Achieving the Heisenberg limit in quantum metrology using quantum error correction

Quantum metrology has many important applications in science and technology, ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on measurement precision, called the Heisenberg limit, which can be achieved for noiseless quantum systems, but is not achievable in general for systems subject to noise. Here we study how measurement precision can be enhanced through quantum error correction, a general method for protecting a quantum system from the damaging effects of noise. We find a necessary and sufficient condition for achieving the Heisenberg limit using quantum probes subject to Markovian noise, assuming that noiseless ancilla systems are available, and that fast, accurate quantum processing can be performed. When the sufficient condition is satisfied, a quantum error-correcting code can be constructed which suppresses the noise without obscuring the signal; the optimal code, achieving the best possible precision, can be found by solving a semidefinite program.Comment: 16 pages, 2 figures, see also arXiv:1704.0628

E-Commerce in Agri-Food Sector : A Systematic Literature Review Based on Service-Dominant Logic

Agricultural e-commerce (AE) has attracted substantial attention within various research disciplines for several years. In this paper, we present a literature review of the recent state of AE research published from 2000 through to 2021 in 83 journals. Based on Service-Dominant Logic (S-D logic) and Qualitative Comparative Analysis (QCA), we identify six research themes, and a theoretical continuum is applied to reveal how research themes and scholarly approaches fit into the S-D logic framework. A general increasing trend in the number of articles confirms the escalating interest in AE research; however, different themes perform unevenly with S-D logic. Even though research themes such as Consumer Willingness are getting closer to S-D logic premises, and ideologies that are increasingly approaching S-D logic have been applied to analyzing AE topics, unfortunately, there remains a paucity of papers that wield S-D logic in the AE field. Our research focuses on an innovative emerging AE field and, simultaneously, provides an approach of integrating S-D logic into analyzing academic papers in the AE domain. This research may shed some light on future possibilities that S-D logic could support the co-creation of value between consumers and agribusiness managers, and other broader disciplines such as management and marketing.Peer reviewe

Classification-based forest management program and farmers' income : evidence from collective forest area in southern China

Purpose This article's purpose is to examine the effect of a Classification-Based Forest Management (CFM) program on farmers' income and determine whether its effect varies with the degree of farmers' concurrent occupations. Design/methodology/approach The authors use representative panel survey data from Longquan to explore the welfare effects of CFM on farmers. The analysis uses differences-in-differences with propensity score matching (PSM-DID) estimation techniques to deal with endogeneity problems when farmers make the decision to participate in CFM. Findings The results show that CFM has a positive effect on part-time forestry households (where forestry income accounts for between 5 and 50% of total income). In contrast, it has a negative impact on full-time forestry households (forestry income accounts for more than 50%), and no clear effect on nonforestry households whose forestry income is less than 5%. This research also shows that the positive effect of CFM on farmers' total income is mainly due to increase of off-farm income driven by CFM, while the negative effects consist of CFM's reduction of forestry income. Originality/value The extent of CFM's economic benefits to farmers is uncertain and largely unexplored. This paper analyzes the impact of CFM on income structure to explore the mechanisms explaining its effects on farmers' income. There are still challenges in ensuring the reliability and accuracy of CFM assessment. This paper collected natural experimental data and used the estimation technology of PSM-DID to solve the possible endogeneity problems.Peer reviewe

Optimized protocols for duplex quantum transduction

Quantum transducers convert quantum signals through hybrid interfaces of physical platforms in quantum networks. Modeled as quantum communication channels, performance of unidirectional quantum transduction can be measured by the quantum channel capacity. However, characterizing performance of quantum transducers used for duplex quantum transduction where signals are converted bidirectionally remains an open question. Here, we propose rate regions to characterize the performance of duplex quantum transduction. Using this tool, we find that quantum transducers optimized for simultaneous duplex transduction can outperform strategies based on the standard protocol of time-shared unidirectional transduction. Integrated over the frequency domain, we demonstrate that rate region can also characterize quantum transducers with finite bandwidth