Optical Synthesis of Large-Amplitude Squeezed Coherent-State Superpositions with Minimal Resources

TLDR

The authors propose and experimentally realize a versatile protocol for engineering heralded optical coherent‑state superpositions. The protocol uses a two‑mode squeezed state, linear mixing, and n‑photon detection, efficiently employing non‑Gaussian resources only for the essential non‑Gaussian component. In experiment, a two‑photon detection with superconducting nanowire detectors produces a freely propagating state with 67 % fidelity to a squeezed even coherent‑state superposition of size |α|² = 3, enabling practical use in future quantum protocols.

Abstract

We propose and experimentally realize a novel versatile protocol that allows the quantum state engineering of heralded optical coherent-state superpositions. This scheme relies on a two-mode squeezed state, linear mixing, and a n-photon detection. It is optimally using expensive non-Gaussian resources to build up only the key non-Gaussian part of the targeted state. In the experimental case of a two-photon detection based on high-efficiency superconducting nanowire single-photon detectors, the freely propagating state exhibits a 67% fidelity with a squeezed even coherent-state superposition with a size |α|(2)=3. The demonstrated procedure and the achieved rate will facilitate the use of such superpositions in subsequent protocols, including fundamental tests and optical hybrid quantum information implementations.