State-independent contextuality sets for a qutrit

We present a generalized set of complex rays for a qutrit in terms of parameter $q=e^{i2\pi/k}$, a $k$-th root of unity. Remarkably, when $k=2,3$, the set reduces to two well known state-independent contextuality (SIC) sets: the Yu-Oh set and the Bengtsson-Blanchfield-Cabello set. Based on the Ramanathan-Horodecki criterion and the violation of a noncontextuality inequality, we have proven that the sets with $k=3m$ and $k=4$ are SIC, while the set with $k=5$ is not. Our generalized set of rays will theoretically enrich the study of SIC proof, and experimentally stimulate the novel application to quantum information processing.Comment: 4 pages, 2 figures; revised versio

Sharp Contradiction for Local-Hidden-State Model in Quantum Steering

In quantum theory, no-go theorems are important as they rule out the existence of a particular physical model under consideration. For instance, the Greenberger-Horne-Zeilinger (GHZ) theorem serves as a no-go theorem for the nonexistence of local hidden variable models by presenting a full contradiction for the multipartite GHZ states. However, the elegant GHZ argument for Bell's nonlocality does not go through for bipartite Einstein-Podolsky-Rosen (EPR) state. Recent study on quantum nonlocality has shown that the more precise description of EPR's original scenario is "steering", i.e., the nonexistence of local hidden state models. Here, we present a simple GHZ-like contradiction for any bipartite pure entangled state, thus proving a no-go theorem for the nonexistence of local hidden state models in the EPR paradox. This also indicates that the very simple steering paradox presented here is indeed the closest form to the original spirit of the EPR paradox.Comment: 9 pages. Revised version for Scientific Report

Productivity Spillovers among Linked Sectors

This paper estimates the impact of inter-sectoral linkages on productivity at the sectoral level. An exhaustive Chinese panel data set for capital, infrastructure and a sectoral agglomeration index is linked with an economic distance matrix derived from inter-sectoral transactions. The latter matrix can replace the conventional geographic distance matrix from spatial econometrics. The impact through spillovers is mixed—the direct impact passing to related sectors and back to the initial sector itself, and the indirect impact arising from changes in all sectors. The results suggest that (1) economic growth in a sector is driven by spillovers among sectors that are linked through flows of goods and services; economic distance plays a more important role in stimulating productivity spillover than spatial distance; a shorter economic distance transmits a larger productivity spillover between sectors; (2) infrastructure spillover improves labor productivity in linked sectors; (3) agglomeration diseconomies can be partially reduced by infrastructure investment.This paper is published in China Economic Review 25 (2013) 44–61