论文标题
$ n $ qubit状态在所有两部分中具有最大的纠缠:图形状态方法
$n$-qubit states with maximum entanglement across all bipartitions: A graph state approach
论文作者
论文摘要
我们讨论了$ n $ qubit的纯状态的构建,在所有可能的选择中,$ k $ vs $ n-k $ bi-bartitioning的所有可能选择都具有最大的两部分纠缠,这意味着每个$ k $ qubit降低密度矩阵的von Neumann熵应为$ k \ ln 2 $。此类州已被称为$ k $ - 均匀,$ k $ -mm的状态。我们表明,“图表”的子集满足了这种情况,因此提供了构建$ k $均匀状态的食谱。使用图形状态查找$ K $均匀状态的构建食谱非常有用,因为每个图形状态都可以从仅使用受控的$ z $门开始从产品状态开始。但是,先验尚不清楚如何构造与任意$ k $统一状态相对应的图形,但尤其是,我们表明没有隔离顶点的图形为$ 1 $ - 均匀。作为圆形线性链条组织的图形对应于$ 2 $ - 均匀状态的情况,我们表明,托管此类状态所需的最小量子数为$ n = 5 $。 $ 3 $ - 均匀的状态可以通过在每一层中形成$ n/2 $ Qubits($ n = 2 \ Mathbb {z} $)的双层图来构建,从而使每个层形成完全连接的图形,而间层之间的连接则是使得在一层中的顶点一层与另一层的连接。 $ 4 $ - 均匀的状态可以通过在沿两个尺寸的周期性边界条件和至少具有至少$ 5 $的顶点的周期性边界条件和两个尺寸的周期性边界条件下绘制2D晶格图(也称为2D群集ising状态)来形成。
We discuss the construction of $n$-qubit pure states with maximum bipartite entanglement across all possible choices of $k$ vs $n-k$ bi-partitioning, which implies that the Von Neumann entropy of every $k$-qubit reduced density matrix corresponding to this state should be $k \ln 2 $. Such states have been referred to as $k$-uniform, $k$-MM states. We show that a subset of the 'graph states' satisfy this condition, hence providing a recipe for constructing $k$-uniform states. Finding recipes for construction of $k$-uniform states using graph states is useful since every graph state can be constructed starting from a product state using only controlled-$Z$ gates. Though, a priori it is not clear how to construct a graph which corresponds to an arbitrary $k$-uniform state, but in particular, we show that graphs with no isolated vertices are $1$-uniform. Graphs organized as a circular linear chain corresponds to the case of $2$-uniform state, where we show that the minimum number of qubits required to host such a state is $n=5$. $3$-uniform states can be constructed by forming bi-layer graphs with $n/2$ qubits ($n=2\mathbb{Z}$) in each layer, such that each layer forms a fully connected graph while inter-layer connections are such that the vertices in one layer has a one to one connectivity to the other layer. $4$-uniform states can be formed by taking 2D lattice graphs( also referred elsewhere as a 2D cluster Ising state ) with periodic boundary conditions along both dimensions and both dimensions having at least $5$ vertices.