1,390 research outputs found

    Measuring the quantum state of a single system with minimum state disturbance

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    Conventionally, unknown quantum states are characterized using quantum-state tomography based on strong or weak measurements carried out on an ensemble of identically prepared systems. By contrast, the use of protective measurements offers the possibility of determining quantum states from a series of weak, long measurements performed on a single system. Because the fidelity of a protectively measured quantum state is determined by the amount of state disturbance incurred during each protective measurement, it is crucial that the initial quantum state of the system is disturbed as little as possible. Here we show how to systematically minimize the state disturbance in the course of a protective measurement, thus enabling the maximization of the fidelity of the quantum-state measurement. Our approach is based on a careful tuning of the time dependence of the measurement interaction and is shown to be dramatically more effective in reducing the state disturbance than the previously considered strategy of weakening the measurement strength and increasing the measurement time. We describe a method for designing the measurement interaction such that the state disturbance exhibits polynomial decay to arbitrary order in the inverse measurement time 1/T1/T. We also show how one can achieve even faster, subexponential decay, and we find that it represents the smallest possible state disturbance in a protective measurement. In this way, our results show how to optimally measure the state of a single quantum system using protective measurements.Comment: 7 pages, 4 figures, identical to published versio

    Breakdown of the perturbative renormalization group for S >= 1 random antiferromagnetic spin chains

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    We investigate the application of a perturbative renormalization group (RG) method to random antiferromagnetic Heisenberg chains with arbitrary spin size. At zero temperature we observe that initial arbitrary probability distributions develop a singularity at J=0, for all values of spin S. When the RG method is extended to finite temperatures, without any additional assumptions, we find anomalous results for S >= 1. These results lead us to conclude that the perturbative scheme is not adequate to study random chains with S >= 1. Therefore a random singlet phase in its more restrictive definition is only assured for spin-1/2 chains.Comment: 5 pages, 3 figures. To appear in Physical Review

    Delayed-choice quantum eraser for the undergraduate laboratory

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    In a delayed-choice quantum eraser, interference fringes are obtained by erasing which-way information after the interfering particle has already been irreversibly detected. Following an introductory review of delayed-choice experiments and quantum erasure, we describe the experimental realization of an optical delayed-choice quantum eraser, suitable for advanced undergraduates, based on polarization-entangled pairs of single photons. In our experiment, the delay of the erasure is implemented using two different setups. The first setup employs an arrangement of mirrors to increase the optical path length of the photons carrying which-way information. In the second setup, we use fiber-optic cables to elongate the path of these photons after their passage through the polarization analyzer but prior to their arrival at the detector. We compare our results to data obtained in the absence of a delay and find excellent agreement. This shows that the timing of the erasure is irrelevant, as also predicted by quantum mechanics. The experiment can serve as a valuable pedagogical tool for conveying the fundamentals of quantum mechanics.Comment: 13 pages, 5 figures, identical to published versio

    Leveraging University-School District Research Partnerships: Exploring the Longitudinal Effects of an Early Kindergarten Transition Program

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    With increasingly tight budgets, many public school districts lack research personnel to evaluate program efficacy or investigate best practices that raise student achievement. We highlight an example of a successful university-district partnership that offers district-driven research support while providing opportunities for practitioner-scholars to learn first-hand how to perform rigorous evaluation work. This article details the Early Kindergarten Transition program evaluation study conducted by a university-district partnership as well as testimony from district leadership on the utility of the research deliverables and long-term benefits of the research collaboration

    No-go theorem for the composition of quantum systems

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    Building on the Pusey-Barrett-Rudolph theorem, we derive a no-go theorem for a vast class of deterministic hidden-variables theories, including those consistent on their targeted domain. The strength of this result throws doubt on seemingly natural assumptions (like the "preparation independence" of the Pusey-Barrett-Rudolph theorem) about how "real states" of subsystems compose for joint systems in nonentangled states. This points to constraints in modeling tensor-product states, similar to constraints demonstrated for more complex states by the Bell and Bell-Kochen-Specker theorems.Comment: 4 pages. v2: new title, significant revisions. v3: condensed, matches final published versio

    Religion in Schools? The Importance of Recognizing the Impact of Religious Experiences

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    The school environment is a place of forced contact between diverse peoples. It is the perfect environment to nurture the diverse identities present. The influences on identity (i.e., language, ethnicity, religion, etc.) shape how students perceive information and learn. Some educators use these influences to help them instruct students. However, often overlooked is the influence of religious practices on language use and behavior in classrooms. This paper argues that the significance of understanding the religious practices of students is equally as important for planning instruction as knowing any other aspect of their culture, (i.e., the students’ native language(s)). Framed by principles of interfaith dialogue, the paper highlights a few examples of language use and behavior at the intersection of religion and education. The author argues that using the religious beliefs of students as strengths of their identity might eliminate some of the misunderstandings in the classroom and help establish an environment of mutual acceptance which might lead to deeper learning. Additionally, dialogue that includes aspects of religious practices might help students makes sense of the world and foster collaboration in the larger society

    Quantum fidelity approach to the ground state properties of the 1D ANNNI model in a transverse field

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    In this work we analyze the ground-state properties of the s=1/2s=1/2 one-dimensional ANNNI model in a transverse field using the quantum fidelity approach. We numerically determined the fidelity susceptibility as a function of the transverse field BxB_x and the strength of the next-nearest-neighbor interaction J2J_2, for systems of up to 24 spins. We also examine the ground-state vector with respect to the spatial ordering of the spins. The ground-state phase diagram shows ferromagnetic, paramagnetic, floating, 2,2\Braket{2,2} phases, and we predict an infinite number of modulated phases in the thermodynamic limit (LL \rightarrow \infty). The transition lines separating the modulated phases seem to be of second-order, whereas the line between the floating and the 2,2\Braket{2,2} phases is possibly of first-order.Comment: 10 pages, 20 figure

    Student Nurse Perceptions of Effective Medication Administration Education

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    Nursing faculty strive to educate students in a manner that prevents errors, promoting quality, patient-centered care. This endeavor is dependent upon meaningful and effective education that incorporates educational experiences reflective of the service sector. Anecdotal reports from clinical faculty and student nurses suggest that academic medication administration education may not optimally prepare students for safe entry into clinical practice. The aim of this phenomenologic qualitative research is to understand student nurse perceptions regarding teaching strategies and learning activities that prepared them for safe medication administration in acute care clinical settings. Focus group interviews resulted in two broad themes that are identified as Effective Education and Gaps in Education. Within these broad themes, findings revealed that students value faculty demonstrations, peer-learning opportunities, and repetitive practice with timely feedback. Study findings also pointed to educational gaps. Students reported needing to learn communication and conflict resolution strategies that would help them manage real-world interruptions, distractions, and computer generated alerts. Study findings recommend implementing relevant decision-support technology within academic lab learning activities

    Self-induced decoherence approach: Strong limitations on its validity in a simple spin bath model and on its general physical relevance

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    The "self-induced decoherence" (SID) approach suggests that (1) the expectation value of any observable becomes diagonal in the eigenstates of the total Hamiltonian for systems endowed with a continuous energy spectrum, and (2), that this process can be interpreted as decoherence. We evaluate the first claim in the context of a simple spin bath model. We find that even for large environments, corresponding to an approximately continuous energy spectrum, diagonalization of the expectation value of random observables does in general not occur. We explain this result and conjecture that SID is likely to fail also in other systems composed of discrete subsystems. Regarding the second claim, we emphasize that SID does not describe a physically meaningful decoherence process for individual measurements, but only involves destructive interference that occurs collectively within an ensemble of presupposed "values" of measurements. This leads us to question the relevance of SID for treating observed decoherence effects.Comment: 11 pages, 4 figures. Final published versio

    Ecology and the Common Good: Sustainability and Catholic Social Teaching

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    In recent years official Roman Catholic documents have addressed the ecological crisis from the perspective of Catholic social teaching. This expansion of Catholic social thought addresses the social and ecological question. This paper links environmental and human ecology with the concept of sustainability and proposes an interpretation of the common good and a definition of sustainability within Catholic social teaching. Our treatment of sustainability and Catholic social teaching includes: an analysis of the ecological processes that sustain nature; insights from human ecology, and an examination of models of sustainability as a foundation for re-structuring society to promote the common good. The paper provides a summary of the historical expansion of the common good within modern Catholic social thought, and concludes with an ecological interpretation of the common good and a definition of sustainability within the Catholic understanding of justice
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