Experimental optimal orienteering via parallel and antiparallel spins

平行与反平行自旋中的量子不相容性

Quantum Incompatibility in Parallel vs Antiparallel Spins

该研究探讨了平行与反平行自旋配置中量子不相容性的联合测量问题，揭示了反平行配置在预测自旋分量方面的独特优势，并探讨了其在加密协议和实验实现中的应用。

Collective versus local measurements on two parallel or antiparallel spins

We give a complete analysis of covariant measurements on two spins. We consider the cases of two parallel and two antiparallel spins, and we consider both collective measurements on the two spins, and measurements which require only Local Quantum Operations and Classical Communication (LOCC). In all cases we obtain the optimal measurements for arbitrary fidelities. In particular we show that if the aim is determine as well as possible the direction in which the spins are pointing, it is best to carry out measurements on antiparallel spins (as already shown by Gisin and Popescu), second best to…

Information-disturbance tradeoff in sending Direction information via antiparallel quantum spin

For sending unknown direction information, antiparallel spins contains more direction information than parallel spins(Gisin and Popescu, 1999, \textit{Phys. Rev. Lett.} 83, 432).In this paper, the optimal information-disturbance tradeoff bound for antiparallel spins is derived. The quantum measurements which attain the optimal tradeoff bound are obtained. This result can be of practical relevance for posing some general limits on Eve's eavesdropping process. Finally, we also present a comparison between the bound for antiparallel spins and the bound for parallel spins.

Maximum violation of Wigner inequality for two-spin entangled states with parallel and antiparallel polarizations

The experimental test of Bell's inequality is mainly focused on Clauser-Horne-Shimony-Holt (CHSH) form, which provides a quantitative bound, while little attention has been pained on the violation of Wigner inequality (WI). Based on the spin coherent state quantum probability statistics we in the present paper extend the WI and its violation to arbitrary two-spin entangled states with antiparallel and parallel spin-polarizations. The local part of density operator gives rise to the WI while the violation is a direct result of non-local interference between two components of the entangled state…

反平行自旋相干对方向估计的全状态信息-干扰权衡

Full-state information-disturbance tradeoff for direction estimation with antiparallel spin-coherent pairs

通过旋转协方差和Choi问题，推导了反平行自旋1/2系统的最优信息-干扰权衡，发现最优操作是标量-矢量相干协变滤波器，其干扰小于平行自旋基准和反平行测量-重制备策略，并推广到任意自旋j的反平行自旋相干态。

Power of unentangled measurements on two antiparallel spins

We consider a pair of antiparallel spins polarized in a random direction to encode quantum information. We wish to extract as much information as possible on the polarization direction attainable by an unentangled measurement, i.e., by a measurement, whose outcomes are associated with product states. We develop analytically the upper bound 0.7935 bits to the Shannon mutual information obtainable by an unentangled measurement, which is definitely less than the value 0.8664 bits attained by an entangled measurement. This proves our main result, that not every ensemble of product states can be op…