gaussian quantum states, specifically squeezed cat states, in free-space optical pulses, surpassing previous amplitude records and advancing quantum information processing.

Contribution

The authors demonstrate a novel protocol for generating large-amplitude squeezed coherent-state superpositions using controlled Fock state mixing and heralding, achieving unprecedented state size.

Findings

Achieved an amplitude of $oldsymbol{ extstyle ext{α} = 2.47}$ in free-space pulses.

State exhibits three negative regions in the Wigner function, indicating non-classicality.

Fidelity of $oldsymbol{0.53}$ with the target state, demonstrating high-quality state generation.

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 $\alpha = 2.47$, which, to our knowledge, exceeds all previously reported values. Our protocol relies on the controlled mixing of the Fock states $|1\rangle$ and $|2\rangle$ 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 $\propto \hat{S}(z)(|\alpha\rangle - |-\alpha\rangle)$, with $\alpha = 2.47$ and squeezing parameter $z = 0.56$. These results constitute a significant milestone for temporal breeding protocols and for the iterative generation of optical GKP states, opening new perspectives for scalable and fault-tolerant photonic quantum architectures.