Dissimilar notions of quantum correlations have been established, each being motivated through particular applications in quantum information science and each competing for being recognized as the most relevant measure of quantumness. In this contribution, we experimentally realize a form of quantum correlation that exists even in the absence of entanglement and discord. We certify the presence of such quantum correlations via negativities in the regularized two-mode Glauber-Sudarshan function. Our data show compatibility with an incoherent mixture of orthonormal photon-number states, ruling out quantum coherence and other kinds of quantum resources. By construction, the quantumness of our state is robust against dephasing, thus requiring fewer experimental resources to ensure stability. In addition, we theoretically show how multimode entanglement can be activated based on the generated, nonentangled state. Therefore, we implement a robust kind of nonclassical photon-photon correlated state with useful applications in quantum information processing.

中文翻译：

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纠缠和不和谐之外的量子相关性

已经建立了不同的量子相关概念，每个概念都是通过量子信息科学中的特殊应用激发的，并且每个都在争夺被认为是最相关的量子度量。在这一贡献中，我们通过实验实现了即使在没有纠缠和不和谐的情况下也存在的一种量子相关形式。我们通过正则化的双模Glauber-Sudarshan函数中的负性来证明这种量子相关性的存在。我们的数据显示出与正交光子数态的非相干混合物的相容性，排除了量子相干性和其他种类的量子资源。通过构造，我们状态的量子强度对于移相具有鲁棒性，因此需要较少的实验资源来确保稳定性。此外，我们从理论上说明了如何根据生成的非纠缠状态激活多模纠缠。因此，我们实现了一种健壮的非经典光子-光子相关态，并在量子信息处理中得到了有用的应用。