# Interfacing a two-photon NOON state with an atomic quantum memory

## TL;DR

This paper demonstrates the first successful storage of a two-photon NOON state in a cold atomic ensemble, preserving its quantum properties, which is a significant step toward quantum memory for multi-photon entangled states.

## Contribution

It provides the first experimental demonstration of storing a multi-photon entangled state in a physical system, advancing quantum memory technology.

## Key findings

- Quantum interference confirms state preservation after storage
- First experimental storage of a multi-photon entangled state
- Supports development of quantum repeaters

## Abstract

Multi-photon entangled states play a crucial role in quantum information applications such as secure quantum communication, scalable computation, and high-precision quantum metrology. Quantum memory for entangled states is a key component of quantum repeaters, which are indispensable in realizing quantum communications. Storing a single photon or an entangled photon has been realized through different protocols. However, there has been no report demonstrating whether a multi-photon state can be stored in any physical system or not. Here, we report on the experimental storage of a two-photon NOON state in a cold atomic ensemble. Quantum interference measured before and after storage clearly shows that the properties of the two-photon NOON state are preserved during storage. Our experiment completes the first step towards storing a multi-photon entangled state.

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Source: https://tomesphere.com/paper/1701.03317