Effect of noise and enhancement of nonlocality in on/off photodetection

Maximal CHSH violations with low efficiency photodetection and homodyne measurements

We study nonlocality tests in which each party performs photodetection and homodyne measurements. The results of such measurements are dichotomized and a Clauser-Horne-Shimony-Holt (CHSH) inequality is used. We prove that in this scenario the maximal violation is attainable and fully characterize the set of maximally violating states. If we restrict our search to states composed by at most 2, 4, and 6 photons per mode, we find critical photodetection efficiencies of 0.48, 0.36, and 0.29. We also found an entangled variation of the famous cat states that has critical efficiency 0.32. These valu…

Photon subtracted states and enhancement of nonlocality in the presence of noise

We address nonlocality of continuous variable systems in the presence of dissipation and noise. Three nonlocality tests have been considered, based on the measurement of displaced-parity, field-quadrature and pseudospin-operator, respectively. Nonlocality of twin beam has been investigated, as well as that of its non-Gaussian counterparts obtained by inconclusive subtraction of photons. Our results indicate that: i) nonlocality of twin beam is degraded but not destroyed by noise; ii) photon subtraction enhances nonlocality in the presence of noise, especially in the low-energy regime.

非局域性辅助增强噪声经典信道中的无误通信

Nonlocality-Assisted Enhancement of Error-Free Communication in Noisy Classical Channels

本文研究贝尔场景中非局域关联对噪声经典信道零错误通信的增强作用，构造出零错误容量为零的信道，借助极值非局域关联可实现1比特或log m比特无误传输，强调其多功能效用。

高维非局域性对双重噪声和顺序测量的鲁棒性

Robustness of Higher Dimensional Nonlocality against dual noise and sequential measurements

本文从测量噪声和态噪声双重角度研究高维CGLMP不等式违反的鲁棒性，引入非局域区域面积量化维度优势，并考察弱测量下顺序违反行为，发现最大违反态在噪声容忍和顺序违反方面与最大纠缠态存在显著差异。

Nonlocal continuous variable correlations and violation of Bell's inequality for light beams with topological singularities

We consider optical beams with topological singularities which possess Schmidt decomposition and show that such classical beams share many features of two mode entanglement in quantum optics. We demonstrate the coherence properties of such beams through the violations of Bell inequality for continuous variables using the Wigner function. This violation is a consequence of correlations between the $(x, p_x)$ and $(y, p_y)$ spaces which mathematically play the same role as nonlocality in quantum mechanics. The Bell violation for the LG beams is shown to increase with higher orbital angular momen…

Robust multipartite quantum correlations without complex encodings

One of the main challenges for the manipulation and storage of multipartite entanglement is its fragility under noise. We present a simple recipe for the systematic enhancement of the resistance of multipartite entanglement against any local noise with a privileged direction in the Bloch sphere. For the case of exact local dephasing along any given basis, and for all noise strengths, our prescription grants full robustness: Even states with exponentially decaying entanglement are mapped to states whose entanglement is constant. In contrast to previous techniques resorting to complex logical-qu…