Sources of entangled electromagnetic radiation are a cornerstone in quantum information processing and offer unique opportunities for the study of quantum many-body physics in a controlled experimental setting. While multi-mode entangled states of radiation have been generated in various platforms, all previous experiments are either probabilistic or restricted to generate specific types of states with a moderate entanglement length. Here, we demonstrate the fully deterministic generation of purely photonic entangled states such as the cluster, GHZ, and W state by sequentially emitting microwave photons from a controlled auxiliary system into a waveguide. We tomographically reconstruct the entire quantum many-body state for up to N=4 photonic modes and infer the quantum state for even larger N from process tomography. We estimate that localizable entanglement persists over a distance of approximately ten photonic qubits, outperforming any previous deterministic scheme.
@article{arxiv.2005.07060,
title = {Realizing a Deterministic Source of Multipartite-Entangled Photonic Qubits},
author = {Jean-Claude Besse and Kevin Reuer and Michele C. Collodo and Arne Wulff and Lucien Wernli and Adrian Copetudo and Daniel Malz and Paul Magnard and Abdulkadir Akin and Mihai Gabureac and Graham J. Norris and J. Ignacio Cirac and Andreas Wallraff and Christopher Eichler},
journal= {arXiv preprint arXiv:2005.07060},
year = {2020}
}