近日，以色列理工学院Bartal, Guy团队研究了总角动量中的近场光子纠缠。这一研究成果发表在2025年4月2日出版的《自然》杂志上。

光子可以携带角动量，这通常归因于两个组成部分——自旋角动量（SAM）和轨道角动量（OAM），自旋角动量是与偏振相关的固有属性，轨道角动量与光子空间分布相关。在近轴光学中，这两种形式的角动量是可分离的，因此可以在单光子或多光子状态下不同光子的SAM和OAM之间诱导纠缠。然而，在纳米光子系统中，光子的SAM和OAM是不可分割的，因此只有总角动量（TAM）才能作为一个好的量子数。

研究组观察到近场区域中两个光子之间的非经典相关性，从而产生了与TAM相关的纠缠。通过将光子对耦合到等离子体模来纠缠这些纳米光子态，并使用量子成像技术来测量它们的相关性。他们观察到，与两个组成角动量相关的纠缠相比，TAM中的纠缠导致光子对量子关联的结构完全不同。这项工作为使用光子的TAM作为量子信息的编码特性进行片上量子信息处理铺平了道路。

附：英文原文

Title: Near-field photon entanglement in total angular momentum

Author: Kam, Amit, Tsesses, Shai, Ilin, Yigal, Cohen, Kobi, Lumer, Yaakov, Fridman, Lior, Lotan, Stav, Patsyk, Anatoly, Nemirovsky-Levy, Liat, Orenstein, Meir, Segev, Mordechai, Bartal, Guy

Issue&Volume: 2025-04-02

Abstract: Photons can carry angular momentum, which is conventionally attributed to two constituents—spin angular momentum (SAM), which is an intrinsic property related to the polarization, and orbital angular momentum (OAM), which is related to the photon spatial distribution. In paraxial optics, these two forms of angular momentum are separable1, such that entanglement can be induced between the SAM and the OAM of a single photon2,3 or of different photons in a multi-photon state4. In nanophotonic systems, however, the SAM and the OAM of a photon are inseparable5,6, so only the total angular momentum (TAM) serves as a good quantum number7,8,9. Here we present the observation of non-classical correlations between two photons in the near-field regime, giving rise to entanglement related to the TAM. We entangle those nanophotonic states by coupling photon pairs to plasmonic modes and use quantum imaging techniques10,11 to measure their correlations. We observe that entanglement in TAM leads to a completely different structure of quantum correlations of photon pairs, compared with entanglement related to the two constituent angular momenta. This work paves the way for on-chip quantum information processing using the TAM of photons as the encoding property for quantum information.

DOI: 10.1038/s41586-025-08761-1

Source: https://www.nature.com/articles/s41586-025-08761-1