A quantum quench is a process in which a parameter of a many-body system or quantum field theory is changed in time, taking an initial stationary state into a complicated excited state. Traditionally “quench” refers to a process where this time dependence is fast compared to all scales in the problem. However in recent years the terminology has been generalized to include smooth changes that are slow compared to initial scales in the problem, but become fast compared to the physical scales at some later time, leading to a breakdown of adiabatic evolution. Quantum quench has been recently used as a theoretical tool to study many aspects of nonequilibrium physics like thermalization and universal aspects of critical dynamics. Relatively recent experiments in cold atom systems have implemented such quench protocols, which explore dynamical passages through critical points, and study in detail the process of relaxation to a steady state. On the other hand, quenches which remain adiabatic have been explored as a useful technique in quantum computation.
Sumit R. Das
Petra Munro Hendry
Within contemporary, conventional, interpretive, qualitative paradigms, narrative and curriculum theorizing have traditionally been understood as primary constructs through which educational researchers seek to explain, represent, and conduct inquiry about education. This article traces shifting understandings of Western constructs of narrative and curriculum theorizing from a modernist perspective, in which they were conceived primarily as methods central to the representation of knowledge, to postmodernist perspectives in which they are conceptualized not as epistemological constructs, but as ethical/ontological systems of becoming through/in relationships. Historically, the emergence of “curriculum” and “narrative” (as phenomena) within a modernist, technocratic paradigm, rooted in an epistemological worldview, were constructed as “technologies” whose purpose was to represent knowledge. Current critiques of narrative and curriculum theorizing from the perspective of postmodern, poststructural, feminist, and new materialist perspectives illuminate understandings of these constructs as ethical-ontological-epistemological phenomena. From this perspective, narrative and curriculum theorizing have shifted from being understood as grounded in epistemology in order to provide “better” understanding/knowledge of experience, and alternatively are understood as ethical obligations to “be” in a web of relationships/intra-actions.
Fernando Hernández-Hernández and Juana M. Sancho-Gil
Researchers from various disciplines collect and generate field notes as a strategy to describe and reflect (through texts, photos, drawings, diagrams, or recordings) the complexity they face when addressing entangled and many-faceted phenomena. Field notes are as common research strategy not only to capture and amass instantly what researchers listen to, observe, think, and feel, but also to make explicit their reflexivity process, based on their observations and experiences. Field notes are not only a method for generating evidence, but a reflection of the ontological, epistemological, methodological, and ethical positionality that guide the researcher’s gaze. Paradoxically, although field notes are something most researchers use and are fundamental in their reports and publications, they are generally the hidden and idiosyncratic side of academic field work. The preparation of field notes is an extremely intricate issue, as the very same meaning, purposes, and roles of field notes heavily rely on the ethnographer’s onto-epistemological positioning. It is useful, then to contextualize field notes within the tradition of ethnography, without ignoring the fact that they are used in a wide range of disciplines (including anthropology, deology, architecture, geography, ethology, archaeology, and biology). It is also important to problematize the practice of taking, collecting, and generating field notes by taking into account the fact that the traditional vision of field notes as written (alphabetic) notes is being challenged by the availability of mobile applications that enable researchers to create and organize multimodal information. It is important to note the relevance of the so-called “headnotes,” as there are many impressions, scenes, and experiences that cannot be written down or can be difficult or impossible to document. In addition, the text goes beyond the reflection of interaction by introducing the notion of intra-action to overcome the metaphysics of individualism underlying conventional understandings of “interactions.” The growing multiplicity of languages, modes, and means of expression and communication must be examined alongside the strengths and limitations of multimodal field notes. Finally, the practice of keeping field notes requires a recognition of the reflexivity imbedded in this process. Field diaries can be seen as the first step toward ethnographic reporting, and here reflexivity becomes a fundamental part of the analyses involved.
Quantum decoherence is a physical process resulting from the entanglement of a system with environmental degrees of freedom. The entanglement allows the environment to behave like a measuring device on the initial system, resulting in the dynamical suppression of interference terms in mutually commuting bases. Because decoherence processes are extremely fast and often practically irreversible, measurements performed on the system after system–environment interactions typically yield outcomes empirically indistinguishable from physical collapse of the wave function. That is: environmental decoherence of a system’s phase relations produces effective eigenstates of a system in certain bases (depending on the details of the interaction) through prodigious damping—but not destruction—of the system’s off-diagonal terms in those bases. Although decoherence by itself is neither an interpretation of quantum physics nor indeed even new physics, there is much debate concerning the implications of this process in both the philosophical and the scientific literature. This is especially true regarding fundamental questions arising from quantum theory about the roles of measurement, observation, the nature of entanglement, and the emergence of classicality. In particular, acknowledging the part decoherence plays in interpretations of quantum mechanics recasts that debate in a new light.
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.
Measurement-based quantum computation is a framework of quantum computation, where entanglement is used as a resource and local measurements on qubits are used to drive the computation. It originates from the one-way quantum computer of Raussendorf and Briegel, who introduced the so-called cluster state as the underlying entangled resource state and showed that any quantum circuit could be executed by performing only local measurement on individual qubits. The randomness in the measurement outcomes can be dealt with by adapting future measurement axes so that computation is deterministic. Subsequent works have expanded the discussions of the measurement-based quantum computation to various subjects, including the quantification of entanglement for such a measurement-based scheme, the search for other resource states beyond cluster states and computational phases of matter. In addition, the measurement-based framework also provides useful connections to the emergence of time ordering, computational complexity and classical spin models, blind quantum computation, and so on, and has given an alternative, resource-efficient approach to implement the original linear-optic quantum computation of Knill, Laflamme, and Milburn. Cluster states and a few other resource states have been created experimentally in various physical systems, and the measurement-based approach offers a potential alternative to the standard circuit approach to realize a practical quantum computer.
The landscape of history of education has become transformed by approaches that up-end traditional assumptions of the vertical unidirectionality of power, policy, and discourse. These have been displaced by notions of relational comparison and crisscrossing entanglements that draw on Lefebvrian ideas of space and time. These ideas help to provide a sense of how the landscape of education can be understood as both a material and symbolic space, as apprehended, perceived, and lived space, in which social relations are constituted and constitutive of everyday realities. The history of South African education, and specifically its teacher education colleges, exemplifies how landscape can be defined and understood as such spaces. Its history can first be apprehended through different conceptual and historiographical approaches, taken over time, for understanding it. Second, the emergence of specific types of institutions, within colonial political, economic, and social frameworks that defined their physical location and unequal structure in terms of racially segregated and often gender-differentiated spaces, assists in an understanding of these as colonial remnants. The historical landscape of education remains as restructured and reconfigured spaces, in which institutions live on as much in social relations as in memory and in actual, but highly altered physical conditions. As lived spaces, third, historical landscapes of education also embodied learning spatial imaginaries, deeply ambivalent memories of formal and hidden curricula, of formative and shaping years, and as such become landscapes of memory and identity.