自旋和极化态的截断SU（2）矩问题
Truncated su(2) moment problem for spin and polarization states
摘要：
我们解决的问题是否一组给定的期望值是兼容的第一和第二时刻的通用自旋运营商的系统与总自旋j。这些运营商出现在量子光学的斯托克斯运营商，以及在原子系综文献的总角动量运营商。我们把这个问题的一个特殊的扩展问题的二分量子比特状态，这个问题是密切相关的对称扩展问题，最近引起了广泛关注的量子信息文献的不同背景下。我们能够为每个大的自旋数提供可操作的近似解，事实上，在无限自旋数的极限情况下，该解变得精确。低自旋数的解决方案制定的超平面表征，类似于纠缠证人，可以有效地解决与半定规划。
英文摘要：
We address the problem whether a given set of expectation values is compatible with the first and second moments of the generic spin operators of a system with total spin j. Those operators appear as the Stokes operator in quantum optics, as well as the total angular momentum operators in the atomic ensemble literature. We link this problem to a particular extension problem for bipartite qubit states; this problem is closely related to the symmetric extension problem that has recently drawn much attention in different contexts of the quantum information literature. We are able to provide operational, approximate solutions for every large spin numbers, and in fact the solution becomes exact in the limiting case of infinite spin numbers. Solutions for low spin numbers are formulated in terms of a hyperplane characterization, similar to entanglement witnesses, that can be efficiently solved with semidefinite programming.
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