Computing entanglement costs of non-local operations on the basis of algebraic geometry

Abstract: In order to realize distributed quantum computations and quantify entanglement, it is crucial to minimize the entanglement consumption of implementing non-local operations by using local operations and classical communications (LOCC) channels. Although this optimization is generally NP-hard even if we relax the condition of LOCC channels to separable ones, many methodologies have been developed. However, each has only succeeded in determining the entanglement cost for specific cases. As a main mathematical result, we introduce a concept based on algebraic geometry to simplify the algebraic constraints in the optimization. This concept makes it possible to generalize previous studies in a unified way. Moreover, via the generalization, we solve an open problem posed by Yu et al. about the entanglement cost for local state discrimination. In addition to its versatility for analysis, this concept enables us to strengthen the DPS (Doherty, Parrilo, and Spedalieri) hierarchy and compute the entanglement cost approximately. By running the algorithm based on our improved DPS hierarchy, we numerically obtain the trade-off between the (one-shot) entanglement cost and the success probability for implementing various non-local quantum operations under separable channels, such as entanglement distillation and local implementation of non-local unitary channels, measurements, and state verification.