The Kondo effect, a hallmark of strong correlation physics, is characterized by the formation of an extended cloud of singlet states around magnetic impurities at low temperatures. While many implications of the Kondo cloud's existence have been verified, the existence of the singlet cloud itself has not been directly demonstrated. We suggest a route for such a demonstration by considering an observable that has no classical analog, but is still experimentally measurable: ``singlet weights'', or projections onto particular entangled two-particle states. Using approximate theoretical arguments, we show that it is possible to construct highly specific energy- and position-resolved probes of Kondo correlations. Furthermore, we consider a quantum transport setup that can be driven away from equilibrium by a bias voltage. There, we show that singlet weights are enhanced by voltage even as the Kondo effect is weakened by it. This exposes a patently nonequilibrium mechanism for the generation of Kondo-like entanglement that is inherently different from its equilibrium counterpart.

中文翻译：

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使用量子测量解决能量和位置空间中的非平衡 Kondo 单线态

近藤效应是强相关物理学的标志，其特征是在低温下在磁性杂质周围形成扩展的单线态云。虽然近藤云存在的许多含义已得到证实，但单线态云本身的存在尚未得到直接证明。我们通过考虑一个没有经典模拟但仍然可以通过实验测量的可观察量来建议这种演示的路线：“单重权重”，或对特定纠缠的两粒子状态的投影。使用近似的理论论证，我们表明可以构建高度特定的近藤相关性能量和位置解析探针。此外，我们考虑了一种可以被偏置电压驱离平衡的量子传输设置。那里，我们表明，即使 Kondo 效应被电压削弱，单线态权重也会被电压增强。这暴露了一种明显的非平衡机制，用于产生类似近藤的纠缠，这种纠缠本质上与其平衡对应物不同。