Heralded generation of a three-mode NOON state

TL;DR

This paper demonstrates a heralded method to generate a three-mode two-photon NOON state using linear optics, achieving high fidelity and genuine multipartite entanglement, advancing multi-mode quantum state generation for quantum information applications.

Contribution

The work introduces a practical heralded scheme for generating three-mode NOON states with high success probability and low resource overhead, suitable for current technology.

Findings

Fidelity of 0.823 +/- 0.018 with ideal NOON state

Successful certification of genuine multipartite entanglement

Feasible with existing linear optical technology

Abstract

Entangled states of photons form the foundation of quantum communication, computation, and metrology. Yet their generation remains fundamentally constrained: in the absence of intrinsic photon-photon interactions, the generation of such states is inherently probabilistic rather than deterministic. The prevalent technique of post-selection verifies the creation of an entangled state by detecting and thus destroying it. Heralding offers a solution in which measuring ancillary photons in auxiliary modes signals the state generation without the need to measure it. Here, we report an experiment to generate a three-mode two-photon NOON state, where the detection of a single photon in one heralding mode signifies the presence of the state in three target modes. We validate the generated state by estimating a fidelity of 0.823 +/- 0.018 with respect to an ideal three-mode NOON state and certifying genuine multipartite entanglement. By virtue of the high success probability and small resource overhead of our scheme, our work provides a theoretical and experimental stepping stone for entangled multi-mode state generation, which is realizable with current technology. These multi-mode entangled states represent a key direction for linear optical quantum information that is complementary to multi-qubit state encoding.