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arXiv 2203.09429quant-ph
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利用贝尔不等式求互无偏基的三种数值方法

Three numerical approaches to find mutually unbiased bases using Bell inequalities

Maria Prat Colomer, Luke Mortimer, Irénée Frérot, Máté Farkas, Antonio Acín

摘要:

相互无偏基对应于量子信息理论中非常有用的测量对。在最小的复合维度6中,已知存在3到7个相互无偏的基,有一个几十年前的猜想,称为Zauner猜想,指出最多存在3个。在这里,我们解决Zauner的猜想数字通过建设的贝尔不等式的每一对整数$n,d \ge 2$,可以最大限度地违反在尺寸$d$当且仅当$n$ MUB存在于该维。因此,我们把Zauner的猜想成一个优化问题,我们解决的三个数值方法:跷跷板优化,非线性半定规划和蒙特卡洛技术。所有三种方法都正确地识别了低维的已知情况,并且都表明在六维中不存在四个相互无偏的基础,并且都找到了在数值上优化相应的贝尔不等式的相同基础。此外,这些数值优化器似乎与六维中的“四个最远的基础”相一致,这是通过在[P. Raynal,X. Lü,B.- G. Englert,Phys.Rev.A,83062303(2011)]。最后,Monte Carlo结果表明,最多有三个MUB存在于10维。

英文摘要:

Mutually unbiased bases correspond to highly useful pairs of measurements in quantum information theory. In the smallest composite dimension, six, it is known that between three and seven mutually unbiased bases exist, with a decades-old conjecture, known as Zauner's conjecture, stating that there exist at most three. Here we tackle Zauner's conjecture numerically through the construction of Bell inequalities for every pair of integers $n,d \ge 2$ that can be maximally violated in dimension $d$ if and only if $n$ MUBs exist in that dimension. Hence we turn Zauner's conjecture into an optimisation problem, which we address by means of three numerical methods: see-saw optimisation, non-linear semidefinite programming and Monte Carlo techniques. All three methods correctly identify the known cases in low dimensions and all suggest that there do not exist four mutually unbiased bases in dimension six, with all finding the same bases that numerically optimise the corresponding Bell inequality. Moreover, these numerical optimisers appear to coincide with the "four most distant bases" in dimension six, found through numerically optimising a distance measure in [P. Raynal, X. Lü, B.-G. Englert, Phys. Rev. A, 83 062303 (2011)]. Finally, the Monte Carlo results suggest that at most three MUBs exist in dimension ten.

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