Coleman, Piers; Schofield, Andrew J
2005-01-20
As we mark the centenary of Albert Einstein's seminal contribution to both quantum mechanics and special relativity, we approach another anniversary--that of Einstein's foundation of the quantum theory of solids. But 100 years on, the same experimental measurement that puzzled Einstein and his contemporaries is forcing us to question our understanding of how quantum matter transforms at ultra-low temperatures.
Energy Technology Data Exchange (ETDEWEB)
Hoehn, Philipp [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Vienna (Austria); Wever, Christopher [Institute for Theoretical Particle Physics, Karlsruhe (Germany)
2016-07-01
In contrast to relativity, quantum theory has evaded a commonly accepted apprehension, in part because of the lack of physical statements that fully characterize it. In an attempt to remedy the situation, we summarize a novel reconstruction of the explicit formalism of quantum theory (for arbitrarily many qubits) from elementary rules on an observer's information acquisition. Our approach is purely operational: we consider an observer O interrogating a system S with binary questions and define S's state as O's ''catalogue of knowledge'' about S; no ontic assumptions are necessary. From the rules, one can derive, among other things, the state spaces, the unitary group, the von Neumann evolution and show that the binary questions correspond to Pauli operators. The reconstruction also offers new structural insights in the form of novel informational charges and informational complementarity relations which define the state spaces and the unitary group. This reconstruction permits a new perspective on quantum theory.
Frappier, Mélanie
2018-03-01
A century after its inception, quantum mechanics continues to puzzle us with dead-and-alive cats, waves "collapsing" into particles, and "spooky action at a distance." In his first book, What Is Real?, science writer and astrophysicist Adam Becker sets out to explore why the physics community is still arguing today about quantum mechanics's true meaning.
Drummond, P. D.; Chaturvedi, S.; Dechoum, K.; Comey, J.
2001-02-01
We investigate the theory of quantum fluctuations in non-equilibrium systems having large critical fluctuations. This allows us to treat the limits imposed by nonlinearities to quantum squeezing and noise reduction, and also to envisage future tests of quantum theory in regions of macroscopic quantum fluctuations. A long-term objective of this research is to identify suitable physical systems in which macroscopic 'Schrödinger cat'-like behaviour may be observed. We investigate two systems in particular of much current experimental interest, namely the degenerate parametric oscillator near threshold, and the evaporatively cooled (BEC). We compare the results obtained in the positive-P representation, as a fully quantum mechanical calculation, with the truncated Wigner phase space equation, also known as semi-classical theory. We show when these results agree and differ in calculations taken beyond the linearized approximation. In the region where the largest quantum fluctuations and Schrödinger cat-like behaviour might be expected, we find that the quantum predictions correspond very closely to the semi-classical theory. Nature abhors observing a Schrödinger cat. -Pacs: 03.65.Bz
Are Quantum Theory Questions Epistemic?
Directory of Open Access Journals (Sweden)
Viviana Yaccuzzi Polisena
2013-12-01
Full Text Available How to displace-move quantum theory [Ǭ] questions-problems to philosophy? Seeing the collapse of our society’s cultural-intellectual-morals, the philosophy of the 21st century has to contribute to the formation of new principles-formalisms: the big task of the contemporary philosophy ©] is to innovate, to transform the building of the knowledge! Which is the role of the contemporary philosopher? (Noam Chomsky. Building science so that it is more human, out of the scientific mercantilism so that it does not continue transgressing that which is most precious: the thought-life. The ideas that I propose demand a deep cultural-epistemiologicscientific-philosophical-ethical rethinking that goes from quantum entities up to life in society. The starting idea is «the quantum [Ǭ], the paradigm of the contemporary science ©]» (Bernard D’Espagnat. I propose to displace-move questions of the quantum theory [Ǭ]: spin, measure, layering to the field of philosophy (φ to build generic symbols. Can the contemporary episteme model the collapse of the ? For a philosopher, can understanding the importance and the behaviour of the spin bring something new to philosophy ? Can information of the states of the spin be used to observe in a holographic way the pattern energy-information contained in the quantum entities? Is quantum [Ǭ] physics mechanical?
Unconventional Quantum Critical Points
Xu, Cenke
2012-01-01
In this paper we review the theory of unconventional quantum critical points that are beyond the Landau's paradigm. Three types of unconventional quantum critical points will be discussed: (1). The transition between topological order and semiclassical spin ordered phase; (2). The transition between topological order and valence bond solid phase; (3). The direct second order transition between different competing orders. We focus on the field theory and universality class of these unconventio...
Frustration and quantum criticality
Vojta, Matthias
2018-06-01
This review article is devoted to the interplay between frustrated magnetism and quantum critical phenomena, covering both theoretical concepts and ideas as well as recent experimental developments in correlated-electron materials. The first part deals with local-moment magnetism in Mott insulators and the second part with frustration in metallic systems. In both cases, frustration can either induce exotic phases accompanied by exotic quantum critical points or lead to conventional ordering with unconventional crossover phenomena. In addition, the competition of multiple phases inherent to frustrated systems can lead to multi-criticality.
Frustration and quantum criticality.
Vojta, Matthias
2018-03-15
This review article is devoted to the interplay between frustrated magnetism and quantum critical phenomena, covering both theoretical concepts and ideas as well as recent experimental developments in correlated-electron materials. The first part deals with local-moment magnetism in Mott insulators and the second part with frustration in metallic systems. In both cases, frustration can either induce exotic phases accompanied by exotic quantum critical points or lead to conventional ordering with unconventional crossover phenomena. In addition, the competition of multiple phases inherent to frustrated systems can lead to multi-criticality. © 2018 IOP Publishing Ltd.
Quantum local asymptotic normality and other questions of quantum statistics
Kahn, Jonas
2008-01-01
This thesis is entitled Quantum Local Asymptotic Normality and other questions of Quantum Statistics ,. Quantum statistics are statistics on quantum objects. In classical statistics, we usually start from the data. Indeed, if we want to predict the weather, and can measure the wind or the
Bellazzini, Brando; Hubisz, Jay; Lee, Seung J.; Serra, Javi; Terning, John
2016-01-01
The appearance of the light Higgs boson at the LHC is difficult to explain, particularly in light of naturalness arguments in quantum field theory. However light scalars can appear in condensed matter systems when parameters (like the amount of doping) are tuned to a critical point. At zero temperature these quantum critical points are directly analogous to the finely tuned standard model. In this paper we explore a class of models with a Higgs near a quantum critical point that exhibits non-mean-field behavior. We discuss the parametrization of the effects of a Higgs emerging from such a critical point in terms of form factors, and present two simple realistic scenarios based on either generalized free fields or a 5D dual in AdS space. For both of these models we consider the processes $gg\\to ZZ$ and $gg\\to hh$, which can be used to gain information about the Higgs scaling dimension and IR transition scale from the experimental data.
Bellazzini, Brando; Csáki, Csaba; Hubisz, Jay; Lee, Seung J.; Serra, Javi; Terning, John
2016-10-01
The appearance of the light Higgs boson at the LHC is difficult to explain, particularly in light of naturalness arguments in quantum field theory. However, light scalars can appear in condensed matter systems when parameters (like the amount of doping) are tuned to a critical point. At zero temperature these quantum critical points are directly analogous to the finely tuned standard model. In this paper, we explore a class of models with a Higgs near a quantum critical point that exhibits non-mean-field behavior. We discuss the parametrization of the effects of a Higgs emerging from such a critical point in terms of form factors, and present two simple realistic scenarios based on either generalized free fields or a 5D dual in anti-de Sitter space. For both of these models, we consider the processes g g →Z Z and g g →h h , which can be used to gain information about the Higgs scaling dimension and IR transition scale from the experimental data.
Quantum critical Hall exponents
Lütken, C A
2014-01-01
We investigate a finite size "double scaling" hypothesis using data from an experiment on a quantum Hall system with short range disorder [1-3]. For Hall bars of width w at temperature T the scaling form is w(-mu)T(-kappa), where the critical exponent mu approximate to 0.23 we extract from the data is comparable to the multi-fractal exponent alpha(0) - 2 obtained from the Chalker-Coddington (CC) model [4]. We also use the data to find the approximate location (in the resistivity plane) of seven quantum critical points, all of which closely agree with the predictions derived long ago from the modular symmetry of a toroidal sigma-model with m matter fields [5]. The value nu(8) = 2.60513 ... of the localisation exponent obtained from the m = 8 model is in excellent agreement with the best available numerical value nu(num) = 2.607 +/- 0.004 derived from the CC-model [6]. Existing experimental data appear to favour the m = 9 model, suggesting that the quantum Hall system is not in the same universality class as th...
Prima facie questions in quantum gravity
Isham, C. J.
The long history of the study of quantum gravity has thrown up a complex web of ideas and approaches. The aim of this article is to unravel this web a little by analysing some of the {\\em prima facie\\/} questions that can be asked of almost any approach to quantum gravity and whose answers assist in classifying the different schemes. Particular emphasis is placed on (i) the role of background conceptual and technical structure; (ii) the role of spacetime diffeomorphisms; and (iii) the problem of time.
International Nuclear Information System (INIS)
Kirchner, Stefan; Si Qimiao
2009-01-01
Antiferromagnetic heavy fermion metals close to their quantum critical points display a richness in their physical properties unanticipated by the traditional approach to quantum criticality, which describes the critical properties solely in terms of fluctuations of the order parameter. This has led to the question as to how the Kondo effect gets destroyed as the system undergoes a phase change. In one approach to the problem, Kondo lattice systems are studied through a self-consistent Bose-Fermi Kondo model within the extended dynamical mean field theory. The quantum phase transition of the Kondo lattice is thus mapped onto that of a sub-Ohmic Bose-Fermi Kondo model. In the present article we address some aspects of the failure of the standard order-parameter functional for the Kondo-destroying quantum critical point of the Bose-Fermi Kondo model.
Quantum critical environment assisted quantum magnetometer
Jaseem, Noufal; Omkar, S.; Shaji, Anil
2018-04-01
A central qubit coupled to an Ising ring of N qubits, operating close to a critical point is investigated as a potential precision quantum magnetometer for estimating an applied transverse magnetic field. We compute the quantum Fisher information for the central, probe qubit with the Ising chain initialized in its ground state or in a thermal state. The non-unitary evolution of the central qubit due to its interaction with the surrounding Ising ring enhances the accuracy of the magnetic field measurement. Near the critical point of the ring, Heisenberg-like scaling of the precision in estimating the magnetic field is obtained when the ring is initialized in its ground state. However, for finite temperatures, the Heisenberg scaling is limited to lower ranges of N values.
Quantum criticality and black holes
International Nuclear Information System (INIS)
Sachdev, Subir; Mueller, Markus
2009-01-01
Many condensed matter experiments explore the finite temperature dynamics of systems near quantum critical points. Often, there are no well-defined quasiparticle excitations, and so quantum kinetic equations do not describe the transport properties completely. The theory shows that the transport coefficients are not proportional to a mean free scattering time (as is the case in the Boltzmann theory of quasiparticles), but are completely determined by the absolute temperature and by equilibrium thermodynamic observables. Recently, explicit solutions of this quantum critical dynamics have become possible via the anti-de Sitter/conformal field theory duality discovered in string theory. This shows that the quantum critical theory provides a holographic description of the quantum theory of black holes in a negatively curved anti-de Sitter space, and relates its transport coefficients to properties of the Hawking radiation from the black hole. We review how insights from this connection have led to new results for experimental systems: (i) the vicinity of the superfluid-insulator transition in the presence of an applied magnetic field, and its possible application to measurements of the Nernst effect in the cuprates, (ii) the magnetohydrodynamics of the plasma of Dirac electrons in graphene and the prediction of a hydrodynamic cyclotron resonance.
Supply chain design: Some critical questions
Directory of Open Access Journals (Sweden)
J. D. Nel
2010-11-01
Full Text Available Effective supply chain management (SCM requires organisations to work together in order to satisfy the needs of their end customers. Since organisations have to determine which processes and relationships will best achieve this aim, the design of their supply chains is important. Supply chain design thus forms an integral part of SCM and embodies the supply chain's structure. Unfortunately, too many organisations allow the design of their supply chain to evolve into its current form instead of planning their supply chain design (SCD efforts. The literature is vague on what SCD efforts constitute. This article consists of a comprehensive literature study in which an effort was made to bring more clarity on exactly what purposeful SCD efforts consist of, and some key questions were formulated that organisations could use as a guide in their SCD practices. From these critical questions a conceptual framework has been developed that can be used to determine whether organisations' SCD practices are aligned with organisational objectives. The conceptual framework was tested at two South African organisations to determine if it indeed can be be used to analyse the SCD practices of organisations.
Approaches to answering critical CER questions.
Kinnier, Christine V; Chung, Jeanette W; Bilimoria, Karl Y
2015-01-01
While randomized controlled trials (RCTs) are the gold standard for research, many research questions cannot be ethically and practically answered using an RCT. Comparative effectiveness research (CER) techniques are often better suited than RCTs to address the effects of an intervention under routine care conditions, an outcome otherwise known as effectiveness. CER research techniques covered in this section include: effectiveness-oriented experimental studies such as pragmatic trials and cluster randomized trials, treatment response heterogeneity, observational and database studies including adjustment techniques such as sensitivity analysis and propensity score analysis, systematic reviews and meta-analysis, decision analysis, and cost effectiveness analysis. Each section describes the technique and covers the strengths and weaknesses of the approach.
Fermion-induced quantum critical points.
Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong
2017-08-22
A unified theory of quantum critical points beyond the conventional Landau-Ginzburg-Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau-Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such type of Landau-forbidden quantum critical points are induced by gapless fermions, we call them fermion-induced quantum critical points. We further introduce a microscopic model of SU(N) fermions on the honeycomb lattice featuring a transition between Dirac semimetals and Kekule valence bond solids. Remarkably, our large-scale sign-problem-free Majorana quantum Monte Carlo simulations show convincing evidences of a fermion-induced quantum critical points for N = 2, 3, 4, 5 and 6, consistent with the renormalization group analysis. We finally discuss possible experimental realizations of the fermion-induced quantum critical points in graphene and graphene-like materials.Quantum phase transitions are governed by Landau-Ginzburg theory and the exceptions are rare. Here, Li et al. propose a type of Landau-forbidden quantum critical points induced by gapless fermions in two-dimensional Dirac semimetals.
Dynamics of quantum discord in a quantum critical environment
International Nuclear Information System (INIS)
Xi Zhengjun; Li Yongming; Lu Xiaoming; Sun Zhe
2011-01-01
We study the dynamics of quantum discord (QD) of two qubits independently coupled to an Ising spin chain in a transverse field, which exhibits a quantum phase transition. For this model, we drive the corresponding Kraus operators, obtain the analytic results of QD and compare the dynamics of QD with the dynamics of relative entropy of entanglement nearby the critical point. It is shown that the impact of the quantum criticality environment on QD can be concentrated in a very narrow region nearby the critical point, so it supplies an efficient way to detect the critical points. In the vicinity of the critical point, the evolution of QD is shown to be more complicated than that of entanglement. Furthermore, we find that separable states can also be used to reflect the quantum criticality of the environment.
Quantum criticality among entangled spin chains
Blanc, N.; Trinh, J.; Dong, L.; Bai, X.; Aczel, A. A.; Mourigal, M.; Balents, L.; Siegrist, T.; Ramirez, A. P.
2018-03-01
An important challenge in magnetism is the unambiguous identification of a quantum spin liquid1,2, of potential importance for quantum computing. In such a material, the magnetic spins should be fluctuating in the quantum regime, instead of frozen in a classical long-range-ordered state. While this requirement dictates systems3,4 wherein classical order is suppressed by a frustrating lattice5, an ideal system would allow tuning of quantum fluctuations by an external parameter. Conventional three-dimensional antiferromagnets can be tuned through a quantum critical point—a region of highly fluctuating spins—by an applied magnetic field. Such systems suffer from a weak specific-heat peak at the quantum critical point, with little entropy available for quantum fluctuations6. Here we study a different type of antiferromagnet, comprised of weakly coupled antiferromagnetic spin-1/2 chains as realized in the molecular salt K2PbCu(NO2)6. Across the temperature-magnetic field boundary between three-dimensional order and the paramagnetic phase, the specific heat exhibits a large peak whose magnitude approaches a value suggestive of the spinon Sommerfeld coefficient of isolated quantum spin chains. These results demonstrate an alternative approach for producing quantum matter via a magnetic-field-induced shift of entropy from one-dimensional short-range order to a three-dimensional quantum critical point.
Metatheoretical critics on current trends in Quantum Mechanics
Directory of Open Access Journals (Sweden)
Carlos C. Aranda
2014-06-01
Full Text Available Is our purpose in this article to review several approaches to modern problems in quantum mechanics from a critical point of view using the approximation of the traditional mathematical thinking. Nevertheless we point out several natural questions that arise in abstract mathematical reasoning.
Controlling superconductivity by tunable quantum critical points.
Seo, S; Park, E; Bauer, E D; Ronning, F; Kim, J N; Shim, J-H; Thompson, J D; Park, Tuson
2015-03-04
The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.
The Oxford Questions on the foundations of quantum physics.
Briggs, G A D; Butterfield, J N; Zeilinger, A
2013-09-08
The twentieth century saw two fundamental revolutions in physics-relativity and quantum. Daily use of these theories can numb the sense of wonder at their immense empirical success. Does their instrumental effectiveness stand on the rock of secure concepts or the sand of unresolved fundamentals? Does measuring a quantum system probe, or even create, reality or merely change belief? Must relativity and quantum theory just coexist or might we find a new theory which unifies the two? To bring such questions into sharper focus, we convened a conference on Quantum Physics and the Nature of Reality. Some issues remain as controversial as ever, but some are being nudged by theory's secret weapon of experiment.
The Oxford Questions on the foundations of quantum physics
Briggs, G. A. D.; Butterfield, J. N.; Zeilinger, A.
2013-01-01
The twentieth century saw two fundamental revolutions in physics—relativity and quantum. Daily use of these theories can numb the sense of wonder at their immense empirical success. Does their instrumental effectiveness stand on the rock of secure concepts or the sand of unresolved fundamentals? Does measuring a quantum system probe, or even create, reality or merely change belief? Must relativity and quantum theory just coexist or might we find a new theory which unifies the two? To bring such questions into sharper focus, we convened a conference on Quantum Physics and the Nature of Reality. Some issues remain as controversial as ever, but some are being nudged by theory's secret weapon of experiment. PMID:24062626
Interplay of quantum and classical fluctuations near quantum critical points
International Nuclear Information System (INIS)
Continentino, Mucio Amado
2011-01-01
For a system near a quantum critical point (QCP), above its lower critical dimension d L , there is in general a critical line of second-order phase transitions that separates the broken symmetry phase at finite temperatures from the disordered phase. The phase transitions along this line are governed by thermal critical exponents that are different from those associated with the quantum critical point. We point out that, if the effective dimension of the QCP, d eff = d + z (d is the Euclidean dimension of the system and z the dynamic quantum critical exponent) is above its upper critical dimension d c there is an intermingle of classical (thermal) and quantum critical fluctuations near the QCP. This is due to the breakdown of the generalized scaling relation ψ = νz between the shift exponent ψ of the critical line and the crossover exponent νz, for d + z > d c by a dangerous irrelevant interaction. This phenomenon has clear experimental consequences, like the suppression of the amplitude of classical critical fluctuations near the line of finite temperature phase transitions as the critical temperature is reduced approaching the QCP. (author)
Spotlighting quantum critical points via quantum correlations at finite temperatures
International Nuclear Information System (INIS)
Werlang, T.; Ribeiro, G. A. P.; Rigolin, Gustavo
2011-01-01
We extend the program initiated by T. Werlang et al. [Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest neighbors and also study the behavior of entanglement and quantum discord for second nearest neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.
Automatic Generation and Ranking of Questions for Critical Review
Liu, Ming; Calvo, Rafael A.; Rus, Vasile
2014-01-01
Critical review skill is one important aspect of academic writing. Generic trigger questions have been widely used to support this activity. When students have a concrete topic in mind, trigger questions are less effective if they are too general. This article presents a learning-to-rank based system which automatically generates specific trigger…
Detecting quantum critical points using bipartite fluctuations.
Rachel, Stephan; Laflorencie, Nicolas; Song, H Francis; Le Hur, Karyn
2012-03-16
We show that the concept of bipartite fluctuations F provides a very efficient tool to detect quantum phase transitions in strongly correlated systems. Using state-of-the-art numerical techniques complemented with analytical arguments, we investigate paradigmatic examples for both quantum spins and bosons. As compared to the von Neumann entanglement entropy, we observe that F allows us to find quantum critical points with much better accuracy in one dimension. We further demonstrate that F can be successfully applied to the detection of quantum criticality in higher dimensions with no prior knowledge of the universality class of the transition. Promising approaches to experimentally access fluctuations are discussed for quantum antiferromagnets and cold gases.
Criticality and entanglement in random quantum systems
International Nuclear Information System (INIS)
Refael, G; Moore, J E
2009-01-01
We review studies of entanglement entropy in systems with quenched randomness, concentrating on universal behavior at strongly random quantum critical points. The disorder-averaged entanglement entropy provides insight into the quantum criticality of these systems and an understanding of their relationship to non-random ('pure') quantum criticality. The entanglement near many such critical points in one dimension shows a logarithmic divergence in subsystem size, similar to that in the pure case but with a different universal coefficient. Such universal coefficients are examples of universal critical amplitudes in a random system. Possible measurements are reviewed along with the one-particle entanglement scaling at certain Anderson localization transitions. We also comment briefly on higher dimensions and challenges for the future.
Random walks, critical phenomena, and triviality in quantum field theory
International Nuclear Information System (INIS)
Fernandez, R.; Froehlich, J.; Sokal, A.D.
1992-01-01
The subject of this book is equilibrium statistical mechanics - in particular the theory of critical phenomena - and quantum field theory. A general review of the theory of critical phenomena in spin systems, field theories, and random-walk and random-surface models is presented. Among the more technical topics treated in this book, the central theme is the use of random-walk representations as a tool to derive correlation inequalities. The consequences of these inequalities for critical-exponent theory and the triviality question in quantum field theory are expounded in detail. The book contains some previously unpublished results. It addresses both the researcher and the graduate student in modern statistical mechanics and quantum field theory. (orig.)
Quench dynamics across quantum critical points
International Nuclear Information System (INIS)
Sengupta, K.; Powell, Stephen; Sachdev, Subir
2004-01-01
We study the quantum dynamics of a number of model systems as their coupling constants are changed rapidly across a quantum critical point. The primary motivation is provided by the recent experiments of Greiner et al. [Nature (London) 415, 39 (2002)] who studied the response of a Mott insulator of ultracold atoms in an optical lattice to a strong potential gradient. In a previous work, it had been argued that the resonant response observed at a critical potential gradient could be understood by proximity to an Ising quantum critical point describing the onset of density wave order. Here we obtain numerical results on the evolution of the density wave order as the potential gradient is scanned across the quantum critical point. This is supplemented by studies of the integrable quantum Ising spin chain in a transverse field, where we obtain exact results for the evolution of the Ising order correlations under a time-dependent transverse field. We also study the evolution of transverse superfluid order in the three-dimensional case. In all cases, the order parameter is best enhanced in the vicinity of the quantum critical point
Fermion-induced quantum critical points
Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai; Yao, Hong
2017-01-01
A unified theory of quantum critical points beyond the conventional Landau?Ginzburg?Wilson paradigm remains unknown. According to Landau cubic criterion, phase transitions should be first-order when cubic terms of order parameters are allowed by symmetry in the Landau?Ginzburg free energy. Here, from renormalization group analysis, we show that second-order quantum phase transitions can occur at such putatively first-order transitions in interacting two-dimensional Dirac semimetals. As such t...
Critical behaviors of gravity under quantum perturbations
Directory of Open Access Journals (Sweden)
ZHANG Hongsheng
2014-02-01
Full Text Available Phase transition and critical phenomenon is a very interesting topic in thermodynamics and statistical mechanics. Gravity is believed to have deep and inherent relation to thermodynamics. Near the critical point,the perturbation becomes significant. Thus for ordinary matter (governed by interactions besides gravity the critical behavior will become very different if we ignore the perturbations around the critical point,such as mean field theory. We find that the critical exponents for RN-AdS spacetime keep the same values even when we consider the full quantum perturbations. This indicates a key difference between gravity and ordinary thermodynamic system.
Developing critical thinking through Socratic Questioning: An Action Research Study
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Husniah Sahamid
2016-07-01
Full Text Available An action research study was conducted among 24 Form 4 level Malaysian students, aged 16. The duration of the study was five months and constituted 16 one-hour literature lessons (short stories from the secondary level Malaysian English Language Upper Secondary Level school syllabus. This paper describes my experience as a teacher-as-researcher to assist students to respond to teacher questions through Paul’s (1993 model of Socratic Questioning which claims to develop students’ critical thinking. Data was collected through researcher’s field notes, students’ writing tasks and student interviews which were analysed after each cycle of the action research study. Changes and adaptations were consequently made based on the data collected and upon teacher reflection to improve practice. The results of this study indicate that repeated practice of Socratic Questioning had a positive effect on student responses and writing tasks. Some of the factors affecting students’ performance included students’ language proficiency, weak reading ability and students’ anxiety towards the questioning method. These issues had to be addressed and dealt with, before Socratic Questioning could be properly implemented in the classroom. Keywords: Socratic questioning, teacher questioning, critical thinking, action research
Question of Consciousness: to Quantum Mechanics for the Answers
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Karpenko Ivan A.
2014-09-01
Full Text Available The article presents the possible role of consciousness in quantum-mechanical description of physical reality. The widely spread interpretations of quantum phenomena are considered as indicating the apparent connection between conscious processes (such as observation and the properties of the microcosm. The reasons for discrepancies between the results of observations of the microcosm and macrocosm and the potential association of consciousness with these reasons are closely investigated. The mentioned connection is meant to be interpreted in the sense that the probable requirement for a complete understanding of quantum theory is the adequate description of consciousness within it and that the correct theory of consciousness should include quantum-mechanical theoretical apparatus. In this context, the question about the methods of scientific cognition is discussed, in particular, the problem of the place and the importance of intellectual intuition in science and philosophy of science. The author draws the conclusions about the current state of the “measuring” consciousness. problem in its relationship with
Dynamical Response near Quantum Critical Points.
Lucas, Andrew; Gazit, Snir; Podolsky, Daniel; Witczak-Krempa, William
2017-02-03
We study high-frequency response functions, notably the optical conductivity, in the vicinity of quantum critical points (QCPs) by allowing for both detuning from the critical coupling and finite temperature. We consider general dimensions and dynamical exponents. This leads to a unified understanding of sum rules. In systems with emergent Lorentz invariance, powerful methods from quantum field theory allow us to fix the high-frequency response in terms of universal coefficients. We test our predictions analytically in the large-N O(N) model and using the gauge-gravity duality and numerically via quantum Monte Carlo simulations on a lattice model hosting the interacting superfluid-insulator QCP. In superfluid phases, interacting Goldstone bosons qualitatively change the high-frequency optical conductivity and the corresponding sum rule.
Universal signatures of fractionalized quantum critical points.
Isakov, Sergei V; Melko, Roger G; Hastings, Matthew B
2012-01-13
Ground states of certain materials can support exotic excitations with a charge equal to a fraction of the fundamental electron charge. The condensation of these fractionalized particles has been predicted to drive unusual quantum phase transitions. Through numerical and theoretical analysis of a physical model of interacting lattice bosons, we establish the existence of such an exotic critical point, called XY*. We measure a highly nonclassical critical exponent η = 1.493 and construct a universal scaling function of winding number distributions that directly demonstrates the distinct topological sectors of an emergent Z(2) gauge field. The universal quantities used to establish this exotic transition can be used to detect other fractionalized quantum critical points in future model and material systems.
Dynamic trapping near a quantum critical point
Kolodrubetz, Michael; Katz, Emanuel; Polkovnikov, Anatoli
2015-02-01
The study of dynamics in closed quantum systems has been revitalized by the emergence of experimental systems that are well-isolated from their environment. In this paper, we consider the closed-system dynamics of an archetypal model: spins driven across a second-order quantum critical point, which are traditionally described by the Kibble-Zurek mechanism. Imbuing the driving field with Newtonian dynamics, we find that the full closed system exhibits a robust new phenomenon—dynamic critical trapping—in which the system is self-trapped near the critical point due to efficient absorption of field kinetic energy by heating the quantum spins. We quantify limits in which this phenomenon can be observed and generalize these results by developing a Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings can potentially be interesting in the context of early universe physics, where the role of the driving field is played by the inflaton or a modulus field.
Deconfined Quantum Critical Points: Symmetries and Dualities
Directory of Open Access Journals (Sweden)
Chong Wang
2017-09-01
Full Text Available The deconfined quantum critical point (QCP, separating the Néel and valence bond solid phases in a 2D antiferromagnet, was proposed as an example of (2+1D criticality fundamentally different from standard Landau-Ginzburg-Wilson-Fisher criticality. In this work, we present multiple equivalent descriptions of deconfined QCPs, and use these to address the possibility of enlarged emergent symmetries in the low-energy limit. The easy-plane deconfined QCP, besides its previously discussed self-duality, is dual to N_{f}=2 fermionic quantum electrodynamics, which has its own self-duality and hence may have an O(4×Z_{2}^{T} symmetry. We propose several dualities for the deconfined QCP with SU(2 spin symmetry which together make natural the emergence of a previously suggested SO(5 symmetry rotating the Néel and valence bond solid orders. These emergent symmetries are implemented anomalously. The associated infrared theories can also be viewed as surface descriptions of (3+1D topological paramagnets, giving further insight into the dualities. We describe a number of numerical tests of these dualities. We also discuss the possibility of “pseudocritical” behavior for deconfined critical points, and the meaning of the dualities and emergent symmetries in such a scenario.
Dark matter and dark energy: The critical questions
International Nuclear Information System (INIS)
Michael S. Turner
2002-01-01
Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% ± 1% baryons; 29% ± 4% cold dark matter; and 66% ± 6% dark energy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious dark energy that is causing the Universe to speed up
Effective and fundamental quantum fields at criticality
Energy Technology Data Exchange (ETDEWEB)
Scherer, Michael
2010-10-28
We employ Wetterich's approach to functional renormalization as a suitable method to investigate universal phenomena in non-perturbative quantum field theories both qualitatively and quantitatively. Therefore we derive and investigate flow equations for a class of chiral Yukawa models with and without gauge bosons and reveal fixed-point mechanisms. In four dimensions chiral Yukawa systems serve as toy models for the standard model Higgs sector and show signatures of asymptotically safe fixed points by a balancing of bosonic and fermionic contributions. In the approximations investigated this renders the theory fundamental and solves the triviality problem. Further, we obtain predictions for the Higgs mass and even for the top mass of our toy model. In three dimensions we compute the critical exponents which define new universality classes and provide benchmark values for systems of strongly correlated chiral fermions. In a Yukawa system of non-relativistic two-component fermions a fixed point dominates the renormalization flow giving rise to universality in the BCS-BEC crossover. We push the functional renormalization method to a quantitative level and we compute the critical temperature and the single-particle gap with a considerable precision for the whole crossover. Finally, we provide further evidence for the asymptotic safety scenario in quantum gravity by confirming the existence of an ultraviolet fixed point under inclusion of a curvature-ghost coupling. (orig.)
Effective and fundamental quantum fields at criticality
International Nuclear Information System (INIS)
Scherer, Michael
2010-01-01
We employ Wetterich's approach to functional renormalization as a suitable method to investigate universal phenomena in non-perturbative quantum field theories both qualitatively and quantitatively. Therefore we derive and investigate flow equations for a class of chiral Yukawa models with and without gauge bosons and reveal fixed-point mechanisms. In four dimensions chiral Yukawa systems serve as toy models for the standard model Higgs sector and show signatures of asymptotically safe fixed points by a balancing of bosonic and fermionic contributions. In the approximations investigated this renders the theory fundamental and solves the triviality problem. Further, we obtain predictions for the Higgs mass and even for the top mass of our toy model. In three dimensions we compute the critical exponents which define new universality classes and provide benchmark values for systems of strongly correlated chiral fermions. In a Yukawa system of non-relativistic two-component fermions a fixed point dominates the renormalization flow giving rise to universality in the BCS-BEC crossover. We push the functional renormalization method to a quantitative level and we compute the critical temperature and the single-particle gap with a considerable precision for the whole crossover. Finally, we provide further evidence for the asymptotic safety scenario in quantum gravity by confirming the existence of an ultraviolet fixed point under inclusion of a curvature-ghost coupling. (orig.)
Detection of quantum critical points by a probe qubit.
Zhang, Jingfu; Peng, Xinhua; Rajendran, Nageswaran; Suter, Dieter
2008-03-14
Quantum phase transitions occur when the ground state of a quantum system undergoes a qualitative change when an external control parameter reaches a critical value. Here, we demonstrate a technique for studying quantum systems undergoing a phase transition by coupling the system to a probe qubit. It uses directly the increased sensibility of the quantum system to perturbations when it is close to a critical point. Using an NMR quantum simulator, we demonstrate this measurement technique for two different types of quantum phase transitions in an Ising spin chain.
New quantum criticality revealed under pressure
International Nuclear Information System (INIS)
Watanabe, Shinji; Miyake, Kazumasa
2017-01-01
Unconventional quantum critical phenomena observed in Yb-based periodic crystals such as YbRh_2Si_2 and β-YbAlB_4 have been one of the central issues in strongly correlated electron systems. The common criticality has been discovered in the quasicrystal Yb_1_5Au_5_1Al_3_4, which surprisingly persists under pressure at least up to P = 1.5 GPa. The T/H scaling where the magnetic susceptibility can be expressed as a single scaling function of the ratio of the temperature T to the magnetic field H has been discovered in the quasicrystal, which is essentially the same as that observed in β-YbAlB_4. Recently, the T/H scaling as well as the common criticality has also been observed even in the approximant crystal Yb_1_4Au_5_1Al_3_5 under pressure. The theory of critical Yb-valence fluctuation gives a natural explanation for these striking phenomena in a unified way. (author)
Pedrosa-de-Jesus, Helena; Moreira, Aurora; Lopes, Betina; Watts, Mike
2014-05-01
Background: Critical thinking is one of the very highest orders of cognitive abilities and a key competency in higher education. Asking questions is an important component of rich learning experiences, structurally embedded in the operations of critical thinking. Our clear sense is that critical thinking and, within that, critical questioning, is heavily context dependent, in the sense that is applied, used by critical learners in a contextualised way. Purpose: Our research deals with enhancing science undergraduates' critical questioning. We are interested in understanding and describing the nature and development of students' critical questioning. The purpose is to conceptualise critical questioning as a competency, into three domains - knowledge, skills and attitudes/dispositions. We have no interest in a taxonomic category of context-free question-types called 'critical questions'. In contrast, our view is that 'being a critical questioner' trades heavily on context. Sources of evidence: Four cases are considered as illuminative of the dimensions of science undergraduates' critical questioning. Data were collected in natural learning environments through non-participant observation, audio-taping teacher-students interactions and semi-structured interviews. Students' written material resulting from diverse learning tasks was also collected. Main argument: Our supposition is that one vehicle for achieving university students as critical thinkers is to enable them not just to ask critical questions, but to be critical questioners. We relate critical questioning to three domains: (1) context, (2) competency and (3) delivery, and propose a model based on illuminating examples of the in-classroom action. Conclusions: The dimensions of the competency-context-delivery model provide a framework for describing successful student critical questioning, showing that students' capacity to be critical can be developed. It is possible, in our view, to generate critical
Quantum field theory and critical phenomena
Zinn-Justin, Jean
1996-01-01
Over the last twenty years quantum field theory has become not only the framework for the discussion of all fundamental interactions except gravity, but also for the understanding of second-order phase transitions in statistical mechanics. This advanced text is based on graduate courses and summer schools given by the author over a number of years. It approaches the subject in terms of path and functional intergrals, adopting a Euclidean metric and using the language of partition and correlation functions. Renormalization and the renormalization group are examined, as are critical phenomena and the role of instantons. Changes for this edition 1. Extensive revision to eliminate a few bugs that had survived the second edition and (mainly) to improve the pedagogical presentation, as a result of experience gathered by lecturing. 2. Additional new topics; holomorphic or coherent state path integral; functional integral and representation of the field theory S-matrix in the holomorphic formalis; non-relativistic li...
Quantum critical dynamics for a prototype class of insulating antiferromagnets
Wu, Jianda; Yang, Wang; Wu, Congjun; Si, Qimiao
2018-06-01
Quantum criticality is a fundamental organizing principle for studying strongly correlated systems. Nevertheless, understanding quantum critical dynamics at nonzero temperatures is a major challenge of condensed-matter physics due to the intricate interplay between quantum and thermal fluctuations. The recent experiments with the quantum spin dimer material TlCuCl3 provide an unprecedented opportunity to test the theories of quantum criticality. We investigate the nonzero-temperature quantum critical spin dynamics by employing an effective O (N ) field theory. The on-shell mass and the damping rate of quantum critical spin excitations as functions of temperature are calculated based on the renormalized coupling strength and are in excellent agreement with experiment observations. Their T lnT dependence is predicted to be dominant at very low temperatures, which will be tested in future experiments. Our work provides confidence that quantum criticality as a theoretical framework, which is being considered in so many different contexts of condensed-matter physics and beyond, is indeed grounded in materials and experiments accurately. It is also expected to motivate further experimental investigations on the applicability of the field theory to related quantum critical systems.
Recollapsing quantum cosmologies and the question of entropy
International Nuclear Information System (INIS)
Bojowald, Martin; Tavakol, Reza
2008-01-01
Recollapsing homogeneous and isotropic models present one of the key ingredients for cyclic scenarios. This is considered here within a quantum cosmological framework in the presence of a free scalar field with, in turn, a negative cosmological constant and spatial curvature. Effective equations shed light on the quantum dynamics around a recollapsing phase and the evolution of state parameters such as fluctuations and correlations through such a turn around. In the models considered here, the squeezing of an initial state is found to be strictly monotonic in time during the expansion, turn around, and contraction phases. The presence of such monotonicity is of potential importance in relation to a long-standing debate concerning the (a)symmetry between the expanding and contracting phases in a recollapsing universe. Furthermore, together with recent analogous results concerning a bounce, one can extend this monotonicity throughout an entire cycle. This provides a strong motivation for employing the degree of squeezing as an alternative measure of (quantum) entropy. It may also serve as a new concept of emergent time described by a variable without classical analog. The evolution of the squeezing in emergent oscillating scenarios can in principle provide constraints on the viability of such models.
Quantum phase transition and critical phenomena
International Nuclear Information System (INIS)
Dutta, A.; Chakrabarti, B.K.
1998-01-01
We intend to describe briefly the generic features associated with the zero temperature transition in quantum mechanical systems. We elucidate the discussion of the introductory section using the very common example of Ising model in a transverse field. We discuss the method of fermionisation for one dimensional systems. The quantum-classical correspondence is discussed using Suzuki-Trotter method. We then introduce the quantum rotor model and discuss its spherical limit. We finally discuss novel features arising due to the presence of quenched randomness in the quantum Ising and rotor systems. (author)
11 critical questions to ask when buying a physician practice.
Jessee, William F
2012-07-01
Answering probing questions in advance of a practice purchase can help hospital and health system leaders make informed decisions. The questions are intended to stimulate careful consideration before entering into a practice acquisition; no single piece of information or answer should be considered definitive in the final decision-making process. Success depends on having a clear game plan and spending time ensuring that all players-board, management, physician leaders, and the physicians who will be employees--understand and support the plan.
Characteristic signatures of quantum criticality driven by geometrical frustration.
Tokiwa, Yoshifumi; Stingl, Christian; Kim, Moo-Sung; Takabatake, Toshiro; Gegenwart, Philipp
2015-04-01
Geometrical frustration describes situations where interactions are incompatible with the lattice geometry and stabilizes exotic phases such as spin liquids. Whether geometrical frustration of magnetic interactions in metals can induce unconventional quantum critical points is an active area of research. We focus on the hexagonal heavy fermion metal CeRhSn, where the Kondo ions are located on distorted kagome planes stacked along the c axis. Low-temperature specific heat, thermal expansion, and magnetic Grüneisen parameter measurements prove a zero-field quantum critical point. The linear thermal expansion, which measures the initial uniaxial pressure derivative of the entropy, displays a striking anisotropy. Critical and noncritical behaviors along and perpendicular to the kagome planes, respectively, prove that quantum criticality is driven be geometrical frustration. We also discovered a spin flop-type metamagnetic crossover. This excludes an itinerant scenario and suggests that quantum criticality is related to local moments in a spin liquid-like state.
Universal Postquench Prethermalization at a Quantum Critical Point
Gagel, Pia; Orth, Peter P.; Schmalian, Jörg
2014-11-01
We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive nonequilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are: (i) a power law rise of order and correlations after an initial collapse of the equilibrium state and (ii) a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches.
On a class of quantum Langevin equations and the question of approach to equilibrium
International Nuclear Information System (INIS)
Maassen, J.D.M.
1982-01-01
This thesis is concerned with a very simple 'open' quantum system, i.e. being in contact with the outer world. It is asked whether the motion of this system shows frictional behaviour in that it tends to thermal equilibrium. A partial positive answer is given to this question, more precisely, to the question if the solution of the quantum mechanical Langevin equation that describes the Lamb-model (a harmonic oscillator damped by coupling with a string), approaches an equilibrium state. In two sections, the classical and quantum Langevin equations are treated analogously. (Auth.)
International Nuclear Information System (INIS)
Hadjisawas, Nicolas.
1982-01-01
After a critical study of the logical quantum mechanics formulations of Jauch and Piron, classical and quantum versions of statistical inference are studied. In order to do this, the significance of the Jaynes and Kulback principles (maximum likelihood, least squares principles) is revealed from the theorems established. In the quantum mechanics inference problem, a ''distance'' between states is defined. This concept is used to solve the quantum equivalent of the classical problem studied by Kulback. The ''projection postulate'' proposition is subsequently deduced [fr
Quantum uncertainty in critical systems with three spins interaction
International Nuclear Information System (INIS)
Carrijo, Thiago M; Avelar, Ardiley T; Céleri, Lucas C
2015-01-01
In this article we consider two spin-1/2 chains described, respectively, by the thermodynamic limit of the XY model with the usual two site interaction, and an extension of this model (without taking the thermodynamics limit), called XYT, were a three site interaction term is presented. To investigate the critical behaviour of such systems we employ tools from quantum information theory. Specifically, we show that the local quantum uncertainty, a quantity introduced in order to quantify the minimum quantum share of the variance of a local measurement, can be used to indicate quantum phase transitions presented by these models at zero temperature. Due to the connection of this quantity with the quantum Fisher information, the results presented here may be relevant for quantum metrology and quantum thermodynamics. (paper)
Two Questions about Critical-Thinking Tests in Higher Education
Benjamin, Roger
2014-01-01
In this article, the author argues first, that critical-thinking skills do exist independent of disciplinary thinking skills and are not compromised by interaction effects with the major; and second, that standardized tests (e.g., the Collegiate Learning Assessment, or CLA, which is his example throughout the article) are the best way to measure…
New Type of Quantum Criticality in the Pyrochlore Iridates
Directory of Open Access Journals (Sweden)
Lucile Savary
2014-11-01
Full Text Available Magnetic fluctuations and electrons couple in intriguing ways in the vicinity of zero-temperature phase transitions—quantum critical points—in conducting materials. Quantum criticality is implicated in non-Fermi liquid behavior of diverse materials and in the formation of unconventional superconductors. Here, we uncover an entirely new type of quantum critical point describing the onset of antiferromagnetism in a nodal semimetal engendered by the combination of strong spin-orbit coupling and electron correlations, and which is predicted to occur in the iridium oxide pyrochlores. We formulate and solve a field theory for this quantum critical point by renormalization group techniques and show that electrons and antiferromagnetic fluctuations are strongly coupled and that both these excitations are modified in an essential way. This quantum critical point has many novel features, including strong emergent spatial anisotropy, a vital role for Coulomb interactions, and highly unconventional critical exponents. Our theory motivates and informs experiments on pyrochlore iridates and constitutes a singular realistic example of a nontrivial quantum critical point with gapless fermions in three dimensions.
Quantum theories of the early universe - a critical appraisal
International Nuclear Information System (INIS)
Hu, B.L.
1988-01-01
A critical appraisal of certain general problems in the study of quantum processes in curved space as applied to the construction of theories of the early universe is presented. Outstanding issues in different cosmological models and the degree of success of different quantum processes in addressing these issues are summarized. (author)
Vector boson excitations near deconfined quantum critical points.
Huh, Yejin; Strack, Philipp; Sachdev, Subir
2013-10-18
We show that the Néel states of two-dimensional antiferromagnets have low energy vector boson excitations in the vicinity of deconfined quantum critical points. We compute the universal damping of these excitations arising from spin-wave emission. Detection of such a vector boson will demonstrate the existence of emergent topological gauge excitations in a quantum spin system.
Directory of Open Access Journals (Sweden)
Katherine J. Janzen
2011-11-01
Full Text Available This paper builds upon a foundational paper (under review which explores the rudiments of the quantum perspective of learning. The quantum perspective of learning uses the principles of exchange theory or borrowed theory from the field of quantum holism pioneered by quantum physicist David Bohm (1971, 1973 to understand learning in a new way. Bohm proposes that everything exists as wholes, rather than as parts, and that everything is connected. Similarly, the quantum perspective of learning proposes that individuals learn in holistic ways as they interact with temporal and in infinitely extending virtual worlds. Further, according to the quantum perspective of learning, learners have infinite potential. In this paper, the quantum perspective of learning is examined utilizing a combination of Schunk’s (1991 and Ertmer and Newby’s (1993 definitive questions for aligning learning theory with instructional design. These seven definitive questions focus on how learning happens, influential factors in learning, the role of memory, transfer of knowledge, modalities of learning that can best explain the quantum perspective of learning, applicable assumptions, and a discussion of how instruction can be organized to optimize learning. Examples of strategies that facilitate the quantum perspective of learning are provided.
Quantum critical scaling and fluctuations in Kondo lattice materials
Yang, Yi-feng; Pines, David; Lonzarich, Gilbert
2017-01-01
We propose a phenomenological framework for three classes of Kondo lattice materials that incorporates the interplay between the fluctuations associated with the antiferromagnetic quantum critical point and those produced by the hybridization quantum critical point that marks the end of local moment behavior. We show that these fluctuations give rise to two distinct regions of quantum critical scaling: Hybridization fluctuations are responsible for the logarithmic scaling in the density of states of the heavy electron Kondo liquid that emerges below the coherence temperature T∗, whereas the unconventional power law scaling in the resistivity that emerges at lower temperatures below TQC may reflect the combined effects of hybridization and antiferromagnetic quantum critical fluctuations. Our framework is supported by experimental measurements on CeCoIn5, CeRhIn5, and other heavy electron materials. PMID:28559308
We experience more than we comprehend. Quantum physics and questions of life. rev. new ed.
International Nuclear Information System (INIS)
Duerr, Hans-Peter; Oesterreicher-Mollwo, Marianne
2015-01-01
The quantum physics has been arrived by thinking and experimenting to revolutioning knowledges, which determine our world, also if only few have understood these theories in their real sense. The present book follows the question, whether and how far a consciousness trained by quantum physics can reach more directly to the understanding of questions of life and religious questions than a thinking, which is obliged to classical physics. It deals especially with fundamental existential questions: The theme of personal responsibility, the value of the individual existence, the evaluation of the personal I-you relation. Hans Peter Duerr, a personality with guiding qualities, as they are necessary in the new millennium, is the ideal speech partner for the dimension of this theme. The connections of natural sciences and religion, ecology, and sociological change have always driven the Heisenberg successor. How can we speech about that, which science cannot comprehend?. What means self, identity, responsibility for the quantum physicist? An exciting meeting.
Quantum criticality in Einstein-Maxwell-dilaton gravity
International Nuclear Information System (INIS)
Wen, Wen-Yu
2012-01-01
We investigate the quantum Lifshitz criticality in a general background of Einstein-Maxwell-dilaton gravity. In particular, we demonstrate the existence of critical point with dynamic critical exponent z by tuning a nonminimal coupling to its critical value. We also study the effect of nonminimal coupling and exponent z to the Efimov states and holographic RG flow in the overcritical region. We have found that the nonminimal coupling increases the instability for a probe scalar to condensate and its back reaction is discussed. At last, we give a quantum mechanics treatment to a solvable system with z=2, and comment for generic z>2.
On foundational and geometric critical aspects of quantum electrodynamics
International Nuclear Information System (INIS)
Prugovecki, E.
1994-01-01
The foundational difficulties encountered by the conventional formulation of quantum electrodynamics, and the criticism by Dirac Schwinger, Rohrlich, and others, aimed at some of the physical and mathematical premises underlying that formulation, are reviewed and discussed. The basic failings of the conventional methods of quantization of the electromagnetic field are pointed out, especially with regard to the issue of local (anti) commutativity of quantum fields as an embodiment of relativistic microcausality. A brief description is given of a recently advanced new type of approach to quantum electrodynamics, and to quantum field theory in general, which is epistemically based on intrinsically quantum ideas about the physical nature of spacetime, and is mathematically based on a fiber theoretical formulation of quantum geometries, aimed in part at removing the aforementioned difficulties and inconsistencies. It is shown that these ideas can be traced to a conceptualization of spacetime outlined by Einstein in the last edition of his well-known semipopular exposition of relativity theory. 57 refs
Itinerant density instability at classical and quantum critical points
Feng, Yejun; van Wezel, Jasper; Flicker, Felix; Wang, Jiyang; Silevitch, D. M.; Littlewood, P. B.; Rosenbaum, T. F.
2015-03-01
Itinerant density waves are model systems for studying quantum critical behavior. In both the model spin- and charge-density-wave systems Cr and NbSe2, it is possible to drive a continuous quantum phase transition with critical pressures below 10 GPa. Using x-ray diffraction techniques, we are able to directly track the evolution of the ordering wave vector Q across the pressure-temperature phase diagram. We find a non-monotonic dependence of Q on pressure. Using a Landau-Ginsburg theoretical framework developed by McMillan for CDWs, we evaluate the importance of the physical terms in driving the formation of ordered states at both the thermal and quantum phase transitions. We find that the itinerant instability is the deciding factor for the emergent order, which is further influenced by the critical fluctuations in both the thermal and quantum limits.
The role of student’s critical asking question in developing student’s critical thinking skills
Santoso, T.; Yuanita, L.; Erman, E.
2018-01-01
Questioning means thinking, and thinking is manifested in the form of questions. Research that studies the relationship between questioning and students’ critical thinking skills is little, if any. The aim of this study is to examine how student’s questions skill correlates to student’s critical thinking skills in learning of chemistry. The research design used was one group pretest-posttest design. The participants involved were 94 students, all of whom attended their last semesters, Chemistry Education of Tadulako University. A pre-test was administered to check participants’ ability to ask critical questions and critical thinking skills in learning chemistry. Then, the students were taught by using questioning technique. After accomplishing the lesson, a post-test was given to evaluate their progress. Obtained data were analyzed by using Pair-Samples T.Test and correlation methods. The result shows that the level of the questions plays an important role in critical thinking skills is the question levels of predictive, analysis, evaluation and inference.
Educating for Critical Thinking: Thought-Encouraging Questions in a Community of Inquiry
Golding, Clinton
2011-01-01
This paper presents one method for educating for critical thinking in Higher Education. It elaborates Richard Paul's method of Socratic questioning to show how students can learn to be critical thinkers. This method combines and uses the wider pedagogical and critical thinking literature in a new way: it emphasises a thinking-encouraging approach…
Quantum critical matter. Quantum phase transitions with multiple dynamics and Weyl superconductors
International Nuclear Information System (INIS)
Meng, Tobias
2012-01-01
In this PhD thesis, the physics of quantum critical matter and exotic quantum state close to quantum phase transitions is investigated. We will focus on three different examples that highlight some of the interesting phenomena related to quantum phase transitions. Firstly, we discuss the physics of quantum phase transitions in quantum wires as a function of an external gate voltage when new subbands are activated. We find that at these transitions, strong correlations lead to the formation of an impenetrable gas of polarons, and identify criteria for possible instabilities in the spin- and charge sectors of the model. Our analysis is based on the combination of exact resummations, renormalization group techniques and Luttinger liquid approaches. Secondly, we turn to the physics of multiple divergent time scales close to a quantum critical point. Using an appropriately generalized renormalization group approach, we identify that the presence of multiple dynamics at a quantum phase transition can lead to the emergence of new critical scaling exponents and thus to the breakdown of the usual scaling schemes. We calculate the critical behavior of various thermodynamic properties and detail how unusual physics can arise. It is hoped that these results might be helpful for the interpretation of experimental scaling puzzles close to quantum critical points. Thirdly, we turn to the physics of topological transitions, and more precisely the physics of Weyl superconductors. The latter are the superconducting variant of the topologically non-trivial Weyl semimetals, and emerge at the quantum phase transition between a topological superconductor and a normal insulator upon perturbing the transition with a time reversal symmetry breaking perturbation, such as magnetism. We characterize the topological properties of Weyl superconductors and establish a topological phase diagram for a particular realization in heterostructures. We discuss the physics of vortices in Weyl
The Foundations of Quantum Mechanics: Historical Analysis and Open Questions -- Cesena, 2004
Garola, Claudio; Rossi, Arcangelo; Sozzo, Sandro
Introduction / C. Garola, A. Rossi and S. Sozzo -- If Bertlmann had three feet / A. Afriat -- Macroscopic interpretability of quantum component systems / R. Ascoli -- Premeasurement versus measurement: a basic form of complementarity / G. Auletta and G. Tarozzi -- Remarks on conditioning / E. G. Beltrametti -- Entangled state preparation in experiments on quantum non-locality / V. Berardi and A. Garuccio -- The first steps of quantum electrodynamics: what is it that's being quantized? / S. Bergia -- On the meaning of element in the science of italic tradition, the question of physical objectivity (and/or physical meaning) and quantum mechanics / G. Boscarino -- Mathematics and epistemology in Planck's theoretical work (1898-1915) / P. Campogalliani -- On the free motion with noise / B. Carazza and R. Tedeschi -- Field quantization and wave/particle duality / M. Cini -- Parastatistics in econophysics? / D. Costantini and U. Garibaldi -- Theory-laden instruments and quantum mechanics / S. D'Agostino -- Quantum non-locality and the mathematical representation of experience / V. Fano -- On the notion of proposition in classical and quantum mechanics / C. Garola and S. Sozzo -- The electromagnetic conception of nature and the origins of quantum physics / E. A. Giannetto -- What we talk about when we talk about universe computability / S. Guccione -- Bohm and Bohmian mechanics / G. Introzzi and M. Rossetti -- An objective background for quantum theory relying on thermodynamic concepts / L. Lanz and B. Vacchini -- The entrance of quantum mechanics in Italy: from Garbasso to Fermi / M. Leone and N. Robotti -- The measure of momentum in quantum mechanics / F. Logiurato and C. Tarsitani -- On the two-slit interference experiment: a statistical discussion / M. Minozzo -- Why the reactivity of the elements is a relational property, and why it matters / V. Mosini -- Detecting non compatible properties in double-slit experiment without erasure / G. Nisticò -- If you can
Universal post-quench prethermalization at a quantum critical point
Orth, Peter P.; Gagel, Pia; Schmalian, Joerg
2015-03-01
We consider an open system near a quantum critical point that is suddenly moved towards the critical point. The bath-dominated diffusive non-equilibrium dynamics after the quench is shown to follow scaling behavior, governed by a critical exponent that emerges in addition to the known equilibrium critical exponents. We determine this exponent and show that it describes universal prethermalized coarsening dynamics of the order parameter in an intermediate time regime. Implications of this quantum critical prethermalization are a powerlaw rise of order and correlations after an initial collapse of the equilibrium state and a crossover to thermalization that occurs arbitrarily late for sufficiently shallow quenches. [1] P. Gagel, P. P. Orth, J. Schmalian, Phys.Rev. Lett. (in press) arXiv:1406.6387
Black holes as critical point of quantum phase transition.
Dvali, Gia; Gomez, Cesar
We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.
Quantum critical phenomena and conformal invariance
International Nuclear Information System (INIS)
Zhe Chang.
1995-05-01
We show that the Abelian bosonization of continuum limit of the 1D Hubbard model corresponds to the 2D explicitly conformal invariant Gaussian model at weak coupling limit. A universality argument is used to extend the equivalence to an entire segment of the critical line of the strongly correlated electron system. An integral equation satisfied by the mapping function between critical lines of the 1D Hubbard model and 2D Gaussian model is obtained and then solved in some limiting cases. By making use of the fact that the free Hubbard system reduces to four fermions and each of them is related to a c = 1/2 conformal field theory, we present exactly the partition function of the Hubbard model on a finite 1D lattice. (author). 16 refs
Universal postquench coarsening and aging at a quantum critical point
Gagel, Pia; Orth, Peter P.; Schmalian, Jörg
2015-09-01
The nonequilibrium dynamics of a system that is located in the vicinity of a quantum critical point is affected by the critical slowing down of order-parameter correlations with the potential for novel out-of-equilibrium universality. After a quantum quench, i.e., a sudden change of a parameter in the Hamiltonian, such a system is expected to almost instantly fall out of equilibrium and undergo aging dynamics, i.e., dynamics that depends on the time passed since the quench. Investigating the quantum dynamics of an N -component φ4 model coupled to an external bath, we determine this universal aging and demonstrate that the system undergoes a coarsening, governed by a critical exponent that is unrelated to the equilibrium exponents of the system. We analyze this behavior in the large-N limit, which is complementary to our earlier renormalization-group analysis, allowing in particular the direct investigation of the order-parameter dynamics in the symmetry-broken phase and at the upper critical dimension. By connecting the long-time limit of fluctuations and response, we introduce a distribution function that shows that the system remains nonthermal and exhibits quantum coherence even on long time scales.
A magnetically induced quantum critical point in holography
Gursoy, U.; Gnecchi, A.; Toldo, C.; Papadoulaki, O.
We investigate quantum critical points in a 2+1 dimensional gauge theory at finite chemical potential χ and magnetic field B. The gravity dual is based on 4D NN = 2 Fayet-Iliopoulos gauged supergravity and the solutions we consider — that are constructed analytically — are extremal, dyonic,
Electron self-trapping at quantum and classical critical points
Auslender, M.I.; Katsnelson, M.I.
2006-01-01
Using Feynman path integral technique estimations of the ground state energy have been found for a conduction electron interacting with order parameter fluctuations near quantum critical points. In some cases only singular perturbation theory in the coupling constant emerges for the electron ground
Critical current in the Integral Quantum Hall Effect
International Nuclear Information System (INIS)
Kostadinov, I.Z.
1985-11-01
A multiparticle theory of the Integral Quantum Hall Effect (IQHE) was constructed operating with pairs wave function as an order parameter. The IQHE is described with bosonic macroscopic states while the fractional QHE with fermionic ones. The calculation of the critical current and Hall conductivity temperature dependence is presented. (author)
Reggeon quantum mechanics: a critical discussion
International Nuclear Information System (INIS)
Ciafaloni, M.; Le Bellac, M.; Rossi, G.C.
1977-01-01
The quantum-mechanical problem of reggeon field theory in zero transverse dimensions is re-examined in order to set up a precise mathematical framework for the case μ=α(0)-1>0. The authors establish a Hamiltonian formulation in a Hilbert space for μ 2 (0, infinity) space. It is proved that the S-matrix and the pomeron Green functions, at fixed rapidity Y and triple-pomeron coupling lambda not equal to 0, have a spectral decomposition and are analytic in μ for -infinity 0, most of the qualitative results found by previous authors are confirmed and in particular the tunnelling shift [approximately exp(-μ 2 /2lambda 2 )] setting the scale for the asymptotic behaviour in Y. In the classical limit of lambda/μ small it is found that the action, for μ>0, develops a singularity in Y at some value Ysub(c). Arguements are given to show that for Y approximately Ysub(c) perturbation theory breaks shown. Most of these results are shown to be stable against the addition of a small quartic coupling of the simplest type [lambda'(anti psipsi) 2 ] up to the 'magic' value lambda'=lambda 2 /μ. The existence of a level crossing at this value is confirmed by an analytic continuation in lambda'. (Auth.)
Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points
Energy Technology Data Exchange (ETDEWEB)
Fischer, I.A.
2006-07-01
This thesis focusses on two classes of systems that exhibit non-Fermi liquid behaviour in experiments: we investigated aspects of chiral ferromagnets and of antiferromagnetic metals close to a quantum critical point. In chiral ferromagnets, the absence of inversion symmetry makes spin-orbit coupling possible, which leads to a helical modulation of the ferromagnetically ordered state. We studied the motion of electrons in the magnetically ordered state of a metal without inversion symmetry by calculating their generic band-structure. We found that spin-orbit coupling, although weak, has a profound effect on the shape of the Fermi surface: On a large portion of the Fermi surface the electron motion parallel to the helix practically stops. Signatures of this effect can be expected to show up in measurements of the anomalous Hall effect. Recent neutron scattering experiments uncovered the existence of a peculiar kind of partial order in a region of the phase diagram adjacent to the ordered state of the chiral ferromagnet MnSi. Starting from the premise that this partially ordered state is a thermodynamically distinct phase, we investigated an extended Ginzburg-Landau theory for chiral ferromagnets. In a certain parameter regime of the Ginzburg-Landau theory we identified crystalline phases that are reminiscent of the so-called blue phases in liquid crystals. Many antiferromagnetic heavy-fermion systems can be tuned into a regime where they exhibit non-Fermi liquid exponents in the temperature dependence of thermodynamic quantities such as the specific heat capacity; this behaviour could be due to a quantum critical point. If the quantum critical behaviour is field-induced, the external field does not only suppress antiferromagnetism but also induces spin precession and thereby influences the dynamics of the order parameter. We investigated the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. We
Quantum critical spin-2 chain with emergent SU(3) symmetry.
Chen, Pochung; Xue, Zhi-Long; McCulloch, I P; Chung, Ming-Chiang; Huang, Chao-Chun; Yip, S-K
2015-04-10
We study the quantum critical phase of an SU(2) symmetric spin-2 chain obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling of the finite-size energies and entanglement entropy by exact diagonalization and density-matrix renormalization group methods. From the numerical results of the energy spectra, central charge, and scaling dimension we identify the conformal field theory describing the whole critical phase to be the SU(3)_{1} Wess-Zumino-Witten model. We find that, while the Hamiltonian is only SU(2) invariant, in this critical phase there is an emergent SU(3) symmetry in the thermodynamic limit.
Quantum critical singularities in two-dimensional metallic XY ferromagnets
Varma, Chandra M.; Gannon, W. J.; Aronson, M. C.; Rodriguez-Rivera, J. A.; Qiu, Y.
2018-02-01
An important problem in contemporary physics concerns quantum-critical fluctuations in metals. A scaling function for the momentum, frequency, temperature, and magnetic field dependence of the correlation function near a 2D-ferromagnetic quantum-critical point (QCP) is constructed, and its singularities are determined by comparing to the recent calculations of the correlation functions of the dissipative quantum XY model (DQXY). The calculations are motivated by the measured properties of the metallic compound YFe2Al10 , which is a realization of the DQXY model in 2D. The frequency, temperature, and magnetic field dependence of the scaling function as well as the singularities measured in the experiments are given by the theory without adjustable exponents. The same model is applicable to the superconductor-insulator transitions, classes of metallic AFM-QCPs, and as fluctuations of the loop-current ordered state in hole-doped cuprates. The results presented here lend credence to the solution found for the 2D-DQXY model and its applications in understanding quantum-critical properties of diverse systems.
Characterization of the critical submanifolds in quantum ensemble control landscapes
International Nuclear Information System (INIS)
Wu Rebing; Rabitz, Herschel; Hsieh, Michael
2008-01-01
The quantum control landscape is defined as the functional that maps the control variables to the expectation values of an observable over the ensemble of quantum systems. Analyzing the topology of such landscapes is important for understanding the origins of the increasing number of laboratory successes in the optimal control of quantum processes. This paper proposes a simple scheme to compute the characteristics of the critical topology of the quantum ensemble control landscapes showing that the set of disjoint critical submanifolds one-to-one corresponds to a finite number of contingency tables that solely depend on the degeneracy structure of the eigenvalues of the initial system density matrix and the observable whose expectation value is to be maximized. The landscape characteristics can be calculated as functions of the table entries, including the dimensions and the numbers of positive and negative eigenvalues of the Hessian quadratic form of each of the connected components of the critical submanifolds. Typical examples are given to illustrate the effectiveness of this method
Quantum Triple Point and Quantum Critical End Points in Metallic Magnets.
Belitz, D; Kirkpatrick, T R
2017-12-29
In low-temperature metallic magnets, ferromagnetic (FM) and antiferromagnetic (AFM) orders can exist, adjacent to one another or concurrently, in the phase diagram of a single system. We show that universal quantum effects qualitatively alter the known phase diagrams for classical magnets. They shrink the region of concurrent FM and AFM order, change various transitions from second to first order, and, in the presence of a magnetic field, lead to either a quantum triple point where the FM, AFM, and paramagnetic phases all coexist or a quantum critical end point.
Entanglement dynamics in critical random quantum Ising chain with perturbations
Energy Technology Data Exchange (ETDEWEB)
Huang, Yichen, E-mail: ychuang@caltech.edu
2017-05-15
We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique. - Highlights: • We study the dynamical quantum phase transition between many-body localized phases. • We simulate the dynamics of a very long random spin chain with matrix product states. • We observe numerically super-logarithmic growth of entanglement entropy with time.
Superconductivity versus quantum criticality: Effects of thermal fluctuations
Wang, Huajia; Wang, Yuxuan; Torroba, Gonzalo
2018-02-01
We study the interplay between superconductivity and non-Fermi liquid behavior of a Fermi surface coupled to a massless SU(N ) matrix boson near the quantum critical point. The presence of thermal infrared singularities in both the fermionic self-energy and the gap equation invalidates the Eliashberg approximation, and makes the quantum-critical pairing problem qualitatively different from that at zero temperature. Taking the large N limit, we solve the gap equation beyond the Eliashberg approximation, and obtain the superconducting temperature Tc as a function of N . Our results show an anomalous scaling between the zero-temperature gap and Tc. For N greater than a critical value, we find that Tc vanishes with a Berezinskii-Kosterlitz-Thouless scaling behavior, and the system retains non-Fermi liquid behavior down to zero temperature. This confirms and extends previous renormalization-group analyses done at T =0 , and provides a controlled example of a naked quantum critical point. We discuss the crucial role of thermal fluctuations in relating our results with earlier work where superconductivity always develops due to the special role of the first Matsubara frequency.
Quantum Critical “Opalescence” around Metal-Insulator Transitions
Misawa, Takahiro; Yamaji, Youhei; Imada, Masatoshi
2006-08-01
Divergent carrier-density fluctuations equivalent to the critical opalescence of gas-liquid transition emerge around a metal-insulator critical point at a finite temperature. In contrast to the gas-liquid transitions, however, the critical temperatures can be lowered to zero, which offers a challenging quantum phase transition. We present a microscopic description of such quantum critical phenomena in two dimensions. The conventional scheme of phase transitions by Ginzburg, Landau, and Wilson is violated because of its topological nature. It offers a clear insight into the criticalities of metal-insulator transitions (MIT) associated with Mott or charge-order transitions. Fermi degeneracy involving the diverging density fluctuations generates emergent phenomena near the endpoint of the first-order MIT and must shed new light on remarkable phenomena found in correlated metals such as unconventional cuprate superconductors. It indeed accounts for the otherwise puzzling criticality of the Mott transition recently discovered in an organic conductor. We propose to accurately measure enhanced dielectric fluctuations at small wave numbers.
Thermal conductivity at a disordered quantum critical point
International Nuclear Information System (INIS)
Hartnoll, Sean A.; Ramirez, David M.; Santos, Jorge E.
2016-01-01
Strongly disordered and strongly interacting quantum critical points are difficult to access with conventional field theoretic methods. They are, however, both experimentally important and theoretically interesting. In particular, they are expected to realize universal incoherent transport. Such disordered quantum critical theories have recently been constructed holographically by deforming a CFT by marginally relevant disorder. In this paper we find additional disordered fixed points via relevant disordered deformations of a holographic CFT. Using recently developed methods in holographic transport, we characterize the thermal conductivity in both sets of theories in 1+1 dimensions. The thermal conductivity is found to tend to a constant at low temperatures in one class of fixed points, and to scale as T"0"."3 in the other. Furthermore, in all cases the thermal conductivity exhibits discrete scale invariance, with logarithmic in temperature oscillations superimposed on the low temperature scaling behavior. At no point do we use the replica trick.
Critical indices for the Yukawa2 quantum field theory
International Nuclear Information System (INIS)
Bonetto, F.
1997-01-01
The understanding of the Yukawa 2 quantum field theory is still incomplete if the fermionic mass is much smaller than the coupling. We analyze the Schwinger functions for small coupling uniformly in the mass and we find that the asymptotic behavior of the two-point Schwinger function is anomalous and described by two critical indices, related to the renormalization of the mass and of the wave function. The indices are explicitly computed by convergent series in the coupling. (orig.)
Entanglement entropy of 2D conformal quantum critical points: hearing the shape of a quantum drum.
Fradkin, Eduardo; Moore, Joel E
2006-08-04
The entanglement entropy of a pure quantum state of a bipartite system A union or logical sumB is defined as the von Neumann entropy of the reduced density matrix obtained by tracing over one of the two parts. In one dimension, the entanglement of critical ground states diverges logarithmically in the subsystem size, with a universal coefficient that for conformally invariant critical points is related to the central charge of the conformal field theory. We find that the entanglement entropy of a standard class of z=2 conformal quantum critical points in two spatial dimensions, in addition to a nonuniversal "area law" contribution linear in the size of the AB boundary, generically has a universal logarithmically divergent correction, which is completely determined by the geometry of the partition and by the central charge of the field theory that describes the critical wave function.
Anomalous quantum critical spin dynamics in YFe2Al10
Huang, K.; Tan, C.; Zhang, J.; Ding, Z.; MacLaughlin, D. E.; Bernal, O. O.; Ho, P.-C.; Baines, C.; Wu, L. S.; Aronson, M. C.; Shu, L.
2018-04-01
We report results of a muon spin relaxation (μ SR ) study of YFe2Al10 , a quasi-two-dimensional (2D) nearly ferromagnetic metal in which unconventional quantum critical behavior is observed. No static Fe2 + magnetism, with or without long-range order, is found down to 19 mK. The dynamic muon spin relaxation rate λ exhibits power-law divergences in temperature and magnetic field, the latter for fields that are too weak to affect the electronic spin dynamics directly. We attribute this to the proportionality of λ (ωμ,T ) to the dynamic structure factor S (ωμ,T ) , where ωμ≈105-107s-1 is the muon Zeeman frequency. These results suggest critical divergences of S (ωμ,T ) in both temperature and frequency. Power-law scaling and a 2D dissipative quantum XY model both yield forms for S (ω ,T ) that agree with neutron scattering data (ω ≈1012s-1 ). Extrapolation to μ SR frequencies agrees semiquantitatively with the observed temperature dependence of λ (ωμ,T ) , but predicts frequency independence for ωμ≪T , in extreme disagreement with experiment. We conclude that the quantum critical spin dynamics of YFe2Al10 is not well understood at low frequencies.
Entropy Flow Through Near-Critical Quantum Junctions
Friedan, Daniel
2017-05-01
This is the continuation of Friedan (J Stat Phys, 2017. doi: 10.1007/s10955-017-1752-8). Elementary formulas are derived for the flow of entropy through a circuit junction in a near-critical quantum circuit close to equilibrium, based on the structure of the energy-momentum tensor at the junction. The entropic admittance of a near-critical junction in a bulk-critical circuit is expressed in terms of commutators of the chiral entropy currents. The entropic admittance at low frequency, divided by the frequency, gives the change of the junction entropy with temperature—the entropic "capacitance". As an example, and as a check on the formalism, the entropic admittance is calculated explicitly for junctions in bulk-critical quantum Ising circuits (free fermions, massless in the bulk), in terms of the reflection matrix of the junction. The half-bit of information capacity per end of critical Ising wire is re-derived by integrating the entropic "capacitance" with respect to temperature, from T=0 to T=∞.
Isomorphism of critical and off-critical operator spaces in two-dimensional quantum field theory
Energy Technology Data Exchange (ETDEWEB)
Delfino, G. [International School of Advanced Studies (SISSA), Trieste (Italy)]|[INFN sezione di Trieste (Italy); Niccoli, G. [Univ. de Cergy-Pontoise (France). LPTM
2007-12-15
For the simplest quantum field theory originating from a non-trivial fixed point of the renormalization group, the Lee-Yang model, we show that the operator space determined by the particle dynamics in the massive phase and that prescribed by conformal symmetry at criticality coincide. (orig.)
Defect production in nonlinear quench across a quantum critical point.
Sen, Diptiman; Sengupta, K; Mondal, Shreyoshi
2008-07-04
We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory.
McAnany, Emile G.; Wilkinson, Kenton T.
1992-01-01
Examines the history of the cultural imperialism debate. Reviews international questions raised concerning the role and influence of the still-popular Hollywood products. Examines changing ownership patterns in Hollywood (buyouts by major foreign interests). Notes important trends, and suggests areas for critical research. (SR)
Quantum critical scaling of fidelity in BCS-like model
International Nuclear Information System (INIS)
Adamski, Mariusz; Jedrzejewski, Janusz; Krokhmalskii, Taras
2013-01-01
We study scaling of the ground-state fidelity in neighborhoods of quantum critical points in a model of interacting spinful fermions—a BCS-like model. Due to the exact diagonalizability of the model, in one and higher dimensions, scaling of the ground-state fidelity can be analyzed numerically with great accuracy, not only for small systems but also for macroscopic ones, together with the crossover region between them. Additionally, in the one-dimensional case we have been able to derive a number of analytical formulas for fidelity and show that they accurately fit our numerical results; these results are reported in the paper. Besides regular critical points and their neighborhoods, where well-known scaling laws are obeyed, there is the multicritical point and critical points in its proximity where anomalous scaling behavior is found. We also consider scaling of fidelity in neighborhoods of critical points where fidelity oscillates strongly as the system size or the chemical potential is varied. Our results for a one-dimensional version of a BCS-like model are compared with those obtained recently by Rams and Damski in similar studies of a quantum spin chain—an anisotropic XY model in a transverse magnetic field. (paper)
Quantum correlation approach to criticality in the XX spin chain with multiple interaction
Energy Technology Data Exchange (ETDEWEB)
Cheng, W.W., E-mail: weien.cheng@gmail.com [Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunication, Nanjing 210003 (China); Department of Physics, Hubei Normal University, Huangshi 435002 (China); Key Lab of Broadband Wireless Communication and Sensor Network Technology, Ministry of Education (China); Shan, C.J. [Department of Physics, Hubei Normal University, Huangshi 435002 (China); Sheng, Y.B.; Gong, L.Y.; Zhao, S.M. [Institute of Signal Processing and Transmission, Nanjing University of Posts and Telecommunication, Nanjing 210003 (China); Key Lab of Broadband Wireless Communication and Sensor Network Technology, Ministry of Education (China)
2012-09-01
We investigate the quantum critical behavior in the XX spin chain with a XZY-YZX type multiple interaction by means of quantum correlation (Concurrence C, quantum discord D{sub Q} and geometric discord D{sub G}). Around the critical point, the values of these quantum correlations and corresponding derivatives are investigated numerically and analytically. The results show that the non-analyticity property of the concurrence cannot signal well the quantum phase transition, but both the quantum discord and geometric discord can characterize the critical behavior in such model exactly.
Commonly asked questions by critically ill patients relatives in Arabic countries
Directory of Open Access Journals (Sweden)
Tayseer Zaytoun
2017-04-01
Full Text Available Background: Relatives often lack important information about intensive care unit patients. Research on ways to improve family satisfaction in the ICU has become a crucial point in ICU quality improvement research. Objective: The aim of this study is to develop and analyze a list of commonly asked questions from relatives of patients in the intensive care unit in Arabic countries. This list might help families to determine which questions they want to ask and help them in decision-making process in emergency situations of their critically ill relatives. Methods: This study was a prospective double center study. It took place in the ICUs of two hospitals in Arabic countries: Egypt and Kingdom of Saudi Arabia. Alexandria University Main Hospital in Egypt and the ICU of King Fahad specialist Hospital in Dammam in Saudi Arabia. Data collection was done by reporting of Questions asked by the relatives of ICU patients during daily interview. The list of questions generated was checked to identify questions that could be eliminated. The remaining questions were categorized into 9 different groups: diagnosis, treatment, prognosis, comfort, patient interaction, family, mortality, post-ICU management and other questions. WE ranked the questions in the preliminary list through ICU staff, patients families and the patient themselves. Results: 115 Health care professional (34 physicians and 81 nurses participated in the data collection, the questions recorded were 2240 questions. It was found that about 1750 questions (78.12% were duplicated or not clear. The remaining 490 questions were classified into different categories. The same 115 Health care professional (34 physicians and 81 nurses who shared in the collection of data also shared in the ranking of the questions. 128 first degree relatives shared in the evaluation of the relevance of questions as well as 62 patients after they have been cured and before their discharge from ICU.A list was created
Single-copy entanglement in critical quantum spin chains
International Nuclear Information System (INIS)
Eisert, J.; Cramer, M.
2005-01-01
We consider the single-copy entanglement as a quantity to assess quantum correlations in the ground state in quantum many-body systems. We show for a large class of models that already on the level of single specimens of spin chains, criticality is accompanied with the possibility of distilling a maximally entangled state of arbitrary dimension from a sufficiently large block deterministically, with local operations and classical communication. These analytical results--which refine previous results on the divergence of block entropy as the rate at which maximally entangled pairs can be distilled from many identically prepared chains--are made quantitative for general isotropic translationally invariant spin chains that can be mapped onto a quasifree fermionic system, and for the anisotropic XY model. For the XX model, we provide the asymptotic scaling of ∼(1/6)log 2 (L), and contrast it with the block entropy
A quantum criticality perspective on the charging of narrow quantum-dot levels
Kashcheyevs, V.; Karrasch, C.; Hecht, T.; Weichselbaum, A.; Meden, V.; Schiller, A.
2008-01-01
Understanding the charging of exceptionally narrow levels in quantum dots in the presence of interactions remains a challenge within mesoscopic physics. We address this fundamental question in the generic model of a narrow level capacitively coupled to a broad one. Using bosonization we show that for arbitrary capacitive coupling charging can be described by an analogy to the magnetization in the anisotropic Kondo model, featuring a low-energy crossover scale that depends in a power-law fashi...
Pushing Critical Thinking Skills With Multiple-Choice Questions: Does Bloom's Taxonomy Work?
Zaidi, Nikki L Bibler; Grob, Karri L; Monrad, Seetha M; Kurtz, Joshua B; Tai, Andrew; Ahmed, Asra Z; Gruppen, Larry D; Santen, Sally A
2018-06-01
Medical school assessments should foster the development of higher-order thinking skills to support clinical reasoning and a solid foundation of knowledge. Multiple-choice questions (MCQs) are commonly used to assess student learning, and well-written MCQs can support learner engagement in higher levels of cognitive reasoning such as application or synthesis of knowledge. Bloom's taxonomy has been used to identify MCQs that assess students' critical thinking skills, with evidence suggesting that higher-order MCQs support a deeper conceptual understanding of scientific process skills. Similarly, clinical practice also requires learners to develop higher-order thinking skills that include all of Bloom's levels. Faculty question writers and examinees may approach the same material differently based on varying levels of knowledge and expertise, and these differences can influence the cognitive levels being measured by MCQs. Consequently, faculty question writers may perceive that certain MCQs require higher-order thinking skills to process the question, whereas examinees may only need to employ lower-order thinking skills to render a correct response. Likewise, seemingly lower-order questions may actually require higher-order thinking skills to respond correctly. In this Perspective, the authors describe some of the cognitive processes examinees use to respond to MCQs. The authors propose that various factors affect both the question writer and examinee's interaction with test material and subsequent cognitive processes necessary to answer a question.
Engineering Surface Critical Behavior of (2 +1 )-Dimensional O(3) Quantum Critical Points
Ding, Chengxiang; Zhang, Long; Guo, Wenan
2018-06-01
Surface critical behavior (SCB) refers to the singularities of physical quantities on the surface at the bulk phase transition. It is closely related to and even richer than the bulk critical behavior. In this work, we show that three types of SCB universality are realized in the dimerized Heisenberg models at the (2 +1 )-dimensional O(3) quantum critical points by engineering the surface configurations. The ordinary transition happens if the surface is gapped in the bulk disordered phase, while the gapless surface state generally leads to the multicritical special transition, even though the latter is precluded in classical phase transitions because the surface is in the lower critical dimension. An extraordinary transition is induced by the ferrimagnetic order on the surface of the staggered Heisenberg model, in which the surface critical exponents violate the results of the scaling theory and thus seriously challenge our current understanding of extraordinary transitions.
Nonequilibrium dynamic critical scaling of the quantum Ising chain.
Kolodrubetz, Michael; Clark, Bryan K; Huse, David A
2012-07-06
We solve for the time-dependent finite-size scaling functions of the one-dimensional transverse-field Ising chain during a linear-in-time ramp of the field through the quantum critical point. We then simulate Mott-insulating bosons in a tilted potential, an experimentally studied system in the same equilibrium universality class, and demonstrate that universality holds for the dynamics as well. We find qualitatively athermal features of the scaling functions, such as negative spin correlations, and we show that they should be robustly observable within present cold atom experiments.
Quantum critical behaviour of the plateau-insulator transition in the quantum Hall regime
International Nuclear Information System (INIS)
Visser, A de; Ponomarenko, L A; Galistu, G; Lang, D T N de; Pruisken, A M M; Zeitler, U; Maude, D
2006-01-01
High-field magnetotransport experiments provide an excellent tool to investigate the plateau-insulator phase transition in the integral quantum Hall effect. Here we review recent low-temperature high-field magnetotransport studies carried out on several InGaAs/InP heterostructures and an InGaAs/GaAs quantum well. We find that the longitudinal resistivity ρ xx near the critical filling factor ν c ∼ 0.5 follows the universal scaling law ρ xx (ν, T) ∝ exp(-Δν/(T/T 0 ) κ ), where Δν = ν-ν c . The critical exponent κ equals 0.56 ± 0.02, which indicates that the plateau-insulator transition falls in a non-Fermi liquid universality class
Quantum Critical Point revisited by the Dynamical Mean Field Theory
Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei
Dynamical mean field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. The QCP is characterized by a universal scaling form of the self energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low energy kink and the high energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high energy antiferromagnetic paramagnons. We use the frequency dependent four-point correlation function of spin operators to calculate the momentum dependent correction to the electron self energy. Our results reveal a substantial difference with the calculations based on the Spin-Fermion model which indicates that the frequency dependence of the the quasiparitcle-paramagnon vertices is an important factor. The authors are supported by Center for Computational Design of Functional Strongly Correlated Materials and Theoretical Spectroscopy under DOE Grant DE-FOA-0001276.
Quantum critical point revisited by dynamical mean-field theory
Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.
2017-03-01
Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. The QCP is characterized by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. We use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. By comparing with the calculations based on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.
Quantum critical point revisited by dynamical mean-field theory
International Nuclear Information System (INIS)
Xu, Wenhu; Kotliar, Gabriel; Rutgers University, Piscataway, NJ; Tsvelik, Alexei M.
2017-01-01
Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. We characterize the QCP by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. Here, we use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. Furthermore, by comparing with the calculations based on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.
Critical exponents for the Reggeon quantum spin model
International Nuclear Information System (INIS)
Brower, R.C.; Furman, M.A.
1978-01-01
The Reggeon quantum spin (RQS) model on the transverse lattice in D dimensional impact parameter space has been conjectured to have the same critical behaviour as the Reggeon field theory (RFT). Thus from a high 'temperature' series of ten (D=2) and twenty (D=1) terms for the RQS model the authors extrapolate to the critical temperature T=Tsub(c) by Pade approximants to obtain the exponents eta=0.238 +- 0.008, z=1.16 +- 0.01, γ=1.271 +- 0.007 for D=2 and eta=0.317 +- 0.002, z=1.272 +- 0.007, γ=1.736 +- 0.001, lambda=0.57 +- 0.03 for D=1. These exponents naturally interpolate between the D=0 and D=4-epsilon results for RFT as expected on the basis of the universality conjecture. (Auth.)
Directory of Open Access Journals (Sweden)
J. H. Pixley
2016-06-01
Full Text Available We numerically study the effect of short-ranged potential disorder on massless noninteracting three-dimensional Dirac and Weyl fermions, with a focus on the question of the proposed (and extensively theoretically studied quantum critical point separating semimetal and diffusive-metal phases. We determine the properties of the eigenstates of the disordered Dirac Hamiltonian (H and exactly calculate the density of states (DOS near zero energy, using a combination of Lanczos on H^{2} and the kernel polynomial method on H. We establish the existence of two distinct types of low-energy eigenstates contributing to the disordered density of states in the weak-disorder semimetal regime. These are (i typical eigenstates that are well described by linearly dispersing perturbatively dressed Dirac states and (ii nonperturbative rare eigenstates that are weakly dispersive and quasilocalized in the real-space regions with the largest (and rarest local random potential. Using twisted boundary conditions, we are able to systematically find and study these two (essentially independent types of eigenstates. We find that the Dirac states contribute low-energy peaks in the finite-size DOS that arise from the clean eigenstates which shift and broaden in the presence of disorder. On the other hand, we establish that the rare quasilocalized eigenstates contribute a nonzero background DOS which is only weakly energy dependent near zero energy and is exponentially small at weak disorder. We also find that the expected semimetal to diffusive-metal quantum critical point is converted to an avoided quantum criticality that is “rounded out” by nonperturbative effects, with no signs of any singular behavior in the DOS at the energy of the clean Dirac point. However, the crossover effects of the avoided (or hidden criticality manifest themselves in a so-called quantum critical fan region away from the Dirac energy. We discuss the implications of our results for
Energy Technology Data Exchange (ETDEWEB)
Ding, L.J., E-mail: dinglinjie82@126.com; Zhong, Y.
2017-07-15
Highlights: • The quantum critical scaling is investigated by Green’s function theory. • The obtained power-law critical exponents (β, δ and α) obey the critical scaling relation α + β(1 + δ) = 2. • The scaling hypothesis equations are proposed to verify the scaling analysis. - Abstract: The quantum phase transition and thermodynamics of a periodic Anderson-like polymer chain in a magnetic field are investigated by Green’s function theory. The T-h phase diagram is explored, wherein a crossover temperature T{sup ∗} denoting the gapless phase crossover into quantum critical regimes, smoothly connects near the critical fields to the universal linear line T{sup ∗} ∼ (h − h{sub c,s}), and ends at h{sub c,s}, providing a new route to capture quantum critical point (QCP). The quantum critical scaling around QCPs is demonstrated by analyzing magnetization, specific heat and Grüneisen parameter Γ{sub h}, which provide direct access to distill the power-law critical exponents (β, δ and α) obeying the critical scaling relation α + β(1 + δ) = 2, analogous to the quantum spin system. Furthermore, scaling hypothesis equations are proposed to check the scaling analysis, for which all the data collapse onto a single curve or two independent branches for the plot against an appropriate scaling variable, indicating the self-consistency and reliability of the obtained critical exponents.
Janzen, Katherine J.; Perry, Beth; Edwards, Margaret
2011-01-01
This paper builds upon a foundational paper (under review) which explores the rudiments of the quantum perspective of learning. The quantum perspective of learning uses the principles of exchange theory or borrowed theory from the field of quantum holism pioneered by quantum physicist David Bohm (1971, 1973) to understand learning in a new way.…
Song, Yi; Ferretti, Ralph P.
2013-01-01
The effects of self-regulated strategy development revising instruction for college students that targeted the use of argumentation schemes and critical questions were assessed in three conditions. In the first condition, students were taught to revise their essays by asking and answering critical questions about the "argument from consequences"…
Critical properties of effective gauge theories for novel quantum fluids
Energy Technology Data Exchange (ETDEWEB)
Smoergrav, Eivind
2005-07-01
Critical properties of U(1) symmetric gauge theories are studied in 2+1 dimensions, analytically through duality transformations and numerically through Monte Carlo simulations. Physical applications range from quantum phase transitions in two dimensional insulating materials to superfluid and superconducting properties of light atoms such as hydrogen under extreme pressure. A novel finite size scaling method, utilizing the third moment M{sub 3} of the action, is developed. Finite size scaling analysis of M{sub 3} yields the ratio (1 + alpha)/ny and 1/ny separately, so that critical exponents alpha and ny can be obtained independently without invoking hyperscaling. This thesis contains eight research papers and an introductory part covering some basic concepts and techniques. Paper 1: The novel M{sub 3} method is introduced and employed together with Monte Carlo simulations to study the compact Abelian Higgs model in the adjoint representation with q = 2. Paper 2: We study phase transitions in the compact Abelian Higgs model for fundamental charge q = 2; 3; 4; 5. Various other models are studied to benchmark the M{sub 3} method. Paper 3: This is a proceeding paper based on a talk given by F. S. Nogueira at the Aachen EPS HEP 2003 conference. A review of the results from Paper 1 and Paper 2 on the compact Abelian Higgs model together with some results on q = 1 obtained by F. S. Nogueira, H. Kleinert, and A. Sudboe is given. Paper 4: The effect of a Chern-Simons (CS) term in the phase structure of two Abelian gauge theories is studied. Paper 5: We study the critical properties of the N-component Ginzburg-Landau theory. Paper 6: We consider the vortices in the 2-component Ginzburg-Landau model in a finite but low magnetic field. The ground state is a lattice of co centered vortices in both order parameters. We find two novel phase transitions. i) A 'vortex sub-lattice melting' transition where vortices in the field with lowest phase stiffness (&apos
Quantum-critical scaling of fidelity in 2D pairing models
Energy Technology Data Exchange (ETDEWEB)
Adamski, Mariusz, E-mail: mariusz.adamski@ift.uni.wroc.pl [Institute of Theoretical Physics, University of Wrocław, pl. Maksa Borna 9, 50–204, Wrocław (Poland); Jȩdrzejewski, Janusz [Institute of Theoretical Physics, University of Wrocław, pl. Maksa Borna 9, 50–204, Wrocław (Poland); Krokhmalskii, Taras [Institute for Condensed Matter Physics, 1 Svientsitski Street, 79011, Lviv (Ukraine)
2017-01-15
The laws of quantum-critical scaling theory of quantum fidelity, dependent on the underlying system dimensionality D, have so far been verified in exactly solvable 1D models, belonging to or equivalent to interacting, quadratic (quasifree), spinless or spinfull, lattice-fermion models. The obtained results are so appealing that in quest for correlation lengths and associated universal critical indices ν, which characterize the divergence of correlation lengths on approaching critical points, one might be inclined to substitute the hard task of determining an asymptotic behavior at large distances of a two-point correlation function by an easier one, of determining the quantum-critical scaling of the quantum fidelity. However, the role of system's dimensionality has been left as an open problem. Our aim in this paper is to fill up this gap, at least partially, by verifying the laws of quantum-critical scaling theory of quantum fidelity in a 2D case. To this end, we study correlation functions and quantum fidelity of 2D exactly solvable models, which are interacting, quasifree, spinfull, lattice-fermion models. The considered 2D models exhibit new, as compared with 1D ones, features: at a given quantum-critical point there exists a multitude of correlation lengths and multiple universal critical indices ν, since these quantities depend on spatial directions, moreover, the indices ν may assume larger values. These facts follow from the obtained by us analytical asymptotic formulae for two-point correlation functions. In such new circumstances we discuss the behavior of quantum fidelity from the perspective of quantum-critical scaling theory. In particular, we are interested in finding out to what extent the quantum fidelity approach may be an alternative to the correlation-function approach in studies of quantum-critical points beyond 1D.
Abrahams, Elihu; Wölfle, Peter
2012-01-01
We use the recently developed critical quasiparticle theory to derive the scaling behavior associated with a quantum critical point in a correlated metal. This is applied to the magnetic-field induced quantum critical point observed in YbRh2Si2, for which we also derive the critical behavior of the specific heat, resistivity, thermopower, magnetization and susceptibility, the Grüneisen coefficient, and the thermal expansion coefficient. The theory accounts very well for the available experimental results. PMID:22331893
Quantum mechanical cluster calculations of critical scintillation processes
International Nuclear Information System (INIS)
Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.
2000-01-01
This paper describes the use of commercial quantum chemistry codes to simulate several critical scintillation processes. The crystal is modeled as a cluster of typically 50 atoms embedded in an array of typically 5,000 point charges designed to reproduce the electrostatic field of the infinite crystal. The Schrodinger equation is solved for the ground, ionized, and excited states of the system to determine the energy and electron wave function. Computational methods for the following critical processes are described: (1) the formation and diffusion of relaxed holes, (2) the formation of excitons, (3) the trapping of electrons and holes by activator atoms, (4) the excitation of activator atoms, and (5) thermal quenching. Examples include hole diffusion in CsI, the exciton in CsI, the excited state of CsI:Tl, the energy barrier for the diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trapping by activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation rise time.
Universal conductance and conductivity at critical points in integer quantum Hall systems.
Schweitzer, L; Markos, P
2005-12-16
The sample averaged longitudinal two-terminal conductance and the respective Kubo conductivity are calculated at quantum critical points in the integer quantum Hall regime. In the limit of large system size, both transport quantities are found to be the same within numerical uncertainty in the lowest Landau band, and , respectively. In the second-lowest Landau band, a critical conductance is obtained which indeed supports the notion of universality. However, these numbers are significantly at variance with the hitherto commonly believed value . We argue that this difference is due to the multifractal structure of critical wave functions, a property that should generically show up in the conductance at quantum critical points.
Theory of finite-entanglement scaling at one-dimensional quantum critical points.
Pollmann, Frank; Mukerjee, Subroto; Turner, Ari M; Moore, Joel E
2009-06-26
Studies of entanglement in many-particle systems suggest that most quantum critical ground states have infinitely more entanglement than noncritical states. Standard algorithms for one-dimensional systems construct model states with limited entanglement, which are a worse approximation to quantum critical states than to others. We give a quantitative theory of previously observed scaling behavior resulting from finite entanglement at quantum criticality. Finite-entanglement scaling in one-dimensional systems is governed not by the scaling dimension of an operator but by the "central charge" of the critical point. An important ingredient is the universal distribution of density-matrix eigenvalues at a critical point [P. Calabrese and A. Lefevre, Phys. Rev. A 78, 032329 (2008)10.1103/PhysRevA.78.032329]. The parameter-free theory is checked against numerical scaling at several quantum critical points.
Phase transition with trivial quantum criticality in an anisotropic Weyl semimetal
Li, Xin; Wang, Jing-Rong; Liu, Guo-Zhu
2018-05-01
When a metal undergoes continuous quantum phase transition, the correlation length diverges at the critical point and the quantum fluctuation of order parameter behaves as a gapless bosonic mode. Generically, the coupling of this boson to fermions induces a variety of unusual quantum critical phenomena, such as non-Fermi liquid behavior and various emergent symmetries. Here, we perform a renormalization group analysis of the semimetal-superconductor quantum criticality in a three-dimensional anisotropic Weyl semimetal. Surprisingly, distinct from previously studied quantum critical systems, the anomalous dimension of anisotropic Weyl fermions flows to zero very quickly with decreasing energy, and the quasiparticle residue takes a nonzero value. These results indicate that the quantum fluctuation of superconducting order parameter is irrelevant at low energies, and a simple mean-field calculation suffices to capture the essential physics of the superconducting transition. We thus obtain a phase transition that exhibits trivial quantum criticality, which is unique comparing to other invariably nontrivial quantum critical systems. Our theoretical prediction can be experimentally verified by measuring the fermion spectral function and specific heat.
Fermionic quantum critical point of spinless fermions on a honeycomb lattice
International Nuclear Information System (INIS)
Wang, Lei; Corboz, Philippe; Troyer, Matthias
2014-01-01
Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of the Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recent discovery (Huffman and Chandrasekharan 2014 Phys. Rev. B 89 111101) of the absence of the fermion sign problem in this model, we study the fermionic quantum critical point using the continuous-time quantum Monte Carlo method with a worm-sampling technique. We estimate the transition point V/t=1.356(1) with the critical exponents ν=0.80(3) and η=0.302(7). Compatible results for the transition point are also obtained with infinite projected entangled-pair states. (paper)
Energy scales and magnetoresistance at a quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Shaginyan, V.R. [Petersburg Nuclear Physics Institute, RAS, Gatchina, 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); CTSPS, Clark Atlanta University, Atlanta, GA 30314 (United States)], E-mail: vrshag@thd.pnpi.spb.ru; Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Msezane, A.Z. [CTSPS, Clark Atlanta University, Atlanta, GA 30314 (United States); Popov, K.G. [Komi Science Center, Ural Division, RAS, 3a Chernova street, Syktyvkar, 167982 (Russian Federation); Stephanovich, V.A. [Opole University, Institute of Mathematics and Informatics, Opole, 45-052 (Poland)
2009-03-02
The magnetoresistance (MR) of CeCoIn{sub 5} is notably different from that in many conventional metals. We show that a pronounced crossover from negative to positive MR at elevated temperatures and fixed magnetic fields is determined by the scaling behavior of quasiparticle effective mass. At a quantum critical point (QCP) this dependence generates kinks (crossover points from fast to slow growth) in thermodynamic characteristics (like specific heat, magnetization, etc.) at some temperatures when a strongly correlated electron system transits from the magnetic field induced Landau-Fermi liquid (LFL) regime to the non-Fermi liquid (NFL) one taking place at rising temperatures. We show that the above kink-like peculiarity separates two distinct energy scales in QCP vicinity - low temperature LFL scale and high temperature one related to NFL regime. Our comprehensive theoretical analysis of experimental data permits to reveal for the first time new MR and kinks scaling behavior as well as to identify the physical reasons for above energy scales.
Saeed, Tanveer; Khan, Shehla; Ahmed, Azra; Gul, Raisa; Cassum, Shanaz; Parpio, Yasmin
2012-03-01
To enhance the Critical Thinking skills of educators associated with the nursing baccalaureate programmes in Pakistan. By focusing on the type and level of questions asked by the educators. Ninety-one faculty members from 14 out of 17 schools participated in the study. Data on the faculty's questioning skills was obtained through classroom observations and field notes. The duration of the observations was 45-60 minutes. Using Bloom's Taxonomy for cognitive thinking, questions were categorised into high and low categories. Most of the questions (68.9 %) asked by the participants were of lower levels, while some (5.37 %) were ambiguous. In many instances, the participants did not allow a sufficient wait-time for students to think and respond. The findings suggest that educators must learn to use the questioning strategy effectively. They should ask higher level questions if they wish to inculcate Critical Thinking in students.
Quantum mechanics: new experiments, new applications, and new formulations of old questions
International Nuclear Information System (INIS)
Menskii, Mikhail B
2000-01-01
Some of the quantum mechanical conceptual problems, their current status, and related theoretical developments are reviewed. The characteristics of the entangled quantum states are analyzed, and new experiments and quantum information applications involving such states are discussed. The well-known paradox of Schroedinger's cat (the impossibility of observing superpositions of macroscopically distinct states that are predicted by quantum mechanics) is discussed. It is shown that decoherence (arising when a quantum system is measured in such a way that some information about its state is recorded in its environment) prevents the distinguishing of a superposition and the corresponding mixture. This overcomes the difficulties associated with the paradoxical nature of quantum measurement provided we remain within the framework of the theory of open systems. Other conceptual difficulties, while actually lying outside physics, are now the subject of much research and have already led to new interesting interpretations of quantum mechanics. The suggestion of Wigner and others that the observer's consciousness be included in the theory of quantum measurement is discussed in this context. A hypothesis is put forward which might enable the functioning of consciousness to be described in quantum measurement terms. (reviews of topical problems)
Quantum criticality of one-dimensional multicomponent Fermi gas with strongly attractive interaction
International Nuclear Information System (INIS)
He, Peng; Jiang, Yuzhu; Guan, Xiwen; He, Jinyu
2015-01-01
Quantum criticality of strongly attractive Fermi gas with SU(3) symmetry in one dimension is studied via the thermodynamic Bethe ansatz (TBA) equations. The phase transitions driven by the chemical potential μ, effective magnetic field H 1 , H 2 (chemical potential biases) are analyzed at the quantum criticality. The phase diagram and critical fields are analytically determined by the TBA equations in the zero temperature limit. High accurate equations of state, scaling functions are also obtained analytically for the strong interacting gases. The dynamic exponent z=2 and correlation length exponent ν=1/2 read off the universal scaling form. It turns out that the quantum criticality of the three-component gases involves a sudden change of density of states of one cluster state, two or three cluster states. In general, this method can be adapted to deal with the quantum criticality of multicomponent Fermi gases with SU(N) symmetry. (paper)
Zero-field quantum critical point in CeCoIn5.
Tokiwa, Y; Bauer, E D; Gegenwart, P
2013-09-06
Quantum criticality in the normal and superconducting states of the heavy-fermion metal CeCoIn5 is studied by measurements of the magnetic Grüneisen ratio ΓH and specific heat in different field orientations and temperatures down to 50 mK. A universal temperature over magnetic field scaling of ΓH in the normal state indicates a hidden quantum critical point at zero field. Within the superconducting state, the quasiparticle entropy at constant temperature increases upon reducing the field towards zero, providing additional evidence for zero-field quantum criticality.
Holographic aspects of black holes, matrix models and quantum criticality
Papadoulaki, O.
2017-01-01
In one word the core subject of this thesis is holography. What we mean by holography broadly is the mapping of a gravitational theory in D dimensions to a quantum mechanics system or quantum field theory in one less dimension In chapter 1, we give a basic and self-contained introduction of the
A critical analysis of the quantum theory of measurement
International Nuclear Information System (INIS)
Fer, F.
1984-01-01
Keeping strictly in the positivist and probabilistic, hence hilbertian frame of Quantum Mechanics, the author tries to ascertain whether or not Quantum Mechanics, starting from its axioms, reaches the aim of any physical theory, that is, comparison with experiment. The answer is: no, as long as it keeps close to the existing axiomatics, and also to accurate mathematics. (Auth.)
Conflicts in Learning to Care for Critically Ill Newborns: "It Makes Me Question My Own Morals".
Boss, Renee D; Geller, Gail; Donohue, Pamela K
2015-09-01
Caring for critically ill and dying patients often triggers both professional and personal growth for physician trainees. In pediatrics, the neonatal intensive care unit (NICU) is among the most distressing settings for trainees. We used longitudinal narrative writing to gain insight into how physician trainees are challenged by and make sense of repetitive, ongoing conflicts experienced as part of caring for very sick and dying babies. The study took place in a 45-bed, university-based NICU in an urban setting in the United States. From November 2009 to June 2010 we enrolled pediatric residents and neonatology fellows at the beginning of their NICU rotations. Participants were asked to engage in individual, longitudinal narrative writing about their "experience in the NICU." Thematic narrative analysis was performed. Thirty-seven physician trainees participated in the study. The mean number of narratives per trainee was 12; a total of 441 narratives were available for analysis. Conflict was the most pervasive theme in the narratives. Trainees experienced conflicts with families and conflicts with other clinicians. Trainees also described multiple conflicts of identity as members of the neonatology team, as members of the medical profession, as members of their own families, and as members of society. Physician trainees experience significant conflict and distress while learning to care for critically ill and dying infants. These conflicts often led them to question their own morals and their role in the medical profession. Physician trainees should be educated to expect various types of distress during intensive care rotations, encouraged to identify their own sources of distress, and supported in mitigating their effects.
Sumner, Isaiah; Iyengar, Srinivasan S
2007-10-18
We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.
Questioning: a critical skill in postmodern health-care service delivery.
Brown, Cary A; Bannigan, Katrina; Gill, Joanna R
2009-06-01
Occupational therapists can no longer rely exclusively on biomedical frameworks to guide their practice and facilitate clinical problem-solving. A postmodernist perspective of health and well-being underlines that the illness experience is not a linear, cause-and-effect equation. Rather, life experiences are constructed through a myriad of social, cultural, physical and economic contexts that are highly unique to each individual. In other words, the assumption that 'one-size-fits-all' is as flawed in health care as it is in clothing design. This paper contributes to the growing discussion of health care within the postmodern context of the twenty-first century through first presenting a brief discussion of emerging postmodern thinking and application within the profession, followed by a rationale for the need to scrutinise prevalent modernist assumptions that guide decision-making. Finally, the paper introduces the method of Socratic questioning as a critical tool in successfully carrying out this scrutiny in an empowering and respectful manner for all stakeholders.
Quantum criticality in electron-doped BaFe2-xNixAs2.
Zhou, R; Li, Z; Yang, J; Sun, D L; Lin, C T; Zheng, Guo-qing
2013-01-01
A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe(2-x)Ni(x)As₂ (0≤x≤0.17). We find two critical points at x(c1)=0.10 and x(c2)=0.14. The electrical resistivity follows ρ=ρ₀+AT(n), with n=1 around x(c1) and another minimal n=1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.
A non-critical string approach to black holes, time and quantum dynamics
Ellis, John R.; Nanopoulos, Dimitri V.
1994-01-01
We review our approach to time and quantum dynamics based on non-critical string theory, developing its relationship to previous work on non-equilibrium quantum statistical mechanics and the microscopic arrow of time. We exhibit specific non-factorizing contributions to the {\
Precise Determination of Quantum Critical Points by the Violation of the Entropic Area Law
Xavier, J. C.; Alcaraz, F. C.
2011-01-01
Finite-size scaling analysis turns out to be a powerful tool to calculate the phase diagram as well as the critical properties of two dimensional classical statistical mechanics models and quantum Hamiltonians in one dimension. The most used method to locate quantum critical points is the so called crossing method, where the estimates are obtained by comparing the mass gaps of two distinct lattice sizes. The success of this method is due to its simplicity and the ability to provide accurate r...
Model for a Ferromagnetic Quantum Critical Point in a 1D Kondo Lattice
Komijani, Yashar; Coleman, Piers
2018-04-01
Motivated by recent experiments, we study a quasi-one-dimensional model of a Kondo lattice with ferromagnetic coupling between the spins. Using bosonization and dynamical large-N techniques, we establish the presence of a Fermi liquid and a magnetic phase separated by a local quantum critical point, governed by the Kondo breakdown picture. Thermodynamic properties are studied and a gapless charged mode at the quantum critical point is highlighted.
Critical components for diamond-based quantum coherent devices
International Nuclear Information System (INIS)
Greentree, Andrew D; Olivero, Paolo; Draganski, Martin; Trajkov, Elizabeth; Rabeau, James R; Reichart, Patrick; Gibson, Brant C; Rubanov, Sergey; Huntington, Shane T; Jamieson, David N; Prawer, Steven
2006-01-01
The necessary elements for practical devices exploiting quantum coherence in diamond materials are summarized, and progress towards their realization documented. A brief review of future prospects for diamond-based devices is also provided
A critical note on the greatest days of quantum theory
International Nuclear Information System (INIS)
Popper, K.
1984-01-01
The paper traces the scientific ideas of Louis de Broglie, concerning quantum theory. Uncertainty and scatter; Copenhagen or realism; the argument of Einstein, Podolski and Rosen; and realistic consequences of aspect's experiment; are all discussed. (U.K.)
Quantum critical scaling at the edge of Fermi liquid stability in a cuprate superconductor.
Butch, Nicholas P; Jin, Kui; Kirshenbaum, Kevin; Greene, Richard L; Paglione, Johnpierre
2012-05-29
In the high-temperature cuprate superconductors, the pervasiveness of anomalous electronic transport properties suggests that violation of conventional Fermi liquid behavior is closely tied to superconductivity. In other classes of unconventional superconductors, atypical transport is well correlated with proximity to a quantum critical point, but the relative importance of quantum criticality in the cuprates remains uncertain. Here, we identify quantum critical scaling in the electron-doped cuprate material La(2-x)Ce(x)CuO(4) with a line of quantum critical points that surrounds the superconducting phase as a function of magnetic field and charge doping. This zero-temperature phase boundary, which delineates a metallic Fermi liquid regime from an extended non-Fermi liquid ground state, closely follows the upper critical field of the overdoped superconducting phase and gives rise to an expanse of distinct non-Fermi liquid behavior at finite temperatures. Together with signatures of two distinct flavors of quantum fluctuations, these facts suggest that quantum criticality plays a significant role in shaping the anomalous properties of the cuprate phase diagram.
Al-Khalili, Jim
2003-01-01
In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.
At the Limits of Criticality-Based Quantum Metrology: Apparent Super-Heisenberg Scaling Revisited
Rams, Marek M.; Sierant, Piotr; Dutta, Omyoti; Horodecki, Paweł; Zakrzewski, Jakub
2018-04-01
We address the question of whether the super-Heisenberg scaling for quantum estimation is indeed realizable. We unify the results of two approaches. In the first one, the original system is compared with its copy rotated by the parameter-dependent dynamics. If the parameter is coupled to the one-body part of the Hamiltonian, the precision of its estimation is known to scale at most as N-1 (Heisenberg scaling) in terms of the number of elementary subsystems used N . The second approach compares the overlap between the ground states of the parameter-dependent Hamiltonian in critical systems, often leading to an apparent super-Heisenberg scaling. However, we point out that if one takes into account the scaling of time needed to perform the necessary operations, i.e., ensuring adiabaticity of the evolution, the Heisenberg limit given by the rotation scenario is recovered. We illustrate the general theory on a ferromagnetic Heisenberg spin chain example and show that it exhibits such super-Heisenberg scaling of ground-state fidelity around the critical value of the parameter (magnetic field) governing the one-body part of the Hamiltonian. Even an elementary estimator represented by a single-site magnetization already outperforms the Heisenberg behavior providing the N-1.5 scaling. In this case, Fisher information sets the ultimate scaling as N-1.75, which can be saturated by measuring magnetization on all sites simultaneously. We discuss universal scaling predictions of the estimation precision offered by such observables, both at zero and finite temperatures, and support them with numerical simulations in the model. We provide an experimental proposal of realization of the considered model via mapping the system to ultracold bosons in a periodically shaken optical lattice. We explicitly derive that the Heisenberg limit is recovered when the time needed for preparation of quantum states involved is taken into account.
One-norm geometric quantum discord and critical point estimation in the XY spin chain
Energy Technology Data Exchange (ETDEWEB)
Cheng, Chang-Cheng; Wang, Yao; Guo, Jin-Liang, E-mail: guojinliang80@163.com
2016-11-15
In contrast with entanglement and quantum discord (QD), we investigate the thermal quantum correlation in terms of Schatten one-norm geometric quantum discord (GQD) in the XY spin chain, and analyze their capabilities in detecting the critical point of quantum phase transition. We show that the one-norm GQD can reveal more properties about quantum correlation between two spins, especially for the long-range quantum correlation at finite temperature. Under the influences of site distance, anisotropy and temperature, one-norm GQD and its first derivative make it possible to detect the critical point efficiently for a general XY spin chain. - Highlights: • Comparing with entanglement and QD, one-norm GQD is more robust versus the temperature. • One-norm GQD is more efficient in characterization of long-range quantum correlation between two distant qubits. • One-norm GQD performs well in highlighting the critical point of QPT at zero or low finite temperature. • One-norm GQD has a number of advantages over QD in detecting the critical point of the spin chain.
Moral Development, Ego Autonomy and Questions of Practicality in the Critical Theory of Schooling.
Young, R. E.
1988-01-01
This article summarizes Habermas' critical theory of education, examines relevant features of the development of children's capacity to enter into rational argumentation, and examines the significance of this development for a critical theory of schooling. (IAH)
Quantum criticality around metal-insulator transitions of strongly correlated electron systems
Misawa, Takahiro; Imada, Masatoshi
2007-03-01
Quantum criticality of metal-insulator transitions in correlated electron systems is shown to belong to an unconventional universality class with violation of the Ginzburg-Landau-Wilson (GLW) scheme formulated for symmetry breaking transitions. This unconventionality arises from an emergent character of the quantum critical point, which appears at the marginal point between the Ising-type symmetry breaking at nonzero temperatures and the topological transition of the Fermi surface at zero temperature. We show that Hartree-Fock approximations of an extended Hubbard model on square lattices are capable of such metal-insulator transitions with unusual criticality under a preexisting symmetry breaking. The obtained universality is consistent with the scaling theory formulated for Mott transitions and with a number of numerical results beyond the mean-field level, implying that preexisting symmetry breaking is not necessarily required for the emergence of this unconventional universality. Examinations of fluctuation effects indicate that the obtained critical exponents remain essentially exact beyond the mean-field level. It further clarifies the whole structure of singularities by a unified treatment of the bandwidth-control and filling-control transitions. Detailed analyses of the criticality, containing diverging carrier density fluctuations around the marginal quantum critical point, are presented from microscopic calculations and reveal the nature as quantum critical “opalescence.” The mechanism of emerging marginal quantum critical point is ascribed to a positive feedback and interplay between the preexisting gap formation present even in metals and kinetic energy gain (loss) of the metallic carrier. Analyses of crossovers between GLW type at nonzero temperature and topological type at zero temperature show that the critical exponents observed in (V,Cr)2O3 and κ-ET -type organic conductors provide us with evidence for the existence of the present marginal
The EPR argument and the question for reality in quantum mechanics
International Nuclear Information System (INIS)
Zapp, H.C.
1982-01-01
The author discusses the EPR paradoxon in the framework of the objectivity principle of P. Mittelstaedt. He shows that the assumption of locality in this paradoxon is not compatible with the assumption that quantum mechanics is statistically correct. The postulate of locality must be weakened in such a way that this form doesn't allow to conclude on the uncompleteness of quantum mechanics. Finally it is shown that the state transformation of an individual system in an ideal measurement of first kind can be formally justified. (HSI) [de
Non-linear quantum critical dynamics and fluctuation-dissipation ratios far from equilibrium
Energy Technology Data Exchange (ETDEWEB)
Zamani, Farzaneh [Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden (Germany); Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Ribeiro, Pedro [CeFEMA, Instituto Superior Tcnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Russian Quantum Center, Novaya Street 100 A, Skolkovo, Moscow Area, 143025 (Russian Federation); Kirchner, Stefan, E-mail: stefan.kirchner@correlated-matter.com [Center for Correlated Matter, Zhejiang University, Hangzhou, Zhejiang 310058 (China)
2016-02-15
Non-thermal correlations of strongly correlated electron systems and the far-from-equilibrium properties of phases of condensed matter have become a topical research area. Here, an overview of the non-linear dynamics found near continuous zero-temperature phase transitions within the context of effective temperatures is presented. In particular, we focus on models of critical Kondo destruction. Such a quantum critical state, where Kondo screening is destroyed in a critical fashion, is realized in a number of rare earth intermetallics. This raises the possibility of experimentally testing for the existence of fluctuation-dissipation relations far from equilibrium in terms of effective temperatures. Finally, we present an analysis of a non-interacting, critical reference system, the pseudogap resonant level model, in terms of effective temperatures and contrast these results with those obtained near interacting quantum critical points. - Highlights: • Critical Kondo destruction explains the unusual properties of quantum critical heavy fermion compounds. • We review the concept of effective temperatures in models of critical Kondo destruction. • We compare effective temperatures found near non-interacting and fully interacting fixed points. • A comparison with non-interacting quantum impurity models is presented.
Criticality of the anisotropic quantum Heisenberg model on a simple cubic lattice
International Nuclear Information System (INIS)
Mariz, A.M.; Santos, R.M.Z. dos; Tsallis, C.; Santos, R.R. dos.
1984-01-01
Within a Real Space Renormalization group framework, the criticality (phase diagram, and critical thermal and crossover exponents) of the spin 1/2 - anisotropic quantum Heisenberg ferromagnet on a simple cubic lattice is studied. The results obtained are in satisfactory agreement with known results whenever available. (Author) [pt
Criticality of the anisotropic quantum Heisenberg model on a simple cubic lattice
International Nuclear Information System (INIS)
Mariz, A.M.; Tsallis, C.; Santos, R.M.Z. dos; Santos, Raimundo R. dos.
1984-11-01
Within a Real Space Renormalization Group Framework, the criticality (phase diagram, and critical thermal and crossover exponents) of the spin 1/2 - anisotropic quantum Heisenberg ferromagnet on a simple cubic lattice is studied. The results obtained are in antisfactory agreement with known results whenever available. (Author) [pt
Environment-assisted Quantum Critical Effect for Excitation Energy Transfer in a LH2-type Trimer
Xu, Lan; Xu, Bo
2015-10-01
In this article, we are investigating excitation energy transfer (EET) in a basic unit cell of light-harvesting complex II (LH2), named a LH2-type trimer. Calculation of energy transfer efficiency (ETE) in the framework of non-Markovian environment is also implemented. With these achievements, we theoretically predict the environment-assisted quantum critical effect, where ETE exhibits a sudden change at the critical point of quantum phase transition (QPT) for the LH2-type trimer. It is found that highly efficient EET with nearly unit efficiency may occur in the vicinity of the critical point of QPT.
Martinson, David L.
1995-01-01
Explains the justified concern over the communication of "truth" in the media. Argues that journalism students need to understand that there can be a critically important difference between what they have a right to publish and what they should publish. Explores various answers to this and other ethical questions, and the ramifications…
Using Teacher Questions to Enhance EFL Students' Critical Thinking Ability
Feng, Zhiwen
2013-01-01
In this era of information and economic globalization, developing critical thinking skills in college students has been set as a primary goal and learning outcome in higher education. Teaching critical thinking, however, is a great challenge to most EFL teachers. This article, therefore, attempts to examine the nature and teachability of critical…
Tunable quantum criticality and super-ballistic transport in a "charge" Kondo circuit.
Iftikhar, Z; Anthore, A; Mitchell, A K; Parmentier, F D; Gennser, U; Ouerghi, A; Cavanna, A; Mora, C; Simon, P; Pierre, F
2018-05-03
Quantum phase transitions (QPTs) are ubiquitous in strongly-correlated materials. However the microscopic complexity of these systems impedes the quantitative understanding of QPTs. Here, we observe and thoroughly analyze the rich strongly-correlated physics in two profoundly dissimilar regimes of quantum criticality. With a circuit implementing a quantum simulator for the three-channel Kondo model, we reveal the universal scalings toward different low-temperature fixed points and along the multiple crossovers from quantum criticality. Notably, an unanticipated violation of the maximum conductance for ballistic free electrons is uncovered. The present charge pseudospin implementation of a Kondo impurity opens access to a broad variety of strongly-correlated phenomena. Copyright © 2018, American Association for the Advancement of Science.
Critical behaviour of SU(n) quantum chains and topological non-linear σ-models
International Nuclear Information System (INIS)
Affleck, I.; British Columbia Univ., Vancouver
1988-01-01
The critical behaviour of SU(n) quantum ''spin'' chains, Wess-Zumino-Witten σ-models and grassmanian σ-models at topological angle θ = π (of possible relevance to the quantum Hall effect) is reexamined. It is argued that an additional Z n symmetry is generally necessary to stabilize the massless phase. This symmetry is not present for the σ-models for n>2 and is only present for certain representations of ''spin'' chains. (orig.)
Characterization of the Quantized Hall Insulator Phase in the Quantum Critical Regime
Song, Juntao; Prodan, Emil
2013-01-01
The conductivity $\\sigma$ and resistivity $\\rho$ tensors of the disordered Hofstadter model are mapped as functions of Fermi energy $E_F$ and temperature $T$ in the quantum critical regime of the plateau-insulator transition (PIT). The finite-size errors are eliminated by using the non-commutative Kubo-formula. The results reproduce all the key experimental characteristics of this transition in Integer Quantum Hall (IQHE) systems. In particular, the Quantized Hall Insulator (QHI) phase is det...
International Nuclear Information System (INIS)
Luo, Da-Wei; Xu, Jing-Bo
2014-01-01
We investigate the phenomenon of sudden transitions in geometric quantum correlation of two qubits in spin chain environments at finite temperature. It is shown that when only one qubit is coupled to the spin environment, the geometric discord exhibits a double sudden transition behavior, which is closely related to the quantum criticality of the spin chain environment. When two qubits are uniformly coupled to a common spin chain environment, the geometric discord is found to display a sudden transition behavior whereby the system transits from pure classical decoherence to pure quantum decoherence. Moreover, an interesting scaling behavior is revealed for the frozen time, and we also present a scheme to prolong the time during which the discord remains constant by applying bang–bang pulses. (paper)
critical race theory and the question of safety in dialogues on race
African Journals Online (AJOL)
ABSTRACT. This study seeks to combine research from critical race theory, as applied to ... Two recurring strands from this body of academic work that are of particular ..... that the above exemplars stem from an online debate in which students.
Bound on quantum computation time: Quantum error correction in a critical environment
International Nuclear Information System (INIS)
Novais, E.; Mucciolo, Eduardo R.; Baranger, Harold U.
2010-01-01
We obtain an upper bound on the time available for quantum computation for a given quantum computer and decohering environment with quantum error correction implemented. First, we derive an explicit quantum evolution operator for the logical qubits and show that it has the same form as that for the physical qubits but with a reduced coupling strength to the environment. Using this evolution operator, we find the trace distance between the real and ideal states of the logical qubits in two cases. For a super-Ohmic bath, the trace distance saturates, while for Ohmic or sub-Ohmic baths, there is a finite time before the trace distance exceeds a value set by the user.
Energy Technology Data Exchange (ETDEWEB)
Huang, Hong [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Liang, Qi-Feng [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Yao, Dao-Xin, E-mail: yaodaox@mail.sysu.edu.cn [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Wang, Zhi, E-mail: physicswangzhi@gmail.com [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China)
2017-06-28
Majorana bound states in topological Josephson junctions induce a 4π period current-phase relation. Direct detection of the 4π periodicity is complicated by the quasiparticle poisoning. We reveal that Majorana bound states are also signaled by the anomalous enhancement on the critical current of the junction. We show the landscape of the critical current for a nanowire Josephson junction under a varying Zeeman field, and reveal a sharp step feature at the topological quantum phase transition point, which comes from the anomalous enhancement of the critical current at the topological regime. In multi-band wires, the anomalous enhancement disappears for an even number of bands, where the Majorana bound states fuse into Andreev bound states. This anomalous critical current enhancement directly signals the existence of the Majorana bound states, and also provides a valid signature for the topological quantum phase transition. - Highlights: • We introduce the critical current step as a signal for the topological quantum phase transition. • We study the quantum phase transition in the topological nanowire under a rotating Zeeman field. • We show that the critical current anomaly gradually disappears for systems with more sub-bands.
Quantum critical point in high-temperature superconductors
Energy Technology Data Exchange (ETDEWEB)
Shaginyan, V.R. [Petersburg Nuclear Physics Institute, RAS, Gatchina 188300 (Russian Federation); Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)], E-mail: vrshag@thd.pnpi.spb.ru; Amusia, M.Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Popov, K.G. [Komi Science Center, Ural Division, RAS, Syktyvkar 167982 (Russian Federation); Stephanovich, V.A. [Opole University, Institute of Mathematics and Informatics, Opole 45-052 (Poland)], E-mail: stef@math.uni.opole.pl
2009-02-02
Recently, in high-T{sub c} superconductors (HTSC), exciting measurements have been performed revealing their physics in superconducting and pseudogap states and in normal one induced by the application of magnetic field, when the transition from non-Fermi liquid to Landau-Fermi liquid behavior occurs. We employ a theory, based on fermion condensation quantum phase transition which is able to explain facts obtained in the measurements. We also show, that in spite of very different microscopic nature of HTSC, heavy-fermion metals and 2D {sup 3}He, the physical properties of these three classes of substances are similar to each other.
The critical point of quantum chromodynamics through lattice and ...
Indian Academy of Sciences (India)
The Padé approximants are the rational functions. PL. M (z) = .... Deviations from a smooth behaviour near the critical point are visible in these extrap- ... see that there is evidence, albeit statistically not very significant, that the kurtosis changes.
Brookfield, Stephen
2008-01-01
Nelson Mandela's autobiography "The Long Walk to Freedom" describes how an iconic political activist and freedom fighter reflected on, and sometimes modified, four core assumptions at the heart of his struggle to overturn the White supremacist, minority hegemony and create a free South Africa. Critical reflection's focus is on…
Origin of chaos near critical points of quantum flow.
Efthymiopoulos, C; Kalapotharakos, C; Contopoulos, G
2009-03-01
The general theory of motion in the vicinity of a moving quantum nodal point (vortex) is studied in the framework of the de Broglie-Bohm trajectory method of quantum mechanics. Using an adiabatic approximation, we find that near any nodal point of an arbitrary wave function psi there is an unstable point (called the X point) in a frame of reference moving with the nodal point. The local phase portrait forms always a characteristic pattern called the "nodal-point- X -point complex." We find general formulas for this complex as well as necessary and sufficient conditions of validity of the adiabatic approximation. We demonstrate that chaos emerges from the consecutive scattering events of the orbits with nodal-point- X -point complexes. The scattering events are of two types (called type I and type II). A theoretical model is constructed yielding the local value of the Lyapunov characteristic numbers in scattering events of both types. The local Lyapunov characteristic number scales as an inverse power of the speed of the nodal point in the rest frame, implying that it scales proportionally to the size of the nodal-point- X -point complex. It is also an inverse power of the distance of a trajectory from the X point's stable manifold far from the complex. This distance plays the role of an effective "impact parameter." The results of detailed numerical experiments with different wave functions, possessing one, two, or three moving nodal points, are reported. Examples are given of regular and chaotic trajectories, and the statistics of the Lyapunov characteristic numbers of the orbits are found and compared to the number of encounter events of each orbit with the nodal-point- X -point complexes. The numerical results are in agreement with the theory, and various phenomena appearing at first as counterintuitive find a straightforward explanation.
Duality between the Deconfined Quantum-Critical Point and the Bosonic Topological Transition
Directory of Open Access Journals (Sweden)
Yan Qi Qin
2017-09-01
Full Text Available Recently, significant progress has been made in (2+1-dimensional conformal field theories without supersymmetry. In particular, it was realized that different Lagrangians may be related by hidden dualities; i.e., seemingly different field theories may actually be identical in the infrared limit. Among all the proposed dualities, one has attracted particular interest in the field of strongly correlated quantum-matter systems: the one relating the easy-plane noncompact CP^{1} model (NCCP^{1} and noncompact quantum electrodynamics (QED with two flavors (N=2 of massless two-component Dirac fermions. The easy-plane NCCP^{1} model is the field theory of the putative deconfined quantum-critical point separating a planar (XY antiferromagnet and a dimerized (valence-bond solid ground state, while N=2 noncompact QED is the theory for the transition between a bosonic symmetry-protected topological phase and a trivial Mott insulator. In this work, we present strong numerical support for the proposed duality. We realize the N=2 noncompact QED at a critical point of an interacting fermion model on the bilayer honeycomb lattice and study it using determinant quantum Monte Carlo (QMC simulations. Using stochastic series expansion QMC simulations, we study a planar version of the S=1/2 J-Q spin Hamiltonian (a quantum XY model with additional multispin couplings and show that it hosts a continuous transition between the XY magnet and the valence-bond solid. The duality between the two systems, following from a mapping of their phase diagrams extending from their respective critical points, is supported by the good agreement between the critical exponents according to the proposed duality relationships. In the J-Q model, we find both continuous and first-order transitions, depending on the degree of planar anisotropy, with deconfined quantum criticality surviving only up to moderate strengths of the anisotropy. This explains previous claims of no deconfined
Rounding by disorder of first-order quantum phase transitions: emergence of quantum critical points.
Goswami, Pallab; Schwab, David; Chakravarty, Sudip
2008-01-11
We give a heuristic argument for disorder rounding of a first-order quantum phase transition into a continuous phase transition. From both weak and strong disorder analysis of the N-color quantum Ashkin-Teller model in one spatial dimension, we find that, for N > or =3, the first-order transition is rounded to a continuous transition and the physical picture is the same as the random transverse field Ising model for a limited parameter regime. The results are strikingly different from the corresponding classical problem in two dimensions where the fate of the renormalization group flows is a fixed point corresponding to N-decoupled pure Ising models.
Good questions require good answers. Critics on current climate research contradicted
International Nuclear Information System (INIS)
Vellinga, P.; Van Dorland, R.; Kabat, P.
2008-01-01
In some of the previous issues of this magazine (Spil 2007, issue 4 and 5-6, and Spil 2008, issue 1) the authors Labohm, Roersch and Thoenes started a frontal attack of the greenhouse theory and the researchers who report on the state of science in the framework of the IPCC. The author of this article addresses two main questions arising from the above-mentioned authors: (1) Does the use of fossil fuels affect global climate?; and (2) Is the warming of the last 30 years related to the increasing concentrations of greenhouse gases in the atmosphere? [mk] [nl
Universality and Quantum Criticality of the One-Dimensional Spinor Bose Gas
PâÅ£u, Ovidiu I.; Klümper, Andreas; Foerster, Angela
2018-06-01
We investigate the universal thermodynamics of the two-component one-dimensional Bose gas with contact interactions in the vicinity of the quantum critical point separating the vacuum and the ferromagnetic liquid regime. We find that the quantum critical region belongs to the universality class of the spin-degenerate impenetrable particle gas which, surprisingly, is very different from the single-component case and identify its boundaries with the peaks of the specific heat. In addition, we show that the compressibility Wilson ratio, which quantifies the relative strength of thermal and quantum fluctuations, serves as a good discriminator of the quantum regimes near the quantum critical point. Remarkably, in the Tonks-Girardeau regime, the universal contact develops a pronounced minimum, reflected in a counterintuitive narrowing of the momentum distribution as we increase the temperature. This momentum reconstruction, also present at low and intermediate momenta, signals the transition from the ferromagnetic to the spin-incoherent Luttinger liquid phase and can be detected in current experiments with ultracold atomic gases in optical lattices.
Critical excitation spectrum of a quantum chain with a local three-spin coupling.
McCabe, John F; Wydro, Tomasz
2011-09-01
Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D(4),A(4)) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.
Critical excitation spectrum of a quantum chain with a local three-spin coupling
International Nuclear Information System (INIS)
McCabe, John F.; Wydro, Tomasz
2011-01-01
Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D 4 ,A 4 ) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.
Energy Technology Data Exchange (ETDEWEB)
Duerr, Hans-Peter; Oesterreicher-Mollwo, Marianne
2015-07-01
The quantum physics has been arrived by thinking and experimenting to revolutioning knowledges, which determine our world, also if only few have understood these theories in their real sense. The present book follows the question, whether and how far a consciousness trained by quantum physics can reach more directly to the understanding of questions of life and religious questions than a thinking, which is obliged to classical physics. It deals especially with fundamental existential questions: The theme of personal responsibility, the value of the individual existence, the evaluation of the personal I-you relation. Hans Peter Duerr, a personality with guiding qualities, as they are necessary in the new millennium, is the ideal speech partner for the dimension of this theme. The connections of natural sciences and religion, ecology, and sociological change have always driven the Heisenberg successor. How can we speech about that, which science cannot comprehend?. What means self, identity, responsibility for the quantum physicist? An exciting meeting.
Quantum critical phase and Lifshitz transition in an extended periodic Anderson model
International Nuclear Information System (INIS)
Laad, M S; Koley, S; Taraphder, A
2012-01-01
We study the quantum phase transition in f-electron systems as a quantum Lifshitz transition driven by selective-Mott localization in a realistic extended Anderson lattice model. Using dynamical mean-field theory (DMFT), we find that a quantum critical phase with anomalous ω/T scaling separates a heavy Landau-Fermi liquid from ordered phase(s). This non-Fermi liquid state arises from a lattice orthogonality catastrophe originating from orbital-selective Mott localization. Fermi surface reconstruction occurs via the interplay between and penetration of the Green function zeros to the poles, leading to violation of Luttinger’s theorem in the strange metal. We show how this naturally leads to scale-invariant responses in transport. Thus, our work represents a specific DMFT realization of the hidden-FL and FL* theories, and holds promise for the study of ‘strange’ metal phases in quantum matter. (fast track communication)
Quantum criticality of geometric phase in coupled optical cavity arrays under linear quench
Sarkar, Sujit
2013-01-01
The atoms trapped in microcavities and interacting through the exchange of virtual photons can be modeled as an anisotropic Heisenberg spin-1/2 lattice. We study the dynamics of the geometric phase of this system under the linear quenching process of laser field detuning which shows the XX criticality of the geometric phase in presence of single Rabi frequency oscillation. We also study the quantum criticality for different quenching rate in the presence of single or two Rabi frequencies osci...
Topology and Edge Modes in Quantum Critical Chains
Verresen, Ruben; Jones, Nick G.; Pollmann, Frank
2018-02-01
We show that topology can protect exponentially localized, zero energy edge modes at critical points between one-dimensional symmetry-protected topological phases. This is possible even without gapped degrees of freedom in the bulk—in contrast to recent work on edge modes in gapless chains. We present an intuitive picture for the existence of these edge modes in the case of noninteracting spinless fermions with time-reversal symmetry (BDI class of the tenfold way). The stability of this phenomenon relies on a topological invariant defined in terms of a complex function, counting its zeros and poles inside the unit circle. This invariant can prevent two models described by the same conformal field theory (CFT) from being smoothly connected. A full classification of critical phases in the noninteracting BDI class is obtained: Each phase is labeled by the central charge of the CFT, c ∈1/2 N , and the topological invariant, ω ∈Z . Moreover, c is determined by the difference in the number of edge modes between the phases neighboring the transition. Numerical simulations show that the topological edge modes of critical chains can be stable in the presence of interactions and disorder.
Directory of Open Access Journals (Sweden)
M. Engracia Martin Valdunciel
2018-03-01
Full Text Available The paper focus on a critical analysis of a discursive formation in Spanish academic libraries: social responsibility and sustainability. The concepts that make up the discourse are historically contextualized in order to clarify their origin and social affiliation. Although the enunciation of social responsibility and sustainability content is formulated ambiguously, its articulation as a discursive practice within the framework of the new corporate management university libraries leads us to infer bias in their rhetorical formulation. We consider that, from a fuzzy concept and its integration into technocratic practices, the discourse can be used as a tool for legitimizing the deregulation of public educational institutions.
Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain
DEFF Research Database (Denmark)
Stone, M.B.; Reich, D.H.; Broholm, C.
2003-01-01
Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...
Matter fields near quantum critical point in (2+1)-dimensional U(1) gauge theory
International Nuclear Information System (INIS)
Liu Guozhu; Li Wei; Cheng Geng
2010-01-01
We study chiral phase transition and confinement of matter fields in (2+1)-dimensional U(1) gauge theory of massless Dirac fermions and scalar bosons. The vanishing scalar boson mass, r=0, defines a quantum critical point between the Higgs phase and the Coulomb phase. We consider only the critical point r=0 and the Coulomb phase with r>0. The Dirac fermion acquires a dynamical mass when its flavor is less than certain critical value N f c , which depends quantitatively on the flavor N b and the scalar boson mass r. When N f f c , the matter fields carrying internal gauge charge are all confined if r≠0 but are deconfined at the quantum critical point r=0. The system has distinct low-energy elementary excitations at the critical point r=0 and in the Coulomb phase with r≠0. We calculate the specific heat and susceptibility of the system at r=0 and r≠0, which can help to detect the quantum critical point and to judge whether dynamical fermion mass generation takes place.
Directory of Open Access Journals (Sweden)
Miško Šuvaković
2005-12-01
Full Text Available Entirely dissimilar endeavours of problematizing a canonic positioning of music, musicology, aesthetics and philosophy through self-comprehensiveness of a piece-as-a-source hoe et tunc, have led to criticism ar deconstruction of 'self-comprehensiveness' and 'objective autonomy' of music as an art, and of a music piece as a carrier or a centred source of music as an art. Those scarce approaches can be specified from Adorno's contextualization in critical theory, Jacques Attali's developing the theory of exchange, to the New Musicology critiques oriented towards studies of culture, such as those of Richard Leppert, Susan McClary or Rose Rosengard Subotnik, which emphasize autonomy of music, or can be recognized in the psychoanalytical theorization of materialistic functions/effects of music and opera, such as of Mladen Dolar and Slavoj Žižek. From the teachings on deconstruction of the philosopher Jacques Derrida, directly ar indirectly entirely different approaches and applications are drawn, concerning hybrid and plural acts of interpretation of the canonic positioning of music, musicology, aesthetics and philosophy. In the further text I shall dwell on identifying and interpreting of a problem-oriented approach to the canonic relation of music, musicology, aesthetics and philosophy.
International Nuclear Information System (INIS)
Fulda, E.
1994-01-01
Renowned practicians and theoreticians engaged in the power economy and energy politics get to grips with the critical issues in this branch of industry such as the deregularisation of the markets; new concepts for companies and politics; altered framework conditions for power companies; and innovations in the power economy. The contributions and discussions point out ways and perspectives for adapting to the new market situation and new framework conditions governing the whole energy sector. The ideas, initiatives and experiences they present stood in the focus of the interdisciplinary exchange of views that took place at the Wissenschaftszentrum in Bonn/Bad Godesberg during the annual meeting of the Gesellschaft fuer Energiewissenschaft und Energiepolitik e.V. (GEE) from 7 to 8 June 1993. (orig.) [de
Energy Technology Data Exchange (ETDEWEB)
Levy, F; Huxley, A [CEA, SPSMS, DRFMC, F-38054 Grenoble, (France); Levy, F; Sheikin, I [CNRS, GHMFL, F-38042 Grenoble, (France); Huxley, A [Univ Edinburgh, Scottish Univ Phys Alliance, Sch Phys, Edinburgh EH9 3JZ, Midlothian, (United Kingdom)
2007-07-01
When a pure material is tuned to the point where a continuous phase-transition line is crossed at zero temperature, known as a quantum critical point (QCP), completely new correlated quantum ordered states can form. These phases include exotic forms of superconductivity. However, as superconductivity is generally suppressed by a magnetic field, the formation of superconductivity ought not to be possible at extremely high field. Here, we report that as we tune the ferromagnet, URhGe, towards a QCP by applying a component of magnetic field in the material's easy magnetic plane, superconductivity survives in progressively higher fields applied simultaneously along the material's magnetic hard axis. Thus, although superconductivity never occurs above a temperature of 0.5 K, we find that it can survive in extremely high magnetic fields, exceeding 28 T. (authors)
Persistent Offenders in the North West of England, 1880-1940: Some Critical Research Questions
Directory of Open Access Journals (Sweden)
David J. Cox, Steve Farrall and Barry Godfrey
2007-04-01
Full Text Available This article examines the concept of the persistent offender as a group within society, and the presumed impact of that discrete group upon society via a case study of offending in Crewe between 1880 and 1940. The findings of persistent offending in Crewe challenge the assumptions and prejudices of the period, about the links between unemployment and crime and the extent to which crime was an enduring ‘career’. There were no ‘hardened’ persistent offenders in the sample of the type envisaged by contemporary comment, though the role of drink in offending was sustained; and there was no clear ‘type’ of offender either. Examination of the life histories of a selection of offenders is shown to raise a number of interdisciplinary questions, challenging the assumptions of criminologists and legal scholars in relation to the role of legislation in the management of criminality, including the concept (of interest also to historians that reformation of the criminal was more achievable in the past than it is in the over-regulated present.
Vertex functions at finite momentum: Application to antiferromagnetic quantum criticality
Wölfle, Peter; Abrahams, Elihu
2016-02-01
We analyze the three-point vertex function that describes the coupling of fermionic particle-hole pairs in a metal to spin or charge fluctuations at nonzero momentum. We consider Ward identities, which connect two-particle vertex functions to the self-energy, in the framework of a Hubbard model. These are derived using conservation laws following from local symmetries. The generators considered are the spin density and particle density. It is shown that at certain antiferromagnetic critical points, where the quasiparticle effective mass is diverging, the vertex function describing the coupling of particle-hole pairs to the spin density Fourier component at the antiferromagnetic wave vector is also divergent. Then we give an explicit calculation of the irreducible vertex function for the case of three-dimensional antiferromagnetic fluctuations, and show that it is proportional to the diverging quasiparticle effective mass.
Field-induced quantum criticality of a spin-1/2 planar ferromagnet
International Nuclear Information System (INIS)
Mercaldo, M T; Rabuffo, I; Cesare, L De; D'Auria, A Caramico
2009-01-01
The low-temperature critical properties and crossovers of a spin- 1/2 planar ferromagnet in a longitudinal magnetic field are explored in terms of an anisotropic bosonic action, suitable to describe the spin model in the low-temperature regime. This is performed adopting a procedure which combines an averaging over dynamic degrees of freedom and the classical Wilson renormalization group transformation. Within this framework we get the phase boundary, ending in a quantum critical point, and general expressions for the correlation length and susceptibility as functions of the temperature and the applied magnetic field within the disordered phase. In particular, two crossovers occur decreasing the temperature with the magnetic field fixed at its quantum critical point value, which might be actually observable in complex magnetic compounds, as suggested by recent experiments.
Quantum influence in the criticality of the spin- {1}/{2} anisotropic Heisenberg model
Ricardo de Sousa, J.; Araújo, Ijanílio G.
1999-07-01
We study the spin- {1}/{2} anisotropic Heisenberg antiferromagnetic model using the effective field renormalization group (EFRG) approach. The EFRG method is illustrated by employing approximations in which clusters with one ( N'=1) and two ( N=2) spins are used. The dependence of the critical temperature Tc (ferromagnetic-F case) and TN (antiferromagnetic-AF case) and thermal critical exponent, Yt, are obtained as a function of anisotropy parameter ( Δ) on a simple cubic lattice. We find that, in our results, TN is higher than Tc for the quantum anisotropic Heisenberg limit and TN= Tc for the Ising and quantum XY limits. We have also shown that the thermal critical exponent Yt for the isotropic Heisenberg model shows a small dependence on the type of interaction (F or AF) due to finite size effects.
Critical behavior of the quantum spin- {1}/{2} anisotropic Heisenberg model
Sousa, J. Ricardo de
A two-step renormalization group approach - a decimation followed by an effective field renormalization group (EFRG) - is proposed in this work to study the critical behavior of the quantum spin- {1}/{2} anisotropic Heisenberg model. The new method is illustrated by employing approximations in which clusters with one, two and three spins are used. The values of the critical parameter and critical exponent, in two- and three-dimensional lattices, for the Ising and isotropic Heisenberg limits are calculated and compared with other renormalization group approaches and exact (or series) results.
Identification of the low-energy excitations in a quantum critical system
Directory of Open Access Journals (Sweden)
Tom Heitmann
2017-05-01
Full Text Available We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.242Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R (2006].
Boscarino, Giuseppe
2006-06-01
It is questioned: Is quantum mechanics a new science or a new (or rather old) philosophy of physical science? It is shown that Einstein's attempt in his article of 1935 to bring the concept of "element" from the classical (we call it Italic) philosophical-epistemological tradition, which goes under the names of Pythagoras Parmenides, Democritus, and Newton, into quantum mechanical theory is unclear, inadequate and contradictory.
Coherent inflationary dynamics for Bose-Einstein condensates crossing a quantum critical point
Feng, Lei; Clark, Logan W.; Gaj, Anita; Chin, Cheng
2018-03-01
Quantum phase transitions, transitions between many-body ground states, are of extensive interest in research ranging from condensed-matter physics to cosmology1-4. Key features of the phase transitions include a stage with rapidly growing new order, called inflation in cosmology5, followed by the formation of topological defects6-8. How inflation is initiated and evolves into topological defects remains a hot topic of debate. Ultracold atomic gas offers a pristine and tunable platform to investigate quantum critical dynamics9-21. We report the observation of coherent inflationary dynamics across a quantum critical point in driven Bose-Einstein condensates. The inflation manifests in the exponential growth of density waves and populations in well-resolved momentum states. After the inflation stage, extended coherent dynamics is evident in both real and momentum space. We present an intuitive description of the quantum critical dynamics in our system and demonstrate the essential role of phase fluctuations in the formation of topological defects.
Vogel, Jason R; Moore, Trisha L; Coffman, Reid R; Rodie, Steven N; Hutchinson, Stacy L; McDonough, Kelsey R; McLemore, Alex J; McMaine, John T
2015-09-01
Since its inception, Low Impact Development (LID) has become part of urban stormwater management across the United States, marking progress in the gradual transition from centralized to distributed runoff management infrastructure. The ultimate goal of LID is full, cost-effective implementation to maximize watershed-scale ecosystem services and enhance resilience. To reach that goal in the Great Plains, the multi-disciplinary author team presents this critical review based on thirteen technical questions within the context of regional climate and socioeconomics across increasing complexities in scale and function. Although some progress has been made, much remains to be done including continued basic and applied research, development of local LID design specifications, local demonstrations, and identifying funding mechanisms for these solutions. Within the Great Plains and beyond, by addressing these technical questions within a local context, the goal of widespread acceptance of LID can be achieved, resulting in more effective and resilient stormwater management.
On the possibility of complete revivals after quantum quenches to a critical point
Najafi, K.; Rajabpour, M. A.
2017-07-01
In a recent letter [J. Cardy, Phys. Rev. Lett. 112, 220401 (2014), 10.1103/PhysRevLett.112.220401], the author made a very interesting observation that complete revivals of quantum states after quantum quench can happen in a period that is a fraction of the system size. This is possible for critical systems that can be described by minimal conformal field theories with central charge c detect a regime in the phase diagram of the XY chain in which one can not determine the period of the partial revivals using the quasiparticle picture.
International Nuclear Information System (INIS)
Ghirardi, G.C.
1985-09-01
Some general methodological considerations aimed to guarantee the necessary logical rigor to the present debate on quantum mechanics are presented. In particular some misunderstandings about the implications of the critical analysis put forward by Einstein, Podolsky and Rosen (EPR) which can be found in the literature, are discussed. These misunderstandings are shown to arise from possible underestimates, overestimates and misinterpretations of the EPR argument. It is argued that the difficulties pointed out by EPR are, in a sense that will be defined precisely, unavoidable. A model which tries to solve the difficulties arising from quantum non separability effects when macroscopic systems are involved, is briefly sketched. (author)
International Nuclear Information System (INIS)
Bianconi, A.; Missori, M.; Saini, N.L.; Oyanagi, H.; Yamaguchi, H.; Nishihara, Y.; Ha, D.H.; Della Longa, S.
1995-01-01
Here we report experimental evidence that the high Tc superconductivity in a cuprate perovskite occurs in a superlattice of quantum wires. The structure of the high Tc superconducting CuO 2 plane in Bi 2 Sr 2 CaCu 2 O 8+y (Bi2212) at the mesoscopic level (10-100 A) has been determined. It is decorated by a plurality of parallel superconducting stripes of width L=14± 1 A defined by the domain walls formed by stripes of width W=11+1 A characterized by a 0.17 A shorter Cu-O (apical) distance and a large tilting angle θ =12±4degree of the distorted square pyramids. We show that this particular heterostructure provides the physical mechanism raising Tc from the low temperature range Tc 2 plane by a factor ∼10 is realized by 1) tuning the Fermi level near the bottom of the second ubband of the stripes, with k y =2π/L, formed by the quantum size effect and 2) by forming a superlattice of wires with domain walls of width W of the order of the superconducting coherence length ξ 0 . (author)
Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling
International Nuclear Information System (INIS)
Karchev, Naoum
2013-01-01
A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T N )/U and parameter t/U is presented. The quantum critical point (T N =0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)
Nonlinear quenches of power-law confining traps in quantum critical systems
International Nuclear Information System (INIS)
Collura, Mario; Karevski, Dragi
2011-01-01
We describe the coherent quantum evolution of a quantum many-body system with a time-dependent power-law confining potential. The amplitude of the inhomogeneous potential is driven in time along a nonlinear ramp which crosses a critical point. Using Kibble-Zurek-like scaling arguments we derive general scaling laws for the density of excitations and energy excess generated during the nonlinear sweep of the confining potential. It is shown that, with respect to the sweeping rate, the densities follow algebraic laws with exponents that depend on the space-time properties of the potential and on the scaling dimensions of the densities. We support our scaling predictions with both analytical and numerical results on the Ising quantum chain with an inhomogeneous transverse field varying in time.
Universal Scaling and Critical Exponents of the Anisotropic Quantum Rabi Model
Liu, Maoxin; Chesi, Stefano; Ying, Zu-Jian; Chen, Xiaosong; Luo, Hong-Gang; Lin, Hai-Qing
2017-12-01
We investigate the quantum phase transition of the anisotropic quantum Rabi model, in which the rotating and counterrotating terms are allowed to have different coupling strengths. The model interpolates between two known limits with distinct universal properties. Through a combination of analytic and numerical approaches, we extract the phase diagram, scaling functions, and critical exponents, which determine the universality class at finite anisotropy (identical to the isotropic limit). We also reveal other interesting features, including a superradiance-induced freezing of the effective mass and discontinuous scaling functions in the Jaynes-Cummings limit. Our findings are extended to the few-body quantum phase transitions with N >1 spins, where we expose the same effective parameters, scaling properties, and phase diagram. Thus, a stronger form of universality is established, valid from N =1 up to the thermodynamic limit.
Wang, Xiaoyu; Schattner, Yoni; Berg, Erez; Fernandes, Rafael M.
2017-05-01
In several unconventional superconductors, the highest superconducting transition temperature Tc is found in a region of the phase diagram where the antiferromagnetic transition temperature extrapolates to zero, signaling a putative quantum critical point. The elucidation of the interplay between these two phenomena—high-Tc superconductivity and magnetic quantum criticality—remains an important piece of the complex puzzle of unconventional superconductivity. In this paper, we combine sign-problem-free quantum Monte Carlo simulations and field-theoretical analytical calculations to unveil the microscopic mechanism responsible for the superconducting instability of a general low-energy model, called the spin-fermion model. In this approach, low-energy electronic states interact with each other via the exchange of quantum critical magnetic fluctuations. We find that even in the regime of moderately strong interactions, both the superconducting transition temperature and the pairing susceptibility are governed not by the properties of the entire Fermi surface, but instead by the properties of small portions of the Fermi surface called hot spots. Moreover, Tc increases with increasing interaction strength, until it starts to saturate at the crossover from hot-spots-dominated to Fermi-surface-dominated pairing. Our work provides not only invaluable insights into the system parameters that most strongly affect Tc, but also important benchmarks to assess the origin of superconductivity in both microscopic models and actual materials.
International Nuclear Information System (INIS)
Lal, Siddhartha; Laad, Mukul S.
2007-08-01
The dynamics of the charge sector of a one-dimensional quarter-filled electronic system with extended Hubbard interactions were recently mapped onto that of an effective pseudospin transverse-field Ising model (TFIM) in the strong coupling limit. Motivated by studying the effects of inter-chain couplings, we investigate the phase diagram for the case of a system of many coupled effective (TFIM) chains. A random phase approximation analysis reveals a phase diagram with an ordered phase existing at finite temperatures. The phase boundary ends at a zero temperature quantum critical point. Critical quantum fluctuations are found to drive a zero temperature deconfinement transition, as well as enhance the dispersion of excitations in the transverse directions, leading to a dimensional crossover at finite temperatures. Our work is potentially relevant for a unified description of a class of strongly correlated, quarter-filled chain and ladder systems. (author)
Ferromagnetic quantum criticality: New aspects from the phase diagram of LaCrGe3
Taufour, Valentin; Kaluarachchi, Udhara S.; Bud'ko, Sergey L.; Canfield, Paul C.
2018-05-01
Recent theoretical and experimental studies have shown that ferromagnetic quantum criticality is always avoided in clean systems. Two possibilities have been identified. In the first scenario, the ferromagnetic transition becomes of the first order at a tricritical point before being suppressed. A wing structure phase diagram is observed indicating the possibility of a new type of quantum critical point under magnetic field. In a second scenario, a transition to a modulated magnetic phase occurs. Our recent studies on the compound LaCrGe3 illustrate a third scenario where not only a new magnetic phase occurs, but also a change of order of the transition at a tricritical point leading to a wing-structure phase diagram. Careful experimental study of the phase diagram near the tricritical point also illustrates new rules near this type of point.
Lin, Z R; Nakamura, Y; Dykman, M I
2015-08-01
We study the dynamics of a nonlinear oscillator near the critical point where period-two vibrations are first excited with the increasing amplitude of parametric driving. Above the threshold, quantum fluctuations induce transitions between the period-two states over the quasienergy barrier. We find the effective quantum activation energies for such transitions and their scaling with the difference of the driving amplitude from its critical value. We also find the scaling of the fluctuation correlation time with the quantum noise parameters in the critical region near the threshold. The results are extended to oscillators with nonlinear friction.
Wang, Qian; Qin, Pinquan; Wang, Wen-ge
2015-10-01
Based on an analysis of Feynman's path integral formulation of the propagator, a relative criterion is proposed for validity of a semiclassical approach to the dynamics near critical points in a class of systems undergoing quantum phase transitions. It is given by an effective Planck constant, in the relative sense that a smaller effective Planck constant implies better performance of the semiclassical approach. Numerical tests of this relative criterion are given in the XY model and in the Dicke model.
Field-induced magnetic instability and quantum criticality in the antiferromagnet CeCu2Ge2.
Liu, Yi; Xie, Donghua; Wang, Xiaoying; Zhu, Kangwei; Yang, Ruilong
2016-01-13
The magnetic quantum criticality in strongly correlated electron systems has been considered to be closely related with the occurrence of unconventional superconductivity. Control parameters such as magnetic field, pressure or chemical doping are frequently used to externally tune the quantum phase transition for a deeper understanding. Here we report the research of a field-induced quantum phase transition using conventional bulk physical property measurements in the archetypal antiferromagnet CeCu2Ge2, which becomes superconductive under a pressure of about 10 GPa with Tc ~ 0.64 K. We offer strong evidence that short-range dynamic correlations start appearing above a magnetic field of about 5 T. Our demonstrations of the magnetic instability and the field-induced quantum phase transition are crucial for the quantum criticality, which may open a new route in experimental investigations of the quantum phase transition in heavy-fermion systems.
Non-critical string theory formulation of microtubule dynamics and quantum aspects of brain function
Mavromatos, Nikolaos E
1995-01-01
Microtubule (MT) networks, subneural paracrystalline cytosceletal structures, seem to play a fundamental role in the neurons. We cast here the complicated MT dynamics in the form of a 1+1-dimensional non-critical string theory, thus enabling us to provide a consistent quantum treatment of MTs, including enviromental {\\em friction} effects. We suggest, thus, that the MTs are the microsites, in the brain, for the emergence of stable, macroscopic quantum coherent states, identifiable with the {\\em preconscious states}. Quantum space-time effects, as described by non-critical string theory, trigger then an {\\em organized collapse} of the coherent states down to a specific or {\\em conscious state}. The whole process we estimate to take {\\cal O}(1\\,{\\rm sec}), in excellent agreement with a plethora of experimental/observational findings. The {\\em microscopic arrow of time}, endemic in non-critical string theory, and apparent here in the self-collapse process, provides a satisfactory and simple resolution to the age...
Quantum criticality and emergence of the T/B scaling in strongly correlated metals
International Nuclear Information System (INIS)
Watanabe, Shinji; Miyake, Kazumasa
2016-01-01
A new type of scaling observed in heavy-electron metal β-YbAlB_4, where the magnetic susceptibility is expressed as a single scaling function of the ratio of temperature T and magnetic field B over four decades, is examined theoretically. We develop the mode-coupling theory for critical Yb-valence fluctuations under a magnetic field, verifying that the T/B scaling behavior appears near the QCP of the valence transition. Emergence of the T/B scaling indicates the presence of the small characteristic temperature of the critical Yb-valence fluctuation due to the strong local correlation effect. It is discussed that the T/B scaling as well as the unconventional criticality is explained from the viewpoint of the quantum valence criticality in a unified way.
Quantum criticality and first-order transitions in the extended periodic Anderson model
Hagymási, I.; Itai, K.; Sólyom, J.
2013-03-01
We investigate the behavior of the periodic Anderson model in the presence of d-f Coulomb interaction (Udf) using mean-field theory, variational calculation, and exact diagonalization of finite chains. The variational approach based on the Gutzwiller trial wave function gives a critical value of Udf and two quantum critical points (QCPs), where the valence susceptibility diverges. We derive the critical exponent for the valence susceptibility and investigate how the position of the QCP depends on the other parameters of the Hamiltonian. For larger values of Udf, the Kondo regime is bounded by two first-order transitions. These first-order transitions merge into a triple point at a certain value of Udf. For even larger Udf valence skipping occurs. Although the other methods do not give a critical point, they support this scenario.
Singularity of the London penetration depth at quantum critical points in superconductors.
Chowdhury, Debanjan; Swingle, Brian; Berg, Erez; Sachdev, Subir
2013-10-11
We present a general theory of the singularity in the London penetration depth at symmetry-breaking and topological quantum critical points within a superconducting phase. While the critical exponents and ratios of amplitudes on the two sides of the transition are universal, an overall sign depends upon the interplay between the critical theory and the underlying Fermi surface. We determine these features for critical points to spin density wave and nematic ordering, and for a topological transition between a superconductor with Z2 fractionalization and a conventional superconductor. We note implications for recent measurements of the London penetration depth in BaFe2(As(1-x)P(x))2 [K. Hashimoto et al., Science 336, 1554 (2012)].
Conductivity of Weakly Disordered Metals Close to a "Ferromagnetic" Quantum Critical Point
Kastrinakis, George
2018-05-01
We calculate analytically the conductivity of weakly disordered metals close to a "ferromagnetic" quantum critical point in the low-temperature regime. Ferromagnetic in the sense that the effective carrier potential V(q,ω ), due to critical fluctuations, is peaked at zero momentum q=0. Vertex corrections, due to both critical fluctuations and impurity scattering, are explicitly considered. We find that only the vertex corrections due to impurity scattering, combined with the self-energy, generate appreciable effects as a function of the temperature T and the control parameter a, which measures the proximity to the critical point. Our results are consistent with resistivity experiments in several materials displaying typical Fermi liquid behaviour, but with a diverging prefactor of the T^2 term for small a.
Quantum criticality and emergence of the T/B scaling in strongly correlated metals
Energy Technology Data Exchange (ETDEWEB)
Watanabe, Shinji [Department of Basic Sciences, Kyushu Institute of Technology, Kitakyushu (Japan); Miyake, Kazumasa [Toyota Physical and Chemical Research Institute, Nagakute (Japan)
2016-02-15
A new type of scaling observed in heavy-electron metal β-YbAlB{sub 4}, where the magnetic susceptibility is expressed as a single scaling function of the ratio of temperature T and magnetic field B over four decades, is examined theoretically. We develop the mode-coupling theory for critical Yb-valence fluctuations under a magnetic field, verifying that the T/B scaling behavior appears near the QCP of the valence transition. Emergence of the T/B scaling indicates the presence of the small characteristic temperature of the critical Yb-valence fluctuation due to the strong local correlation effect. It is discussed that the T/B scaling as well as the unconventional criticality is explained from the viewpoint of the quantum valence criticality in a unified way.
Ising critical behaviour in the one-dimensional frustrated quantum XY model
International Nuclear Information System (INIS)
Granato, E.
1993-06-01
A generalization of the one-dimensional frustrated quantum XY model is considered in which the inter and intra-chain coupling constants of the two infinite XY (planar rotor) chains have different strengths. The model can describe the superconductor-insulator transition due to charging effects in a ladder of Josephson junctions in a magnetic field with half a flux quantum per plaquette. From a fluctuation-effective action, this transition is expected to be in the universality class of the two-dimensional classical XY-Ising model. The critical behaviour is studied using a Monte Carlo transfer matrix applied to the path-integral representation of the model and a finite-size-scaling analysis of data on small system sizes. It is found that, unlike the previous studied case of equal inter and intra-chain coupling constants, the XY and Ising-like excitations of the quantum model decouple for large interchain coupling, giving rise to pure Ising model critical behaviour for the chirality order parameter in good agreement with the results for the XY-Ising model. (author). 18 refs, 4 figs
Directory of Open Access Journals (Sweden)
Yuichi Otsuka
2016-03-01
Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.
dc Resistivity of Quantum Critical, Charge Density Wave States from Gauge-Gravity Duality
Amoretti, Andrea; Areán, Daniel; Goutéraux, Blaise; Musso, Daniele
2018-04-01
In contrast to metals with weak disorder, the resistivity of weakly pinned charge density waves (CDWs) is not controlled by irrelevant processes relaxing momentum. Instead, the leading contribution is governed by incoherent, diffusive processes which do not drag momentum and can be evaluated in the clean limit. We compute analytically the dc resistivity for a family of holographic charge density wave quantum critical phases and discuss its temperature scaling. Depending on the critical exponents, the ground state can be conducting or insulating. We connect our results to dc electrical transport in underdoped cuprate high Tc superconductors. We conclude by speculating on the possible relevance of unstable, semilocally critical CDW states to the strange metallic region.
dc Resistivity of Quantum Critical, Charge Density Wave States from Gauge-Gravity Duality.
Amoretti, Andrea; Areán, Daniel; Goutéraux, Blaise; Musso, Daniele
2018-04-27
In contrast to metals with weak disorder, the resistivity of weakly pinned charge density waves (CDWs) is not controlled by irrelevant processes relaxing momentum. Instead, the leading contribution is governed by incoherent, diffusive processes which do not drag momentum and can be evaluated in the clean limit. We compute analytically the dc resistivity for a family of holographic charge density wave quantum critical phases and discuss its temperature scaling. Depending on the critical exponents, the ground state can be conducting or insulating. We connect our results to dc electrical transport in underdoped cuprate high T_{c} superconductors. We conclude by speculating on the possible relevance of unstable, semilocally critical CDW states to the strange metallic region.
Magnetic-field control of quantum critical points of valence transition.
Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques
2008-06-13
We study the mechanism of how critical end points of first-order valence transitions are controlled by a magnetic field. We show that the critical temperature is suppressed to be a quantum critical point (QCP) by a magnetic field, and unexpectedly, the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to the emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be cooperative phenomena of the Zeeman and Kondo effects, which create a distinct energy scale from the Kondo temperature. This mechanism explains the peculiar magnetic response in CeIrIn(5) and the metamagnetic transition in YbXCu(4) for X=In as well as the sharp contrast between X=Ag and Cd.
Avoided Quantum Criticality and Magnetoelastic Coupling in BaFe2-xNixAs2
DEFF Research Database (Denmark)
Lu, Xingye; Gretarsson, H.; Zhang, Rui
2013-01-01
suppressed and separated, resulting in sNT>T with increasing x, as was previously observed. However, the temperature separation between sT and NT decreases with increasing x for x≥0.065, tending toward a quantum bicritical point near optimal superconductivity at x≈0.1. The zero-temperature transition...... is preempted by the formation of a secondary incommensurate magnetic phase in the region 0.088≲x≲0.104, resulting in a finite value of NT≈cT+10 K above the superconducting dome around x≈0.1. Our results imply an avoided quantum critical point, which is expected to strongly influence the properties of both...
Inhomogeneous quasi-adiabatic driving of quantum critical dynamics in weakly disordered spin chains
International Nuclear Information System (INIS)
Rams, Marek M; Mohseni, Masoud; Campo, Adolfo del
2016-01-01
We introduce an inhomogeneous protocol to drive a weakly disordered quantum spin chain quasi-adiabatically across a quantum phase transition and minimize the residual energy of the final state. The number of spins that simultaneously reach the critical point is controlled by the length scale in which the magnetic field is modulated, introducing an effective size that favors adiabatic dynamics. The dependence of the residual energy on this length scale and the velocity at which the magnetic field sweeps out the chain is shown to be nonmonotonic. We determine the conditions for an optimal suppression of the residual energy of the final state and show that inhomogeneous driving can outperform conventional adiabatic schemes based on homogeneous control fields by several orders of magnitude. (paper)
Dipolar Antiferromagnetism and Quantum Criticality in LiErF4
International Nuclear Information System (INIS)
Kraemer, Conradin; Nikseresht, Neda; Piatek, Julian; Tsyrulin, Nikolay; Piazza, Bastien; Kiefer, Klaus; Klemke, Bastian; Rosenbaum, Thomas; Aeppli, Gabriel; Gannarelli, Che; Prokes, Karel; Straessle, Thierry; Keller, Lukas; Zaharko, Oksana; Kraemer, Karl; Ronnow, Henrik
2012-01-01
Magnetism has been predicted to occur in systems in which dipolar interactions dominate exchange. We present neutron scattering, specific heat, and magnetic susceptibility data for LiErF 4 , establishing it as a model dipolar-coupled antiferromagnet with planar spin-anisotropy and a quantum phase transition in applied field H c# parallel# = 4.0 ± 0.1 kilo-oersteds. We discovered non-mean-field critical scaling for the classical phase transition at the antiferromagnetic transition temperature that is consistent with the two-dimensional XY/h 4 universality class; in accord with this, the quantum phase transition at H c exhibits three-dimensional classical behavior. The effective dimensional reduction may be a consequence of the intrinsic frustrated nature of the dipolar interaction, which strengthens the role of fluctuations.
Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5.
Ronning, F; Helm, T; Shirer, K R; Bachmann, M D; Balicas, L; Chan, M K; Ramshaw, B J; McDonald, R D; Balakirev, F F; Jaime, M; Bauer, E D; Moll, P J W
2017-08-17
Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of fluctuating nematic character in a heavy-fermion superconductor, CeRhIn 5 (ref. 5). We observe a magnetic-field-induced state in the vicinity of a field-tuned antiferromagnetic quantum critical point at H c ≈ 50 tesla. This phase appears above an out-of-plane critical field H* ≈ 28 tesla and is characterized by a substantial in-plane resistivity anisotropy in the presence of a small in-plane field component. The in-plane symmetry breaking has little apparent connection to the underlying lattice, as evidenced by the small magnitude of the magnetostriction anomaly at H*. Furthermore, no anomalies appear in the magnetic torque, suggesting the absence of metamagnetism in this field range. The appearance of nematic behaviour in a prototypical heavy-fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials.
International Nuclear Information System (INIS)
Val’kov, V. V.; Zlotnikov, A. O.
2013-01-01
Mechanisms of the appearance of anomalous properties experimentally observed at the transition through the quantum critical point in rare-earth intermetallides have been studied. Quantum phase transitions are induced by the external pressure and are manifested as the destruction of the long-range antiferromagnetic order at zero temperature. The suppression of the long-range order is accompanied by an increase in the area of the Fermi surface, and the effective electron mass is strongly renormalized near the quantum critical point. It has been shown that such a renormalization is due to the reconstruction of the quasiparticle band, which is responsible for the formation of heavy fermions. It has been established that these features hold when the coexistence phase of antiferromagnetism and superconductivity is implemented near the quantum critical point.
Quantum Critical Quasiparticle Scattering within the Superconducting State of CeCoIn_{5}.
Paglione, Johnpierre; Tanatar, M A; Reid, J-Ph; Shakeripour, H; Petrovic, C; Taillefer, Louis
2016-07-01
The thermal conductivity κ of the heavy-fermion metal CeCoIn_{5} was measured in the normal and superconducting states as a function of temperature T and magnetic field H, for a current and field parallel to the [100] direction. Inside the superconducting state, when the field is lower than the upper critical field H_{c2}, κ/T is found to increase as T→0, just as in a metal and in contrast to the behavior of all known superconductors. This is due to unpaired electrons on part of the Fermi surface, which dominate the transport above a certain field. The evolution of κ/T with field reveals that the electron-electron scattering (or transport mass m^{⋆}) of those unpaired electrons diverges as H→H_{c2} from below, in the same way that it does in the normal state as H→H_{c2} from above. This shows that the unpaired electrons sense the proximity of the field-tuned quantum critical point of CeCoIn_{5} at H^{⋆}=H_{c2} even from inside the superconducting state. The fact that the quantum critical scattering of the unpaired electrons is much weaker than the average scattering of all electrons in the normal state reveals a k-space correlation between the strength of pairing and the strength of scattering, pointing to a common mechanism, presumably antiferromagnetic fluctuations.
Origin of quantum criticality in Yb-Al-Au approximant crystal and quasicrystal
International Nuclear Information System (INIS)
Watanabe, Shinji; Miyake, Kazumasa
2016-01-01
To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb 15 Al 34 Au 51 , the approximant crystal Yb 14 Al 35 Au 51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits χ ∼ T -0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size. (author)
High spin cycles: topping the spin record for a single molecule verging on quantum criticality
Baniodeh, Amer; Magnani, Nicola; Lan, Yanhua; Buth, Gernot; Anson, Christopher E.; Richter, Johannes; Affronte, Marco; Schnack, Jürgen; Powell, Annie K.
2018-03-01
The cyclisation of a short chain into a ring provides fascinating scenarios in terms of transforming a finite array of spins into a quasi-infinite structure. If frustration is present, theory predicts interesting quantum critical points, where the ground state and thus low-temperature properties of a material change drastically upon even a small variation of appropriate external parameters. This can be visualised as achieving a very high and pointed summit where the way down has an infinity of possibilities, which by any parameter change will be rapidly chosen, in order to reach the final ground state. Here we report a mixed 3d/4f cyclic coordination cluster that turns out to be very near or even at such a quantum critical point. It has a ground state spin of S = 60, the largest ever observed for a molecule (120 times that of a single electron). [Fe10Gd10(Me-tea)10(Me-teaH)10(NO3)10].20MeCN forms a nano-torus with alternating gadolinium and iron ions with a nearest neighbour Fe-Gd coupling and a frustrating next-nearest neighbour Fe-Fe coupling. Such a spin arrangement corresponds to a cyclic delta or saw-tooth chain, which can exhibit unusual frustration effects. In the present case, the quantum critical point bears a `flatland' of tens of thousands of energetically degenerate states between which transitions are possible at no energy costs with profound caloric consequences. Entropy-wise the energy flatland translates into the pointed summit overlooking the entropy landscape. Going downhill several target states can be reached depending on the applied physical procedure which offers new prospects for addressability.
Stokes phenomena and quantum integrability in non-critical string/M theory
International Nuclear Information System (INIS)
Chan, Chuan-Tsung; Irie, Hirotaka; Yeh, Chi-Hsien
2012-01-01
We study Stokes phenomena of the k×k isomonodromy systems with an arbitrary Poincaré index r, especially which correspond to the fractional-superstring (or parafermionic-string) multi-critical points (p-hat,q-hat)=(1,r-1) in the k-cut two-matrix models. Investigation of this system is important for the purpose of figuring out the non-critical version of M theory which was proposed to be the strong-coupling dual of fractional superstring theory as a two-matrix model with an infinite number of cuts. Surprisingly the multi-cut boundary-condition recursion equations have a universal form among the various multi-cut critical points, and this enables us to show explicit solutions of Stokes multipliers in quite wide classes of (k,r). Although these critical points almost break the intrinsic Z k symmetry of the multi-cut two-matrix models, this feature makes manifest a connection between the multi-cut boundary-condition recursion equations and the structures of quantum integrable systems. In particular, it is uncovered that the Stokes multipliers satisfy multiple Hirota equations (i.e. multiple T-systems). Therefore our result provides a large extension of the ODE/IM correspondence to the general isomonodromy ODE systems endowed with the multi-cut boundary conditions. We also comment about a possibility that N=2 QFT of Cecotti-Vafa would be “topological series” in non-critical M theory equipped with a single quantum integrability.
Theory of critical phenomena in finite-size systems scaling and quantum effects
Brankov, Jordan G; Tonchev, Nicholai S
2000-01-01
The aim of this book is to familiarise the reader with the rich collection of ideas, methods and results available in the theory of critical phenomena in systems with confined geometry. The existence of universal features of the finite-size effects arising due to highly correlated classical or quantum fluctuations is explained by the finite-size scaling theory. This theory (1) offers an interpretation of experimental results on finite-size effects in real systems; (2) gives the most reliable tool for extrapolation to the thermodynamic limit of data obtained by computer simulations; (3) reveals
Finite-dimensional effects and critical indices of one-dimensional quantum models
International Nuclear Information System (INIS)
Bogolyubov, N.M.; Izergin, A.G.; Reshetikhin, N.Yu.
1986-01-01
Critical indices, depending on continuous parameters in Bose-gas quantum models and Heisenberg 1/2 spin antiferromagnetic in two-dimensional space-time at zero temperature, have been calculated by means of finite-dimensional effects. In this case the long-wave asymptotics of the correlation functions is of a power character. Derivation of man asymptotics terms is reduced to the determination of a central charge in the appropriate Virassoro algebra representation and the anomalous dimension-operator spectrum in this representation. The finite-dimensional effects allow to find these values
CRITIC2: A program for real-space analysis of quantum chemical interactions in solids
Otero-de-la-Roza, A.; Johnson, Erin R.; Luaña, Víctor
2014-03-01
We present CRITIC2, a program for the analysis of quantum-mechanical atomic and molecular interactions in periodic solids. This code, a greatly improved version of the previous CRITIC program (Otero-de-la Roza et al., 2009), can: (i) find critical points of the electron density and related scalar fields such as the electron localization function (ELF), Laplacian, … (ii) integrate atomic properties in the framework of Bader’s Atoms-in-Molecules theory (QTAIM), (iii) visualize non-covalent interactions in crystals using the non-covalent interactions (NCI) index, (iv) generate relevant graphical representations including lines, planes, gradient paths, contour plots, atomic basins, … and (v) perform transformations between file formats describing scalar fields and crystal structures. CRITIC2 can interface with the output produced by a variety of electronic structure programs including WIEN2k, elk, PI, abinit, Quantum ESPRESSO, VASP, Gaussian, and, in general, any other code capable of writing the scalar field under study to a three-dimensional grid. CRITIC2 is parallelized, completely documented (including illustrative test cases) and publicly available under the GNU General Public License. Catalogue identifier: AECB_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECB_v2_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: yes No. of lines in distributed program, including test data, etc.: 11686949 No. of bytes in distributed program, including test data, etc.: 337020731 Distribution format: tar.gz Programming language: Fortran 77 and 90. Computer: Workstations. Operating system: Unix, GNU/Linux. Has the code been vectorized or parallelized?: Shared-memory parallelization can be used for most tasks. Classification: 7.3. Catalogue identifier of previous version: AECB_v1_0 Journal reference of previous version: Comput. Phys. Comm. 180 (2009) 157 Nature of problem: Analysis of quantum
International Nuclear Information System (INIS)
Dulin, V.V.
2006-01-01
A method of determination neutrons multiplication in deep sub-critical multiplying media has been developed. It is based on a modified of Rossi - alpha method. It will consist in use of integral on time (a method of the areas) from correlated parts of distribution and integral in area, independent of time a part of distribution (area of a constant background). It allows to spend the calculated analysis, using the integrated equation on time for a neutrons flux and to not use representation of point kinetic model. A calculation spatially-correlation factor the adjoint (relative the detector count rate) inhomogeneous equation is used. Its calculation takes into account fission both in multiplying media and in a spontaneous neutron source. Measurements with plutonium-steel and uranium-steel blocks, and blocks from uranium and plutonium dioxide of different enrichment are have been carried out. The measured values of neutrons multiplication in a range 1.03-1.82 will be well coordinated to results of calculations. The question on an opportunity of definition of weight of the measured blocks of fissile material is considered [ru
Extraction of conformal data in critical quantum spin chains using the Koo-Saleur formula
Milsted, Ashley; Vidal, Guifre
2017-12-01
We study the emergence of two-dimensional conformal symmetry in critical quantum spin chains on the finite circle. Our goal is to characterize the conformal field theory (CFT) describing the universality class of the corresponding quantum phase transition. As a means to this end, we propose and demonstrate automated procedures which, using only the lattice Hamiltonian H =∑jhj as an input, systematically identify the low-energy eigenstates corresponding to Virasoro primary and quasiprimary operators, and assign the remaining low-energy eigenstates to conformal towers. The energies and momenta of the primary operator states are needed to determine the primary operator scaling dimensions and conformal spins, an essential part of the conformal data that specifies the CFT. Our techniques use the action, on the low-energy eigenstates of H , of the Fourier modes Hn of the Hamiltonian density hj. The Hn were introduced as lattice representations of the Virasoro generators by Koo and Saleur [Nucl. Phys. B 426, 459 (1994), 10.1016/0550-3213(94)90018-3]. In this paper, we demonstrate that these operators can be used to extract conformal data in a nonintegrable quantum spin chain.
Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field
International Nuclear Information System (INIS)
Liu Guanghua; Li Ruoyan; Tian Guangshan
2012-01-01
By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h c = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h < 2.0), a logarithmically divergent behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1. (paper)
CePdAl. A frustrated Kondo lattice at a quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Fritsch, Veronika [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Karlsruhe Institute of Technology (Germany); Sakai, Akito; Gegenwart, Philipp [EP 6, Electronic Correlations and Magnetism, University of Augsburg (Germany); Huesges, Zita; Lucas, Stefan; Stockert, Oliver [Max Planck Institute for Chemical Physics of Solids, Dresden (Germany); Kittler, Wolfram; Taubenheim, Christian; Grube, Kai; Loehneysen, Hilbert von [Karlsruhe Institute of Technology (Germany); Huang, Chien-Lung [Karlsruhe Institute of Technology (Germany); Max Planck Institute for Chemical Physics of Solids, Dresden (Germany)
2016-07-01
CePdAl is one of the rare frustrated Kondo lattice systems that can be tuned across a quantum critical point (QCP) by means of chemical pressure, i. e., the substitution of Pd by Ni. Magnetic frustration and Kondo effect are antithetic phenomena: The Kondo effect with the incipient delocalization of the magnetic moments, is not beneficial for the formation of a frustrated state. On the other hand, magnetic frustrated exchange interactions between the local moments can result in a breakdown of Kondo screening. Furthermore, the fate of frustration is unclear when approaching the QCP, since there is no simple observable to quantify the degree of frustration. We present thermodynamic and neutron scattering experiments on CePd{sub 1-x}Ni{sub x}Al close to the critical concentration x ∼0.14. Our experiments indicate that even at the QCP magnetic frustration is still present, opening the perspective to find new universality classes at such a quantum phase transition.
Bristol, S.
2014-12-01
In 2007, the U.S. Geological Survey (USGS) published a science strategy that resulted in an organizational pivot toward more focused attention on societal challenges and our ability to predict changes and study mitigation and resilience. The strategy described a number of global dynamics including climate and resource-related critical zone (CZ) impacts and emphasized the need for data integration as a significant underpinning for all of the science questions raised in the report. Organizational changes that came about as a result of the science strategy sparked a new entity called Core Science Systems, which has set as its mission the creation of a Modular Science Framework designed to seamlessly organize and integrate all data, information, and knowledge from the CZ. A part of this grand challenge is directly within the purview of the USGS mission and our science programs, while the data integration framework itself is part of a much larger global scientific cyberinfrastructure. This talk describes current research and development in pursuit of the USGS Modular Science Framework and how the work is being conducted in the context of the broader earth system sciences. Communities of practice under the banner of the Earth Science Information Partners are fostering working relationships vital to cohesion and interoperability between contributing institutions. The National Science Foundation's EarthCube and Cyberinfrastructure for the 21st Century initiatives are providing some of the necessary building blocks through foundational informatics and data science research. The U.S. Group on Earth Observations is providing leadership and coordination across agencies who operate earth observation systems. The White House Big Data Initiative is providing long term research and development vision to set the stage for sustainable, long term infrastructure across government data agencies. The end result will be a major building block of CZ science.
Quantum criticality in He3 bi-layers and heavy fermion compounds
International Nuclear Information System (INIS)
Benlagra, A.
2009-11-01
Despite intense experimental as well as theoretical efforts the understanding of physical phenomena peculiar to heavy fermion compounds remains one of the major problems in condensed matter physics; this research thesis considers the recently proposed theoretical approaches to describe the critical regime properties. This approach is based on the following idea: critical modes which are responsible for this regime are non-magnetic and are associated to the destruction of the Kondo effect between localized magnetic impurities and travelling conduction electrons at the quantum critical point. The author derives an analytic expression for the free energy within this model by using the Luttinger-Ward functional approach within the frame of the Eliashberg theory. The obtained expressions are transparently including the effect of critical fluctuations, integrated in a self-coherent way. The behaviour of different thermodynamic quantities is then deduced from these expressions. The result is compared with recent experiments on heavy fermion compounds as well as on a Helium-3 bilayer system adsorbed on graphite substrate in order to test the validity of such a model. Strengths and drawbacks of the model are outlined
Entropy excess in strongly correlated Fermi systems near a quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Clark, J.W., E-mail: jwc@wuphys.wustl.edu [McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States); Zverev, M.V. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); Moscow Institute of Physics and Technology, Moscow, 123098 (Russian Federation); Khodel, V.A. [Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation); McDonnell Center for the Space Sciences and Department of Physics, Washington University, St. Louis, MO 63130 (United States)
2012-12-15
A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau
Enhanced pairing of quantum critical metals near $d=3+1$
Energy Technology Data Exchange (ETDEWEB)
Fitzpatrick, A. Liam; Kachru, Shamit; Kaplan, Jared; Raghu, S.; Torroba, Gonzalo; Wang, Huajia
2015-07-20
We study the dynamics of a quantum critical boson coupled to a Fermi surface in intermediate energy regimes where the Landau damping of the boson can be parametrically controlled, either via large Fermi velocity or by large- N techniques. We develop a systematic approach to the BCS instability of such systems, including careful treatment of the enhanced log 2 and log 3 singularities which appear already at 1-loop. These singularities arise due to the exchange of a critical boson in the Cooper channel and are absent in Fermi liquid theory. We also treat possible instabilities to charge density wave (CDW) formation, and compare the scales Λ BCS and Λ CDW of the onset of the instabilities in different parametric regimes. We address the question of whether the dressing of the fermions into a non-Fermi liquid via interactions with the order parameter field can happen at energies > Λ BCS , Λ CDW .
Quantum critical fluctuations due to nested Fermi surface: The case of spinless fermions
International Nuclear Information System (INIS)
Schlottmann, P.
2007-01-01
A quantum critical point (QCP) can be obtained by tuning the critical temperature of a second-order phase transition to zero. A simple model of spinless fermions with nested Fermi surface leading to a charge density wave is considered. The QCP is obtained by tuning the nesting mismatch of the Fermi surface, which has the following consequences: (i) For the tuned QCP, the specific heat over T and the effective mass increase with the logarithm of the temperature as T is lowered. (ii) For the tuned QCP the linewidth of the quasi-particles is sublinear in T and ω. (iii) The specific heat and the linewidth display a crossover from non-Fermi liquid (∼T) to Fermi liquid (∼T 2 ) behavior with increasing nesting mismatch and decreasing temperature. (iv) For the tuned QCP, the dynamical charge susceptibility has a quasi-elastic peak with a linewidth proportional to T. (v) For non-critical Fermi vector mismatch the peak is inelastic. (vi) While the specific heat and the quasi-particle linewidth are only weakly dependent on the geometry of the nested Fermi surfaces, the momentum-dependent dynamical susceptibility is expected to be affected by the shape of the Fermi surface
Two-loop disorder effects on the nematic quantum criticality in d-wave superconductors
International Nuclear Information System (INIS)
Wang, Jing
2015-01-01
The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic quantum critical point that is supposed to exist in some d-wave cuprate superconductors. This non-Fermi liquid state may be turned into a disorder-dominated diffusive metal if the fermions also couple to a disordered potential that generates a relevant perturbation in the sense of renormalization group theory. It is therefore necessary to examine whether a specific disorder is relevant or not. We study the interplay between critical nematic fluctuation and random chemical potential by performing renormalization group analysis. The parameter that characterizes the strength of random chemical potential is marginal at the one-loop level, but becomes marginally relevant after including the two-loop corrections. Thus even weak random chemical potential leads to diffusive motion of nodal fermions and the significantly critical behaviors of physical implications, since the strength flows eventually to large values at low energies. - Highlights: • The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic QCP. • The strength of random chemical potential is marginal at the one-loop level. • The strength becomes marginally relevant after including the two-loop corrections. • The diffusive metallic state is induced by the marginally relevant disorder. • The behaviors of some physical observables are presented at the nematic QCP
Chen, Wei
2018-03-01
For D -dimensional weakly interacting topological insulators in certain symmetry classes, the topological invariant can be calculated from a D - or (D +1 ) -dimensional integration over a certain curvature function that is expressed in terms of single-particle Green's functions. Based on the divergence of curvature function at the topological phase transition, we demonstrate how a renormalization group approach circumvents these integrations and reduces the necessary calculation to that for the Green's function alone, rendering a numerically efficient tool to identify topological phase transitions in a large parameter space. The method further unveils a number of statistical aspects related to the quantum criticality in weakly interacting topological insulators, including correlation function, critical exponents, and scaling laws, that can be used to characterize the topological phase transitions driven by either interacting or noninteracting parameters. We use 1D class BDI and 2D class A Dirac models with electron-electron and electron-phonon interactions to demonstrate these principles and find that interactions may change the critical exponents of the topological insulators.
Landau-Ginzburg Limit of Black Hole's Quantum Portrait: Self Similarity and Critical Exponent
Dvali, Gia
2012-01-01
Recently we have suggested that the microscopic quantum description of a black hole is an overpacked self-sustained Bose-condensate of N weakly-interacting soft gravitons, which obeys the rules of 't Hooft's large-N physics. In this note we derive an effective Landau-Ginzburg Lagrangian for the condensate and show that it becomes an exact description in a semi-classical limit that serves as the black hole analog of 't Hooft's planar limit. The role of a weakly-coupled Landau-Ginzburg order parameter is played by N. This description consistently reproduces the known properties of black holes in semi-classical limit. Hawking radiation, as the quantum depletion of the condensate, is described by the slow-roll of the field N. In the semiclassical limit, where black holes of arbitrarily small size are allowed, the equation of depletion is self similar leading to a scaling law for the black hole size with critical exponent 1/3.
Transport anomalies and quantum criticality in electron-doped cuprate superconductors
Energy Technology Data Exchange (ETDEWEB)
Zhang, Xu; Yu, Heshan; He, Ge; Hu, Wei; Yuan, Jie; Zhu, Beiyi [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Jin, Kui, E-mail: kuijin@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Collaborative Innovation Center of Quantum Matter, Beijing 100190 (China)
2016-06-15
Highlights: • Electrical transport and its complementary thermal transport on electron-doped cuprates are reviewed. • The common features of electron-doped cuprates are sorted out and shown in the last figure. • The complex superconducting fluctuations and quantum fluctuations are distinguished. - Abstract: Superconductivity research is like running a marathon. Three decades after the discovery of high-T{sub c} cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, complex quantum criticality. Most of them have been challenging the existing theories, nevertheless, a unified diagram certainly helps to approach the nature of electron-doped cuprates.
Directory of Open Access Journals (Sweden)
Salehi L
2015-04-01
Full Text Available Aims: Critical thinking has the 2 aspects skill and attitude. The skill aspect will not take place without the attitude to critical thinking. The aim of this study was to compare between problem-based and question-answer learning methods on critical thinking attitude of environmental health students. Instrument & Methods: In this quasi-experimental study all 27 environmental health students of Alborz University of Medical Sciences were entered the study by census method. Critical thinking attitudes’ parameters were studied by the California critical thinking disposition inventory (CCTDI before and after the intervention. The problem-based learning group (14 persons held some scenarios for studying and investigating and question-answer group (13 persons held 4 questioning sessions. Data were collected and analyzed by SPSS 17 using independent- and paired-T tests. Findings: There were no significant differences between the average of CCTDI scores for problem-based learning group before (278.00±28.14 and after (309.29±13.80 the intervention and also between the average of CCTDI scores for question-answer group before (276.00±7.12 and after (306.62±16.32 the intervention (p>0.05. Both methods caused a significant increase in analytic power, information categorization and self-confidence of students (p<0.05. Conclusion: Using both question-answer and problem-based educational methods can improve the attitude to critical thinking in students.
Electron spin resonance and quantum critical phenomena in VOx multiwall nanotubes
International Nuclear Information System (INIS)
Demishev, S.V.; Chernobrovkin, A.L.; Glushkov, V.V.; Samarin, N.A.; Sluchanko, N.E.; Semeno, A.V.; Goodilin, E.A.; Grigorieva, A.V.; Tretyakov, Yu.D.
2008-01-01
Basing on the high frequency (60 GHz) electron spin resonance study of the VO x multiwall nanotubes (VO x -NTs) carried out in the temperature range 4.2-200 K we report: (i) the first direct experimental evidence of the presence of the antiferromagnetic dimers in VO x -NTs and (ii) the observation of an anomalous low temperature growth of the magnetic susceptibility for quasi-free spins, which obey the power law χ(T)∝1/T α with the exponent α∼0.6 in a wide temperature range 4.2-50 K. We argue that the observed departures from the Curie-Weiss behaviour manifest the onset of the quantum critical regime and formation of the Griffiths phase as a magnetic ground state of these spin species. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E₈ symmetry.
Wu, Jianda; Kormos, Márton; Si, Qimiao
2014-12-12
A spectrum exhibiting E₈ symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E₈ description for CoNb₂O₆.
Quantum criticality and duality in the Sachdev-Ye-Kitaev/AdS2 chain
Jian, Shao-Kai; Xian, Zhuo-Yu; Yao, Hong
2018-05-01
We show that the quantum critical point (QCP) between a diffusive metal and ferromagnetic (or antiferromagnetic) phases in the SYK chain has a gravitational description corresponding to the double-trace deformation in an AdS2 chain. Specifically, by studying a double-trace deformation of a Z2 scalar in an AdS2 chain where the Z2 scalar is dual to the order parameter in the SYK chain, we find that the susceptibility and renormalization group equation describing the QCP in the SYK chain can be exactly reproduced in the holographic model. Our results suggest that the infrared geometry in the gravity theory dual to the diffusive metal of the SYK chain is also an AdS2 chain. We further show that the transition in SYK model captures universal information about double-trace deformation in generic black holes with near horizon AdS2 space-time.
LaCu6-xAgx : A promising host of an elastic quantum critical point
Poudel, L.; Cruz, C. de la; Koehler, M. R.; McGuire, M. A.; Keppens, V.; Mandrus, D.; Christianson, A. D.
2018-05-01
Structural properties of LaCu6-xAgx have been investigated using neutron and x-ray diffraction, and resonant ultrasound spectroscopy (RUS) measurements. Diffraction measurements indicate a continuous structural transition from orthorhombic (Pnma) to monoclinic (P21 / c) structure. RUS measurements show softening of natural frequencies at the structural transition, consistent with the elastic nature of the structural ground state. The structural transition temperatures in LaCu6-xAgx decrease with Ag composition until the monoclinic phase is completely suppressed at xc = 0.225 . All of the evidence is consistent with the presence of an elastic quantum critical point in LaCu6-xAgx .
Critical strain region evaluation of self-assembled semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Sales, D L [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain); Pizarro, J [Departamento de Lenguajes y Sistemas Informaticos, Universidad de Cadiz, Puerto Real, Cadiz (Spain); Galindo, P L [Departamento de Lenguajes y Sistemas Informaticos, Universidad de Cadiz, Puerto Real, Cadiz (Spain); Garcia, R [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain); Trevisi, G [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Frigeri, P [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Nasi, L [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Franchi, S [CNR-IMEM Institute, Parco delle Scienze 37a, 43100, Parma (Italy); Molina, S I [Departamento de Ciencia de los Materiales e I. M. y Q. I., Universidad de Cadiz, Puerto Real, Cadiz (Spain)
2007-11-28
A novel peak finding method to map the strain from high resolution transmission electron micrographs, known as the Peak Pairs method, has been applied to In(Ga)As/AlGaAs quantum dot (QD) samples, which present stacking faults emerging from the QD edges. Moreover, strain distribution has been simulated by the finite element method applying the elastic theory on a 3D QD model. The agreement existing between determined and simulated strain values reveals that these techniques are consistent enough to qualitatively characterize the strain distribution of nanostructured materials. The correct application of both methods allows the localization of critical strain zones in semiconductor QDs, predicting the nucleation of defects, and being a very useful tool for the design of semiconductor devices.
Tienken, Christopher H.; Goldberg, Stephanie; DiRocco, Dominic
2010-01-01
Historical accounts of questioning used in the education process trace back to Socrates. One of the best examples of his use of questioning is found in Plato's "The Republic." Socrates used a series of strategic questions to help his student Glaucon come to understand the concept of justice. Socrates purposefully posed a series of…
Moon, Byoung Hee; Bae, Jung Jun; Joo, Min-Kyu; Choi, Homin; Han, Gang Hee; Lim, Hanjo; Lee, Young Hee
2018-05-24
Quantum localization-delocalization of carriers are well described by either carrier-carrier interaction or disorder. When both effects come into play, however, a comprehensive understanding is not well established mainly due to complexity and sparse experimental data. Recently developed two-dimensional layered materials are ideal in describing such mesoscopic critical phenomena as they have both strong interactions and disorder. The transport in the insulating phase is well described by the soft Coulomb gap picture, which demonstrates the contribution of both interactions and disorder. Using this picture, we demonstrate the critical power law behavior of the localization length, supporting quantum criticality. We observe asymmetric critical exponents around the metal-insulator transition through temperature scaling analysis, which originates from poor screening in insulating regime and conversely strong screening in metallic regime due to free carriers. The effect of asymmetric scaling behavior is weakened in monolayer MoS 2 due to a dominating disorder.
International Nuclear Information System (INIS)
Warnock, R.L.
1996-02-01
Ordinary quantum theory is a statistical theory without an underlying probability space. The Wiener-Siegel theory provides a probability space, defined in terms of the usual wave function and its ''stochastic coordinates''; i.e., projections of its components onto differentials of complex Wiener processes. The usual probabilities of quantum theory emerge as measures of subspaces defined by inequalities on stochastic coordinates. Since each point α of the probability space is assigned values (or arbitrarily small intervals) of all observables, the theory gives a pseudo-classical or ''hidden-variable'' view in which normally forbidden concepts are allowed. Joint probabilities for values of noncommuting variables are well-defined. This paper gives a brief description of the theory, including a new generalization to incorporate spin, and reports the first concrete calculation of a joint probability for noncommuting components of spin of a single particle. Bohm's form of the Einstein-Podolsky-Rosen Gedankenexperiment is discussed along the lines of Carlen's paper at this Congress. It would seem that the ''EPR Paradox'' is avoided, since to each α the theory assigns opposite values for spin components of two particles in a singlet state, along any axis. In accordance with Bell's ideas, the price to pay for this attempt at greater theoretical detail is a disagreement with usual quantum predictions. The disagreement is computed and found to be large
International Nuclear Information System (INIS)
Mishchenko, Yuriy
2004-01-01
MISHCHENKO, YURIY. Applications of Canonical Transformations and Nontrivial Vacuum Solutions to flavor mixing and critical phenomena in Quantum Field Theory. (Under the direction of Chueng-Ryong Ji.) In this dissertation we consider two recent applications of Bogoliubov Transformation to the phenomenology of quantum mixing and the theory of critical phenomena. In recent years quantum mixing got in the focus of the searches for New Physics due to its unparalleled sensitivity to SM parameters and indications of neutrino mixing. It was recently suggested that Bogoliubov Transformation may be important in proper definition of the flavor states that otherwise results in problems in perturbative treatment. As first part of this dissertation we investigate this conjecture and develop a complete formulation of such a mixing field theory involving introduction of general formalism, analysis of space-time conversion and phenomenological implications. As second part of this dissertati
Energy Technology Data Exchange (ETDEWEB)
Mishchenko, Yuriy [North Carolina State Univ., Raleigh, NC (United States)
2004-12-01
MISHCHENKO, YURIY. Applications of Canonical Transformations and Nontrivial Vacuum Solutions to flavor mixing and critical phenomena in Quantum Field Theory. (Under the direction of Chueng-Ryong Ji.) In this dissertation we consider two recent applications of Bogoliubov Transformation to the phenomenology of quantum mixing and the theory of critical phenomena. In recent years quantum mixing got in the focus of the searches for New Physics due to its unparalleled sensitivity to SM parameters and indications of neutrino mixing. It was recently suggested that Bogoliubov Transformation may be important in proper definition of the flavor states that otherwise results in problems in perturbative treatment. As first part of this dissertation we investigate this conjecture and develop a complete formulation of such a mixing field theory involving introduction of general formalism, analysis of space-time conversion and phenomenological implications. As second part of this dissertati
International Nuclear Information System (INIS)
Gurtovoi, V. L.; Dubonos, S. V.; Karpii, S. V.; Nikulov, A. V.; Tulin, V. A.
2007-01-01
Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta
Zembylas, Michalinos
2018-01-01
This article argues that there is an urgent need to engage with a deeper analysis of the contemporary culture of "political depression" and its affective implications in human rights education (HRE). In particular, the article focuses on the following questions: How might a theorization of political depression be relevant to efforts that…
Žunkovič, Bojan; Heyl, Markus; Knap, Michael; Silva, Alessandro
2018-03-01
We theoretically study the dynamics of a transverse-field Ising chain with power-law decaying interactions characterized by an exponent α , which can be experimentally realized in ion traps. We focus on two classes of emergent dynamical critical phenomena following a quantum quench from a ferromagnetic initial state: The first one manifests in the time-averaged order parameter, which vanishes at a critical transverse field. We argue that such a transition occurs only for long-range interactions α ≤2 . The second class corresponds to the emergence of time-periodic singularities in the return probability to the ground-state manifold which is obtained for all values of α and agrees with the order parameter transition for α ≤2 . We characterize how the two classes of nonequilibrium criticality correspond to each other and give a physical interpretation based on the symmetry of the time-evolved quantum states.
International Nuclear Information System (INIS)
Kim, Ki-Seok
2005-01-01
We investigate the quantum phase transition of the O(3) nonlinear σ model without Berry phase in two spatial dimensions. Utilizing the CP 1 representation of the nonlinear σ model, we obtain an effective action in terms of bosonic spinons interacting via compact U(1) gauge fields. Based on the effective field theory, we find that the bosonic spinons are deconfined to emerge at the quantum critical point of the nonlinear σ model. It is emphasized that the deconfinement of spinons is realized in the absence of Berry phase. This is in contrast to the previous study of Senthil et al. [Science 303, 1490 (2004)], where the Berry phase plays a crucial role, resulting in the deconfinement of spinons. It is the reason why the deconfinement is obtained even in the absence of the Berry phase effect that the quantum critical point is described by the XY ('neutral') fixed point, not the IXY ('charged') fixed point. The IXY fixed point is shown to be unstable against instanton excitations and the instanton excitations are proliferated. At the IXY fixed point it is the Berry phase effect that suppresses the instanton excitations, causing the deconfinement of spinons. On the other hand, the XY fixed point is found to be stable against instanton excitations because an effective internal charge is zero at the neutral XY fixed point. As a result the deconfinement of spinons occurs at the quantum critical point of the O(3) nonlinear σ model in two dimensions
Themelis, Spyros
2009-01-01
This article deals with issues pertinent to the "inclusion" of Roma/Traveller children and young people in Europe and, in particular, England. It discusses some key issues that pertain to the inclusion of Roma/Traveller groups in society and it critically presents some key policies that have been advanced to tackle educational and social…
Nematic quantum critical point without magnetism in FeSe1-xSx superconductors.
Hosoi, Suguru; Matsuura, Kohei; Ishida, Kousuke; Wang, Hao; Mizukami, Yuta; Watashige, Tatsuya; Kasahara, Shigeru; Matsuda, Yuji; Shibauchi, Takasada
2016-07-19
In most unconventional superconductors, the importance of antiferromagnetic fluctuations is widely acknowledged. In addition, cuprate and iron-pnictide high-temperature superconductors often exhibit unidirectional (nematic) electronic correlations, including stripe and orbital orders, whose fluctuations may also play a key role for electron pairing. In these materials, however, such nematic correlations are intertwined with antiferromagnetic or charge orders, preventing the identification of the essential role of nematic fluctuations. This calls for new materials having only nematicity without competing or coexisting orders. Here we report systematic elastoresistance measurements in FeSe1-xSx superconductors, which, unlike other iron-based families, exhibit an electronic nematic order without accompanying antiferromagnetic order. We find that the nematic transition temperature decreases with sulfur content x; whereas, the nematic fluctuations are strongly enhanced. Near [Formula: see text], the nematic susceptibility diverges toward absolute zero, revealing a nematic quantum critical point. The obtained phase diagram for the nematic and superconducting states highlights FeSe1-xSx as a unique nonmagnetic system suitable for studying the impact of nematicity on superconductivity.
Quench dynamics near a quantum critical point: Application to the sine-Gordon model
International Nuclear Information System (INIS)
De Grandi, C.; Polkovnikov, A.; Gritsev, V.
2010-01-01
We discuss the quench dynamics near a quantum critical point focusing on the sine-Gordon model as a primary example. We suggest a unified approach to sudden and slow quenches, where the tuning parameter λ(t) changes in time as λ(t)∼υt r , based on the adiabatic expansion of the excitation probability in powers of υ. We show that the universal scaling of the excitation probability can be understood through the singularity of the generalized adiabatic susceptibility χ 2r+2 (λ), which for sudden quenches (r=0) reduces to the fidelity susceptibility. In turn this class of susceptibilities is expressed through the moments of the connected correlation function of the quench operator. We analyze the excitations created after a sudden quench of the cosine potential using a combined approach of form-factors expansion and conformal perturbation theory for the low-energy and high-energy sector, respectively. We find the general scaling laws for the probability of exciting the system, the density of excited quasiparticles, the entropy and the heat generated after the quench. In the two limits where the sine-Gordon model maps to hard-core bosons and free massive fermions we provide the exact solutions for the quench dynamics and discuss the finite temperature generalizations.
Increasing the critical thickness of InGaAs quantum wells using strain-relief technologies
Jones, Andrew Marquis
The advantages of optical communication through silica fiber have made long-distance electrical communication through copper wire obsolete. The two windows of operation for long-haul optical communication are centered around the wavelengths of 1.3 mum and 1.55 mum, which have minimal amounts of signal attenuation and dispersion. Benefits of optical communications within these windows include low system costs, high bandwidth, and high system reliability which have encouraged the development of emitters and receivers at these relatively long wavelengths. Long-wavelength semiconductor lasers are typically fabricated on InP substrates, but their performance suffers greatly with increases in operating temperature. Laser diodes on GaAs substrates are not as sensitive to operating temperature due to quantum-well active regions with relative deep potential barriers, but critical thickness limits the wavelength ceiling to 1.1 mum. Strain-relief technologies are currently being investigated to enable long-wavelength lasers with deeper potential wells leading to a corresponding increase in characteristic temperatures. Having a larger lattice constant than GaAs enables ternary InGaAs substrates to increase the 1.1-mum wavelength ceiling. Extending this ceiling to one of the optical communication windows could enable high-characteristic-temperature, long-wavelength lasers. Broad-area and buried-heterostructure lasers have demonstrated the potential of ternary substrates to increase characteristic temperatures and emission wavelengths. Wavelengths as long as 1.15 mum and characteristic temperatures as high as 145 K have been achieved. Reduced-area metalorganic chemical vapor deposition involves the deposition of strained materials on isolated islands. Due to the discontinuous nature of reduced-area epitaxy, strained materials are allowed to expand near the mesa edges, decreasing the overall strain in the structure. Laser diodes using this technology have been successfully
Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5
Energy Technology Data Exchange (ETDEWEB)
Helm, T. [MPI-CPFS (Germany); Bachmann, M. [MPI-CPFS (Germany); Moll, P.J.W. [MPI-CPFS (Germany); Balicas, L. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Chan, Mun Keat [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ramshaw, Brad [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Mcdonald, Ross David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Balakirev, Fedor Fedorovich [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Bauer, Eric Dietzgen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Ronning, Filip [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2017-03-23
Electronic nematicity appears in proximity to unconventional high-temperature superconductivity in the cuprates and iron-arsenides, yet whether they cooperate or compete is widely discussed. While many parallels are drawn between high-T_{c} and heavy fermion superconductors, electronic nematicity was not believed to be an important aspect in their superconductivity. We have found evidence for a field-induced strong electronic in-plane symmetry breaking in the tetragonal heavy fermion superconductor CeRhIn_{5}. At ambient pressure and zero field, it hosts an anti-ferromagnetic order (AFM) of nominally localized 4f electrons at TN=3.8K(1). Moderate pressure of 17kBar suppresses the AFM order and a dome of superconductivity appears around the quantum critical point. Similarly, a density-wave-like correlated phase appears centered around the field-induced AFM quantum critical point. In this phase, we have now observed electronic nematic behavior.
Directory of Open Access Journals (Sweden)
Thomas Harder
2014-10-01
Full Text Available Decisions in healthcare should be based on information obtained according to the principles of Evidence-Based Medicine (EBM. An increasing number of systematic reviews are published which summarize the results of prevalence studies. Interpretation of the results of these reviews should be accompanied by an appraisal of the methodological quality of the included data and studies. The critical appraisal tool for prevalence studies developed and tested by Munn et al. comprises 10 items and aims at targeting all kinds of prevalence studies. This comment discusses the pros and cons of different designs of quality appraisal tools and highlights their importance for systematic reviews of prevalence studies. Beyond piloting, which has been performed in the study by Munn et al., it is suggested here that the validity of the tool should be tested, including reproducibility and inter-rater reliability. It is concluded that studies as the one by Munn et al. will help to establish a critical understanding of methodological quality and will support the use of systematic reviews of non-intervention studies for health policy making.
Harder, Thomas
2014-10-01
Decisions in healthcare should be based on information obtained according to the principles of Evidence-Based Medicine (EBM). An increasing number of systematic reviews are published which summarize the results of prevalence studies. Interpretation of the results of these reviews should be accompanied by an appraisal of the methodological quality of the included data and studies. The critical appraisal tool for prevalence studies developed and tested by Munn et al. comprises 10 items and aims at targeting all kinds of prevalence studies. This comment discusses the pros and cons of different designs of quality appraisal tools and highlights their importance for systematic reviews of prevalence studies. Beyond piloting, which has been performed in the study by Munn et al., it is suggested here that the validity of the tool should be tested, including reproducibility and inter-rater reliability. It is concluded that studies as the one by Munn et al. will help to establish a critical understanding of methodological quality and will support the use of systematic reviews of non-intervention studies for health policy making.
Aroche, Raúl Riera; Rosas-Cabrera, Rodrigo Arturo; Burgos, Rodrigo Arturo Rosas; Betancourt-Riera, René; Betancourt-Riera, Ricardo
2017-01-01
The formation of Correlated Electron Pairs Oscillating around the Fermi level in Resonant Quantum States (CEPO-RQS), when a metal is cooled to its critical temperature T=Tc, is studied. The necessary conditions for the existence of CEPO-RQS are analyzed. The participation of electron-electron interaction screened by an electron dielectric constant of the form proposed by Thomas Fermi is considered and a physical meaning for the electron-phonon-electron interaction in the formation of the CEPO...
Fu, Bo; Zhu, Wei; Shi, Qinwei; Li, Qunxiang; Yang, Jinlong; Zhang, Zhenyu
2017-04-07
Exploiting the enabling power of the Lanczos method in momentum space, we determine accurately the quasiparticle and scaling properties of disordered three-dimensional Dirac semimetals surrounding the quantum critical point separating the semimetal and diffusive metal regimes. We unveil that the imaginary part of the quasiparticle self-energy obeys a common power law before, at, and after the quantum phase transition, but the power law is nonuniversal, whose exponent is dependent on the disorder strength. More intriguingly, whereas a common power law is also found for the real part of the self-energy before and after the phase transition, a distinctly different behavior is identified at the critical point, characterized by the existence of a nonanalytic logarithmic singularity. This nonanalytical correction serves as the very basis for the unusual power-law behaviors of the quasiparticles and many other physical properties surrounding the quantum critical point. Our approach also allows the ready and reliable determination of the scaling properties of the correlation length and dynamical exponents. We further show that the central findings are valid for both uncorrelated and correlated disorder distributions and should be directly comparable with future experimental observations.
Off-criticality behaviour of the Blume-Capel quantum chain as a check of Zamolodchikov's conjecture
International Nuclear Information System (INIS)
Gehlen, G. v.
1989-07-01
Using finite-size numerical calculations, we study the off-criticality behaviour of the Blume-Capel quantum chain in the neighbourhood of the c=7/10 tricritical Ising point. Moving from the tricritical point in the (1/10, 1/10)- and (3/5, 3/5)-directions into the disordered region, we find masses and thresholds in agreement with the structure proposed by Zamolodchikov from conformal field theory. Moving in the opposite directions, the spectrum is degenerate between the Z 2 -even and Z 2 -odd sectors, suggesting an underlying supersymmetry. The free-particle energy momentum relation and the scaling properties off criticality are checked. (orig.)
Atomic spin-chain realization of a model for quantum criticality
Toskovic, R.; van den Berg, R.; Spinelli, A.; Eliens, I.S.; van den Toorn, B.; Bryant, B.; Caux, J.-S.; Otte, A.F.
The ability to manipulate single atoms has opened up the door to constructing interesting and useful quantum structures from the ground up. On the one hand, nanoscale arrangements of magnetic atoms are at the heart of future quantum computing and spintronic devices; on the other hand, they can be
International Nuclear Information System (INIS)
Li Yanchao
2010-01-01
Using the transfer matrix renormalization group (TMRG) method, we study the connection between the first derivative of the thermal average of driving-term Hamiltonian (DTADH) and the trace of quantum critical behaviors at finite temperatures. Connecting with the exact diagonalization method, we give the phase diagrams and analyze the properties of each phase for both the ferromagnetic and anti-ferromagnetic frustrated J 3 anisotropy diamond chain models. The finite-temperature scaling behaviors near the critical regions are also investigated. Further, we show the critical behaviors driven by external magnetic field, analyze the formation of the 1/3 magnetic plateau and the influence of different interactions on those critical points for both the ferrimagnetic and anti-ferromagnetic distorted diamond chains.
Directory of Open Access Journals (Sweden)
Nicholas J L Brown
Full Text Available We critically re-examine Fredrickson et al.'s renewed claims concerning the differential relationship between hedonic and eudaimonic forms of well-being and gene expression, namely that people who experience a preponderance of eudaimonic well-being have gene expression profiles that are associated with more favorable health outcomes. By means of an extensive reanalysis of their data, we identify several discrepancies between what these authors claimed and what their data support; we further show that their different analysis models produce mutually contradictory results. We then show how Fredrickson et al.'s most recent article on this topic not only fails to adequately address our previously published concerns about their earlier related work, but also introduces significant further problems, including inconsistency in their hypotheses. Additionally, we demonstrate that regardless of which statistical model is used to analyze their data, Fredrickson et al.'s method can be highly sensitive to the inclusion (or exclusion of data from a single subject. We reiterate our previous conclusions, namely that there is no evidence that Fredrickson et al. have established a reliable empirical distinction between their two delineated forms of well-being, nor that eudaimonic well-being provides any overall health benefits over hedonic well-being.
International Nuclear Information System (INIS)
Yuan Jipei; Guo Weiwei; Wang Erkang
2008-01-01
The unique surface-sensitive properties make quantum dots (QDs) great potential in the development of sensors for various analytes. However, quantum dots are not only sensitive to a certain analyte, but also to the surrounding conditions. The controlled response to analyte may be the first step in the designing of functional quantum dots sensors. In this study, taking the quenching effect of benzoquinone (BQ) on CdTe QDs as model, several critical parameters of buffer solution conditions with potential effect on the sensors were investigated. The pH value and the concentration of sodium citrate in the buffer solution critically influenced the quenching effects of BQ. Dozens folds elevation of the quenching extents were observed with the increase of concentrations of H + and sodium citrate, and the quenching mechanisms were also fundamentally different with the changes of the surrounding buffer solutions. The quenching models were proposed and analyzed at different buffer conditions. Taking pH values for example, QDs quenching obeyed the sphere of effective quenching model with the sphere radii of 8.29 nm at pH 8.0, the linear Stern-Volmer equation with Stern-Volmer constant of 2.0 x 10 3 mol -1 L at pH 7.0, and the two binding site static quenching model at basic conditions. The elucidation of parameters for assay performance was important in the development of QDs-based optical sensors
From critical phenomena to gauge gields
International Nuclear Information System (INIS)
Le Bellac, M.
1988-01-01
In this book the author gives an introduction to the following questions: critical phenomena (Landau theory, renormalization group, two dimensional models); Perturbation theory and renormalization, scalar euclidian field (Feynman diagrams, Callan-Symanzik equations); Quantum theory of scalar fields (path integrals in quantum mechanics and statistical mechanics, green functions and S matrix, quantization of Klein-Gordon field); Gauge theories (quantization of Dirac field and electromagnetic field, quantum electrodynamics, non-abelian gauge theories) [fr
Directory of Open Access Journals (Sweden)
Daniel Kanstroom
2017-08-01
Full Text Available This article considers the relationship between two human rights discourses (and two specific legal regimes: refugee and asylum protection and the evolving body of international law that regulates expulsions and deportations. Legal protections for refugees and asylum seekers are, of course, venerable, well-known, and in many respects still cherished, if challenged and perhaps a bit frail. Anti-deportation discourse is much newer, multifaceted, and evolving. It is in many respects a young work in progress. It has arisen in response to a rising tide of deportations, and the worrisome development of massive, harsh deportation machinery in the United States, Germany, the United Kingdom, France, Mexico, Australia, and South Africa, among others. This article’s main goal is to consider how these two discourses do and might relate to each other. More specifically, it suggests that the development of procedural and substantive rights against removal — as well as rights during and after removal — aids our understanding of the current state and possible future of the refugee protection regime. The article’s basic thesis is this: The global refugee regime, though challenged both theoretically and in practice, must be maintained and strengthened. Its historical focus on developing criteria for admission into safe states, on protections against expulsion (i.e., non-refoulement, and on regimes of temporary protection all remain critically important. However, a focus on other protections for all noncitizens facing deportation is equally important. Deportation has become a major international system that transcends the power of any single nation-state. Its methods have migrated from one regime to another; its size and scope are substantial and expanding; its costs are enormous; and its effects frequently constitute major human rights violations against millions who do not qualify as refugees. In recent years there has been increasing reliance by states
Critical regions with central charge c=1/2,7/10,4/5 in the spin-1 quantum chain
International Nuclear Information System (INIS)
Mueller, E.
1991-01-01
The phase diagramm of the Blume-Emery-Griffiths spin-1-quantum chain is calculated by finite-size scaling with respect to all four parameters. We locate the three-dimensional critical manifold and determine a two-dimensional tricritical surface where the spectra exhibit conformal invariance corresponding to the central charges c=7/10 and 4/5. Choosing one parameter to be zero, we can treat the model analytically and from this the spectrum on a large part of the Ising-like critical region can be understood: there the spectrum consists of conformal c=1/2-levels on which a massive spectrum is superimposed. Calculating three-point functions we study which perturbations by primary fields lead from c=4/5 or c=7/10-critical points to Ising-type regions. (orig.) [de
Zaletel, Michael P; Bardarson, Jens H; Moore, Joel E
2011-07-08
Universal logarithmic terms in the entanglement entropy appear at quantum critical points (QCPs) in one dimension (1D) and have been predicted in 2D at QCPs described by 2D conformal field theories. The entanglement entropy in a strip geometry at such QCPs can be obtained via the "Shannon entropy" of a 1D spin chain with open boundary conditions. The Shannon entropy of the XXZ chain is found to have a logarithmic term that implies, for the QCP of the square-lattice quantum dimer model, a logarithm with universal coefficient ±0.25. However, the logarithm in the Shannon entropy of the transverse-field Ising model, which corresponds to entanglement in the 2D Ising conformal QCP, is found to have a singular dependence on the replica or Rényi index resulting from flows to different boundary conditions at the entanglement cut.
Ferromagnetic quantum criticality in the uranium-based ternary compounds URhSi, URhAl, and UCoAl
International Nuclear Information System (INIS)
Combier, Tristan
2014-01-01
In this thesis we explore the ferromagnetic quantum criticality in three uranium-based ternary compounds, by means of thermodynamical and transport measurements on single crystal samples, at low temperature and high pressure. URhSi and URhAl are itinerant ferromagnets, while UCoAl is a paramagnet being close to a ferromagnetic instability. All of them have Ising-type magnetic ordering. In the orthorhombic compound URhSi, we show that the Curie temperature decreases upon applying a magnetic field perpendicular to the easy magnetization axis, and a quantum phase transition is expected around 40 T. In the hexagonal system URhAl, we establish the pressure-temperature phase diagram for the first time, indicating a quantum phase transition around 5 GPa. In the isostructural compound UCoAl, we investigate the metamagnetic transition with measurements of magnetization, Hall effect, resistivity and X-ray magnetic circular dichroism. Some intriguing magnetic relaxation phenomena are observed, with step-like features. Hall effect and resistivity have been measured at dilution temperatures, under hydrostatic pressure up to 2.2 GPa and magnetic field up to 16 T. The metamagnetic transition terminates under pressure and magnetic field at a quantum critical endpoint. In this region, a strong effective mass enhancement occurs, and an intriguing difference between up and down field sweeps appears in transverse resistivity. This may be the signature of a new phase, supposedly linked to the relaxation phenomena observed in magnetic measurements, arising from frustration on the quasi-Kagome lattice of uranium atoms in this crystal structure. (author) [fr
Critical investigation of Jauch's approach to the quantum theory of measurement
International Nuclear Information System (INIS)
Herbut, Fedor
1986-01-01
To make Jauch's approach more realistic, his assumptions are modified in two ways: (1) On the quantum system plus the measuring apparatus (S + MA) after the measuring interaction has ceased, one can actually measure only operators of the form given. (2) Measurement is defined in the most general way (including, besides first-kind, also second-kind and third-kind or indirect measurements). It is shown that Jauch's basic result that the microstates (statistical operators) of S + MA before and after the collapse correspond to the same macrostate (belong to the same equivalence class of microstates) remains valid under the above modifications, and that the significance of this result goes beyond measurement theory. On the other hand, it is argued that taking the orthodox (i.e. uncompromisingly quantum) view of quantum mechanics, it is not the collapse, but the Jauch-type macrostates that are spurious in a Jauch-type theory. (author)
A criticism to the fundamental principles of physics: The problem of the quantum measurement (I)
International Nuclear Information System (INIS)
Mormontoy Cardenas, Oscar; Marquez Jacome, Mateo
2008-01-01
The wave packet model collapse debt to extremely fast fluctuations of quantum field leads to interpreting the phase speed of the harmonic waves that compose the packet, as the speed of time flux. If it consider that harmonics waves keep different phases, the waves packet scattered almost instantly and, as consequence of that, allows the possibility of the quantum system energy it is measure with exactitude absolute in given time. These results induce to think that the time would being a superforce which would determine finally the events of universe and being responsible of the intrinsic pulsations observable in the physics systems. (author)
Yoshida, J; Abe, S; Takahashi, D; Segawa, Y; Komai, Y; Tsujii, H; Matsumoto, K; Suzuki, H; Onuki, Y
2008-12-19
We report linear thermal expansion and magnetostriction measurements for CeRu2Si2 in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.
Quantum criticality and the formation of a putative electronic liquid crystal in Sr3Ru2O7
International Nuclear Information System (INIS)
Mackenzie, A.P.; Bruin, J.A.N.; Borzi, R.A.; Rost, A.W.; Grigera, S.A.
2012-01-01
We present a brief review of the physical properties of Sr 3 Ru 2 O 7 , in which the approach to a magnetic-field-tuned quantum critical point is cut off by the formation of a novel phase with transport characteristics consistent with those of a nematic electronic liquid crystal. Our goal is to summarise the physics that led to that conclusion being drawn, describing the key experiments and discussing the theoretical approaches that have been adopted. Throughout the review we also attempt to highlight observations that are not yet understood, and to discuss the future challenges that will need to be addressed by both experiment and theory.
Energy Technology Data Exchange (ETDEWEB)
Cong, P. T., E-mail: t.pham@hzdr.de [Dresden High Magnetic Field Laboratory, Helmholtz-Zentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Postulka, L.; Wolf, B.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M., E-mail: michael.lang@physik.uni-frankfurt.de [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Well, N. van [Physics Institute, Goethe University Frankfurt, D-60438 Frankfurt am Main (Germany); Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen (Switzerland)
2016-10-14
Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs{sub 2}CuCl{sub 4} were performed for the longitudinal modes c{sub 11} and c{sub 33} in magnetic fields along the a-axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at T{sub N}. Isothermal measurements at T < T{sub N} of the sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at B{sub s} ≈ 8.5 T for B || a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature T{sub N}(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material's spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/k{sub B} ≈ 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.
International Nuclear Information System (INIS)
Casati, G.; Chirikov, B.V.
1996-01-01
Various fluctuations in quantum systems with discrete spectrum are discussed, including recent unpublished results. Open questions and unexplained peculiarities of quantum fluctuations are formulated [ru
Wang, Zhe; Lorenz, T.; Gorbunov, D. I.; Cong, P. T.; Kohama, Y.; Niesen, S.; Breunig, O.; Engelmayer, J.; Herman, A.; Wu, Jianda; Kindo, K.; Wosnitza, J.; Zherlitsyn, S.; Loidl, A.
2018-05-01
We report on magnetization, sound-velocity, and magnetocaloric-effect measurements of the Ising-like spin-1 /2 antiferromagnetic chain system BaCo2V2O8 as a function of temperature down to 1.3 K and an applied transverse magnetic field up to 60 T. While across the Néel temperature of TN˜5 K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity v (B ) and a clear minimum of temperature T (B ) at B⊥c,3 D=21.4 T , indicating the suppression of the antiferromagnetic order. At higher fields, the T (B ) curve shows a broad minimum at B⊥c=40 T , accompanied by a broad minimum in the sound velocity and a saturationlike magnetization. These features signal a quantum phase transition, which is further characterized by the divergent behavior of the Grüneisen parameter ΓB∝(B -B⊥c)-1. By contrast, around the critical field, the Grüneisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.
International Nuclear Information System (INIS)
Kojima, Fumio; Nagashima, Yoshinori; Suzuki, Daisuke; Kasai, Naoko
1998-01-01
This paper is concerned with a computational method for detecting and characterizing defect shapes in conducting materials using superconducting quantum interference device (SQUID). The mathematical model is described by electrical potential problems with mixed boundary condition. The model output is then represented by Biot-Savart's law. The estimation scheme is proposed for reconstructing defect shapes in sample materials with defect. Successful numerical results are reported in order to show the feasibility of the proposed algorithms. (author)
Energy Technology Data Exchange (ETDEWEB)
Kojima, Fumio; Nagashima, Yoshinori [Osaka Inst. of Tech. (Japan); Suzuki, Daisuke; Kasai, Naoko
1998-06-01
This paper is concerned with a computational method for detecting and characterizing defect shapes in conducting materials using superconducting quantum interference device (SQUID). The mathematical model is described by electrical potential problems with mixed boundary condition. The model output is then represented by Biot-Savart`s law. The estimation scheme is proposed for reconstructing defect shapes in sample materials with defect. Successful numerical results are reported in order to show the feasibility of the proposed algorithms. (author)
Critical Investigation of Jauch's Approach to the Quantum Theory of Measurement
Herbut, Fedor
1986-08-01
To make Jauch's approach more realistic, his assumptions are modified in two ways: (1) On the quantum system plus the measuring apparatus (S+MA) after the measuring interaction has ceased, one can actually measure only operators of the form A⊗∑ k b k Q k ,where A is any Hermitian operator for S, the resolution of the identity ∑kQk=1 defines MA as a classical system (following von Neumann), and the b k are real numbers (S and MA are distant). (2) Measurement is defined in the most general way (including, besides first-kind, also second-kind and third-kind or indirect measurements). It is shown that Jauch's basic result that the microstates (statistical operators) of S+MA before and after the collapse correspond to the same macrostate (belong to the same equivalence class of microstates) remains valid under the above modifications, and that the significance of this result goes beyond measurement theory. On the other hand, it is argued that taking the orthodox (i.e. uncompromisingly quantum) view of quantum mechanics, it is not the collapse, but the Jauch-type macrostates that are spurious in a Jauch-type theory.
Xiu-Xing, Zhang; Fu-Li, Li
2012-01-01
We study the classical correlation (CC) and quantum discord (QD) between two spin subgroups of the Lipkin-Meshkov-Glick (LMG) model in both binary and trinary decompositions of spins. In the case of bipartition, we find that the classical correlations and all the quantum correlations including the QD, the entanglement of formation (EoF) and the logarithmic negativity (LN) are divergent in the same singular behavior at the critical point of the LMG model. In the case of tripartition, however, ...
Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments
Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.
2018-04-01
We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.
One-Way Deficit and Quantum Phase Transitions in XX Model
Wang, Yao-Kun; Zhang, Yu-Ran
2018-02-01
Quantum correlations including entanglement and quantum discord have drawn much attention in characterizing quantum phase transitions. Quantum deficit originates in questions regarding work extraction from quantum systems coupled to a heat bath (Oppenheim et al. Phys. Rev. Lett. 89, 180402, 2002). It links quantum thermodynamics with quantum correlations and provides a new standpoint for understanding quantum non-locality. In this paper, we evaluate the one-way deficit of two adjacent spins in the bulk for the XX model. In the thermodynamic limit, the XX model undergoes a first order transition from fully polarized to a critical phase with quasi-long-range order with decrease of quantum parameter. We find that the one-way deficit becomes nonzero after the critical point. Therefore, the one-way deficit characterizes the quantum phase transition in the XX model.
Critical properties of the D=3 bond-mixed quantum Heisenberg ferromagnet
International Nuclear Information System (INIS)
Tsallis, C.; Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro); Stinchcombe, R.B.; Buck, B.
1983-01-01
Within a Migdal-Kadanoff-like real-space renormalisation group procedure critical properties of the quenched bond-mixed spin 1/2 Heisenberg ferromagnet in simple cubic lattice are treated. It is verified that it is possible, within a very simple framework, to obtain quite reliable results for the critical temperatures. In addition to that, a general method for renormalising arbitrary clusters of Heisenberg-coupled spins 1/2 is outlined. (Author) [pt
Criticality of the D=2 quantum Heisenberg ferromagnet with quenched random anisotropic
International Nuclear Information System (INIS)
Mariz, A.M.; Tsallis, C.
1985-01-01
The square-lattice spin 1/2 anisotropic Heisenberg ferromagnet is considered, with interactions whose symmetry can independently (quenched model) and randomly be of two competing types, namely the isotropic Heisenberg type and the Ising one. Within a real space renormalization group framework, a quite precise numerical calculation of the critical frontier is performed, and its main asymptotic behaviour are established. The relevant universality classes are also characterized, through the analysis of the correlation length critical exponent. (Author) [pt
Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2.
Walmsley, P; Putzke, C; Malone, L; Guillamón, I; Vignolles, D; Proust, C; Badoux, S; Coldea, A I; Watson, M D; Kasahara, S; Mizukami, Y; Shibauchi, T; Matsuda, Y; Carrington, A
2013-06-21
We report a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As(1-x)P(x))2. Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x=0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.
International Nuclear Information System (INIS)
Lal, Siddhartha
2007-09-01
Motivated by surprises in recent experimental findings, we study transport in a model of a quantum Hall edge system with a gate-voltage controlled constriction. A finite backscattered current at finite edge-bias is explained as arising from the splitting of edge current caused by the difference in the filling fractions of the bulk (ν 1 ) and constriction (ν 2 ) quantum Hall fluid regions. We develop a hydrodynamic theory for bosonic edge modes inspired by this model. The constriction region splits the incident long-wavelength chiral edge density-wave excitations among the transmitting and reflecting edge states encircling it. The competition between two interedge tunneling processes taking place inside the constriction, related by a quasiparticle-quasihole (qp-qh) symmetry, is accounted for by computing the boundary theories of the system. This competition is found to determine the strong coupling configuration of the system. A separatrix of qp-qh symmetric gapless critical states is found to lie between the relevant RG flows to a metallic and an insulating configuration of the constriction system. This constitutes an interesting generalisation of the Kane-Fisher quantum impurity model. The features of the RG phase diagram are also confirmed by computing various correlators and chiral linear conductances of the system. In this way, our results find excellent agreement with many recent puzzling experimental results for the cases of ν 1 = 1/3, 1. We also discuss and make predictions for the case of a constriction system with ν 2 = 5/2. (author)
Directory of Open Access Journals (Sweden)
E. Svanidze
2015-03-01
Full Text Available A quantum critical point (QCP occurs upon chemical doping of the weak itinerant ferromagnet Sc_{3.1}In. Remarkable for a system with no local moments, the QCP is accompanied by non-Fermi liquid behavior, manifested in the logarithmic divergence of the specific heat both in the ferro-and the paramagnetic states, as well as linear temperature dependence of the low-temperature resistivity. With doping, critical scaling is observed close to the QCP, as the critical exponents δ, γ, and β have weak composition dependence, with δ nearly twice and β almost half of their respective mean-field values. The unusually large paramagnetic moment μ_{PM}∼1.3μ_{B}/F.U. is nearly composition independent. Evidence for strong spin fluctuations, accompanying the QCP at x_{c}=0.035±0.005, may be ascribed to the reduced dimensionality of Sc_{3.1}In, associated with the nearly one-dimensional Sc-In chains.
The quantum phase-transitions of water
Fillaux, François
2017-08-01
It is shown that hexagonal ices and steam are macroscopically quantum condensates, with continuous spacetime-translation symmetry, whereas liquid water is a quantum fluid with broken time-translation symmetry. Fusion and vaporization are quantum phase-transitions. The heat capacities, the latent heats, the phase-transition temperatures, the critical temperature, the molar volume expansion of ice relative to water, as well as neutron scattering data and dielectric measurements are explained. The phase-transition mechanisms along with the key role of quantum interferences and that of Hartley-Shannon's entropy are enlightened. The notions of chemical bond and force-field are questioned.
Kliemt, K.; Krellner, C.
2016-09-01
The tetragonal YbNi4P2 is one of the rare examples of compounds that allow the investigation of a ferromagnetic quantum critical point. We report in detail on two different methods which have been used to grow YbNi4P2 single crystals from a self-flux. The first, a modified Bridgman method, using a closed crucible system yields needle-shaped single crystals oriented along the [001]-direction. The second method, the Czochralski growth from a levitating melt, yields large single crystals which can be cut in any desired orientation. With this crucible-free method, samples without flux inclusions and a resistivity ratio at 1.8 K of RR1.8K = 17 have been grown.
Greiter, Martin
2011-01-01
This monograph introduces an exact model for a critical spin chain with arbitrary spin S, which includes the Haldane--Shastry model as the special case S=1/2. While spinons in the Haldane-Shastry model obey abelian half-fermi statistics, the spinons in the general model introduced here obey non-abelian statistics. This manifests itself through topological choices for the fractional momentum spacings. The general model is derived by mapping exact models of quantized Hall states onto spin chains. The book begins with pedagogical review of all the relevant models including the non-abelian statistics in the Pfaffian Hall state, and is understandable to every student with a graduate course in quantum mechanics.
Pressure-induced unconventional superconductivity near a quantum critical point in CaFe2As2
International Nuclear Information System (INIS)
Kawasaki, S; Tabuchi, T; Zheng Guoqing; Wang, X F; Chen, X H
2010-01-01
75 As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe 2 As 2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependencies of nuclear-spin-lattice relaxation rate (1/T 1 ) measured in the tetragonal phase show no coherence peak just below T c (P) and decrease with decreasing temperature. The superconductivity is gapless at P = 4.7 kbar but evolves to that with multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point under pressures in the range 4.7 kbar ≤ P ≤ 10.8 kbar. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.
Critical behavior in two-dimensional quantum gravity and equations of motion of the string
International Nuclear Information System (INIS)
Das, S.R.; Dhar, A.; Wadia, S.R.
1990-01-01
The authors show how consistent quantization determines the renormalization of couplings in a quantum field theory coupled to gravity in two dimensions. The special status of couplings corresponding to conformally invariant matter is discussed. In string theory, where the dynamical degree of freedom of the two-dimensional metric plays the role of time in target space, these renormalization group equations are themselves the classical equations of motion. Time independent solutions, like classical vacuua, correspond to the situation in which matter is conformally invariant. Time dependent solutions, like tunnelling configurations between vacuua, correspond to special trajectories in theory space. The authors discuss an example of such a trajectory in the space containing the c ≤ 1 minimal models. The authors also discuss the connection between this work and the recent attempts to construct non-pertubative string theories based on matrix models
Critical issues in the formation of quantum computer test structures by ion implantation
Energy Technology Data Exchange (ETDEWEB)
Schenkel, T.; Lo, C. C.; Weis, C. D.; Schuh, A.; Persaud, A.; Bokor, J.
2009-04-06
The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO2/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, 121Sb25+, in SiO2/Si is also discussed.
Critical tunnel currents and dissipation of Quantum-Hall bilayers in the excitonic condensate state
International Nuclear Information System (INIS)
Yoon, Y; Huang, X; Yarar, E; Dietsche, W; Tiemann, L; Schmult, S; Klitzing, K v
2011-01-01
Transport and tunneling is studied in the regime of the excitonic condensate at total filling factor one using the counterflow geometry. At small currents the coupling between the layers is large making the two layers virtually electrically inseparable. Above a critical current the tunneling becomes negligible. An onset of dissipation in the longitudinal transport is observed in the same current range.
Hark-Weber, Amara G., Ed.
2013-01-01
The author is pleased to introduce a new section in "TAJ," Four Questions. The structure is simple: four questions are asked to teaching artists working in various media and locations. The questions are always the same, but because each teaching artist's approach is unique, their answers will provide an insight into particular methodologies that…
Shields, William
2004-05-01
Karl Popper, though not trained as a physicist and embarrassed early in his career by a physics error pointed out by Einstein and Bohr, ultimately made substantial contributions to the interpretation of quantum mechanics. As was often the case, Popper initially formulated his position by criticizing the views of others - in this case Niels Bohr and Werner Heisenberg. Underlying Popper's criticism was his belief that, first, the "standard interpretation" of quantum mechanics, sometimes called the Copenhagen interpretation, abandoned scientific realism and second, the assertion that quantum theory was "complete" (an assertion rejected by Einstein among others) amounted to an unfalsifiable claim. Popper insisted that the most basic predictions of quantum mechanics should continue to be tested, with an eye towards falsification rather than mere adding of decimal places to confirmatory experiments. His persistent attacks on the Copenhagen interpretation were aimed not at the uncertainty principle itself and the formalism from which it was derived, but at the acceptance by physicists of an unclear epistemology and ontology that left critical questions unanswered. In 1999, physicists at the University of Maryland conducted a version of Popper's Experiment, re-igniting the debate over quantum predictions and the role of locality in physics.
Critical values of the Yang-Yang functional in the quantum sine-Gordon model
International Nuclear Information System (INIS)
Lukyanov, Sergei L.
2011-01-01
The critical values of the Yang-Yang functional corresponding to the vacuum states of the sine-Gordon QFT in the finite-volume are studied. Two major applications are discussed: (i) generalization of Fendley-Saleur-Zamolodchikov relations to arbitrary values of the sine-Gordon coupling constant, and (ii) connection problem for a certain two-parameter family of solutions of the Painleve III equation.
Field induced magnetic quantum critical behavior in the Kondo necklace model
International Nuclear Information System (INIS)
Reyes, Daniel; Continentino, Mucio
2008-01-01
The Kondo necklace model augmented by a Zeeman term, serves as a useful model for heavy fermion compounds in an applied magnetic field. The phase diagram and thermodynamic behavior for arbitrary dimensions d has been investigated previously in the zero field case [D. Reyes, M. Continentino, Phys. Rev. B 76 (2007) 075114. ]. Here we extend the treatment to finite fields using a generalized bond operator representation for the localized and conduction electrons spins. A decoupling scheme on the double time Green's functions yields the dispersion relation for the excitations of the system. Two critical magnetic fields are found namely, a critical magnetic field called henceforth h c1 and a saturation field nominated h c2 . Then three important regions can be investigated: (i) Kondo spin liquid state (KSL) at low fields h c1 ; (ii) destruction of KSL state at h≥h c1 and appearance of a antiferromagnetic state; and (iii) saturated paramagnetic region above the upper critical field h c2
Quantum entanglement and quantum teleportation
International Nuclear Information System (INIS)
Shih, Y.H.
2001-01-01
One of the most surprising consequences of quantum mechanics is the entanglement of two or more distance particles. The ''ghost'' interference and the ''ghost'' image experiments demonstrated the astonishing nonlocal behavior of an entangled photon pair. Even though we still have questions in regard to fundamental issues of the entangled quantum systems, quantum entanglement has started to play important roles in quantum information and quantum computation. Quantum teleportation is one of the hot topics. We have demonstrated a quantum teleportation experiment recently. The experimental results proved the working principle of irreversibly teleporting an unknown arbitrary quantum state from one system to another distant system by disassembling into and then later reconstructing from purely classical information and nonclassical EPR correlations. The distinct feature of this experiment is that the complete set of Bell states can be distinguished in the Bell state measurement. Teleportation of a quantum state can thus occur with certainty in principle. (orig.)
Huge residual resistivity in the quantum critical region of CeAgSb2
International Nuclear Information System (INIS)
Nakashima, Miho; Kirita, Shingo; Asai, Rihito; Kobayashi, Tatsuo C; Okubo, Tomoyuki; Yamada, Mineko; Thamizhavel, Arumugam; Inada, Yoshihiko; Settai, Rikio; Galatanu, Andre; Yamamoto, Etsuji; Ebihara, Takao; Onuki, Yoshichika
2003-01-01
We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb 2 which has a small net ferromagnetic moment of 0.4μ B /Ce. The magnetic ordering temperature T ord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure p c ≅ 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55μΩ cm at p c . A huge residual resistivity is found to appear when the magnetic order disappears. (letter to the editor)
Nelsen, Jane; DeLorenzo, Chip
2010-01-01
Have you ever found yourself lecturing a child, with the best of intentions, in an attempt to help him or her learn a lesson or process a situation in a manner that you feel will be productive? Curiosity questions, which the authors also call What and How questions, help children process an experience, event, or natural consequence so that they…
International Nuclear Information System (INIS)
Berg, Eugene
2012-01-01
Civilian and military nuclear questions fill a multitude of publications these days, especially after the Japanese tsunami and the Fukushima disaster. The author analyses some of them and highlights the links between civil and military nuclear industries, the realities of the nuclear cycle and related industrial questions before concluding on the controversial issue of weapons and their proliferation potential
Schuler, Michael; Whitsitt, Seth; Henry, Louis-Paul; Sachdev, Subir; Läuchli, Andreas M
2016-11-18
The low-energy spectra of many body systems on a torus, of finite size L, are well understood in magnetically ordered and gapped topological phases. However, the spectra at quantum critical points separating such phases are largely unexplored for (2+1)D systems. Using a combination of analytical and numerical techniques, we accurately calculate and analyze the low-energy torus spectrum at an Ising critical point which provides a universal fingerprint of the underlying quantum field theory, with the energy levels given by universal numbers times 1/L. We highlight the implications of a neighboring topological phase on the spectrum by studying the Ising* transition (i.e. the transition between a Z_{2} topological phase and a trivial paramagnet), in the example of the toric code in a longitudinal field, and advocate a phenomenological picture that provides qualitative insight into the operator content of the critical field theory.
Interactions between superconductivity and quantum criticality in CeCoIn5, URhGe and UCoGe
International Nuclear Information System (INIS)
Howald, L.
2011-01-01
The subject of this thesis is the analyze of the superconducting upper critical field (Hc2) and the interaction between superconductivity and quantum critical points (QCP), for the compounds CeCoIn 5 , URhGe and UCoGe. In CeCoIn 5 , study by mean of resistivity of the Fermi liquid domain allows us to localize precisely the QCP at ambient pressure. This analyze rule out the previously suggested pinning of Hc2(0) at the QCP. In a second part, the evolution of Hc2 under pressure is analyzed. The superconducting dome is unconventional in this compound with two characteristic pressures: at 1.6 GPa, the superconducting transition temperature is maximum but it is at 0.4 GPa that physical properties (maximum of Hc2(0), maximum of the initial slope dHc2/dT, maximum of the specific heat jump DC/C,... ) suggest a QCP. We explain this antagonism with pair-breaking effects in the proximity of the QCP. With these two experiments, we suggest a new phase diagram for CeCoIn 5 . In a third part, measurements of thermal conductivity on URhGe and UCoGe are presented. We obtained the bulk superconducting phase transition and confirmed the unusual curvature of the slope dHc2/dT observed by resistivity. The temperatures and fields dependence of thermal conductivity allow us to identify a non-electronic contribution for heat transport down to the lowest temperature (50 mK) and probably associated with magnon or longitudinal fluctuations. We also identified two different domains in the superconducting region, These domains are compatible with a two bands model for superconductivity. Thermopower measurements on UCoGe reveal a strong anisotropy to current direction and several anomaly under field applied in the b direction. We suggest a Lifshitz transition to explain our observations in these two compounds. (author) [fr
International Nuclear Information System (INIS)
Healy, J.W.
1977-01-01
The legacy question discussed refers to the definition of appropriate actions in this generation to provide a world that will allow future generations to use the earth without excessive limitations caused by our use and disposal of potentially hazardous materials
International Nuclear Information System (INIS)
Bastien, Gael
2017-01-01
This thesis is concentrated on the ferromagnetic superconductors UCoGe and URhGe and on the hidden order state in URu 2 Si 2 . In the first part the pressure temperature phase diagram of UCoGe was studied up to 10.5 GPa. Ferromagnetism vanishes at the critical pressure pc≅1 GPa. Unconventional superconductivity and non Fermi liquid behavior can be observed in a broad pressure range around pc. The superconducting upper critical field properties were explained by the suppression of the magnetic fluctuations under field. In the second part the Fermi surfaces of UCoGe and URhGe were investigated by quantum oscillations. In UCoGe four Fermi surface pockets were observed. Under magnetic field successive Lifshitz transitions of the Fermi surface have been detected. The observed Fermi surface pockets in UCoGe evolve smoothly with pressure up to 2.5 GPa and do not show any Fermi surface reconstruction at the critical pressure pc. In URhGe, three heavy Fermi surface pockets were detected by quantum oscillations. In the last part the quantum oscillation study in the hidden order state of URu 2 Si 2 shows a strong g factor anisotropy for two Fermi surface pockets, which is compared to the macroscopic g factor anisotropy extracted from the upper critical field study. (author) [fr
The quantum world philosophical debates on quantum physics
Zwirn, Hervé
2017-01-01
In this largely nontechnical book, eminent physicists and philosophers address the philosophical impact of recent advances in quantum physics. These are shown to shed new light on profound questions about realism, determinism, causality or locality. The participants contribute in the spirit of an open and honest discussion, reminiscent of the time when science and philosophy were inseparable. After the editors’ introduction, the next chapter reveals the strangeness of quantum mechanics and the subsequent discussions examine our notion of reality. The spotlight is then turned to the topic of decoherence. Bohm’s theory is critically examined in two chapters, and the relational interpretation of quantum mechanics is likewise described and discussed. The penultimate chapter presents a proposal for resolving the measurement problem, and finally the topic of loop quantum gravity is presented by one of its founding fathers, Carlo Rovelli. The original presentations and discussions on which this volume is based t...
International Nuclear Information System (INIS)
Zhang, Xiu-xing; Li, Fu-li
2013-01-01
By using the lowest order expansion in the number of spins, we study the classical correlation (CC) and quantum correlations (QCs) between two spin subgroups of the Lipkin–Meshkov–Glick (LMG) model in both binary and trinary decompositions of spins. In the case of bipartitions, we find that the CC and all the QCs are divergent in the same singular behavior at the critical point of the LMG model. In the case of tripartitions, however, the CC is still divergent but the QCs remain finite at the critical point. The present result shows that the CC is very robust but the QCs are much frangible to the environment disturbance.
DEFF Research Database (Denmark)
2012-01-01
(perhaps as an expanded Turing test) on its listeners. These questions are extracted in real-time from Twitter with the keyword search of the ‘?’ symbol to create a spatio-temporal experience. The computerized voice the audience hears is a collective one, an entanglement of humans and non-humans......In this work the network asks “If I wrote you a love letter would you write back?” Like the love letters which appeared mysteriously on the noticeboards of Manchester University’s Computer Department in the 1950s, thousands of texts circulate as computational processes perform the questions......, that circulates across networks. If I wrote you a love letter would you write back? (and thousands of other questions’ ) (封不回的情書？千言萬語無人回 was commissioned by the Microwave International New Media Festival 2012....
DEFF Research Database (Denmark)
Hoeyer, Klaus
2016-01-01
In this paper, I argue that uncertainty and nonknowledge, and not just research results, can be important vehicles of translation through which genetic research participation comes to affect the lives of research participants. Based on interviews with participants in a genetic research project, I....... Research questions, and not just results, may serve as a generative form of knowledge that can travel as fast as any answer....
Directory of Open Access Journals (Sweden)
Olivier Christin
2013-08-01
Full Text Available A few years ago, together with Franz Schultheis, of the University of Saint-Gallen and coordinator of the social sciences network ESSE, we chose to study the international circulation of the categories and concepts that are in use in European social sciences. With the publication of the Dictionnaire des concepts nomades (“Dictionary of nomadic concepts”, that includes only a small number of quite lengthy entries, what we tried to propose were not ready-made solutions, or vademecums for the comparative academic, but a series of questions, or rather the means to ask crucial questions for anyone who practises history, political science, history of economic ideas, or comparative sociology. We did so with two considerations in mind: one political, and the other academic, both of which I will evoke in turn in this paper.
Directory of Open Access Journals (Sweden)
Tatiana A. Alekseeva
2016-01-01
Full Text Available The article deals with the evolution of constructivist paradigm of international relations. The issue is of utmost importance in terms of the search for theoretical alternatives in the IR thinking. First, we are giving basic introduction of constructivism on the basis of historical and hermeneutical approaches. There is no doubt that the paradigm has faced different theoretical challenges and a lot of critics which has to be addressed. The authors reconsider some constructivist theories and notions in Alexander Wendt's works and the way Wendt tried to reinforce and reassure the constructivist paradigm. This allows us to claim that quantum turn in recent Wendt's work was almost inevitable. Second, the article attempts to answer a question whether the fundamentals of quantum physics are relevant when speaking about social and political processes. At first glance, quantum physics approach has nothing in common with the theory of politics and the theory of international relations. However, there are some grounds to believe that certain problem issues of the political science and IR theory are not deadlocks. In the second part of the article we use the unleashed and underestimated potential of analytical philosophy. To conclude, we believe that today there are more questions than answers but the quantum paradigm is expected to be the important part of the political studies and IR theory as well.
Le Gouët, Jean-Louis; Moiseev, Sergey
2012-06-01
quest for higher efficiency, better fidelity, broader bandwidth, multimode capacity and longer storage lifetime is pursued in all those approaches, as shown in this special issue. The improvement of quantum memory operation specifically requires in-depth study and control of numerous physical processes leading to atomic decoherence. The present issue reflects the development of rare earth ion doped matrices offering long lifetime superposition states, either as bulk crystals or as optical waveguides. The need for quantum sources and high efficiency detectors at the single photon level is also illustrated. Several papers address the networking of quantum memories either in long-haul cryptography or in the prospect of quantum processing. In this context, much attention has been paid recently to interfacing quantum light with superconducting qubits and with nitrogen-vacancy centers in diamond. Finally, the quantum interfacing of light with matter raises questions on entanglement. The last two papers are devoted to the generation of entanglement by dissipative processes. It is shown that long lifetime entanglement may be built in this way. We hope this special issue will help readers to become familiar with the exciting field of ensemble-based quantum memories and will stimulate them to bring deeper insights and new ideas to this area.
International Nuclear Information System (INIS)
Enders, P.
2006-01-01
This book goes a novel way from classical physics to quantum physics. After the description of Euler's and Helmholtz's representations of classical mechanics the Schroedinger equation is derivated without making any additional assumptions about the nature of quantum mechanical systems. Thereby not the differences between but the common properties of classical and quantum mechanics are accentuated and four fundamental problems of the quantization named by Schroedinger are solved. Extensively to the historical literature is related. This book applies not only to students and scientists but also to teachers and historians of natural sciences: It contains many details which enter no more into modern presentations of classical mechanics, but are important for the understanding of quantum mechanics [de
Einstein's strugges with quantum theory a reappraisal
Home, Dipankar
2007-01-01
Einstein’s Struggles with Quantum Theory: A Reappraisal by Dipankar Home and Andrew Whitaker provides a detailed account of Albert Einstein’s thinking in regard to quantum physics. Until recently, most of Einstein’s views on quantum physics were dismissed and even ridiculed; some critics even suggested that Einstein was not able to grasp the complexities of the formalism of quantum theory and subtleties of the standard interpretation of this theory known as the Copenhagen interpretation put forward by Niels Bohr and his colleagues. But was that true? Modern scholarship argues otherwise, insist Drs. Home and Whitaker, who painstakingly explain the questions Einstein raised as well as offer a detailed discussion of Einstein’s position and major contributions to quantum theory, connecting them with contemporary studies on fundamental aspects of this theory. This unique book presents a mathematical as well as a non-mathematical route through the theories, controversies, and investigations, making the disc...
Quantum memory for images: A quantum hologram
International Nuclear Information System (INIS)
Vasilyev, Denis V.; Sokolov, Ivan V.; Polzik, Eugene S.
2008-01-01
Matter-light quantum interface and quantum memory for light are important ingredients of quantum information protocols, such as quantum networks, distributed quantum computation, etc. [P. Zoller et al., Eur. Phys. J. D 36, 203 (2005)]. In this paper we present a spatially multimode scheme for quantum memory for light, which we call a quantum hologram. Our approach uses a multiatom ensemble which has been shown to be efficient for a single spatial mode quantum memory. Due to the multiatom nature of the ensemble and to the optical parallelism it is capable of storing many spatial modes, a feature critical for the present proposal. A quantum hologram with the fidelity exceeding that of classical hologram will be able to store quantum features of an image, such as multimode superposition and entangled quantum states, something that a standard hologram is unable to achieve
Quantum symmetry in quantum theory
International Nuclear Information System (INIS)
Schomerus, V.
1993-02-01
Symmetry concepts have always been of great importance for physical problems like explicit calculations, classification or model building. More recently, new 'quantum symmetries' ((quasi) quantum groups) attracted much interest in quantum theory. It is shown that all these quantum symmetries permit a conventional formulation as symmetry in quantum mechanics. Symmetry transformations can act on the Hilbert space H of physical states such that the ground state is invariant and field operators transform covariantly. Models show that one must allow for 'truncation' in the tensor product of representations of a quantum symmetry. This means that the dimension of the tensor product of two representations of dimension σ 1 and σ 2 may be strictly smaller than σ 1 σ 2 . Consistency of the transformation law of field operators local braid relations leads us to expect, that (weak) quasi quantum groups are the most general symmetries in local quantum theory. The elements of the R-matrix which appears in these local braid relations turn out to be operators on H in general. It will be explained in detail how examples of field algebras with weak quasi quantum group symmetry can be obtained. Given a set of observable field with a finite number of superselection sectors, a quantum symmetry together with a complete set of covariant field operators which obey local braid relations are constructed. A covariant transformation law for adjoint fields is not automatic but will follow when the existence of an appropriate antipode is assumed. At the example of the chiral critical Ising model, non-uniqueness of the quantum symmetry will be demonstrated. Generalized quantum symmetries yield examples of gauge symmetries in non-commutative geometry. Quasi-quantum planes are introduced as the simplest examples of quasi-associative differential geometry. (Weak) quasi quantum groups can act on them by generalized derivations much as quantum groups do in non-commutative (differential-) geometry
Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.
2016-04-01
In this work we study the quantum phase transition, the phase diagram and the quantum criticality induced by the easy-plane single-ion anisotropy in a d-dimensional quantum spin-1 XY model in absence of an external longitudinal magnetic field. We employ the two-time Green function method by avoiding the Anderson-Callen decoupling of spin operators at the same sites which is of doubtful accuracy. Following the original Devlin procedure we treat exactly the higher order single-site anisotropy Green functions and use Tyablikov-like decouplings for the exchange higher order ones. The related self-consistent equations appear suitable for an analysis of the thermodynamic properties at and around second order phase transition points. Remarkably, the equivalence between the microscopic spin model and the continuous O(2) -vector model with transverse-Ising model (TIM)-like dynamics, characterized by a dynamic critical exponent z=1, emerges at low temperatures close to the quantum critical point with the single-ion anisotropy parameter D as the non-thermal control parameter. The zero-temperature critic anisotropy parameter Dc is obtained for dimensionalities d > 1 as a function of the microscopic exchange coupling parameter and the related numerical data for different lattices are found to be in reasonable agreement with those obtained by means of alternative analytical and numerical methods. For d > 2, and in particular for d=3, we determine the finite-temperature critical line ending in the quantum critical point and the related TIM-like shift exponent, consistently with recent renormalization group predictions. The main crossover lines between different asymptotic regimes around the quantum critical point are also estimated providing a global phase diagram and a quantum criticality very similar to the conventional ones.
Quantum space and quantum completeness
Jurić, Tajron
2018-05-01
Motivated by the question whether quantum gravity can "smear out" the classical singularity we analyze a certain quantum space and its quantum-mechanical completeness. Classical singularity is understood as a geodesic incompleteness, while quantum completeness requires a unique unitary time evolution for test fields propagating on an underlying background. Here the crucial point is that quantum completeness renders the Hamiltonian (or spatial part of the wave operator) to be essentially self-adjoint in order to generate a unique time evolution. We examine a model of quantum space which consists of a noncommutative BTZ black hole probed by a test scalar field. We show that the quantum gravity (noncommutative) effect is to enlarge the domain of BTZ parameters for which the relevant wave operator is essentially self-adjoint. This means that the corresponding quantum space is quantum complete for a larger range of BTZ parameters rendering the conclusion that in the quantum space one observes the effect of "smearing out" the singularity.
International Nuclear Information System (INIS)
Cook, R.J.
1988-01-01
This paper answers the title question by giving an operational definition of quantum jumps based on measurement theory. This definition forms the basis of a theory of quantum jumps which leads to a number of testable predictions. Experiments are proposed to test the theory. The suggested experiments also test the quantum Zeno paradox, i.e., they test the proposition that frequent observation of a quantum system inhibits quantum jumps in that system. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Vellinga, P. [Milieuwetenschappen, Vrije Universiteit, Amsterdam (Netherlands); Van Dorland, R. [KNMI, De Bilt (Netherlands); Kabat, P. [Aardsystemen en Klimaatstudies, Wageningen Universiteit, Wageningen (Netherlands)
2008-07-01
In some of the previous issues of this magazine (Spil 2007, issue 4 and 5-6, and Spil 2008, issue 1) the authors Labohm, Roersch and Thoenes started a frontal attack of the greenhouse theory and the researchers who report on the state of science in the framework of the IPCC. The author of this article addresses two main questions arising from the above-mentioned authors: (1) Does the use of fossil fuels affect global climate?; and (2) Is the warming of the last 30 years related to the increasing concentrations of greenhouse gases in the atmosphere? [mk]. [Dutch] In enkele vorige afleveringen van dit tijdschrift (Spil 2007, nummers 4 en 5-6, en Spil 2008, nummer 1) hebben de auteurs Labohm, Roersch en Thoenes een frontale aanval ingezet op de broeikastheorie en de onderzoekers die in IPCC-verband verslag doen van de stand van de wetenschap. De auteur van dit artikel gaat in op twee door voornoemde auteurs gestelde hoofdvragen: (1) Heeft het gebruik van fossiele brandstoffen invloed op het wereldklimaat?; en (2) Houdt de opwarming van de laatste dertig jaar verband met de gestegen concentraties van broeikasgassen in de atmosfeer?.
Effect of anisotropic strain on the quantum critical phase of Sr{sub 3}Ru{sub 2}O{sub 7}
Energy Technology Data Exchange (ETDEWEB)
Brodsky, Daniel; Barber, Mark; Mackenzie, Andrew [MPI-Chemische Physik fester Stoffe, Dresden (Germany); Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St Andrews, St Andrews (United Kingdom); Hicks, Clifford [MPI-Chemische Physik fester Stoffe, Dresden (Germany); Perry, Robin [SUPA, School of Physics, University of Edinburgh, Edinburgh (United Kingdom)
2015-07-01
We have developed a novel piezoelectric-based device for applying both compressive and tensile strains to single crystals. One particularly appealing target for such studies is Sr{sub 3}Ru{sub 2}O{sub 7}. Sr{sub 3}Ru{sub 2}O{sub 7} has a novel quantum critical phase around a metamagnetic transition at 8 T, which shows very strong transport anisotropy in the presence of weak symmetry-breaking fields. We discuss the response of this phase to applied anisotropic lattice strain.
Directory of Open Access Journals (Sweden)
Böyükata M.
2014-03-01
Full Text Available Quantum phase transitions in odd-nuclei are investigated within the framework of the interacting boson-fermion model with a description based on the concept of intrinsic states. We consider the case of a single j=9/2 odd-particle coupled to an even-even boson core that performs a transition from spherical to deformed prolate and to deformed gamma-unstable shapes varying a control parameter in the boson Hamiltonian. The effect of the coupling of the odd particle to this core is discussed along the shape transition and, in particular, at the critical point.
Effects of quantum coherence on work statistics
Xu, Bao-Ming; Zou, Jian; Guo, Li-Sha; Kong, Xiang-Mu
2018-05-01
In the conventional two-point measurement scheme of quantum thermodynamics, quantum coherence is destroyed by the first measurement. But as we know the coherence really plays an important role in the quantum thermodynamics process, and how to describe the work statistics for a quantum coherent process is still an open question. In this paper, we use the full counting statistics method to investigate the effects of quantum coherence on work statistics. First, we give a general discussion and show that for a quantum coherent process, work statistics is very different from that of the two-point measurement scheme, specifically the average work is increased or decreased and the work fluctuation can be decreased by quantum coherence, which strongly depends on the relative phase, the energy level structure, and the external protocol. Then, we concretely consider a quenched one-dimensional transverse Ising model and show that quantum coherence has a more significant influence on work statistics in the ferromagnetism regime compared with that in the paramagnetism regime, so that due to the presence of quantum coherence the work statistics can exhibit the critical phenomenon even at high temperature.
Dynamical quantum phase transitions: a review
Heyl, Markus
2018-05-01
Quantum theory provides an extensive framework for the description of the equilibrium properties of quantum matter. Yet experiments in quantum simulators have now opened up a route towards the generation of quantum states beyond this equilibrium paradigm. While these states promise to show properties not constrained by equilibrium principles, such as the equal a priori probability of the microcanonical ensemble, identifying the general properties of nonequilibrium quantum dynamics remains a major challenge, especially in view of the lack of conventional concepts such as free energies. The theory of dynamical quantum phase transitions attempts to identify such general principles by lifting the concept of phase transitions to coherent quantum real-time evolution. This review provides a pedagogical introduction to this field. Starting from the general setting of nonequilibrium dynamics in closed quantum many-body systems, we give the definition of dynamical quantum phase transitions as phase transitions in time with physical quantities becoming nonanalytic at critical times. We summarize the achieved theoretical advances as well as the first experimental observations, and furthermore provide an outlook to major open questions as well as future directions of research.
Dynamical quantum phase transitions: a review.
Heyl, Markus
2018-05-01
Quantum theory provides an extensive framework for the description of the equilibrium properties of quantum matter. Yet experiments in quantum simulators have now opened up a route towards the generation of quantum states beyond this equilibrium paradigm. While these states promise to show properties not constrained by equilibrium principles, such as the equal a priori probability of the microcanonical ensemble, identifying the general properties of nonequilibrium quantum dynamics remains a major challenge, especially in view of the lack of conventional concepts such as free energies. The theory of dynamical quantum phase transitions attempts to identify such general principles by lifting the concept of phase transitions to coherent quantum real-time evolution. This review provides a pedagogical introduction to this field. Starting from the general setting of nonequilibrium dynamics in closed quantum many-body systems, we give the definition of dynamical quantum phase transitions as phase transitions in time with physical quantities becoming nonanalytic at critical times. We summarize the achieved theoretical advances as well as the first experimental observations, and furthermore provide an outlook to major open questions as well as future directions of research.
Quantum language and the migration of scientific concepts
Burwell, Jennifer
2018-01-01
How highly abstract quantum concepts were represented in language, and how these concepts were later taken up by philosophers, literary critics, and new-age gurus. The principles of quantum physics -- and the strange phenomena they describe -- are represented most precisely in highly abstract algebraic equations. Why, then, did these mathematically driven concepts compel founders of the field, particularly Erwin Schrödinger, Niels Bohr, and Werner Heisenberg, to spend so much time reflecting on ontological, epistemological, and linguistic concerns? What is it about quantum concepts that appeals to latter-day Eastern mystics, poststructuralist critics, and get-rich-quick schemers? How did their interpretations and misinterpretations of quantum phenomena reveal their own priorities? In this book, Jennifer Burwell examines these questions and considers what quantum phenomena -- in the context of the founders' debates over how to describe them -- reveal about the relationship between everyday experience, percep...
Reliability of analog quantum simulation
Energy Technology Data Exchange (ETDEWEB)
Sarovar, Mohan [Sandia National Laboratories, Digital and Quantum Information Systems, Livermore, CA (United States); Zhang, Jun; Zeng, Lishan [Shanghai Jiao Tong University, Joint Institute of UMich-SJTU, Key Laboratory of System Control and Information Processing (MOE), Shanghai (China)
2017-12-15
Analog quantum simulators (AQS) will likely be the first nontrivial application of quantum technology for predictive simulation. However, there remain questions regarding the degree of confidence that can be placed in the results of AQS since they do not naturally incorporate error correction. Specifically, how do we know whether an analog simulation of a quantum model will produce predictions that agree with the ideal model in the presence of inevitable imperfections? At the same time there is a widely held expectation that certain quantum simulation questions will be robust to errors and perturbations in the underlying hardware. Resolving these two points of view is a critical step in making the most of this promising technology. In this work we formalize the notion of AQS reliability by determining sensitivity of AQS outputs to underlying parameters, and formulate conditions for robust simulation. Our approach naturally reveals the importance of model symmetries in dictating the robust properties. To demonstrate the approach, we characterize the robust features of a variety of quantum many-body models. (orig.)
Fluctuation dynamics near the quantum critical point in the S=1/2 Ising chain CoNb{sub 2}O{sub 6}
Energy Technology Data Exchange (ETDEWEB)
Harms, Steffen; Engelmayer, Johannes; Lorenz, Thomas; Hemberger, Joachim [II. Physikalisches Institut, Koeln Univ. (Germany)
2016-07-01
CoNb{sub 2}O{sub 6} is a model system for quantum phase transitions in magnetic field. Its structure consists of layers of CoO{sub 6} octahedrons separated by non-magnetic NbO{sub 6} layers. The edge-sharing oxygen octahedrons link the Co{sup 2+} spins via Co-O-Co superexchange and form 1D ferromagnetic zigzag chains along the orthorhombic c axis. Crystal field effects lead to an easy-axis anisotropy of the Co{sup 2+} moments in the ac plane and to an effective spin-1/2 chain system. The 1D spin system can be described by the Ising model. At T=0 K a transverse magnetic field can induce a quantum phase transition from a long range ferromagnetic state into a quantum paramagnetic state. Employing measurements of the complex AC-susceptibility in the frequency range 10 MHz < ν < 5 GHz for temperatures down to 50 mK we investigate the slowing down of the magnetic fluctuation dynamics in the vicinity of the critical field at μ{sub 0}H=5.25 T.
Baracca, Angelo; Bergia, Silvio; Del Santo, Flavio
2017-02-01
We present a reconstruction of the studies on the Foundations of Quantum Mechanics carried out in Italy at the turn of the 1960s. Actually, they preceded the revival of the interest of the American physicists towards the foundations of quantum mechanics around mid-1970s, recently reconstructed by David Kaiser in a book of 2011. An element common to both cases is the role played by the young generation, even though the respective motivations were quite different. In the US they reacted to research cuts after the war in Vietnam, and were inspired by the New Age mood. In Italy the dissatisfaction of the young generations was rooted in the student protests of 1968 and the subsequent labour and social fights, which challenged the role of scientists. The young generations of physicists searched for new scientific approaches and challenged their own scientific knowledge and role. The criticism to the foundations of quantum mechanics and the perspectives of submitting them to experimental tests were perceived as an innovative research field and this attitude was directly linked to the search for an innovative and radical approach in the history of science. All these initiatives gave rise to booming activity throughout the 1970s, contributing to influence the scientific attitude and the teaching approach.
Quaternionic quantum field theory
International Nuclear Information System (INIS)
Adler, S.L.
1986-01-01
In this paper the author describes a new kind of quantum mechanics or quantum field theory based on quaternions. Quaternionic quantum mechanics has a Schrodinger equation, a Dirac transformation theory, and a functional integral. Quaternionic quantum mechanics does not seem to have (except in the complex quantum mechanics specialization): A correspondence principle, and beyond this a commuting tensor product, asymptotic states, an S-matrix, a canonical formalism, coherent states or a Euclidean continuation. A new kind of quantum mechanics exists. There are many interesting formal questions to study, which should enable one to decide whether quaternionic quantum field theory is relevant for particle physics
Quantum Information Processing
Leuchs, Gerd
2005-01-01
Quantum processing and communication is emerging as a challenging technique at the beginning of the new millennium. This is an up-to-date insight into the current research of quantum superposition, entanglement, and the quantum measurement process - the key ingredients of quantum information processing. The authors further address quantum protocols and algorithms. Complementary to similar programmes in other countries and at the European level, the German Research Foundation (DFG) started a focused research program on quantum information in 1999. The contributions - written by leading experts - bring together the latest results in quantum information as well as addressing all the relevant questions
International Nuclear Information System (INIS)
Hawking, S.W.
1984-01-01
The subject of these lectures is quantum effects in cosmology. The author deals first with situations in which the gravitational field can be treated as a classical, unquantized background on which the quantum matter fields propagate. This is the case with inflation at the GUT era. Nevertheless the curvature of spacetime can have important effects on the behaviour of the quantum fields and on the development of long-range correlations. He then turns to the question of the quantization of the gravitational field itself. The plan of these lectures is as follows: Euclidean approach to quantum field theory in flat space; the extension of techniques to quantum fields on a curved background with the four-sphere, the Euclidean version of De Sitter space as a particular example; the GUT era; quantization of the gravitational field by Euclidean path integrals; mini superspace model. (Auth.)
Roy, Bitan; Foster, Matthew S.
2018-01-01
We compute the effects of generic short-range interactions on gapless electrons residing at the quantum critical point separating a two-dimensional Dirac semimetal and a symmetry-preserving band insulator. The electronic dispersion at this critical point is anisotropic (Ek=±√{v2kx2+b2ky2 n } with n =2 ), which results in unconventional scaling of thermodynamic and transport quantities. Because of the vanishing density of states [ϱ (E )˜|E |1 /n ], this anisotropic semimetal (ASM) is stable against weak short-range interactions. However, for stronger interactions, the direct Dirac-semimetal to band-insulator transition can either (i) become a fluctuation-driven first-order transition (although unlikely in a particular microscopic model considered here, the anisotropic honeycomb lattice extended Hubbard model) or (ii) get avoided by an intervening broken-symmetry phase. We perform a controlled renormalization group analysis with the small parameter ɛ =1 /n , augmented with a 1 /n expansion (parametrically suppressing quantum fluctuations in the higher dimension) by perturbing away from the one-dimensional limit, realized by setting ɛ =0 and n →∞ . We identify charge density wave (CDW), antiferromagnet (AFM), and singlet s -wave superconductivity as the three dominant candidates for broken symmetry. The onset of any such order at strong coupling (˜ɛ ) takes place through a continuous quantum phase transition across an interacting multicritical point, where the ordered phase, band insulator, Dirac, and anisotropic semimetals meet. We also present the phase diagram of an extended Hubbard model for the ASM, obtained via the controlled deformation of its counterpart in one dimension. The latter displays spin-charge separation and instabilities to CDW, spin density wave, and Luther-Emery liquid phases at arbitrarily weak coupling. The spin density wave and Luther-Emery liquid phases deform into pseudospin SU(2)-symmetric quantum critical points separating the
Directory of Open Access Journals (Sweden)
Bitan Roy
2018-03-01
Full Text Available We compute the effects of generic short-range interactions on gapless electrons residing at the quantum critical point separating a two-dimensional Dirac semimetal and a symmetry-preserving band insulator. The electronic dispersion at this critical point is anisotropic (E_{k}=±sqrt[v^{2}k_{x}^{2}+b^{2}k_{y}^{2n}] with n=2, which results in unconventional scaling of thermodynamic and transport quantities. Because of the vanishing density of states [ϱ(E∼|E|^{1/n}], this anisotropic semimetal (ASM is stable against weak short-range interactions. However, for stronger interactions, the direct Dirac-semimetal to band-insulator transition can either (i become a fluctuation-driven first-order transition (although unlikely in a particular microscopic model considered here, the anisotropic honeycomb lattice extended Hubbard model or (ii get avoided by an intervening broken-symmetry phase. We perform a controlled renormalization group analysis with the small parameter ε=1/n, augmented with a 1/n expansion (parametrically suppressing quantum fluctuations in the higher dimension by perturbing away from the one-dimensional limit, realized by setting ε=0 and n→∞. We identify charge density wave (CDW, antiferromagnet (AFM, and singlet s-wave superconductivity as the three dominant candidates for broken symmetry. The onset of any such order at strong coupling (∼ε takes place through a continuous quantum phase transition across an interacting multicritical point, where the ordered phase, band insulator, Dirac, and anisotropic semimetals meet. We also present the phase diagram of an extended Hubbard model for the ASM, obtained via the controlled deformation of its counterpart in one dimension. The latter displays spin-charge separation and instabilities to CDW, spin density wave, and Luther-Emery liquid phases at arbitrarily weak coupling. The spin density wave and Luther-Emery liquid phases deform into pseudospin SU(2-symmetric quantum critical
DEFF Research Database (Denmark)
Larsen, J.; Schäffer, T. K.; Hansen, U. B.
2017-01-01
We present experimental evidence for a quantum phase transition in the easy-axis S = 3/2 anisotropic quasione-dimensional ferromagnet CoCl2 · 2D2O in a transverse field. Elastic neutron scattering shows that the magnetic order parameter vanishes at a transverse critical field μ0Hc = 16.05(4) T......, while inelastic neutron scattering shows that the gap in the magnetic excitation spectrum vanishes at the same field value, and reopens for H>Hc. The field dependence of the order parameter and the gap are well described by critical exponents β = 0.45 ± 0.09 and zν close to 1/2, implying...... that the quantum phase transition in CoCl2 · 2D2O differs significantly from the textbook version of a S = 1/2 Ising chain in a transverse field. We attribute the difference to weak but finite three-dimensionality of the magnetic interactions....
Spin dynamics in the high-field phase of quantum-critical S =1/2 TlCuCl sub 3
Rueegg, C; Furrer, A; Krämer, K; Güdel, H U; Vorderwisch, P; Mutka, H
2002-01-01
An external magnetic field suppresses the spin-energy gap in singlet ground state S=1/2 TlCuCl sub 3. The system becomes quantum-critical at H sub c approx 5.7 T, where the energy of the lowest Zeeman-split triplet excitation crosses the nonmagnetic ground state. Antiferromagnetic ordering is reported above H sub c , which underlines the three-dimensional nature of the observed quantum phase transition. The intrinsic parameters of S=1/2 TlCuCl sub 3 allow us to access the critical region microscopically by neutron scattering. A substantial study of the spin dynamics in the high-field phase of TlCuCl sub 3 at T=1.5 K up to H=12 T was performed for the first time. The results possibly indicate two dynamical regimes, which can be understood within characteristically renormalized triplet modes and a low-lying dynamics of potentially collective origin. (orig.)
A first course in topos quantum theory
International Nuclear Information System (INIS)
Flori, Cecilia
2013-01-01
Written by a leading researcher in the field. Concise course-tested textbook. Includes worked-out problems In the last five decades various attempts to formulate theories of quantum gravity have been made, but none has fully succeeded in becoming the quantum theory of gravity. One possible explanation for this failure might be the unresolved fundamental issues in quantum theory as it stands now. Indeed, most approaches to quantum gravity adopt standard quantum theory as their starting point, with the hope that the theory's unresolved issues will get solved along the way. However, these fundamental issues may need to be solved before attempting to define a quantum theory of gravity. The present text adopts this point of view, addressing the following basic questions: What are the main conceptual issues in quantum theory? How can these issues be solved within a new theoretical framework of quantum theory? A possible way to overcome critical issues in present-day quantum physics - such as a priori assumptions about space and time that are not compatible with a theory of quantum gravity, and the impossibility of talking about systems without reference to an external observer - is through a reformulation of quantum theory in terms of a different mathematical framework called topos theory. This course-tested primer sets out to explain to graduate students and newcomers to the field alike, the reasons for choosing topos theory to resolve the above-mentioned issues and how it brings quantum physics back to looking more like a ''neo-realist'' classical physics theory again.
VQABQ: Visual Question Answering by Basic Questions
Huang, Jia-Hong
2017-03-19
Taking an image and question as the input of our method, it can output the text-based answer of the query question about the given image, so called Visual Question Answering (VQA). There are two main modules in our algorithm. Given a natural language question about an image, the first module takes the question as input and then outputs the basic questions of the main given question. The second module takes the main question, image and these basic questions as input and then outputs the text-based answer of the main question. We formulate the basic questions generation problem as a LASSO optimization problem, and also propose a criterion about how to exploit these basic questions to help answer main question. Our method is evaluated on the challenging VQA dataset and yields state-of-the-art accuracy, 60.34% in open-ended task.
VQABQ: Visual Question Answering by Basic Questions
Huang, Jia-Hong; Alfadly, Modar; Ghanem, Bernard
2017-01-01
Taking an image and question as the input of our method, it can output the text-based answer of the query question about the given image, so called Visual Question Answering (VQA). There are two main modules in our algorithm. Given a natural language question about an image, the first module takes the question as input and then outputs the basic questions of the main given question. The second module takes the main question, image and these basic questions as input and then outputs the text-based answer of the main question. We formulate the basic questions generation problem as a LASSO optimization problem, and also propose a criterion about how to exploit these basic questions to help answer main question. Our method is evaluated on the challenging VQA dataset and yields state-of-the-art accuracy, 60.34% in open-ended task.
Some open questions in 'wave chaos'
International Nuclear Information System (INIS)
Nonnenmacher, Stéphane
2008-01-01
The subject area referred to as 'wave chaos', 'quantum chaos' or 'quantum chaology' has been investigated mostly by the theoretical physics community in the last 30 years. The questions it raises have more recently also attracted the attention of mathematicians and mathematical physicists, due to connections with number theory, graph theory, Riemannian, hyperbolic or complex geometry, classical dynamical systems, probability, etc. After giving a rough account on 'what is quantum chaos?', I intend to list some pending questions, some of them having been raised a long time ago, some others more recent. The choice of problems (and of references) is of course partial and personal. (open problem)
The question of criticism in Marxist theory
Directory of Open Access Journals (Sweden)
Fernando Forero Medina
2012-02-01
Full Text Available This article is written in the belief that a widespread view exists among social scientists that contemporary social theory needs a radical revision of the works of those writers who established the principal frames of reference of modern theory of society. In this respect, three names stand out above all others: Karl Marx, Émile Durkheim and Max Weber. The objective of this work is to examine and analyze Marx’s concept of critique regarding the concepts of praxis, critique of the political economy, critique of ideology, and critique as political action in relation to the theoretical perspective of western Marxism and, especially, in relation to Habermas’s idea of Marx’s theory.
Machine learning & artificial intelligence in the quantum domain: a review of recent progress.
Dunjko, Vedran; Briegel, Hans J
2018-03-05
Quantum information technologies, on the one hand, and intelligent learning systems, on the other, are both emergent technologies that are likely to have a transformative impact on our society in the future. The respective underlying fields of basic research-quantum information versus machine learning (ML) and artificial intelligence (AI)-have their own specific questions and challenges, which have hitherto been investigated largely independently. However, in a growing body of recent work, researchers have been probing the question of the extent to which these fields can indeed learn and benefit from each other. Quantum ML explores the interaction between quantum computing and ML, investigating how results and techniques from one field can be used to solve the problems of the other. Recently we have witnessed significant breakthroughs in both directions of influence. For instance, quantum computing is finding a vital application in providing speed-ups for ML problems, critical in our 'big data' world. Conversely, ML already permeates many cutting-edge technologies and may become instrumental in advanced quantum technologies. Aside from quantum speed-up in data analysis, or classical ML optimization used in quantum experiments, quantum enhancements have also been (theoretically) demonstrated for interactive learning tasks, highlighting the potential of quantum-enhanced learning agents. Finally, works exploring the use of AI for the very design of quantum experiments and for performing parts of genuine research autonomously, have reported their first successes. Beyond the topics of mutual enhancement-exploring what ML/AI can do for quantum physics and vice versa-researchers have also broached the fundamental issue of quantum generalizations of learning and AI concepts. This deals with questions of the very meaning of learning and intelligence in a world that is fully described by quantum mechanics. In this review, we describe the main ideas, recent developments and
Recent progress in the theory of random surfaces and simplicial quantum gravity
International Nuclear Information System (INIS)
Ambjoern, J.
1995-01-01
Some of the recent developments in the theory of random surfaces and simplicial quantum gravity is reviewed. For 2d quantum gravity this includes the failure of Regge calculus, our improved understanding of the c>1 regime, some surprises for q-state Potts models with q>4, attempts to use renormalization group techniques, new critical behavior of random surface models with extrinsic curvature and improved algorithms. For simplicial quantum gravity in higher dimensions it includes a discussion of the exponential entropy bound needed for the models to be well defined, the question of ''computational ergodicity'' and the question of how to extract continuum behavior from the lattice simulations. ((orig.))
Quantum Statistics and Entanglement Problems
Trainor, L. E. H.; Lumsden, Charles J.
2002-01-01
Interpretations of quantum measurement theory have been plagued by two questions, one concerning the role of observer consciousness and the other the entanglement phenomenon arising from the superposition of quantum states. We emphasize here the remarkable role of quantum statistics in describing the entanglement problem correctly and discuss the relationship to issues arising from current discussions of intelligent observers in entangled, decohering quantum worlds.
Wetting layer states in low density InAs/InGaAs quantum dots from sub-critical InAs coverages
International Nuclear Information System (INIS)
Seravalli, L; Trevisi, G; Frigeri, P; Rossi, F; Buffagni, E; Ferrari, C
2013-01-01
In this work we study the properties of wetting layers in InAs/InGaAs/GaAs quantum dot (QD) structures suitable for single photon emission; the mandatory low density of QDs is obtained by an molecular beam epitaxy (MBE) approach based on the deposition of sub-critical InAs coverages followed by post-growth annealing. Such a growth regime is fundamentally different from the Stranski–Krastanow (SK) one commonly used for the deposition of QDs. By fitting x-ray diffraction (XRD) spectra, ten-steps composition profiles were derived and used as inputs of model calculations of the two-dimensional quantum energy system: model results were validated by comparison with photoluminescence spectra. A strong reduction of In molar fraction in wetting layers in comparison with SK structures was found, causing a larger wavefunction delocalization for carriers that populate the wetting layer energy levels. Moreover, by considering the limits for strain relaxation when In x Ga 1−x As capping layers are used, we grew structures with the highest possible values of x to study the modifications of the energy system. When x = 0.20 the electron–heavy hole overlap is almost halved and the carriers' probability of being in the first nanometre of the wetting layer is reduced by 60%. These results will be useful for advanced design of QD nanostructures for single photon sources. (paper)
Hechster, Elad; Sarusi, Gabby
2017-07-01
The complex dielectric function ɛ(E )=ɛR(E )+i ɛI(E ) of a semiconductor is a key parameter that dictates the material's optical and electrical properties. Surprisingly, the ɛ(E ) of Lead Sulfide (PbS) quantum dots (QDs) has not been widely studied. In the present work, we develop a new model that aims to simulate the ɛ(E ) of QDs. Our model is based on the fact that the quantum confinement in the nano regime affects all the electronic transitions throughout the entire Brillouin zone. Hence, as a first approximation, we attribute an equal contribution of energy, equivalent to the bandgap broadening, to each critical point (CP) in the E-k diagram. This is mathematically realized by adding these energy contributions to the central energy parameters of the Lorentz oscillator model. In order to validate our model, we used the CP parameters of bulk PbS to simulate the ɛ(E ) of PbS QDs. Next, we use Maxwell Relations to calculate the refractive index and the extinction coefficient of PbS QDs from ɛ(" separators="|E ). Our results were compared with those published in the previous literature and showed good agreement. Our findings open a new avenue that may enable the calculation of the ɛ(" separators="|E ) for nanoparticle systems.
Quantum discord and quantum phase transition in spin chains
Dillenschneider, Raoul
2008-01-01
Quantum phase transitions of the transverse Ising and antiferromagnetic XXZ spin S=1/2 chains are studied using quantum discord. Quantum discord allows the measure of quantum correlations present in many-body quantum systems. It is shown that the amount of quantum correlations increases close to the critical points. The observations are in agreement with the information provided by the concurrence which measures the entanglement of the many-body system.
Effect of uniaxial strain on the quantum critical phase of Sr{sub 3}Ru{sub 2}O{sub 7}
Energy Technology Data Exchange (ETDEWEB)
Barber, Mark E.; Brodsky, Daniel O.; Mackenzie, Andrew P. [Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS (United Kingdom); Max Planck Institute for Chemical Physics of Solids, Noethnitzer Strasse 40, Dresden 01187 (Germany); Hicks, Clifford W. [Max Planck Institute for Chemical Physics of Solids, Noethnitzer Strasse 40, Dresden 01187 (Germany); Perry, Robin [School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD (United Kingdom)
2016-07-01
Sr{sub 3}Ru{sub 2}O{sub 7} has a metamagnetic quantum critical endpoint, which in highly pure samples is masked by a novel phase. This phase is isotropic in the absence of symmetry-breaking fields, but weak in-plane magnetic fields are well-known to induce strong resistive anisotropy, leading to speculation that the phase intrinsically breaks the tetragonal symmetry of the lattice. We have used uniaxial strain to break the symmetry of the lattice and have found a dramatic response: compression by 0.1%, for example, induces a resistive anisotropy of ∝ 2.5. I will discuss these results in the context of the underlying symmetry of the anomalous phase.
LaCu_{6-x}Ag_{x}: A promising host of an elastic quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Poudel, Lekh [ORNL; Dela Cruz, Clarina R. [ORNL; Koehler, Michael R. [University of Tennessee, Knoxville (UTK); McGuire, Michael A. [ORNL; Keppens, Veerle [University of Tennessee, Knoxville (UTK); Mandrus, David [ORNL; Christianson, Andrew D. [ORNL
2018-05-01
Structural properties of LaCu_{6-x}Ag_{x} have been investigated using neutron and x-ray diffraction, and resonant ultrasound spectroscopy (RUS) measurements. Diffraction measurements indicate a continuous structural transition from orthorhombic (Pnma) to monoclinic (P2₁/C) structure. RUS measurements show softening of natural frequencies at the structural transition, consistent with the elastic nature of the structural ground state. The structural transition temperatures in LaCu_{6-x}Ag_{x} decrease with Ag composition until the monoclinic phase is completely suppressed at x_{c}=0.225. All of the evidence is consistent with the presence of an elastic quantum critical point in LaCu_{6-x}Ag_{x}.
EPR and Bell's theorem: A critical review
International Nuclear Information System (INIS)
Stapp, H.P.
1991-01-01
The argument of Einstein, Podolsky, and Rosen is reviewed with attention to logical structure and character of assumptions. Bohr's reply is discussed. Bell's contribution is formulated without use of hidden variables, and efforts to equate hidden variables to realism are critically examined. An alternative derivation of nonlocality that makes no use of hidden variables, microrealism, counterfactual definiteness, or any other assumption alien to orthodox quantum thinking is described in detail, with particular attention to the quartet or broken-square question
Fermion condensation quantum phase transition versus conventional quantum phase transitions
International Nuclear Information System (INIS)
Shaginyan, V.R.; Han, J.G.; Lee, J.
2004-01-01
The main features of fermion condensation quantum phase transition (FCQPT), which are distinctive in several aspects from that of conventional quantum phase transition (CQPT), are considered. We show that in contrast to CQPT, whose physics in quantum critical region is dominated by thermal and quantum fluctuations and characterized by the absence of quasiparticles, the physics of a Fermi system near FCQPT or undergone FCQPT is controlled by the system of quasiparticles resembling the Landau quasiparticles. Contrary to the Landau quasiparticles, the effective mass of these quasiparticles strongly depends on the temperature, magnetic fields, density, etc. This system of quasiparticles having general properties determines the universal behavior of the Fermi system in question. As a result, the universal behavior persists up to relatively high temperatures comparatively to the case when such a behavior is determined by CQPT. We analyze striking recent measurements of specific heat, charge and heat transport used to study the nature of magnetic field-induced QCP in heavy-fermion metal CeCoIn 5 and show that the observed facts are in good agreement with our scenario based on FCQPT and certainly seem to rule out the critical fluctuations related with CQPT. Our general consideration suggests that FCQPT and the emergence of novel quasiparticles near and behind FCQPT and resembling the Landau quasiparticles are distinctive features intrinsic to strongly correlated substances
Boechat, B; Florencio, J; Saguia, A; de Alcantara Bonfim, O F
2014-03-01
We study the ground-state properties of a spin-1/2 model on a chain containing four-spin Ising-like interactions in the presence of both transverse and longitudinal magnetic fields. We use entanglement entropy and finite-size scaling methods to obtain the phase diagrams of the model. Our numerical calculations reveal a rich variety of phases and the existence of multicritical points in the system. We identify phases with both ferromagnetic and antiferromagnetic orderings. We also find periodically modulated orderings formed by a cluster of like spins followed by another cluster of opposite like spins. The quantum phases in the model are found to be separated by either first- or second-order transition lines.
Macroscopic Quantum Resonators (MAQRO): 2015 update
International Nuclear Information System (INIS)
Kaltenbaek, Rainer; Aspelmeyer, Markus; Kiesel, Nikolai; Barker, Peter F.; Bose, Sougato; Bassi, Angelo; Bateman, James; Bongs, Kai; Cruise, Adrian Michael; Braxmaier, Claus; Brukner, Caslav; Christophe, Bruno; Rodrigues, Manuel; Chwalla, Michael; Johann, Ulrich; Cohadon, Pierre-Francois; Heidmann, Antoine; Lambrecht, Astrid; Reynaud, Serge; Curceanu, Catalina; Dholakia, Kishan; Mazilu, Michael; Diosi, Lajos; Doeringshoff, Klaus; Peters, Achim; Ertmer, Wolfgang; Rasel, Ernst M.; Gieseler, Jan; Novotny, Lukas; Rondin, Loic; Guerlebeck, Norman; Herrmann, Sven; Laemmerzahl, Claus; Hechenblaikner, Gerald; Hossenfelder, Sabine; Kim, Myungshik; Milburn, Gerard J.; Mueller, Holger; Paternostro, Mauro; Pikovski, Igor; Pilan Zanoni, Andre; Riedel, Charles Jess; Roura, Albert; Schleich, Wolfgang P.; Schmiedmayer, Joerg; Schuldt, Thilo; Schwab, Keith C.; Tajmar, Martin; Tino, Guglielmo M.; Ulbricht, Hendrik; Ursin, Rupert; Vedral, Vlatko
2016-01-01
Do the laws of quantum physics still hold for macroscopic objects - this is at the heart of Schroedinger's cat paradox - or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission Macroscopic Quantum Resonators (MAQRO) may overcome these limitations and allow addressing such fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal is to probe the vastly unexplored 'quantum-classical' transition for increasingly massive objects, testing the predictions of quantum theory for objects in a size and mass regime unachievable in ground-based experiments. The hardware will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the 4th Cosmic Vision call for a medium-sized mission (M4) in 2014 of the European Space Agency (ESA) with a possible launch in 2025, and we review the progress with respect to the original MAQRO proposal for the 3rd Cosmic Vision call for a medium-sized mission (M3) in 2010. In particular, the updated proposal overcomes several critical issues of the original proposal by relying on established experimental techniques from high-mass matter-wave interferometry and by introducing novel ideas for particle loading and manipulation. Moreover, the mission design was improved to better fulfill the stringent environmental requirements for macroscopic quantum experiments. (orig.)
Macroscopic Quantum Resonators (MAQRO): 2015 update
Energy Technology Data Exchange (ETDEWEB)
Kaltenbaek, Rainer [University of Vienna, Vienna Center for Quantum Science and Technology, Vienna (Austria); Aspelmeyer, Markus; Kiesel, Nikolai [University of Vienna, Vienna Center for Quantum Science and Technology, Vienna (Austria); Barker, Peter F.; Bose, Sougato [University College London, Department of Physics and Astronomy, London (United Kingdom); Bassi, Angelo [University of Trieste, Department of Physics, Trieste (Italy); INFN - Trieste Section, Trieste (Italy); Bateman, James [University of Swansea, Department of Physics, College of Science, Swansea (United Kingdom); Bongs, Kai; Cruise, Adrian Michael [University of Birmingham, School of Physics and Astronomy, Birmingham (United Kingdom); Braxmaier, Claus [University of Bremen, Center of Applied Space Technology and Micro Gravity (ZARM), Bremen (Germany); Institute of Space Systems, German Aerospace Center (DLR), Bremen (Germany); Brukner, Caslav [University of Vienna, Vienna Center for Quantum Science and Technology, Vienna (Austria); Austrian Academy of Sciences, Institute of Quantum Optics and Quantum Information (IQOQI), Vienna (Austria); Christophe, Bruno; Rodrigues, Manuel [The French Aerospace Lab, ONERA, Chatillon (France); Chwalla, Michael; Johann, Ulrich [Airbus Defence and Space GmbH, Immenstaad (Germany); Cohadon, Pierre-Francois; Heidmann, Antoine; Lambrecht, Astrid; Reynaud, Serge [ENS-PSL Research University, Laboratoire Kastler Brossel, UPMC-Sorbonne Universites, CNRS, College de France, Paris (France); Curceanu, Catalina [Laboratori Nazionali di Frascati dell' INFN, Frascati (Italy); Dholakia, Kishan; Mazilu, Michael [University of St. Andrews, School of Physics and Astronomy, St. Andrews (United Kingdom); Diosi, Lajos [Wigner Research Center for Physics, P.O. Box 49, Budapest (Hungary); Doeringshoff, Klaus; Peters, Achim [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Berlin (Germany); Ertmer, Wolfgang; Rasel, Ernst M. [Leibniz Universitaet Hannover, Institut fuer Quantenoptik, Hannover (Germany); Gieseler, Jan; Novotny, Lukas; Rondin, Loic [ETH Zuerich, Photonics Laboratory, Zuerich (Switzerland); Guerlebeck, Norman; Herrmann, Sven; Laemmerzahl, Claus [University of Bremen, Center of Applied Space Technology and Micro Gravity (ZARM), Bremen (Germany); Hechenblaikner, Gerald [Airbus Defence and Space GmbH, Immenstaad (Germany); European Southern Observatory (ESO), Garching bei Muenchen (Germany); Hossenfelder, Sabine [KTH Royal Institute of Technology and Stockholm University, Nordita, Stockholm (Sweden); Kim, Myungshik [Imperial College London, QOLS, Blackett Laboratory, London (United Kingdom); Milburn, Gerard J. [University of Queensland, ARC Centre for Engineered Quantum Systems, Brisbane (Australia); Mueller, Holger [University of California, Department of Physics, Berkeley, CA (United States); Paternostro, Mauro [Queen' s University, Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Belfast (United Kingdom); Pikovski, Igor [Harvard-Smithsonian Center for Astrophysics, ITAMP, Cambridge, MA (United States); Pilan Zanoni, Andre [Airbus Defence and Space GmbH, Immenstaad (Germany); CERN - European Organization for Nuclear Research, EN-STI-TCD, Geneva (Switzerland); Riedel, Charles Jess [Perimeter Institute for Theoretical Physics, Waterloo, ON (Canada); Roura, Albert [Universitaet Ulm, Institut fuer Quantenphysik, Ulm (Germany); Schleich, Wolfgang P. [Universitaet Ulm, Institut fuer Quantenphysik, Ulm (Germany); Texas A and M University Institute for Advanced Study (TIAS), Institute for Quantum Science and Engineering (IQSE), and Department of Physics and Astronomy, College Station, TX (United States); Schmiedmayer, Joerg [Vienna University of Technology, Vienna Center for Quantum Science and Technology, Institute of Atomic and Subatomic Physics, Vienna (Austria); Schuldt, Thilo [Institute of Space Systems, German Aerospace Center (DLR), Bremen (Germany); Schwab, Keith C. [California Institute of Technology, Applied Physics, Pasadena, CA (United States); Tajmar, Martin [Technische Universitaet Dresden, Institut fuer Luft- und Raumfahrttechnik, Dresden (Germany); Tino, Guglielmo M. [Universita di Firenze, Dipartimento di Fisica e Astronomia and LENS, INFN, Sesto Fiorentino, Firenze (Italy); Ulbricht, Hendrik [University of Southampton, Physics and Astronomy, Southampton (United Kingdom); Ursin, Rupert [Austrian Academy of Sciences, Institute of Quantum Optics and Quantum Information (IQOQI), Vienna (Austria); Vedral, Vlatko [University of Oxford, Atomic and Laser Physics, Clarendon Laboratory, Oxford (United Kingdom); National University of Singapore, Center for Quantum Technologies, Singapore (SG)
2016-12-15
Do the laws of quantum physics still hold for macroscopic objects - this is at the heart of Schroedinger's cat paradox - or do gravitation or yet unknown effects set a limit for massive particles? What is the fundamental relation between quantum physics and gravity? Ground-based experiments addressing these questions may soon face limitations due to limited free-fall times and the quality of vacuum and microgravity. The proposed mission Macroscopic Quantum Resonators (MAQRO) may overcome these limitations and allow addressing such fundamental questions. MAQRO harnesses recent developments in quantum optomechanics, high-mass matter-wave interferometry as well as state-of-the-art space technology to push macroscopic quantum experiments towards their ultimate performance limits and to open new horizons for applying quantum technology in space. The main scientific goal is to probe the vastly unexplored 'quantum-classical' transition for increasingly massive objects, testing the predictions of quantum theory for objects in a size and mass regime unachievable in ground-based experiments. The hardware will largely be based on available space technology. Here, we present the MAQRO proposal submitted in response to the 4th Cosmic Vision call for a medium-sized mission (M4) in 2014 of the European Space Agency (ESA) with a possible launch in 2025, and we review the progress with respect to the original MAQRO proposal for the 3rd Cosmic Vision call for a medium-sized mission (M3) in 2010. In particular, the updated proposal overcomes several critical issues of the original proposal by relying on established experimental techniques from high-mass matter-wave interferometry and by introducing novel ideas for particle loading and manipulation. Moreover, the mission design was improved to better fulfill the stringent environmental requirements for macroscopic quantum experiments. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Smiseth, Jo
2005-07-01
The critical properties of three-dimensional U(1)-symmetric lattice gauge theories have been studied. The models apply to various physical systems such as insulating phases of strongly correlated electron systems as well as superconducting and superfluid states of liquid metallic hydrogen under extreme pressures. The thesis contains an introductory part and a collection of research papers of which seven are published works and one is submitted for publication. The outline of this thesis is as follows. In Chapter 2 the theory of phase transitions is discussed with emphasis on continuous phase transitions, critical phenomena and phase transitions in gauge theories. In the next chapter the phases of the abelian Higgs model are presented, and the critical phenomena are discussed. Furthermore, the multicomponent Ginzburg-Landau theory and the applications to liquid metallic hydrogen are presented. Chapter 4 contains an overview of the Monte Carlo integration scheme, including the Metropolis algorithm, error estimates, and re weighting techniques. This chapter is followed by the papers I-VIII. Paper I: Criticality in the (2+1)-Dimensional Compact Higgs Model and Fractionalized Insulators. Paper II: Phase structure of (2+1)-dimensional compact lattice gauge theories and the transition from Mott insulator to fractionalized insulator. Paper III: Compact U(1) gauge theories in 2+1 dimensions and the physics of low dimensional insulating materials. Paper IV: Phase structure of Abelian Chern-Simons gauge theories. Paper V: Critical Properties of the N-Color London Model. Paper VI: Field- and temperature induced topological phase transitions in the three-dimensional N-component London superconductor. Paper VII: Vortex Sublattice Melting in a Two-Component Superconductor. Paper VIII: Observation of a metallic superfluid in a numerical experiment (ml)
International Nuclear Information System (INIS)
Ramesh, S.
1985-01-01
This thesis constitutes the first precise, quantitative experimental study of layering transitions, two-dimensional critical temperatures, and their relation to surface roughening. The experiments used superfluid fourth sound to probe the liquid solid 4 He interface, by coupling with surface waves unique to this interface. An annular resonator with electric transducers was used to measure the fourth sound velocity c 4 in an exfoliated graphite (Grafoil) superleak. Measurements of the pressure dependence of the fourth sound resonance frequencies (and attenuation) from ∼6 bar to ∼26 bar were made along eight isotherms from 1.0 K to 1.7 K. Plots of fourth sound resonance frequency versus coverage clearly indicate layer-by-layer solid nucleation and epitaxal growth of hcp solid 4 He on the basal plane of graphite. Further analysis yielded solid adsorption isotherms and a kinetic growth coefficient for the 4 He crystal surface and also indicated the existence of a critical temperature region and also indicated the existence of a critical temperature region around 1.0-1.2 K (the region of a bulk roughening transition). The acoustical theory for the experimental system was worked out using a parallel waveguide model; Landau's thermohydrodynamic equations were reformulated by including the mass- and heat-exchange effects occurring in the system; the equations were solved to obtain expressions for the velocity of sound propagation and attenuation
Directory of Open Access Journals (Sweden)
J. K. Dong
2011-09-01
Full Text Available The in-plane resistivity ρ and thermal conductivity κ of the heavy-fermion superconductor Ce_{2}PdIn_{8} single crystals were measured down to 50 mK. A field-induced quantum critical point, occurring at the upper critical field H_{c2}, is demonstrated from the ρ(T∼T near H_{c2} and ρ(T∼T^{2} when further increasing the field. The large residual linear term κ_{0}/T at zero field and the rapid increase of κ(H/T at low field give evidence for nodal superconductivity in Ce_{2}PdIn_{8}. The jump of κ(H/T near H_{c2} suggests a first-order-like phase transition at low temperature. These results mimic the features of the famous CeCoIn_{5} superconductor, implying that Ce_{2}PdIn_{8} may be another interesting compound to investigate for the interplay between magnetism and superconductivity.
Introduction to topological quantum matter & quantum computation
Stanescu, Tudor D
2017-01-01
What is -topological- about topological quantum states? How many types of topological quantum phases are there? What is a zero-energy Majorana mode, how can it be realized in a solid state system, and how can it be used as a platform for topological quantum computation? What is quantum computation and what makes it different from classical computation? Addressing these and other related questions, Introduction to Topological Quantum Matter & Quantum Computation provides an introduction to and a synthesis of a fascinating and rapidly expanding research field emerging at the crossroads of condensed matter physics, mathematics, and computer science. Providing the big picture, this book is ideal for graduate students and researchers entering this field as it allows for the fruitful transfer of paradigms and ideas amongst different areas, and includes many specific examples to help the reader understand abstract and sometimes challenging concepts. It explores the topological quantum world beyond the well-know...
What is quantum in quantum randomness?
Grangier, P; Auffèves, A
2018-07-13
It is often said that quantum and classical randomness are of different nature, the former being ontological and the latter epistemological. However, so far the question of 'What is quantum in quantum randomness?', i.e. what is the impact of quantization and discreteness on the nature of randomness, remains to be answered. In a first part, we make explicit the differences between quantum and classical randomness within a recently proposed ontology for quantum mechanics based on contextual objectivity. In this view, quantum randomness is the result of contextuality and quantization. We show that this approach strongly impacts the purposes of quantum theory as well as its areas of application. In particular, it challenges current programmes inspired by classical reductionism, aiming at the emergence of the classical world from a large number of quantum systems. In a second part, we analyse quantum physics and thermodynamics as theories of randomness, unveiling their mutual influences. We finally consider new technological applications of quantum randomness that have opened up in the emerging field of quantum thermodynamics.This article is part of a discussion meeting issue 'Foundations of quantum mechanics and their impact on contemporary society'. © 2018 The Author(s).
Quorum sensing: a quantum perspective.
Majumdar, Sarangam; Pal, Sukla
2016-09-01
Quorum sensing is the efficient mode of communication in the bacterial world. After a lot of advancements in the classical theory of quorum sensing few basic questions of quorum sensing still remain unanswered. The sufficient progresses in quantum biology demands to explain these questions from the quantum perspective as non trivial quantum effects already have manifested in various biological processes like photosynthesis, magneto-reception etc. Therefore, it's the time to review the bacterial communications from the quantum view point. In this article we carefully accumulate the latest results and arguments to strengthen quantum biology through the addition of quorum sensing mechanism in the light of quantum mechanics.
On quantum statistical inference
DEFF Research Database (Denmark)
Barndorff-Nielsen, Ole Eiler; Gill, Richard D.; Jupp, Peter E.
Recent developments in the mathematical foundations of quantum mechanics have brought the theory closer to that of classical probability and statistics. On the other hand, the unique character of quantum physics sets many of the questions addressed apart from those met classically in stochastics....... Furthermore, concurrent advances in experimental techniques and in the theory of quantum computation have led to a strong interest in questions of quantum information, in particular in the sense of the amount of information about unknown parameters in given observational data or accessible through various...
Stapp, Henry P.
2012-05-01
Robert Griffiths has recently addressed, within the framework of a `consistent quantum theory' that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues that the putative proofs of this property that involve hidden variables include in their premises some essentially classical-physics-type assumptions that are not entailed by the precepts of quantum mechanics. Thus whatever is proved is not a feature of quantum mechanics, but is a property of a theory that tries to combine quantum theory with quasi-classical features that go beyond what is entailed by quantum theory itself. One cannot logically prove properties of a system by establishing, instead, properties of a system modified by adding properties alien to the original system. Hence Griffiths' rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his `consistent quantum theory' shows that the cited proof is valid within that restrictive version of quantum theory. An added section responds to Griffiths' reply, which cites general possibilities of ambiguities that might make what is to be proved ill-defined, and hence render the pertinent `consistent framework' ill defined. But the vagaries that he cites do not upset the proof in question, which, both by its physical formulation and by explicit identification, specify the framework to be used. Griffiths confirms the validity of the proof insofar as that pertinent framework is used. The section also shows
Tognetti, Vincent; Joubert, Laurent; Raucoules, Roman; De Bruin, Theodorus; Adamo, Carlo
2012-06-07
In this paper, we extend the work of Popelier and Logothetis [J. Organomet. Chem. 1998, 555, 101] on the characterization of agosticity by considerably enlarging the set of the studied organometallic molecules. To this aim, 23 representative complexes have been considered, including all first line transition metals at various oxidation states and exhibiting four types of agosticity (α, β, γ, and δ). From these examples, the concepts of agostic atom, agostic bond, and agostic interaction are defined and discussed, notably by advocating Bader's analysis of the electron density. The nature and the local properties of the bond critical points are then investigated, and the relationships with the main geometric parameters of the complexes are particularly examined. Moreover, new local descriptors based on kinetic energy densities are developed in order to provide new tools for bond characterization.
Arakcheev, V. G.; Bagratashvili, Viktor N.; Valeev, A. A.; Gordienko, Vyacheslav M.; Kireev, Vyacheslav V.; Morozov, V. B.; Olenin, A. N.; Popov, Vladimir K.; Tunkin, V. G.; Yakovlev, D. V.
2004-01-01
The transformation of the Q-band of the low-frequency 1285-cm-1 component of the 2v2/v1 Fermi doublet of a CO2 molecule is studied in the critical point vicinity (Tc=31.03 °C, Pc=72.8 atm) by the CARS method. CARS spectra were recorded by changing pressure isothermically from 48 to 120 atm at several temperatures in the range between 25 and 36°C. At the temperature above 29°C, the pressure dependences of the Q-band width pass through the maximum, which exceeds by 40% —50% the typical Q-band width in the liquid phase. The position of the maximum shifts to higher pressures with increasing temperature. The inhomogeneous broadening of the Q-band is interpreted based on the cluster microstructure of a supercritical fluid.
Quantum signatures of chaos or quantum chaos?
Energy Technology Data Exchange (ETDEWEB)
Bunakov, V. E., E-mail: bunakov@VB13190.spb.edu [St. Petersburg State University (Russian Federation)
2016-11-15
A critical analysis of the present-day concept of chaos in quantum systems as nothing but a “quantum signature” of chaos in classical mechanics is given. In contrast to the existing semi-intuitive guesses, a definition of classical and quantum chaos is proposed on the basis of the Liouville–Arnold theorem: a quantum chaotic system featuring N degrees of freedom should have M < N independent first integrals of motion (good quantum numbers) specified by the symmetry of the Hamiltonian of the system. Quantitative measures of quantum chaos that, in the classical limit, go over to the Lyapunov exponent and the classical stability parameter are proposed. The proposed criteria of quantum chaos are applied to solving standard problems of modern dynamical chaos theory.
Quantum signatures of chaos or quantum chaos?
International Nuclear Information System (INIS)
Bunakov, V. E.
2016-01-01
A critical analysis of the present-day concept of chaos in quantum systems as nothing but a “quantum signature” of chaos in classical mechanics is given. In contrast to the existing semi-intuitive guesses, a definition of classical and quantum chaos is proposed on the basis of the Liouville–Arnold theorem: a quantum chaotic system featuring N degrees of freedom should have M < N independent first integrals of motion (good quantum numbers) specified by the symmetry of the Hamiltonian of the system. Quantitative measures of quantum chaos that, in the classical limit, go over to the Lyapunov exponent and the classical stability parameter are proposed. The proposed criteria of quantum chaos are applied to solving standard problems of modern dynamical chaos theory.
Quantum neuromorphic hardware for quantum artificial intelligence
Prati, Enrico
2017-08-01
The development of machine learning methods based on deep learning boosted the field of artificial intelligence towards unprecedented achievements and application in several fields. Such prominent results were made in parallel with the first successful demonstrations of fault tolerant hardware for quantum information processing. To which extent deep learning can take advantage of the existence of a hardware based on qubits behaving as a universal quantum computer is an open question under investigation. Here I review the convergence between the two fields towards implementation of advanced quantum algorithms, including quantum deep learning.
Quantum computing. Defining and detecting quantum speedup.
Rønnow, Troels F; Wang, Zhihui; Job, Joshua; Boixo, Sergio; Isakov, Sergei V; Wecker, David; Martinis, John M; Lidar, Daniel A; Troyer, Matthias
2014-07-25
The development of small-scale quantum devices raises the question of how to fairly assess and detect quantum speedup. Here, we show how to define and measure quantum speedup and how to avoid pitfalls that might mask or fake such a speedup. We illustrate our discussion with data from tests run on a D-Wave Two device with up to 503 qubits. By using random spin glass instances as a benchmark, we found no evidence of quantum speedup when the entire data set is considered and obtained inconclusive results when comparing subsets of instances on an instance-by-instance basis. Our results do not rule out the possibility of speedup for other classes of problems and illustrate the subtle nature of the quantum speedup question. Copyright © 2014, American Association for the Advancement of Science.
National Research Council Canada - National Science Library
Agarwal, G. S
2013-01-01
.... Focusing on applications of quantum optics, the textbook covers recent developments such as engineering of quantum states, quantum optics on a chip, nano-mechanical mirrors, quantum entanglement...
Quantum Chess: Making Quantum Phenomena Accessible
Cantwell, Christopher
Quantum phenomena have remained largely inaccessible to the general public. There tends to be a scare factor associated with the word ``Quantum''. This is in large part due to the alien nature of phenomena such as superposition and entanglement. However, Quantum Computing is a very active area of research and one day we will have games that run on those quantum computers. Quantum phenomena such as superposition and entanglement will seem as normal as gravity. Is it possible to create such games today? Can we make games that are built on top of a realistic quantum simulation and introduce players of any background to quantum concepts in a fun and mentally stimulating way? One of the difficulties with any quantum simulation run on a classical computer is that the Hilbert space grows exponentially, making simulations of an appreciable size physically impossible due largely to memory restrictions. Here we will discuss the conception and development of Quantum Chess, and how to overcome some of the difficulties faced. We can then ask the question, ``What's next?'' What are some of the difficulties Quantum Chess still faces, and what is the future of quantum games?
Monthus, Cécile
2015-06-01
We consider M ⩾ 2 pure or random quantum Ising chains of N spins when they are coupled via a single star junction at their origins or when they are coupled via two star junctions at the their two ends leading to the watermelon geometry. The energy gap is studied via a sequential self-dual real-space renormalization procedure that can be explicitly solved in terms of Kesten variables containing the initial couplings and and the initial transverse fields. In the pure case at criticality, the gap is found to decay as a power-law {ΔM}\\propto {{N}-z(M)} with the dynamical exponent z(M)=\\frac{M}{2} for the single star junction (the case M = 2 corresponds to z = 1 for a single chain with free boundary conditions) and z(M) = M - 1 for the watermelon (the case M = 2 corresponds to z = 1 for a single chain with periodic boundary conditions). In the random case at criticality, the gap follows the Infinite Disorder Fixed Point scaling \\ln {ΔM}=-{{N}\\psi}g with the same activated exponent \\psi =\\frac{1}{2} as the single chain corresponding to M = 2, and where g is an O(1) random positive variable, whose distribution depends upon the number M of chains and upon the geometry (star or watermelon).
Understanding Bitcoins: Facts and Questions
Directory of Open Access Journals (Sweden)
Bruno Saboia de Albuquerque
2015-03-01
Full Text Available The objective of this work is to do a research challenge about the digital currency named Bitcoins, as well as exploit the general concept behind digital currencies and cryptocurrencies, and enumerate some of its current criticism and problems. Such currencies usage and public knowledge is increasing hastily on the last few months, and many questions arise with its popularity.
Rhetorical questions or rhetorical uses of questions?
Directory of Open Access Journals (Sweden)
Špago Džemal
2016-12-01
Full Text Available This paper aims to explore whether some rhetorical questions contain certain linguistic elements or forms which would differentiate them from answer-eliciting and action-eliciting questions, and thereby hint at their rhetorical nature even outside the context. Namely, despite the fact that the same questions can be rhetorical in one context, and answer-eliciting in another, some of them are more likely to be associated with rhetorical or non-rhetorical use. The analysis is based on extensive data (over 1200 examples of rhetorical questions taken from 30 plays by two British and two American writers, and the results are expected to give an insight into whether we can talk about rhetorical questions or just a rhetorical use of questions.
Kendon, Vivien M; Nemoto, Kae; Munro, William J
2010-08-13
We briefly review what a quantum computer is, what it promises to do for us and why it is so hard to build one. Among the first applications anticipated to bear fruit is the quantum simulation of quantum systems. While most quantum computation is an extension of classical digital computation, quantum simulation differs fundamentally in how the data are encoded in the quantum computer. To perform a quantum simulation, the Hilbert space of the system to be simulated is mapped directly onto the Hilbert space of the (logical) qubits in the quantum computer. This type of direct correspondence is how data are encoded in a classical analogue computer. There is no binary encoding, and increasing precision becomes exponentially costly: an extra bit of precision doubles the size of the computer. This has important consequences for both the precision and error-correction requirements of quantum simulation, and significant open questions remain about its practicality. It also means that the quantum version of analogue computers, continuous-variable quantum computers, becomes an equally efficient architecture for quantum simulation. Lessons from past use of classical analogue computers can help us to build better quantum simulators in future.
Talluri, Bhusankar; Prasad, Edamana; Thomas, Tiju
2018-04-01
Synthesis of ultra-small (r photovoltaics to sensing. Digestive ripening (DR), a method for preparing uniformly-sized particles is critically influenced by nature and concentrations of the starting materials, solvent, and surfactant. To better understand the DR process there is a need to study the effect of each synthetic parameter. In this work, we investigate the effect of surfactant on a ceramic-DR process, with copper oxide as the chosen material. To study the influence of surfactant; aminoalcohols (triethanolamine, diethanolamine, monoethanolamine), alkylamines (ethyl amine) and aqua ligands are chosen. Digestively ripened quantum dots (QDs) are formed in case of all surfactants except ethyl amine and water. Aminoalchols based surfactants which contain both hydroxyl and amine moieties are efficient ligands (due to their chelation ability) for achieving DR. With the increase of denticity of the ligand, average size of QDs do not vary; however the variance in size does. QDs formed using aminoalchols are more monodispersed when compared to alkyl amine and aqua ligand systems. Furthermore, absorption and photoluminescence spectra suggest that choice of surfactant is important for achieving DR in ceramic nanostructures (when compared to other parameters). Hard-soft-acid-base-interactions between surfactant and copper oxide seem primarily responsible for the observed DR in copper oxide QDs. The absorption and photoluminescence spectra indicate that the energy migration and relaxation pathways taking place in DR QDs depend on the type of capping agent used.
International Nuclear Information System (INIS)
Ohta, Tetsuya; Nakai, Yusuke; Ihara, Yoshihiko; Ishida, Kenji; Deguchi, Kazuhiko; Sato, Noriaki K.; Satoh, Isamu
2008-01-01
Co nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies were carried out for the recently discovered UCoGe, in which the ferromagnetic and superconducting (SC) transitions are reported to occur at T Curie - 3 K and T S - 0.8 K, in order to investigate the coexistence of ferromagnetism and superconductivity as well as the normal-state and SC properties from a microscopic point of view. From the nuclear spin-lattice relaxation rate 1/T 1 and Knight-shift measurements, we confirm that ferromagnetic fluctuations that possess a quantum critical character are present above T Curie and also the occurrence of a ferromagnetic transition at 2.5 K in our polycrystalline sample. The magnetic fluctuations in the normal state show that UCoGe is an itinerant ferromagnet similar to ZrZn 2 and YCo 2 . The onset SC transition is identified at T S - 0.7 K, below which 1/T 1 arising from 30% of the volume fraction starts to decrease due to the opening of the SC gap. This component of 1/T 1 , which follows a T 3 dependence in the temperature range 0.3-0.1 K, coexists with the magnetic components of 1/T 1 showing a √T dependence below T S . From the NQR measurements in the SC state, we suggest that the self-induced vortex state is realized in UCoGe. (author)
Scaling behavior near the itinerant ferromagnetic quantum critical point (FQCP) of NiCoCrx for 0.8
Sales, Brian; Jin, Ke; Bei, Hongbin; Nichols, John; Chisholm, Matthew; May, Andrew; McGuire, Michael
Low temperature magnetization, resistivity and heat capacity data are reported for the concentrated solid solution NiCoCrx as a function of temperature and magnetic field. In the quantum critical region the low field (0.001-0.01 T) magnetic susceptibility, Chi, diverges as T- 1 / 2 and the magnetization data exhibits T/B scaling from 0.001 2 Tesla, the crossover temperature from the QC to Fermi liquid regime is no longer linear in B, and is better described by B0.75. This scaling behavior is particularly accurate in describing the normalized magnetoresistance data [Rho(B,T)-Rho(0,T)]/T, which is equivalent to the ratio of relaxation rates associated with magnetic field and temperature TauT/TauB. The location of the QCP is sensitive to the composition x and the strain generated during synthesis. These medium-entropy alloys are interesting model systems to explore the role of chemical disorder at FQCP. Research supported by the DOE Office of Science, Materials Science and Engineering Division, and the Energy Dissipation to Defect Evolution EFRC.
International Nuclear Information System (INIS)
Hoekzema, D.J.
1993-01-01
This volume deals with the question whether quantum mechanics can provide a picture of physical reality. This question is investigated from physical, philosophical, and logical perspectives on the basis of modern views on measurement and open quantum systems. New ways are found of respecting the rules of classical logic in quantum mechanics, by developing a formalization of the concept of 'context' within modularized version of modal logic. Various applications of this are given, also outside quantum theory. A 'contextual quantum process theory' is presented as a general framework for further interpretation. Several such interpretations are outlined, and ensuing problems of completeness and (non)locality are discussed. A special chapter is devoted to a manifestly covariant relativistic interpretation in terms of 'quantum events'. (author). refs
Nuclear questions; Le nucleaire en questions
Energy Technology Data Exchange (ETDEWEB)
Berg, Eugene
2012-02-15
Civilian and military nuclear questions fill a multitude of publications these days, especially after the Japanese tsunami and the Fukushima disaster. The author analyses some of them and highlights the links between civil and military nuclear industries, the realities of the nuclear cycle and related industrial questions before concluding on the controversial issue of weapons and their proliferation potential
Mathematics and quantum mechanics
International Nuclear Information System (INIS)
Santander, M.
2000-01-01
Several episodes in the relation between Mathematics and Quantum Mechanics are discussed; and the emphasis is put in the existence of multiple and sometimes unexpected connections between ideas originating in Mathematics and in Quantum Physics. The question of the unresasonable effectiveness of Mathematics in Physics is also presented in the same light. (Author) 3 refs
Boeyens, Jan C A
2016-01-01
This volume, written by a highly cited author, presents the history of quantum theory together with open questions and remaining problems in terms of the plausibility of quantum chemistry and physics. It also provides insights into the theory of matter-wave mechanics. The content is aimed at students and lecturers in chemistry, physics and the philosophy of science.
On quantum statistical inference
Barndorff-Nielsen, O.E.; Gill, R.D.; Jupp, P.E.
2001-01-01
Recent developments in the mathematical foundations of quantum mechanics have brought the theory closer to that of classical probability and statistics. On the other hand, the unique character of quantum physics sets many of the questions addressed apart from those met classically in stochastics.
Abstract quantum computing machines and quantum computational logics
Chiara, Maria Luisa Dalla; Giuntini, Roberto; Sergioli, Giuseppe; Leporini, Roberto
2016-06-01
Classical and quantum parallelism are deeply different, although it is sometimes claimed that quantum Turing machines are nothing but special examples of classical probabilistic machines. We introduce the concepts of deterministic state machine, classical probabilistic state machine and quantum state machine. On this basis, we discuss the question: To what extent can quantum state machines be simulated by classical probabilistic state machines? Each state machine is devoted to a single task determined by its program. Real computers, however, behave differently, being able to solve different kinds of problems. This capacity can be modeled, in the quantum case, by the mathematical notion of abstract quantum computing machine, whose different programs determine different quantum state machines. The computations of abstract quantum computing machines can be linguistically described by the formulas of a particular form of quantum logic, termed quantum computational logic.
Directory of Open Access Journals (Sweden)
Alessandro Sergi
2009-06-01
Full Text Available A critical assessment of the recent developmentsof molecular biology is presented.The thesis that they do not lead to a conceptualunderstanding of life and biological systems is defended.Maturana and Varela's concept of autopoiesis is briefly sketchedand its logical circularity avoided by postulatingthe existence of underlying living processes,entailing amplification from the microscopic to the macroscopic scale,with increasing complexity in the passage from one scale to the other.Following such a line of thought, the currently accepted model of condensed matter, which is based on electrostatics and short-ranged forces,is criticized. It is suggested that the correct interpretationof quantum dispersion forces (van der Waals, hydrogen bonding, and so onas quantum coherence effects hints at the necessity of includinglong-ranged forces (or mechanisms for them incondensed matter theories of biological processes.Some quantum effects in biology are reviewedand quantum mechanics is acknowledged as conceptually important to biology since withoutit most (if not all of the biological structuresand signalling processes would not even exist. Moreover, it is suggested that long-rangequantum coherent dynamics, including electron polarization,may be invoked to explain signal amplificationprocess in biological systems in general.
Haven, Emmanuel
2013-01-01
Written by world experts in the foundations of quantum mechanics and its applications to social science, this book shows how elementary quantum mechanical principles can be applied to decision-making paradoxes in psychology and used in modelling information in finance and economics. The book starts with a thorough overview of some of the salient differences between classical, statistical and quantum mechanics. It presents arguments on why quantum mechanics can be applied outside of physics and defines quantum social science. The issue of the existence of quantum probabilistic effects in psychology, economics and finance is addressed and basic questions and answers are provided. Aimed at researchers in economics and psychology, as well as physics, basic mathematical preliminaries and elementary concepts from quantum mechanics are defined in a self-contained way.
International Nuclear Information System (INIS)
Banai, M.
1983-11-01
A quantum relativity theory formulated in terms of Davis' quantum relativity principle is outlined. The first task in this theory as in classical relativity theory is to model space-time, the arena of natural processes. It is argued that the quantum space-time models of Banai introduced in an earlier paper is formulated in terms of Davis' quantum relativity. Then it is shown that the recently proposed classical relativistic quantum theory of Prugovecki and his corresponding classical relativistic quantum model of space-time open the way to introduce in a consistent way the quantum space-time model (the 'canonically quantized Minkowski space') proposed by Banai earlier. The main new aspect of the quantum mechanics of the quantum relativistic particles is, in this model of space-time, that it provides a true mass eigenvalue problem and, that the excited mass states of such particles can be interpreted as classifically relativistic (massive) quantum particles ('elementary particles'). The question of field theory over quantum relativistic models of space-time is also discussed. Finally, it is suggested that 'quarks' should be considered as quantum relativistic particles. (author)
Are Quantum Models for Order Effects Quantum?
Moreira, Catarina; Wichert, Andreas
2017-12-01
The application of principles of Quantum Mechanics in areas outside of physics has been getting increasing attention in the scientific community in an emergent disciplined called Quantum Cognition. These principles have been applied to explain paradoxical situations that cannot be easily explained through classical theory. In quantum probability, events are characterised by a superposition state, which is represented by a state vector in a N-dimensional vector space. The probability of an event is given by the squared magnitude of the projection of this superposition state into the desired subspace. This geometric approach is very useful to explain paradoxical findings that involve order effects, but do we really need quantum principles for models that only involve projections? This work has two main goals. First, it is still not clear in the literature if a quantum projection model has any advantage towards a classical projection. We compared both models and concluded that the Quantum Projection model achieves the same results as its classical counterpart, because the quantum interference effects play no role in the computation of the probabilities. Second, it intends to propose an alternative relativistic interpretation for rotation parameters that are involved in both classical and quantum models. In the end, instead of interpreting these parameters as a similarity measure between questions, we propose that they emerge due to the lack of knowledge concerned with a personal basis state and also due to uncertainties towards the state of world and towards the context of the questions.
Quantum Erasure: Quantum Interference Revisited
Walborn, Stephen P.; Cunha, Marcelo O. Terra; Pádua, Sebastião; Monken, Carlos H.
2005-01-01
Recent experiments in quantum optics have shed light on the foundations of quantum physics. Quantum erasers - modified quantum interference experiments - show that quantum entanglement is responsible for the complementarity principle.
On quantum mechanics for macroscopic systems
International Nuclear Information System (INIS)
Primas, H.
1992-01-01
The parable of Schroedinger's cat may lead to several up-to date questions: how to treat open systems in quantum theory, how to treat thermodynamically irreversible processes in the quantum mechanics framework, how to explain, following the quantum theory, the existence, phenomenologically evident, of classical observables, what implies the predicted existence by the quantum theory of non localized macroscopic material object ?
Quantum information, cognition, and music
Dalla Chiara, Maria L.; Giuntini, Roberto; Leporini, Roberto; Negri, Eleonora; Sergioli, Giuseppe
2015-01-01
Parallelism represents an essential aspect of human mind/brain activities. One can recognize some common features between psychological parallelism and the characteristic parallel structures that arise in quantum theory and in quantum computation. The article is devoted to a discussion of the following questions: a comparison between classical probabilistic Turing machines and quantum Turing machines.possible applications of the quantum computational semantics to cognitive problems.parallelism in music. PMID:26539139
Quantum information, cognition and music.
Directory of Open Access Journals (Sweden)
Maria Luisa eDalla Chiara
2015-10-01
Full Text Available Parallelism represents an essential aspect of human mind/brain activities. One can recognize some common features between psychological parallelism and the characteristic parallel structures that arise in quantum theory and in quantum computation. The article is devoted to a discussion of the following questions:1 a comparison between classical probabilistic Turing machines and quantum Turing machines;2 possible applications of the quantum computational semantics to cognitive problems;3 parallelism in music.
Nanodesign: some basic questions
Schommers, Wolfram
2013-01-01
There is no doubt that nanoscience will be the dominant direction for technology in this century, and that this science will influence our lives to a large extent as well as open completely new perspectives on all scientific and technological disciplines. To be able to produce optimal nanosystems with tailor-made properties, it is necessary to analyze and construct such systems in advance by adequate theoretical and computational methods. Since we work in nanoscience and nanotechnology at the ultimate level, we have to apply the basic laws of physics. What methods and tools are relevant here? The book gives an answer to this question. The background of the theoretical methods and tools is critically discussed, and also the world view on which these physical laws are based. Such a debate is not only of academic interest but is of highly general concern, and this is because we constantly move in nanoscience and nanotechnology between two extreme poles, between infinite life and total destruction . On the one ...
International Nuclear Information System (INIS)
Schroer, Bert; Freie Universitaet, Berlin
2003-05-01
After recalling episodes from Pascual Jordan's biography including his pivotal role in the shaping of quantum field theory and his much criticized conduct during the NS regime, I draw attention to his presentation of the first phase of development of quantum field theory in a talk presented at the 1929 Kharkov conference. He starts by giving a comprehensive account of the beginnings of quantum theory, emphasising that particle-like properties arise as a consequence of treating wave-motions quantum-mechanically. He then goes on to his recent discovery of quantization of 'wave fields' and problems of gauge invariance. The most surprising aspect of Jordan's presentation is however his strong belief that his field quantization is a transitory not yet optimal formulation of the principles underlying causal, local quantum physics. The expectation of a future more radical change coming from the main architect of field quantization already shortly after his discovery is certainly quite startling. I try to answer the question to what extent Jordan's 1929 expectations have been vindicated. The larger part of the present essay consists in arguing that Jordan's plea for a formulation without 'classical correspondence crutches', i.e. for an intrinsic approach (which avoids classical fields altogether), is successfully addressed in past and recent publications on local quantum physics. (author)
Quantifying quantum coherence with quantum Fisher information.
Feng, X N; Wei, L F
2017-11-14
Quantum coherence is one of the old but always important concepts in quantum mechanics, and now it has been regarded as a necessary resource for quantum information processing and quantum metrology. However, the question of how to quantify the quantum coherence has just been paid the attention recently (see, e.g., Baumgratz et al. PRL, 113. 140401 (2014)). In this paper we verify that the well-known quantum Fisher information (QFI) can be utilized to quantify the quantum coherence, as it satisfies the monotonicity under the typical incoherent operations and the convexity under the mixing of the quantum states. Differing from most of the pure axiomatic methods, quantifying quantum coherence by QFI could be experimentally testable, as the bound of the QFI is practically measurable. The validity of our proposal is specifically demonstrated with the typical phase-damping and depolarizing evolution processes of a generic single-qubit state, and also by comparing it with the other quantifying methods proposed previously.
Frequent Questions on Recycling
This is a list of frequent questions on recycling, broken down into five categories. These are answers to common questions that EPA has received from press and web inquiries. This list is located on the Reduce, Reuse, Recycle website.
Quantum ballistic evolution in quantum mechanics: Application to quantum computers
International Nuclear Information System (INIS)
Benioff, P.
1996-01-01
Quantum computers are important examples of processes whose evolution can be described in terms of iterations of single-step operators or their adjoints. Based on this, Hamiltonian evolution of processes with associated step operators T is investigated here. The main limitation of this paper is to processes which evolve quantum ballistically, i.e., motion restricted to a collection of nonintersecting or distinct paths on an arbitrary basis. The main goal of this paper is proof of a theorem which gives necessary and sufficient conditions that T must satisfy so that there exists a Hamiltonian description of quantum ballistic evolution for the process, namely, that T is a partial isometry and is orthogonality preserving and stable on some basis. Simple examples of quantum ballistic evolution for quantum Turing machines with one and with more than one type of elementary step are discussed. It is seen that for nondeterministic machines the basis set can be quite complex with much entanglement present. It is also proven that, given a step operator T for an arbitrary deterministic quantum Turing machine, it is decidable if T is stable and orthogonality preserving, and if quantum ballistic evolution is possible. The proof fails if T is a step operator for a nondeterministic machine. It is an open question if such a decision procedure exists for nondeterministic machines. This problem does not occur in classical mechanics. Also the definition of quantum Turing machines used here is compared with that used by other authors. copyright 1996 The American Physical Society
DEFF Research Database (Denmark)
Hansen, Annette Skovsted
2014-01-01
Motivation for the activity In academia the most important skill is to ask academically relevant and sound questions. This is not easy and students need to practice asking questions orally and in writing before they write research papers.......Motivation for the activity In academia the most important skill is to ask academically relevant and sound questions. This is not easy and students need to practice asking questions orally and in writing before they write research papers....
Improving Student Question Classification
Heiner, Cecily; Zachary, Joseph L.
2009-01-01
Students in introductory programming classes often articulate their questions and information needs incompletely. Consequently, the automatic classification of student questions to provide automated tutorial responses is a challenging problem. This paper analyzes 411 questions from an introductory Java programming course by reducing the natural…
Quantum relativity theory and quantum space-time
International Nuclear Information System (INIS)
Banai, M.
1984-01-01
A quantum relativity theory formulated in terms of Davis' quantum relativity principle is outlined. The first task in this theory as in classical relativity theory is to model space-time, the arena of natural processes. It is shown that the quantum space-time models of Banai introduced in another paper is formulated in terms of Davis's quantum relativity. The recently proposed classical relativistic quantum theory of Prugovecki and his corresponding classical relativistic quantum model of space-time open the way to introduce, in a consistent way, the quantum space-time model (the quantum substitute of Minkowski space) of Banai proposed in the paper mentioned. The goal of quantum mechanics of quantum relativistic particles living in this model of space-time is to predict the rest mass system properties of classically relativistic (massive) quantum particles (''elementary particles''). The main new aspect of this quantum mechanics is that it provides a true mass eigenvalue problem, and that the excited mass states of quantum relativistic particles can be interpreted as elementary particles. The question of field theory over quantum relativistic model of space-time is also discussed. Finally it is suggested that ''quarks'' should be considered as quantum relativistic particles. (author)
Quantum mechanics for pedestrians
Pade, Jochen
2014-01-01
This book provides an introduction into the fundamentals of non-relativistic quantum mechanics. In Part 1, the essential principles are developed. Applications and extensions of the formalism can be found in Part 2. The book includes not only material that is presented in traditional textbooks on quantum mechanics, but also discusses in detail current issues such as interaction-free quantum measurements, neutrino oscillations, various topics in the field of quantum information as well as fundamental problems and epistemological questions, such as the measurement problem, entanglement, Bell's inequality, decoherence, and the realism debate. A chapter on current interpretations of quantum mechanics concludes the book. To develop quickly and clearly the main principles of quantum mechanics and its mathematical formulation, there is a systematic change between wave mechanics and algebraic representation in the first chapters. The required mathematical tools are introduced step by step. Moreover, the appendix coll...
On the Power of Quantum Memory
Koenig, Robert; Maurer, Ueli; Renner, Renato
2003-01-01
We address the question whether quantum memory is more powerful than classical memory. In particular, we consider a setting where information about a random n-bit string X is stored in r classical or quantum bits, for r
Uncertain for a century: quantum mechanics and the dilemma of interpretation.
Frank, Adam
2015-12-01
Quantum mechanics, the physical theory describing the microworld, is one of science's greatest triumphs. Remarkably, however, after more than 100 years it is still unclear what quantum mechanics means in terms of basic philosophical questions about the nature of reality. While there are many interpretations of the mathematical machinery of quantum physics, there remain no experimental means to distinguish between most of them. In this contribution, I wish to consider the ways in which the enduring lack of an agreed-upon interpretation of quantum physics influences a number of critical philosophical debates about physics and reality. I briefly review two problems affected by quantum interpretations: the meaning of the term universe and the nature of consciousness. © 2015 New York Academy of Sciences.
Dynamical quantum phase transitions in the quantum Potts chain
Karrasch, C.; Schuricht, D.|info:eu-repo/dai/nl/369284690
2017-01-01
We analyze the dynamics of the return amplitude following a sudden quench in the three-state quantum Potts chain. For quenches crossing the quantum critical point from the paramagnetic to the ferromagnetic phase, the corresponding rate function is non-analytic at critical times and behaves linearly
Experimental entanglement of 25 individually accessible atomic quantum interfaces.
Pu, Yunfei; Wu, Yukai; Jiang, Nan; Chang, Wei; Li, Chang; Zhang, Sheng; Duan, Luming
2018-04-01
A quantum interface links the stationary qubits in a quantum memory with flying photonic qubits in optical transmission channels and constitutes a critical element for the future quantum internet. Entanglement of quantum interfaces is an important step for the realization of quantum networks. Through heralded detection of photon interference, we generate multipartite entanglement between 25 (or 9) individually addressable quantum interfaces in a multiplexed atomic quantum memory array and confirm genuine 22-partite (or 9-partite) entanglement. This experimental entanglement of a record-high number of individually addressable quantum interfaces makes an important step toward the realization of quantum networks, long-distance quantum communication, and multipartite quantum information processing.
Krabbe, Erik C. W.; van Laar, Jan Albert
This paper attempts to systematically characterize critical reactions in argumentative discourse, such as objections, critical questions, rebuttals, refutations, counterarguments, and fallacy charges, in order to contribute to the dialogical approach to argumentation. We shall make use of four
Interference and inequality in quantum decision theory
International Nuclear Information System (INIS)
Cheon, Taksu; Takahashi, Taiki
2010-01-01
The quantum decision theory is examined in its simplest form of two-condition two-choice setting. A set of inequalities to be satisfied by any quantum conditional probability describing the decision process is derived. Experimental data indicating the breakdown of classical explanations are critically examined with quantum theory using the full set of quantum phases.
Quantum logic: is it necessarily orthocomplemented
International Nuclear Information System (INIS)
Mielnik, B.
1976-01-01
There exist conservative arguments supporting the necessity of the present day form of quantum theory, which are found in the axiomatics of quantum logic. In this paper the axioms of quantum logic are critically reexamined. The lattice macroscopic measurements, the motivation of the Hilbert space formalism and the convex scheme of quantum mechanics are among the topics discussed. (B.R.H.)
Interference and inequality in quantum decision theory
Energy Technology Data Exchange (ETDEWEB)
Cheon, Taksu, E-mail: taksu.cheon@kochi-tech.ac.j [Laboratory of Physics, Kochi University of Technology, Tosa Yamada, Kochi 782-8502 (Japan); Takahashi, Taiki, E-mail: ttakahashi@lynx.let.hokudai.ac.j [Laboratory of Social Psychology, Department of Behavioral Science, Faculty of Letters, Hokkaido University, N.10, W.7, Kita-ku, Sapporo 060-0810 (Japan)
2010-12-01
The quantum decision theory is examined in its simplest form of two-condition two-choice setting. A set of inequalities to be satisfied by any quantum conditional probability describing the decision process is derived. Experimental data indicating the breakdown of classical explanations are critically examined with quantum theory using the full set of quantum phases.
National Research Council Canada - National Science Library
Agarwal, G. S
2013-01-01
..., quantum metrology, spin squeezing, control of decoherence and many other key topics. Readers are guided through the principles of quantum optics and their uses in a wide variety of areas including quantum information science and quantum mechanics...
DEFF Research Database (Denmark)
Richter, Line
Based on fieldwork in Mali this paper discusses the role of anthropology (and the anthropologist) in a large public health research project on children's health. In the uncertainty and disquiet that comes with the battle to combat and avoid diseases in a setting where poverty and abysmal diseases......, is the ability to move beyond even the best hidden assumptions and question our own questions, thereby enabling us to ask the right questions....
Brownrigg, Jenny
2016-01-01
'Live Your Questions Now' is a case study for Cubitt Education's publication 'Aging in Public: creative practice in ageing and the public realm from across the UK', edited by Daniel Baker and published by Cubitt Gallery, Studios and Education, London in 2016. The publication was linked to Cubitt's programme 'Public Wisdom' (2011-2015). My case study is about 'Live your questions now', a group exhibition I curated in 2011 for Mackintosh Museum, The Glasgow School of Art. 'Live your questions n...
2D quantum gravity from quantum entanglement.
Gliozzi, F
2011-01-21
In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.
Quantum Instantons and Quantum Chaos
Jirari, H.; Kröger, H.; Luo, X. Q.; Moriarty, K. J. M.; Rubin, S. G.
1999-01-01
Based on a closed form expression for the path integral of quantum transition amplitudes, we suggest rigorous definitions of both, quantum instantons and quantum chaos. As an example we compute the quantum instanton of the double well potential.
Quantum Quasi-Paradoxes and Quantum Sorites Paradoxes
Smarandache, F
1997-01-01
There can be generated many paradoxes or quasi-paradoxes that may occur from the combination of quantum and non-quantum worlds in physics. Even the passage from the micro-cosmos to the macro-cosmos, and reciprocally, can generate unsolved questions or counter-intuitive ideas. We define a quasi-paradox as a statement which has a prima facie self-contradictory support or an explicit contradiction, but which is not completely proven as a paradox. We present herein four elementary quantum quasi-paradoxes and their corresponding quantum Sorites paradoxes, which form a class of quantum quasi-paradoxes.
Quantum Quasi-Paradoxes and Quantum Sorites Paradoxes
Directory of Open Access Journals (Sweden)
Smarandache F.
2005-04-01
Full Text Available There can be generated many paradoxes or quasi-paradoxes that may occur from the combination of quantum and non-quantum worlds in physics. Even the passage from the micro-cosmos to the macro-cosmos, and reciprocally, can generate unsolved questions or counter-intuitive ideas. We define a quasi-paradox as a statement which has a prima facie self-contradictory support or an explicit contradiction, but which is not completely proven as a paradox. We present herein four elementary quantum quasi-paradoxes and their corresponding quantum Sorites paradoxes, which form a class of quantum quasi-paradoxes.
Quantum computers: Definition and implementations
International Nuclear Information System (INIS)
Perez-Delgado, Carlos A.; Kok, Pieter
2011-01-01
The DiVincenzo criteria for implementing a quantum computer have been seminal in focusing both experimental and theoretical research in quantum-information processing. These criteria were formulated specifically for the circuit model of quantum computing. However, several new models for quantum computing (paradigms) have been proposed that do not seem to fit the criteria well. Therefore, the question is what are the general criteria for implementing quantum computers. To this end, a formal operational definition of a quantum computer is introduced. It is then shown that, according to this definition, a device is a quantum computer if it obeys the following criteria: Any quantum computer must consist of a quantum memory, with an additional structure that (1) facilitates a controlled quantum evolution of the quantum memory; (2) includes a method for information theoretic cooling of the memory; and (3) provides a readout mechanism for subsets of the quantum memory. The criteria are met when the device is scalable and operates fault tolerantly. We discuss various existing quantum computing paradigms and how they fit within this framework. Finally, we present a decision tree for selecting an avenue toward building a quantum computer. This is intended to help experimentalists determine the most natural paradigm given a particular physical implementation.
International Nuclear Information System (INIS)
Xiang Guo-Yong; Guo Guang-Can
2013-01-01
The statistical error is ineluctable in any measurement. Quantum techniques, especially with the development of quantum information, can help us squeeze the statistical error and enhance the precision of measurement. In a quantum system, there are some quantum parameters, such as the quantum state, quantum operator, and quantum dimension, which have no classical counterparts. So quantum metrology deals with not only the traditional parameters, but also the quantum parameters. Quantum metrology includes two important parts: measuring the physical parameters with a precision beating the classical physics limit and measuring the quantum parameters precisely. In this review, we will introduce how quantum characters (e.g., squeezed state and quantum entanglement) yield a higher precision, what the research areas are scientists most interesting in, and what the development status of quantum metrology and its perspectives are. (topical review - quantum information)
Scaling of quantum Fisher information close to the quantum phase transition in the XY spin chain
Energy Technology Data Exchange (ETDEWEB)
Ye, En-Jia, E-mail: yeenjia@jiangnan.edu.cn [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Hu, Zheng-Da [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Wu, Wei [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)
2016-12-01
The quantum phase transition of an XY spin chain is investigated by employing the quantum Fisher information encoded in the ground state. It is shown that the quantum Fisher information is an effective tool for characterizing the quantum criticality. The quantum Fisher information, its first and second derivatives versus the transverse field display the phenomena of sudden transition, sudden jump and divergence, respectively. Besides, the analysis of finite size scaling for the second derivative of quantum Fisher information is performed.
Quantum memories: emerging applications and recent advances
Heshami, Khabat; England, Duncan G.; Humphreys, Peter C.; Bustard, Philip J.; Acosta, Victor M.; Nunn, Joshua; Sussman, Benjamin J.
2016-01-01
Quantum light–matter interfaces are at the heart of photonic quantum technologies. Quantum memories for photons, where non-classical states of photons are mapped onto stationary matter states and preserved for subsequent retrieval, are technical realizations enabled by exquisite control over interactions between light and matter. The ability of quantum memories to synchronize probabilistic events makes them a key component in quantum repeaters and quantum computation based on linear optics. This critical feature has motivated many groups to dedicate theoretical and experimental research to develop quantum memory devices. In recent years, exciting new applications, and more advanced developments of quantum memories, have proliferated. In this review, we outline some of the emerging applications of quantum memories in optical signal processing, quantum computation and non-linear optics. We review recent experimental and theoretical developments, and their impacts on more advanced photonic quantum technologies based on quantum memories. PMID:27695198
Quantum Distinction: Quantum Distinctiones!
Zeps, Dainis
2009-01-01
10 pages; How many distinctions, in Latin, quantum distinctiones. We suggest approach of anthropic principle based on anthropic reference system which should be applied equally both in theoretical physics and in mathematics. We come to principle that within reference system of life subject of mathematics (that of thinking) should be equated with subject of physics (that of nature). For this reason we enter notions of series of distinctions, quantum distinction, and argue that quantum distinct...
Legal Philosophy - Five Questions
DEFF Research Database (Denmark)
This collection gathers together a host of the most eminent contemporary legal philosophers, who writes about their take on legal philosophy, its fundamental questions and potential.......This collection gathers together a host of the most eminent contemporary legal philosophers, who writes about their take on legal philosophy, its fundamental questions and potential....
DEFF Research Database (Denmark)
Epistemology: 5 Questions is a collection of short interviews based on 5 questions presented to some of the most influential and prominent scholars in epistemology. We hear their views on epistemology with particular emphasis on the intersection between mainstream and formal approaches to the field...
Mayato, R; Egusquiza, I
2002-01-01
The treatment of time in quantum mechanics is still an important and challenging open question in the foundation of the theory. This book describes the problems, and the attempts and achievements in defining, formalizing and measuring different time quantities in quantum theory, such as the parametric (clock) time, tunneling times, decay times, dwell times, delay times, arrival times or jump times. This multiauthored book, written as an introductory guide for the non-initiated as well as a useful source of information for the expert, covers many of the open questions. A brief historical overview is to be found in the introduction. It is followed by 12 chapters devoted to conceptual and theoretical investigations as well as experimental issues in quantum-mechanical time measurements. This unique monograph should attract physicists as well as philosophers of science working in the foundations of quantum physics.
International Nuclear Information System (INIS)
Chomaz, Ph.
2000-01-01
This document gathers the slides and their commentaries that have been presented at the conference 'physics and fundamental questions' by P. Chomaz. The author reviews the different quantum aspects of nuclei: tunnel effect, symmetries, magic numbers, wave functions, size, shapes and deformations. The author shows that nuclei are quantum objects of great complexity, their structures are not yet well understood and the study of exotic nuclei will continue bringing valuable information
Decoherence and quantum measurements
Namiki, Mikio; Pascazio, Saverio
1997-01-01
The quantum measurement problem is one of the most fascinating and challenging topics in physics both theoretically and experimentally. It involves deep questions and the use of very sophisticated and elegant techniques. After analyzing the fundamental principles of quantum mechanics and of the Copenhagen interpretation, this book reviews the most important approaches to the measurement problem and rigorously reformulates the "collapse of the wave function" by measurement, as a dephasing process quantitatively characterized by an order parameter (called the decoherence parameter), according to
Topological phases: Wormholes in quantum matter
Schoutens, K.
2009-01-01
Proliferation of so-called anyonic defects in a topological phase of quantum matter leads to a critical state that can be visualized as a 'quantum foam', with topology-changing fluctuations on all length scales.
Dolev, S; Kolenda, N
2005-01-01
For more than a century, quantum mechanics has served as a very powerful theory that has expanded physics and technology far beyond their classical limits, yet it has also produced some of the most difficult paradoxes known to the human mind. This book represents the combined efforts of sixteen of today's most eminent theoretical physicists to lay out future directions for quantum physics. The authors include Yakir Aharonov, Anton Zeilinger; the Nobel laureates Anthony Leggett and Geradus 't Hooft; Basil Hiley, Lee Smolin and Henry Stapp. Following a foreword by Roger Penrose, the individual chapters address questions such as quantum non-locality, the measurement problem, quantum insights into relativity, cosmology and thermodynamics, and the possible bearing of quantum phenomena on biology and consciousness.
Quantum Glass of Interacting Bosons with Off-Diagonal Disorder
Piekarska, A. M.; Kopeć, T. K.
2018-04-01
We study disordered interacting bosons described by the Bose-Hubbard model with Gaussian-distributed random tunneling amplitudes. It is shown that the off-diagonal disorder induces a spin-glass-like ground state, characterized by randomly frozen quantum-mechanical U(1) phases of bosons. To access criticality, we employ the "n -replica trick," as in the spin-glass theory, and the Trotter-Suzuki method for decomposition of the statistical density operator, along with numerical calculations. The interplay between disorder, quantum, and thermal fluctuations leads to phase diagrams exhibiting a glassy state of bosons, which are studied as a function of model parameters. The considered system may be relevant for quantum simulators of optical-lattice bosons, where the randomness can be introduced in a controlled way. The latter is supported by a proposition of experimental realization of the system in question.
Aerts, Sven; Ronde, Christian de; Probing the Meaning of Quantum Mechanics : Physical, Philosophical, and Logical Perspectives
2014-01-01
This book provides a new original perspective on one of the most fascinating and important open questions in science: What is quantum mechanics talking about? Quantum theory is perhaps our best confirmed physical theory. However, in spite of its great empirical effectiveness and the subsequent technological developments that it gave rise to in the 20th century, from the interpretation of the periodic table of elements to CD players, holograms and quantum state teleportation, it stands even today without a universally accepted interpretation. The novelty of the book comes from the multiple view
Decoherence in adiabatic quantum computation
Albash, Tameem; Lidar, Daniel A.
2015-06-01
Recent experiments with increasingly larger numbers of qubits have sparked renewed interest in adiabatic quantum computation, and in particular quantum annealing. A central question that is repeatedly asked is whether quantum features of the evolution can survive over the long time scales used for quantum annealing relative to standard measures of the decoherence time. We reconsider the role of decoherence in adiabatic quantum computation and quantum annealing using the adiabatic quantum master-equation formalism. We restrict ourselves to the weak-coupling and singular-coupling limits, which correspond to decoherence in the energy eigenbasis and in the computational basis, respectively. We demonstrate that decoherence in the instantaneous energy eigenbasis does not necessarily detrimentally affect adiabatic quantum computation, and in particular that a short single-qubit T2 time need not imply adverse consequences for the success of the quantum adiabatic algorithm. We further demonstrate that boundary cancellation methods, designed to improve the fidelity of adiabatic quantum computing in the closed-system setting, remain beneficial in the open-system setting. To address the high computational cost of master-equation simulations, we also demonstrate that a quantum Monte Carlo algorithm that explicitly accounts for a thermal bosonic bath can be used to interpolate between classical and quantum annealing. Our study highlights and clarifies the significantly different role played by decoherence in the adiabatic and circuit models of quantum computing.
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Rabies: Questions and Answers Information about the disease and vaccines What causes rabies? Rabies is caused by a virus. The virus invades ... nervous system and disrupts its functioning. How does rabies spread? The rabies virus is transmitted in the ...
Repetitive Questioning Exasperates Caregivers
Directory of Open Access Journals (Sweden)
R. C. Hamdy MD
2018-01-01
Full Text Available Repetitive questioning is due to an impaired episodic memory and is a frequent, often presenting, problem in patients with Alzheimer’s disease (amnestic type. It is due to the patients’ difficulties learning new information, retaining it, and recalling it, and is often aggravated by a poor attention span and easy distractibility. A number of factors may trigger and maintain repetitive questioning. Caregivers should try to identify and address these triggers. In the case discussion presented, it is due to the patient’s concerns about her and her family’s safety triggered by watching a particularly violent movie aired on TV. What went wrong in the patient/caregiver interaction and how it could have been avoided or averted are explored. Also reviewed are the impact of repetitive questioning, the challenges it raises for caregivers, and some effective intervention strategies that may be useful to diffuse the angst that caregivers experience with repetitive questioning.
International Nuclear Information System (INIS)
1993-02-01
This document, prepared in February 1993, addresses the most common questions asked by APS Collaborative Access Teams (CATs). The answers represent the best judgment on the part of the APS at this time. In some cases, details are provided in separate documents to be supplied by the APS. Some of the answers are brief because details are not yet available. The questions are separated into five categories representing different aspects of CAT interactions with the APS: (1) Memorandum of Understanding (MOU), (2) CAT Beamline Review and Construction, (3) CAT Beamline Safety, (4) CAT Beamline Operations, and (5) Miscellaneous. The APS plans to generate similar documents as needed to both address new questions and clarify answers to present questions
Directory of Open Access Journals (Sweden)
R. C. Hamdy MD
2018-02-01
Full Text Available Repetitive questioning is a major problem for caregivers, particularly taxing if they are unable to recognize and understand the reasons why their loved one keeps asking the same question over and over again. Caregivers may be tempted to believe that the patient does not even try to remember the answer given or is just getting obnoxious. This is incorrect. Repetitive questioning is due to the underlying disease: The patient’s short term memory is impaired and he is unable to register, encode, retain and retrieve the answer. If he is concerned about a particular topic, he will keep asking the same question over and over again. To the patient each time she asks the question, it is as if she asked it for the first time. Just answering repetitive questioning by providing repeatedly the same answer is not sufficient. Caregivers should try to identify the underlying cause for this repetitive questioning. In an earlier case study, the patient was concerned about her and her family’s safety and kept asking whether the doors are locked. In this present case study, the patient does not know how to handle the awkward situation he finds himself in. He just does not know what to do. He is not able to adjust to the new unexpected situation. So he repeatedly wants to reassure himself that he is not intruding by asking the same question over and over again. We discuss how the patient’s son-in-law could have avoided this situation and averted the catastrophic ending.
Quantum walks, quantum gates, and quantum computers
International Nuclear Information System (INIS)
Hines, Andrew P.; Stamp, P. C. E.
2007-01-01
The physics of quantum walks on graphs is formulated in Hamiltonian language, both for simple quantum walks and for composite walks, where extra discrete degrees of freedom live at each node of the graph. It is shown how to map between quantum walk Hamiltonians and Hamiltonians for qubit systems and quantum circuits; this is done for both single-excitation and multiexcitation encodings. Specific examples of spin chains, as well as static and dynamic systems of qubits, are mapped to quantum walks, and walks on hyperlattices and hypercubes are mapped to various gate systems. We also show how to map a quantum circuit performing the quantum Fourier transform, the key element of Shor's algorithm, to a quantum walk system doing the same. The results herein are an essential preliminary to a Hamiltonian formulation of quantum walks in which coupling to a dynamic quantum environment is included
Nonequilibrium quantum mechanics: A "hot quantum soup" of paramagnons
Scammell, H. D.; Sushkov, O. P.
2017-01-01
Motivated by recent measurements of the lifetime (decay width) of paramagnons in quantum antiferromagnet TlCuCl3, we investigate paramagnon decay in a heat bath and formulate an appropriate quantum theory. Our formulation can be split into two regimes: (i) a nonperturbative, "hot quantum soup" regime where the paramagnon width is comparable to its energy; (ii) a usual perturbative regime where the paramagnon width is significantly lower than its energy. Close to the Neel temperature, the paramagnon width becomes comparable to its energy and falls into the hot quantum soup regime. To describe this regime, we develop a new finite frequency, finite temperature technique for a nonlinear quantum field theory; the "golden rule of quantum kinetics." The formulation is generic and applicable to any three-dimensional quantum antiferromagnet in the vicinity of a quantum critical point. Specifically, we apply our results to TlCuCl3 and find agreement with experimental data. Additionally, we show that logarithmic running of the coupling constant in the upper critical dimension changes the commonly accepted picture of the quantum disordered and quantum critical regimes.
Bera, Anindita; Mishra, Utkarsh; Singha Roy, Sudipto; Biswas, Anindya; Sen(De), Aditi; Sen, Ujjwal
2018-06-01
Benford's law is an empirical edict stating that the lower digits appear more often than higher ones as the first few significant digits in statistics of natural phenomena and mathematical tables. A marked proportion of such analyses is restricted to the first significant digit. We employ violation of Benford's law, up to the first four significant digits, for investigating magnetization and correlation data of paradigmatic quantum many-body systems to detect cooperative phenomena, focusing on the finite-size scaling exponents thereof. We find that for the transverse field quantum XY model, behavior of the very first significant digit of an observable, at an arbitrary point of the parameter space, is enough to capture the quantum phase transition in the model with a relatively high scaling exponent. A higher number of significant digits do not provide an appreciable further advantage, in particular, in terms of an increase in scaling exponents. Since the first significant digit of a physical quantity is relatively simple to obtain in experiments, the results have potential implications for laboratory observations in noisy environments.
New developments in quantum mechanics
Aharonov, Yakir
1994-01-01
After a general introduction, some new developments on the more subtle predictions of Quantum Mechanics and their interpretation will be discussed. These include non-local topological effects, physics of pre- and post-selected quantum systems, and the question of observability of the Schrödinger wave itself.
Energy Technology Data Exchange (ETDEWEB)
Stapp, Henry
2011-11-10
Robert Griffiths has recently addressed, within the framework of a ‘consistent quantum theory’ (CQT) that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues, on the basis of his examination of certain arguments that claim to demonstrate the existence of such nonlocal influences, that such influences do not exist. However, his examination was restricted mainly to hidden-variable-based arguments that include in their premises some essentially classical-physics-type assumptions that are fundamentally incompatible with the precepts of quantum physics. One cannot logically prove properties of a system by attributing to the system properties alien to that system. Hence Griffiths’ rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his ‘consistent quantum theory’ shows that the cited proof is valid within that restrictive framework. This necessary existence, within the ‘consistent’ framework, of long range essentially instantaneous influences refutes the claim made by Griffiths that his ‘consistent’ framework is superior to the orthodox quantum theory of von Neumann because it does not entail instantaneous influences. An added section responds to Griffiths’ reply, which cites a litany of ambiguities that seem to restrict, devastatingly, the scope of his CQT formalism, apparently to buttress his claim that my use of that formalism to validate the nonlocality theorem is flawed. But the
Microscopic approaches to quantum nonequilibriumthermodynamics and information
2018-02-09
perspective on quantum thermalization for Science [8]. Wrote a joint experiment- theory paper on studying connections between quantum and classical chaos in...on the random matrix theory (eigenstate thermalization) and macroscopic phenomena (both equilibrium and non-equilibrium). Understanding thermodynamics...information. Specific questions to be addressed: connections of microscopic description of quantum chaotic systems based on the random matrix theory
Chang, Mou-Hsiung
2015-01-01
The classical probability theory initiated by Kolmogorov and its quantum counterpart, pioneered by von Neumann, were created at about the same time in the 1930s, but development of the quantum theory has trailed far behind. Although highly appealing, the quantum theory has a steep learning curve, requiring tools from both probability and analysis and a facility for combining the two viewpoints. This book is a systematic, self-contained account of the core of quantum probability and quantum stochastic processes for graduate students and researchers. The only assumed background is knowledge of the basic theory of Hilbert spaces, bounded linear operators, and classical Markov processes. From there, the book introduces additional tools from analysis, and then builds the quantum probability framework needed to support applications to quantum control and quantum information and communication. These include quantum noise, quantum stochastic calculus, stochastic quantum differential equations, quantum Markov semigrou...
Quantum tasks in Minkowski space
International Nuclear Information System (INIS)
Kent, Adrian
2012-01-01
The fundamental properties of quantum information and its applications to computing and cryptography have been greatly illuminated by considering information-theoretic tasks that are provably possible or impossible within non-relativistic quantum mechanics. I describe here a general framework for defining tasks within (special) relativistic quantum theory and illustrate it with examples from relativistic quantum cryptography and relativistic distributed quantum computation. The framework gives a unified description of all tasks previously considered and also defines a large class of new questions about the properties of quantum information in relation to Minkowski causality. It offers a way of exploring interesting new fundamental tasks and applications, and also highlights the scope for a more systematic understanding of the fundamental information-theoretic properties of relativistic quantum theory. (paper)
Quantum Effects in Biological Systems
2016-01-01
Since the last decade the study of quantum mechanical phenomena in biological systems has become a vibrant field of research. Initially sparked by evidence of quantum effects in energy transport that is instrumental for photosynthesis, quantum biology asks the question of how methods and models from quantum theory can help us to understand fundamental mechanisms in living organisms. This approach entails a paradigm change challenging the related disciplines: The successful framework of quantum theory is taken out of its low-temperature, microscopic regimes and applied to hot and dense macroscopic environments, thereby extending the toolbox of biology and biochemistry at the same time. The Quantum Effects in Biological Systems conference is a platform for researchers from biology, chemistry and physics to present and discuss the latest developments in the field of quantum biology. After meetings in Lisbon (2009), Harvard (2010), Ulm (2011), Berkeley (2012), Vienna (2013), Singapore (2014) and Florence (2015),...
The Question Concerning Thinking
DEFF Research Database (Denmark)
Riis, Søren
2008-01-01
Martin Heidegger's thought-provoking essay "The Question Concerning Technology" (1977a) placed technology at the heart of philosophy. Heidegger tried to show that the essence of technology provokes humans to think about the world in a very dangerous way. Yet if we follow Heidegger's analysis...... of technology, what role does that ascribe to philosophy? To be able to understand the programmatic scope of Heidegger's question ‘concerning' technology, we need to see it as inseparable from his famous thesis about the end of philosophy (1977c) and what he considers to be the ideal kind of thinking. However......, by doing so, we will in the end realize two important things. First, that Heidegger's declaration of the end of philosophy in fact also means the end of anything we can meaningfully call thinking. Second, that Heidegger's own thinking is completely different from his own ideal of thinking. Our question...
Generating ethnographic research questions
DEFF Research Database (Denmark)
Friberg, Torbjörn
2015-01-01
? By drawing on the conceptual history of anthropology, the aim of this article is to generate ethnographic-oriented research questions concerned with higher education. The first part of the article provides an ethnographic background, while the second part focuses on Paul Willis's reasoning on ethnographic......As part of recent complex transformations, it seems that higher educational organisations are being forced to reorganise, standardise and streamline in order to survive in the new political and economic context. How are ethnographers in general going to approach these contemporary phenomena...... imagination, as a prerequisite for generating alternative research questions. The third part makes explicit anthropologist Maurice Godelier's theoretical imagination, carving out some specific theoretical parts which may be used in the generating process. The conclusion then suggests a number of questions...
Scarani, Valerio
1998-01-01
The aim of this thesis was to explain what quantum computing is. The information for the thesis was gathered from books, scientific publications, and news articles. The analysis of the information revealed that quantum computing can be broken down to three areas: theories behind quantum computing explaining the structure of a quantum computer, known quantum algorithms, and the actual physical realizations of a quantum computer. The thesis reveals that moving from classical memor...
Wu, Lian-Ao; Lidar, Daniel A.
2005-01-01
When quantum communication networks proliferate they will likely be subject to a new type of attack: by hackers, virus makers, and other malicious intruders. Here we introduce the concept of "quantum malware" to describe such human-made intrusions. We offer a simple solution for storage of quantum information in a manner which protects quantum networks from quantum malware. This solution involves swapping the quantum information at random times between the network and isolated, distributed an...
Foundations of Quantum Mechanics and Quantum Computation
Aspect, Alain; Leggett, Anthony; Preskill, John; Durt, Thomas; Pironio, Stefano
2013-03-01
I ask the question: What can we infer about the nature and structure of the physical world (a) from experiments already done to test the predictions of quantum mechanics (b) from the assumption that all future experiments will agree with those predictions? I discuss existing and projected experiments related to the two classic paradoxes of quantum mechanics, named respectively for EPR and Schrödinger's Cat, and show in particular that one natural conclusion from both types of experiment implies the abandonment of the concept of macroscopic counterfactual definiteness.
Quantum measurement and algebraic quantum field theories
International Nuclear Information System (INIS)
DeFacio, B.
1976-01-01
It is shown that the physics and semantics of quantum measurement provide a natural interpretation of the weak neighborhoods of the states on observable algebras without invoking any ideas of ''a reading error'' or ''a measured range.'' Then the state preparation process in quantum measurement theory is shown to give the normal (or locally normal) states on the observable algebra. Some remarks are made concerning the physical implications of normal state for systems with an infinite number of degrees of freedom, including questions on open and closed algebraic theories
Fundamental limits to single-photon detection determined by quantum coherence and backaction
Young, Steve M.; Sarovar, Mohan; Léonard, François
2018-03-01
Single-photon detectors have achieved impressive performance and have led to a number of new scientific discoveries and technological applications. Existing models of photodetectors are semiclassical in that the field-matter interaction is treated perturbatively and time-separated from physical processes in the absorbing matter. An open question is whether a fully quantum detector, whereby the optical field, the optical absorption, and the amplification are considered as one quantum system, could have improved performance. Here we develop a theoretical model of such photodetectors and employ simulations to reveal the critical role played by quantum coherence and amplification backaction in dictating the performance. We show that coherence and backaction lead to trade-offs between detector metrics and also determine optimal system designs through control of the quantum-classical interface. Importantly, we establish the design parameters that result in a ideal photodetector with 100% efficiency, no dark counts, and minimal jitter, thus paving the route for next-generation detectors.
Turbocharging Quantum Tomography
Energy Technology Data Exchange (ETDEWEB)
Blume-Kohout, Robin J. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Gamble, John King [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Nielsen, Erik [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Maunz, Peter Lukas Wilhelm [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Scholten, Travis L. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Rudinger, Kenneth Michael [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2015-01-01
Quantum tomography is used to characterize quantum operations implemented in quantum information processing (QIP) hardware. Traditionally, state tomography has been used to characterize the quantum state prepared in an initialization procedure, while quantum process tomography is used to characterize dynamical operations on a QIP system. As such, tomography is critical to the development of QIP hardware (since it is necessary both for debugging and validating as-built devices, and its results are used to influence the next generation of devices). But tomography suffers from several critical drawbacks. In this report, we present new research that resolves several of these flaws. We describe a new form of tomography called gate set tomography (GST), which unifies state and process tomography, avoids prior methods critical reliance on precalibrated operations that are not generally available, and can achieve unprecedented accuracies. We report on theory and experimental development of adaptive tomography protocols that achieve far higher fidelity in state reconstruction than non-adaptive methods. Finally, we present a new theoretical and experimental analysis of process tomography on multispin systems, and demonstrate how to more effectively detect and characterize quantum noise using carefully tailored ensembles of input states.
Quantumness beyond quantum mechanics
International Nuclear Information System (INIS)
Sanz, Ángel S
2012-01-01
Bohmian mechanics allows us to understand quantum systems in the light of other quantum traits than the well-known ones (coherence, diffraction, interference, tunnelling, discreteness, entanglement, etc.). Here the discussion focusses precisely on two of these interesting aspects, which arise when quantum mechanics is thought within this theoretical framework: the non-crossing property, which allows for distinguishability without erasing interference patterns, and the possibility to define quantum probability tubes, along which the probability remains constant all the way. Furthermore, taking into account this hydrodynamic-like description as a link, it is also shown how this knowledge (concepts and ideas) can be straightforwardly transferred to other fields of physics (for example, the transmission of light along waveguides).
International Nuclear Information System (INIS)
Ishikawa, Fumitaro; Luna, Esperanza; Trampert, Achim; Ploog, Klaus H.
2006-01-01
The authors discuss the effect of substrate temperature and As beam equivalent pressure (BEP) on the molecular beam epitaxial growth of (Ga,In)(N,As) multiple quantum wells (MQWs). Transmission electron microscopy studies reveal that a low substrate temperature essentially prevents composition modulations. Secondary ion mass spectrometry results indicate that a low As BEP reduces the incorporation competition of group V elements. The low substrate temperature and low As BEP growth condition leads to (Ga,In)(N,As) MQWs containing more than 4% N preserving good structural and optical properties, and hence demonstrating 1.55 μm photoluminescence emission at room temperature
Directory of Open Access Journals (Sweden)
Vukotić Veselin
2011-01-01
Full Text Available The globalization is breaking-down the idea of national state, which was the base for the development of economic theory which is dominant today. Global economic crisis puts emphasis on limited possibilities of national governments in solving economic problems and general problems of society. Does it also mean that globalization and global economic crisis points out the need to think about new economic theory and new understanding of economics? In this paper I will argue that globalization reveals the need to change dominant economic paradigm - from traditional economic theory (mainstream with macroeconomic stability as the goal of economic policy, to the “quantum economics“, which is based on “economic quantum” and immanent to the increase of wealth (material and non-material of every individual in society and promoting set of values immanent to the wealth increase as the goal of economic policy. Practically the question is how we can use global market for our development!
Realism and Antirealism in Informational Foundations of Quantum Theory
Directory of Open Access Journals (Sweden)
Tina Bilban
2014-08-01
Full Text Available Zeilinger-Brukner's informational foundations of quantum theory, a theory based on Zeilinger's foundational principle for quantum mechanics that an elementary system carried one bit of information, explains seemingly unintuitive quantum behavior with simple theoretical framework. It is based on the notion that distinction between reality and information cannot be made, therefore they are the same. As the critics of informational foundations of quantum theory show, this antirealistic move captures the theory in tautology, where information only refers to itself, while the relationships outside the information with the help of which the nature of information would be defined are lost and the questions "Whose information? Information about what?" cannot be answered. The critic's solution is a return to realism, where the observer's effects on the information are neglected. We show that radical antirealism of informational foundations of quantum theory is not necessary and that the return to realism is not the only way forward. A comprehensive approach that exceeds mere realism and antirealism is also possible: we can consider both sources of the constraints on the information, those coming from the observer and those coming from the observed system/nature/reality. The information is always the observer's information about the observed. Such a comprehensive philosophical approach can still support the theoretical framework of informational foundations of quantum theory: If we take that one bit is the smallest amount of information in the form of which the observed reality can be grasped by the observer, we can say that an elementary system (grasped and defined as such by the observer correlates to one bit of information. Our approach thus explains all the features of the quantum behavior explained by informational foundations of quantum theory: the wave function and its collapse, entanglement, complementarity and quantum randomness. However, it does
Nonlinear Dynamics In Quantum Physics -- Quantum Chaos and Quantum Instantons
Kröger, H.
2003-01-01
We discuss the recently proposed quantum action - its interpretation, its motivation, its mathematical properties and its use in physics: quantum mechanical tunneling, quantum instantons and quantum chaos.
DEFF Research Database (Denmark)
Kenneth, Petersson; Olsson, Ulf; Krejsler, John B.
2015-01-01
The focus of this chapter is the re-installation of the social question as a historical practice. The purpose is to investigate how historic figures return and are applied in contemporary political discourses, more precisely in the context of education, education policy and teacher education...
Questioning Danish Cartoon Images
DEFF Research Database (Denmark)
Bojsen, Heidi
2007-01-01
Danes today when it is considered demeaning and racist in most other countries. The conclusion does emphatically not plead in favour of law enforced limitations of the freedom of expression, but does question the prevalent "freedom of ignorance" concerning black identities which means...
Frequently Asked Questions: The Higgs!
CERN Bulletin
2012-01-01
Why have we tried so hard to find the Higgs particle? How does the Higgs mechanism work? What is the difference in physics between strong evidence and a discovery? Why do physicists speak in terms of "sigmas"? Find out here! Why have we tried so hard to find the Higgs particle? Because it could be the answer to the question: how does Nature decide whether or not to assign mass to particles? All the fundamental particles making up matter – the electron, the quarks, etc. – have masses. Moreover, quantum physics requires that forces are also carried by particles. The W and Z particles that carry the weak force responsible for radioactivity must also have masses, whereas the photon, the carrier of the electromagnetic force, has no mass at all. This is the root of the “Higgs problem”: how to give masses to the fundamental particles and break the symmetry between the massive W and Z and the massless photon? Just assigning masses by hand...
PREFACE Quantum Groups, Quantum Foundations and Quantum Information: a Festschrift for Tony Sudbery
Weigert, Stefan
2010-11-01
and international reputation; for instance he joined Roger Penrose in a discussion on 'The Physics of Reality' in Melvyn Bragg's radio series 'In our time'. He was much in demand for contributions to the 'News and Views' section in Nature and has written numerous book reviews in scientific and semi-popular journals as well as newspaper commentaries on important scientific developments. Quantum foundations and quantum information have remained Tony's main professional preoccupations. As a contribution to the conceptual problems surrounding quantum measurement, he undertook a detailed analysis of the observation of decay, introducing the crucial distinction between continuous measurement and continual observation. A red thread through his work in quantum mechanics has been the critical scrutiny of different interpretations of quantum mechanics and the question of their experimental testability. As a result he has become an eloquent proponent of a version of what is commonly known as the 'many-worlds' interpretation in his most recent paper (arXiv:1009.3914), Tony explains why he considers the name 'Everett-Wheeler interpretation' as most appropriate and 'many worlds' unnecessary. Tony started directing his research effort to quantum information theory in the late 1990s. He quickly established himself in the quantum information community, putting York on the map in this field. He was among the first people to investigate entanglement properties of multipartite states, particularly the 3-qubit states. While studying the pure 4-qubit states he mysteriously came up with what could rightly be called the 'Sudbery state': equation (where ω is a primitive root of 1), which is the most entangled 4-qubit state in natural measures of entanglement. He continues to work in quantum information theory, particularly on quantum entanglement. Not least there is also Tony the philosopher who wrote articles with such intriguing titles as 'The necessity of not doing otherwise' or 'Why am I
Singh, R. R. P.; Young, A. P.
2017-08-01
We study the ±J transverse-field Ising spin-glass model at zero temperature on d -dimensional hypercubic lattices and in the Sherrington-Kirkpatrick (SK) model, by series expansions around the strong-field limit. In the SK model and in high dimensions our calculated critical properties are in excellent agreement with the exact mean-field results, surprisingly even down to dimension d =6 , which is below the upper critical dimension of d =8 . In contrast, at lower dimensions we find a rich singular behavior consisting of critical and Griffiths-McCoy singularities. The divergence of the equal-time structure factor allows us to locate the critical coupling where the correlation length diverges, implying the onset of a thermodynamic phase transition. We find that the spin-glass susceptibility as well as various power moments of the local susceptibility become singular in the paramagnetic phase before the critical point. Griffiths-McCoy singularities are very strong in two dimensions but decrease rapidly as the dimension increases. We present evidence that high enough powers of the local susceptibility may become singular at the pure-system critical point.
International Nuclear Information System (INIS)
Caceres, Manuel O; Nizama, Marco
2010-01-01
We introduce the quantum Levy walk to study transport and decoherence in a quantum random model. We have derived from second-order perturbation theory the quantum master equation for a Levy-like particle that moves along a lattice through scale-free hopping while interacting with a thermal bath of oscillators. The general evolution of the quantum Levy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation and the probability to be in a lattice site, all of them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general, our approach allows us to study analytically quantum fluctuations and decoherence in a long-range hopping model.
Towards Quantum Experiments with Human Eye Detectors Based on Cloning via Stimulated Emission ?
De Martini, Francesco
2010-05-01
In a recent theoretical paper published in Physical Review Letters, Sekatsky, Brunner, Branciard, Gisin, Simon report an extended investigation on some properties of the human eye that affect its behavior as a quantum detector. We believe that the content of this work, albeit appealing at fist sight, is highly questionable simply because the human eye cannot be adopted as a sensing device within any quantum measurement apparatus. Furthermore, the criticism raised by these Authors against a real experiment on Micro—Macro entanglement recently published in Physical Review Letters (100, 253601, 2008) is found misleading and misses its target.
Quantum phase transitions in semilocal quantum liquids
Iqbal, Nabil; Liu, Hong; Mezei, Márk
2015-01-01
We consider several types of quantum critical phenomena from finite-density gauge-gravity duality which to different degrees lie outside the Landau-Ginsburg-Wilson paradigm. These include: (i) a "bifurcating" critical point, for which the order parameter remains gapped at the critical point, and thus is not driven by soft order parameter fluctuations. Rather it appears to be driven by "confinement" which arises when two fixed points annihilate and lose conformality. On the condensed side, there is an infinite tower of condensed states and the nonlinear response of the tower exhibits an infinite spiral structure; (ii) a "hybridized" critical point which can be described by a standard Landau-Ginsburg sector of order parameter fluctuations hybridized with a strongly coupled sector; (iii) a "marginal" critical point which is obtained by tuning the above two critical points to occur together and whose bosonic fluctuation spectrum coincides with that postulated to underly the "Marginal Fermi Liquid" description of the optimally doped cuprates.
Bojowald, Martin
2008-06-06
When quantum gravity is used to discuss the big bang singularity, the most important, though rarely addressed, question is what role genuine quantum degrees of freedom play. Here, complete effective equations are derived for isotropic models with an interacting scalar to all orders in the expansions involved. The resulting coupling terms show that quantum fluctuations do not affect the bounce much. Quantum correlations, however, do have an important role and could even eliminate the bounce. How quantum gravity regularizes the big bang depends crucially on properties of the quantum state.
From Monte Carlo to Quantum Computation
Heinrich, Stefan
2001-01-01
Quantum computing was so far mainly concerned with discrete problems. Recently, E. Novak and the author studied quantum algorithms for high dimensional integration and dealt with the question, which advantages quantum computing can bring over classical deterministic or randomized methods for this type of problem. In this paper we give a short introduction to the basic ideas of quantum computing and survey recent results on high dimensional integration. We discuss connections to the Monte Carl...
Fundamental principles of quantum theory
International Nuclear Information System (INIS)
Bugajski, S.
1980-01-01
After introducing general versions of three fundamental quantum postulates - the superposition principle, the uncertainty principle and the complementarity principle - the question of whether the three principles are sufficiently strong to restrict the general Mackey description of quantum systems to the standard Hilbert-space quantum theory is discussed. An example which shows that the answer must be negative is constructed. An abstract version of the projection postulate is introduced and it is demonstrated that it could serve as the missing physical link between the general Mackey description and the standard quantum theory. (author)
Bricmont, Jean
2017-01-01
Permeated by the author's delightful humor, this little book explains, with nearly no mathematics, the main conceptual issues associated with quantum mechanics: The issue of determinism. Does quantum mechanics signify the end of a deterministic word-view? The role of the human subject or of the "observer" in science. Since Copernicus, science has increasingly tended to dethrone Man from his formerly held special position in the Universe. But quantum mechanics, with its emphasis on the notion of observation, may once more have given a central role to the human subject. The issue of locality. Does quantum mechanics imply that instantaneous actions at a distance exist in Nature? In these pages the author offers a variety of views and answers - bad as well as good - to these questions. The reader will be both entertained and enlightened by Jean Bricmont's clear and incisive arguments.
Engelbrecht, Jüri
2015-01-01
This book addresses the modelling of mechanical waves by asking the right questions about them and trying to find suitable answers. The questions follow the analytical sequence from elementary understandings to complicated cases, following a step-by-step path towards increased knowledge. The focus is on waves in elastic solids, although some examples also concern non-conservative cases for the sake of completeness. Special attention is paid to the understanding of the influence of microstructure, nonlinearity and internal variables in continua. With the help of many mathematical models for describing waves, physical phenomena concerning wave dispersion, nonlinear effects, emergence of solitary waves, scales and hierarchies of waves as well as the governing physical parameters are analysed. Also, the energy balance in waves and non-conservative models with energy influx are discussed. Finally, all answers are interwoven into the canvas of complexity.
International Nuclear Information System (INIS)
Sachdev, S.
1999-01-01
Phase transitions are normally associated with changes of temperature but a new type of transition - caused by quantum fluctuations near absolute zero - is possible, and can tell us more about the properties of a wide range of systems in condensed-matter physics. Nature abounds with phase transitions. The boiling and freezing of water are everyday examples of phase transitions, as are more exotic processes such as superconductivity and superfluidity. The universe itself is thought to have passed through several phase transitions as the high-temperature plasma formed by the big bang cooled to form the world as we know it today. Phase transitions are traditionally classified as first or second order. In first-order transitions the two phases co-exist at the transition temperature - e.g. ice and water at 0 deg., or water and steam at 100 deg. In second-order transitions the two phases do not co-exist. In the last decade, attention has focused on phase transitions that are qualitatively different from the examples noted above: these are quantum phase transitions and they occur only at the absolute zero of temperature. The transition takes place at the ''quantum critical'' value of some other parameter such as pressure, composition or magnetic field strength. A quantum phase transition takes place when co-operative ordering of the system disappears, but this loss of order is driven solely by the quantum fluctuations demanded by Heisenberg's uncertainty principle. The physical properties of these quantum fluctuations are quite distinct from those of the thermal fluctuations responsible for traditional, finite-temperature phase transitions. In particular, the quantum system is described by a complex-valued wavefunction, and the dynamics of its phase near the quantum critical point requires novel theories that have no analogue in the traditional framework of phase transitions. In this article the author describes the history of quantum phase transitions. (UK)
Fromm, Jochen
2005-01-01
Self-Organization is of growing importance for large distributed computing systems. In these systems, a central control and manual management is exceedingly difficult or even impossible. Emergence is widely recognized as the core principle behind self-organization. Therefore the idea to use both principles to control and organize large-scale distributed systems is very attractive and not so far off. Yet there are many open questions about emergence and self-organization, ranging from a clear ...
501 reading comprehension questions
2014-01-01
This updated edition offers the most extensive and varied practice for all types of questions students might face on standardized and in-class tests. With this guide, students will learn to develop expert reading strategies, understand how to read faster and with greater comprehension, overcome reading anxiety, and increase appreciation of reading for pleasure. This book's step-by-step approach provides graduated coverage that moves from the basics to more advanced reading.
Eight Questions about Corruption
Jakob Svensson
2005-01-01
This paper will discuss eight frequently asked questions about public corruption: (1) What is corruption? (2) Which countries are the most corrupt? (3) What are the common characteristics of countries with high corruption? (4) What is the magnitude of corruption? (5) Do higher wages for bureaucrats reduce corruption? (6) Can competition reduce corruption? (7) Why have there been so few (recent) successful attempts to fight corruption? (8) Does corruption adversely affect growth?
International Nuclear Information System (INIS)
Anon.
1990-01-01
The book is on quantum mechanics. The emphasis is on the basic concepts and the methodology. The chapters include: Breakdown of classical concepts; Quantum mechanical concepts; Basic postulates of quantum mechanics; solution of problems in quantum mechanics; Simple harmonic oscillator; and Angular Momentum
International Nuclear Information System (INIS)
Buechler, Hans Peter; Calcarco, Tommaso; Dressel, Martin
2008-01-01
The following topics are dealt with: Artificial atoms and molecules, tailored from solids, fractional flux quanta, molecular magnets, controlled interaction in quantum gases, the theory of quantum correlations in mott matter, cold gases, and mesoscopic systems, Bose-Einstein condensates on the chip, on the route to the quantum computer, a quantum computer in diamond. (HSI)
International Nuclear Information System (INIS)
Reynaud, S.; Giacobino, S.; Zinn-Justin, J.
1997-01-01
This course is dedicated to present in a pedagogical manner the recent developments in peculiar fields concerned by quantum fluctuations: quantum noise in optics, light propagation through dielectric media, sub-Poissonian light generated by lasers and masers, quantum non-demolition measurements, quantum electrodynamics applied to cavities and electrical circuits involving superconducting tunnel junctions. (A.C.)
International Nuclear Information System (INIS)
Hanson, Andrew J; Sabry, Amr; Ortiz, Gerardo; Tai, Yu-Tsung
2014-01-01
We explore finite-field frameworks for quantum theory and quantum computation. The simplest theory, defined over unrestricted finite fields, is unnaturally strong. A second framework employs only finite fields with no solution to x 2 + 1 = 0, and thus permits an elegant complex representation of the extended field by adjoining i=√(−1). Quantum theories over these fields recover much of the structure of conventional quantum theory except for the condition that vanishing inner products arise only from null states; unnaturally strong computational power may still occur. Finally, we are led to consider one more framework, with further restrictions on the finite fields, that recovers a local transitive order and a locally-consistent notion of inner product with a new notion of cardinal probability. In this framework, conventional quantum mechanics and quantum computation emerge locally (though not globally) as the size of the underlying field increases. Interestingly, the framework allows one to choose separate finite fields for system description and for measurement: the size of the first field quantifies the resources needed to describe the system and the size of the second quantifies the resources used by the observer. This resource-based perspective potentially provides insights into quantitative measures for actual computational power, the complexity of quantum system definition and evolution, and the independent question of the cost of the measurement process. (paper)
Critical sizes and critical characteristics of nanoclusters, nanostructures and nanomaterials
International Nuclear Information System (INIS)
Suzdalev, I.P.
2005-01-01
Full text: Critical sizes and characteristics of nanoclusters and nanostructures are introduced as the parameters of nanosystems and nanomaterials. The next critical characteristics are considered: atomic and electronic 'magic number', critical size of cluster nucleation, critical size of melting-freezing of cluster, critical size of quantum (laser) radiation, critical sizes for the single electron conductivity, critical energy and magnetic field for the magnetic tunneling, critical cluster sizes for the giant magnetic resistance, critical size of the first order magnetic phase transition. The critical characteristics are estimated by thermodynamic approaches, by Moessbauer spectroscopy, AFM, heat capacity, SQUID magnetometry and other technique, The influence of cluster-cluster interactions, cluster-matrix interactions and cluster defects on cluster atomic dynamics, cluster melting, cluster critical sizes, Curie or Neel points and the character of magnetic phase transitions were investigated. The applications of critical size and critical characteristic parameters for the nanomaterial characterization are considered
Lanzagorta, Marco
2011-01-01
This book offers a concise review of quantum radar theory. Our approach is pedagogical, making emphasis on the physics behind the operation of a hypothetical quantum radar. We concentrate our discussion on the two major models proposed to date: interferometric quantum radar and quantum illumination. In addition, this book offers some new results, including an analytical study of quantum interferometry in the X-band radar region with a variety of atmospheric conditions, a derivation of a quantum radar equation, and a discussion of quantum radar jamming.This book assumes the reader is familiar w
International Nuclear Information System (INIS)
Kilin, Sergei Ya
1999-01-01
A new research direction known as quantum information is a multidisciplinary subject which involves quantum mechanics, optics, information theory, programming, discrete mathematics, laser physics and spectroscopy, and depends heavily on contributions from such areas as quantum computing, quantum teleportation and quantum cryptography, decoherence studies, and single-molecule and impurity spectroscopy. Some new results achieved in this rapidly growing field are discussed. (reviews of topical problems)
Energy Technology Data Exchange (ETDEWEB)
Kilin, Sergei Ya [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus)
1999-05-31
A new research direction known as quantum information is a multidisciplinary subject which involves quantum mechanics, optics, information theory, programming, discrete mathematics, laser physics and spectroscopy, and depends heavily on contributions from such areas as quantum computing, quantum teleportation and quantum cryptography, decoherence studies, and single-molecule and impurity spectroscopy. Some new results achieved in this rapidly growing field are discussed. (reviews of topical problems)
International Nuclear Information System (INIS)
Stapp, H.P.
1988-12-01
Quantum ontologies are conceptions of the constitution of the universe that are compatible with quantum theory. The ontological orientation is contrasted to the pragmatic orientation of science, and reasons are given for considering quantum ontologies both within science, and in broader contexts. The principal quantum ontologies are described and evaluated. Invited paper at conference: Bell's Theorem, Quantum Theory, and Conceptions of the Universe, George Mason University, October 20-21, 1988. 16 refs
Quantum entanglement: theory and applications
Energy Technology Data Exchange (ETDEWEB)
Schuch, N.
2007-10-10
This thesis deals with various questions concerning the quantification, the creation, and the application of quantum entanglement. Entanglement arises due to the restriction to local operations and classical communication. We investigate how the notion of entanglement changes if additional restrictions in form of a superselection rule are imposed and show that they give rise to a new resource. We characterize this resource and demonstrate that it can be used to overcome the restrictions, very much as entanglement can overcome the restriction to local operations by teleportation. We next turn towards the optimal generation of resources. We show how squeezing can be generated as efficiently as possible from noisy squeezing operations supplemented by noiseless passive operations, and discuss the implications of this result to the optimal generation of entanglement. The difficulty in describing the behaviour of correlated quantum many-body systems is ultimately due to the complicated entanglement structure of multipartite states. Using quantum information techniques, we investigate the ground state properties of lattices of harmonic oscillators. We derive an exponential decay of correlations for gapped systems, compute the dependence of correlation length and gap, and investigate the notion of criticality by relating a vanishing energy gap to an algebraic decay of correlations. Recently, ideas from entanglement theory have been applied to the description of many-body systems. Matrix Product States (MPS), which have a particularly simple interpretation from the point of quantum information, perform extremely well in approximating the ground states of local Hamiltonians. It is generally believed that this is due to the fact that both ground states and MPS obey an entropic area law. We clarify the relation between entropy scaling laws and approximability by MPS, and in particular find that an area law does not necessarily imply approximability. Using the quantum
Quantum entanglement: theory and applications
International Nuclear Information System (INIS)
Schuch, N.
2007-01-01
This thesis deals with various questions concerning the quantification, the creation, and the application of quantum entanglement. Entanglement arises due to the restriction to local operations and classical communication. We investigate how the notion of entanglement changes if additional restrictions in form of a superselection rule are imposed and show that they give rise to a new resource. We characterize this resource and demonstrate that it can be used to overcome the restrictions, very much as entanglement can overcome the restriction to local operations by teleportation. We next turn towards the optimal generation of resources. We show how squeezing can be generated as efficiently as possible from noisy squeezing operations supplemented by noiseless passive operations, and discuss the implications of this result to the optimal generation of entanglement. The difficulty in describing the behaviour of correlated quantum many-body systems is ultimately due to the complicated entanglement structure of multipartite states. Using quantum information techniques, we investigate the ground state properties of lattices of harmonic oscillators. We derive an exponential decay of correlations for gapped systems, compute the dependence of correlation length and gap, and investigate the notion of criticality by relating a vanishing energy gap to an algebraic decay of correlations. Recently, ideas from entanglement theory have been applied to the description of many-body systems. Matrix Product States (MPS), which have a particularly simple interpretation from the point of quantum information, perform extremely well in approximating the ground states of local Hamiltonians. It is generally believed that this is due to the fact that both ground states and MPS obey an entropic area law. We clarify the relation between entropy scaling laws and approximability by MPS, and in particular find that an area law does not necessarily imply approximability. Using the quantum
Six questions about translational due diligence.
Selinger, Evan
2010-04-28
To maintain stable respect and support, translational research must be guided by appropriate ethical, social, legal, and political concerns and carry out culturally competent practices. Considering six key questions concerning due diligence will enable the translational research community to examine critically how it approaches these endeavors.
Dog Bite Reflections--Socratic Questioning Revisited
Toledo, Cheri A.
2015-01-01
In the online environment, the asynchronous discussion is an important tool for creating community, developing critical thinking skills, and checking for understanding. As students learn how to use Socratic questions for effective interactions, the discussion boards can become the most exciting part of the course. This sequel to the article…
Quantum Computer Games: Quantum Minesweeper
Gordon, Michal; Gordon, Goren
2010-01-01
The computer game of quantum minesweeper is introduced as a quantum extension of the well-known classical minesweeper. Its main objective is to teach the unique concepts of quantum mechanics in a fun way. Quantum minesweeper demonstrates the effects of superposition, entanglement and their non-local characteristics. While in the classical…
The question about paleoinformatics
Vartic, Andrei
2006-12-01
The author is treating questions about development of informatics in ancient Dacia during Y-th Century B.C. - 2-nd Century A.C. He is introducing a new terminology (paleoinformatics) in view of defining the interests of Daces in numbering, the elementary numbers theory and various aspects of numbers representation. A relation between elementary numbers theory and informatisation has been discussed. A particular interest has been given to calculation of the Circle length/Diameter ratio (number Pi), its calculation by Daces.
International Nuclear Information System (INIS)
Branco, G.C.; Senjanovic, G.
1978-01-01
We investigate the question of neutrino mass in theories in which neutrinos are four-component Dirac particles. Our analysis is done in the framework of left-right--symmetric theories. The requirement of calculability and natural smallness of neutrino mass leads to the following constraints: (i) left and right charged weak currents must be ''orthogonal'' to each other, and (ii) there should be no W/sub L/-W/sub R/ mixing at the three level. Finally, we exhibit a model in which, due to the existence of an unbroken symmetry of the total Lagrangian, the electron and muon neutrinos remain massless to all orders in perturbation theory
Social Epistemology: 5 Questions
DEFF Research Database (Denmark)
Social Epistemology: 5 Questions is a collection of interviews with some of the world’s most influential scholars working on social epistemology from a range of disciplinary perspectives. We hear their views on social epistemology; its aim, scope, use, broader intellectual environment, future...... direction, and how the work of the interviewees fits in these respects. Interviews with David Bloor, Cristina Bicchieri, Richard Bradley, Lorraine Code, Hans van Ditmarsch, Miranda Fricker, Steve Fuller, Sanford Goldberg, Alvin Goldman, Philip Kitcher, Martin Kusch, Jennifer Lackey, Helen E. Longino, Philip...
Fixed points of quantum operations
International Nuclear Information System (INIS)
Arias, A.; Gheondea, A.; Gudder, S.
2002-01-01
Quantum operations frequently occur in quantum measurement theory, quantum probability, quantum computation, and quantum information theory. If an operator A is invariant under a quantum operation φ, we call A a φ-fixed point. Physically, the φ-fixed points are the operators that are not disturbed by the action of φ. Our main purpose is to answer the following question. If A is a φ-fixed point, is A compatible with the operation elements of φ? We shall show in general that the answer is no and we shall give some sufficient conditions under which the answer is yes. Our results will follow from some general theorems concerning completely positive maps and injectivity of operator systems and von Neumann algebras
Prospects and applications near ferroelectric quantum phase transitions: a key issues review
Chandra, P.; Lonzarich, G. G.; Rowley, S. E.; Scott, J. F.
2017-11-01
The emergence of complex and fascinating states of quantum matter in the neighborhood of zero temperature phase transitions suggests that such quantum phenomena should be studied in a variety of settings. Advanced technologies of the future may be fabricated from materials where the cooperative behavior of charge, spin and current can be manipulated at cryogenic temperatures. The progagating lattice dynamics of displacive ferroelectrics make them appealing for the study of quantum critical phenomena that is characterized by both space- and time-dependent quantities. In this key issues article we aim to provide a self-contained overview of ferroelectrics near quantum phase transitions. Unlike most magnetic cases, the ferroelectric quantum critical point can be tuned experimentally to reside at, above or below its upper critical dimension; this feature allows for detailed interplay between experiment and theory using both scaling and self-consistent field models. Empirically the sensitivity of the ferroelectric T c’s to external and to chemical pressure gives practical access to a broad range of temperature behavior over several hundreds of Kelvin. Additional degrees of freedom like charge and spin can be added and characterized systematically. Satellite memories, electrocaloric cooling and low-loss phased-array radar are among possible applications of low-temperature ferroelectrics. We end with open questions for future research that include textured polarization states and unusual forms of superconductivity that remain to be understood theoretically.
Quantum scaling in many-body systems an approach to quantum phase transitions
Continentino, Mucio
2017-01-01
Quantum phase transitions are strongly relevant in a number of fields, ranging from condensed matter to cold atom physics and quantum field theory. This book, now in its second edition, approaches the problem of quantum phase transitions from a new and unifying perspective. Topics addressed include the concepts of scale and time invariance and their significance for quantum criticality, as well as brand new chapters on superfluid and superconductor quantum critical points, and quantum first order transitions. The renormalisation group in real and momentum space is also established as the proper language to describe the behaviour of systems close to a quantum phase transition. These phenomena introduce a number of theoretical challenges which are of major importance for driving new experiments. Being strongly motivated and oriented towards understanding experimental results, this is an excellent text for graduates, as well as theorists, experimentalists and those with an interest in quantum criticality.
Razavy, Mohsen
2014-01-01
In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...
Trick questions: cosmopolitan hospitality
Directory of Open Access Journals (Sweden)
Eleanor Byrne
2013-08-01
Full Text Available Byrne’s paper consists of two parallel texts. The first explores the limits of cosmopolitanism in practice, taking as its subject the Life in the UK Citizenship Test, inaugurated under the Labour Government in 2005. It argues that the test exemplifies the predicament of all attempts at cosmopolitan hospitality as unconditional welcoming, through a discussion of the relation between questioning and welcoming the stranger. Establishing the relationship between cosmopolitanism and hospitality as envisaged in Derrida’s reading of Kant it asks what kind of cosmopolitan hospitality is either possible or desirable by exploring what Derrida calls the ‘perversions’ inherent in the structures of hospitality. It focuses on the concept of the ‘trick questions’ that the state asks the foreigner observed by Derrida in his reading of The Apology of Socrates; questions that seem to invite answers but foreclose the possibilities of a free response. The second text asks how this logic that Derrida identifies can be pushed or coaxed into new ways of addressing the perceived threats of ‘unconditional’ hospitality through a reading of ‘unconditional hospitality’ as queer in the work of Tove Jansson.
Distinguishability of quantum states and shannon complexity in quantum cryptography
Arbekov, I. M.; Molotkov, S. N.
2017-07-01
The proof of the security of quantum key distribution is a rather complex problem. Security is defined in terms different from the requirements imposed on keys in classical cryptography. In quantum cryptography, the security of keys is expressed in terms of the closeness of the quantum state of an eavesdropper after key distribution to an ideal quantum state that is uncorrelated to the key of legitimate users. A metric of closeness between two quantum states is given by the trace metric. In classical cryptography, the security of keys is understood in terms of, say, the complexity of key search in the presence of side information. In quantum cryptography, side information for the eavesdropper is given by the whole volume of information on keys obtained from both quantum and classical channels. The fact that the mathematical apparatuses used in the proof of key security in classical and quantum cryptography are essentially different leads to misunderstanding and emotional discussions [1]. Therefore, one should be able to answer the question of how different cryptographic robustness criteria are related to each other. In the present study, it is shown that there is a direct relationship between the security criterion in quantum cryptography, which is based on the trace distance determining the distinguishability of quantum states, and the criterion in classical cryptography, which uses guesswork on the determination of a key in the presence of side information.
Bojowald, Martin
2008-01-01
Quantum gravity is expected to be necessary in order to understand situations in which classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular theory is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. The main effects are introduced into effective classical equations, which allow one to avoid the interpretational problems of quantum theory. They give rise to new kinds of early-universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function, which allows an extension of quantum spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds light on more general issues, such as the nature of time. Supplementary material is available for this article at 10.12942/lrr-2008-4.
Directory of Open Access Journals (Sweden)
Bojowald Martin
2008-07-01
Full Text Available Quantum gravity is expected to be necessary in order to understand situations in which classical general relativity breaks down. In particular in cosmology one has to deal with initial singularities, i.e., the fact that the backward evolution of a classical spacetime inevitably comes to an end after a finite amount of proper time. This presents a breakdown of the classical picture and requires an extended theory for a meaningful description. Since small length scales and high curvatures are involved, quantum effects must play a role. Not only the singularity itself but also the surrounding spacetime is then modified. One particular theory is loop quantum cosmology, an application of loop quantum gravity to homogeneous systems, which removes classical singularities. Its implications can be studied at different levels. The main effects are introduced into effective classical equations, which allow one to avoid the interpretational problems of quantum theory. They give rise to new kinds of early-universe phenomenology with applications to inflation and cyclic models. To resolve classical singularities and to understand the structure of geometry around them, the quantum description is necessary. Classical evolution is then replaced by a difference equation for a wave function, which allows an extension of quantum spacetime beyond classical singularities. One main question is how these homogeneous scenarios are related to full loop quantum gravity, which can be dealt with at the level of distributional symmetric states. Finally, the new structure of spacetime arising in loop quantum gravity and its application to cosmology sheds light on more general issues, such as the nature of time.
Global quantum discord in multipartite systems
Energy Technology Data Exchange (ETDEWEB)
Rulli, C. C.; Sarandy, M. S. [Instituto de Fisica, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, Gragoata, 24210-346 Niteroi, RJ (Brazil)
2011-10-15
We propose a global measure for quantum correlations in multipartite systems, which is obtained by suitably recasting the quantum discord in terms of relative entropy and local von Neumann measurements. The measure is symmetric with respect to subsystem exchange and is shown to be nonnegative for an arbitrary state. As an illustration, we consider tripartite correlations in the Werner-GHZ (Greenberger-Horne-Zeilinger) state and multipartite correlations at quantum criticality. In particular, in contrast with the pairwise quantum discord, we show that the global quantum discord is able to characterize the infinite-order quantum phase transition in the Ashkin-Teller spin chain.
Quantum mechanical irreversibility and measurement
Grigolini, P
1993-01-01
This book is intended as a tutorial approach to some of the techniques used to deal with quantum dissipation and irreversibility, with special focus on their applications to the theory of measurements. The main purpose is to provide readers without a deep expertise in quantum statistical mechanics with the basic tools to develop a critical judgement on whether the major achievements in this field have to be considered a satisfactory solution of quantum paradox, or rather this ambitious achievement has to be postponed to when a new physics, more general than quantum and classical physics, will
Approximate quantum Markov chains
Sutter, David
2018-01-01
This book is an introduction to quantum Markov chains and explains how this concept is connected to the question of how well a lost quantum mechanical system can be recovered from a correlated subsystem. To achieve this goal, we strengthen the data-processing inequality such that it reveals a statement about the reconstruction of lost information. The main difficulty in order to understand the behavior of quantum Markov chains arises from the fact that quantum mechanical operators do not commute in general. As a result we start by explaining two techniques of how to deal with non-commuting matrices: the spectral pinching method and complex interpolation theory. Once the reader is familiar with these techniques a novel inequality is presented that extends the celebrated Golden-Thompson inequality to arbitrarily many matrices. This inequality is the key ingredient in understanding approximate quantum Markov chains and it answers a question from matrix analysis that was open since 1973, i.e., if Lieb's triple ma...