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Article

Jonathan Pierce and Katherine Hicks

The advocacy coalition framework (ACF) was developed to explain policy processes where contentious coalitions of actors seek to translate competing belief systems into public policy. Advocacy coalitions may include interest groups, members of the media, scientists and academics, and government officials that share beliefs about a public issue and coordinate their behavior. These advocacy coalitions engage in various strategies using resources to influence policy change or stasis. As part of this process, advocacy coalition members may learn within and/or across coalitions. This framework is one of the most prominent and widely applied approaches to explain public policy. While it has been applied hundreds of times, in over 50 different countries, the vast majority of ACF applications have sought to explain domestic policy processes. A reason for the paucity of applications to foreign policy is that some ACF assumptions may not seem congruent to foreign policy issues. For example, the ACF uses a policy subsystem as the unit of analysis that may include a territorial dimension. Yet, the purpose of the territorial dimension is to limit the scope of the study. Therefore, this dimension can be substituted for a government body that has the authority or potential authority to make and implement foreign policy. In addition, the ACF assumes a central role for technical and scientific information in the policy process. Such information makes learning across coalitions more conducive, but the ACF can and should also be applied to normative issues, such as those more common among foreign policy research. This article introduces the ACF; provides an overview of the framework, including assumptions, key concepts and theories, and transferability of the ACF to foreign policy analysis; and discusses four exemplary applications. In addition, it proposes future research that scholars should explore as part of the nexus of the ACF and foreign policy analysis. In the final analysis, the authors suggest the ACF can and should be applied to foreign policy analysis to better understand the development of advocacy coalitions and how they influence changes and stasis in foreign policy.

Article

Todd A. Brun

Quantum error correction is a set of methods to protect quantum information—that is, quantum states—from unwanted environmental interactions (decoherence) and other forms of noise. The information is stored in a quantum error-correcting code, which is a subspace in a larger Hilbert space. This code is designed so that the most common errors move the state into an error space orthogonal to the original code space while preserving the information in the state. It is possible to determine whether an error has occurred by a suitable measurement and to apply a unitary correction that returns the state to the code space without measuring (and hence disturbing) the protected state itself. In general, codewords of a quantum code are entangled states. No code that stores information can protect against all possible errors; instead, codes are designed to correct a specific error set, which should be chosen to match the most likely types of noise. An error set is represented by a set of operators that can multiply the codeword state. Most work on quantum error correction has focused on systems of quantum bits, or qubits, which are two-level quantum systems. These can be physically realized by the states of a spin-1/2 particle, the polarization of a single photon, two distinguished levels of a trapped atom or ion, the current states of a microscopic superconducting loop, or many other physical systems. The most widely used codes are the stabilizer codes, which are closely related to classical linear codes. The code space is the joint +1 eigenspace of a set of commuting Pauli operators on n qubits, called stabilizer generators; the error syndrome is determined by measuring these operators, which allows errors to be diagnosed and corrected. A stabilizer code is characterized by three parameters [ [ n , k , d ] ] , where n is the number of physical qubits, k is the number of encoded logical qubits, and d is the minimum distance of the code (the smallest number of simultaneous qubit errors that can transform one valid codeword into another). Every useful code has n > k ; this physical redundancy is necessary to detect and correct errors without disturbing the logical state. Quantum error correction is used to protect information in quantum communication (where quantum states pass through noisy channels) and quantum computation (where quantum states are transformed through a sequence of imperfect computational steps in the presence of environmental decoherence to solve a computational problem). In quantum computation, error correction is just one component of fault-tolerant design. Other approaches to error mitigation in quantum systems include decoherence-free subspaces, noiseless subsystems, and dynamical decoupling.