Universität Bayreuth, Lehrstuhl für Theoretische Physik III, Universitätsstraße 30, 95447 Bayreuth, Germany.
ITMO University, St. Petersburg 197101, Russia.
Phys Rev Lett. 2019 Sep 27;123(13):137401. doi: 10.1103/PhysRevLett.123.137401.
We report on simulations of the degree of polarization entanglement of photon pairs simultaneously emitted from a quantum dot-cavity system that demand revisiting the role of phonons. Since coherence is a fundamental precondition for entanglement and phonons are known to be a major source of decoherence, it seems unavoidable that phonons can only degrade entanglement. In contrast, we demonstrate that phonons can cause a degree of entanglement that even surpasses the corresponding value for the phonon-free case. In particular, we consider the situation of comparatively small biexciton binding energies and either finite exciton or cavity mode splitting. In both cases, combinations of the splitting and the dot-cavity coupling strength are found where the entanglement exhibits a nonmonotonic temperature dependence which enables entanglement above the phonon-free level in a finite parameter range. This unusual behavior can be explained by phonon-induced renormalizations of the dot-cavity coupling g in combination with a nonmonotonic dependence of the entanglement on g that is present already without phonons.
我们报告了对同时从量子点-腔系统发射的光子对的偏振纠缠程度的模拟，这需要重新审视声子的作用。由于相干性是纠缠的基本前提，并且已知声子是退相干的主要来源，因此似乎不可避免的是，声子只能降低纠缠度。相比之下，我们证明了声子可以引起的纠缠程度甚至超过了无声子情况下的相应值。具体来说，我们考虑了相对较小的双激子束缚能以及有限的激子或腔模分裂的情况。在这两种情况下，都发现了分裂和点-腔耦合强度的组合，其中纠缠表现出非单调的温度依赖性，从而在有限的参数范围内实现了超过无声子水平的纠缠。这种异常行为可以通过声子诱导的点-腔耦合 g 的重整化以及纠缠对 g 的非单调依赖性来解释，而这种依赖性即使在没有声子的情况下也存在。
