Quantum critical points in quantum impurity systems
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyun Jung [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Universitaet Augsburg (Germany); Bulla, Ralf [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Universitaet Augsburg (Germany)]. E-mail: bulla@cpfs.mpg.de
2005-04-30
The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the soft-gap Anderson model, where an impurity couples to a non-trivial fermionic bath. In this case, zero-temperature phase transitions occur between two different phases whose fixed points can be built up of non-interacting single-particle states. However, the quantum critical point cannot be described by non-interacting fermionic or bosonic excitations.
Quantum critical points in quantum impurity systems
Lee, Hyun Jung; Bulla, Ralf
2005-04-01
The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the soft-gap Anderson model, where an impurity couples to a non-trivial fermionic bath. In this case, zero-temperature phase transitions occur between two different phases whose fixed points can be built up of non-interacting single-particle states. However, the quantum critical point cannot be described by non-interacting fermionic or bosonic excitations.
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.
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.
Dynamical Response near Quantum Critical Points
Lucas, Andrew; Gazit, Snir; Podolsky, Daniel; Witczak-Krempa, William
2017-02-01
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.
Holographic Butterfly Effect at Quantum Critical Points
Ling, Yi; Wu, Jian-Pin
2016-01-01
When the Lyapunov exponent $\\lambda_L$ in a quantum chaotic system saturates the bound $\\lambda_L\\leqslant 2\\pi k_BT$, it is proposed that this system has a holographic dual described by a gravity theory. In particular, the butterfly effect as a prominent phenomenon of chaos can ubiquitously exist in a black hole system characterized by a shockwave solution near the horizon. In this letter we propose that the butterfly velocity $v_B$ can be used to diagnose quantum phase transition (QPT) in holographic theories. We provide evidences for this proposal with two holographic models exhibiting metal-insulator transitions (MIT), in which the second derivative of $v_B$ with respect to system parameters characterizes quantum critical points (QCP) with local extremes. We also point out that this proposal can be tested by experiments in the light of recent progress on the measurement of out-of-time-order correlation function (OTOC).
Quantum-to-classical crossover near quantum critical point.
Vasin, M; Ryzhov, V; Vinokur, V M
2015-12-21
A quantum phase transition (QPT) is an inherently dynamic phenomenon. However, while non-dissipative quantum dynamics is described in detail, the question, that is not thoroughly understood is how the omnipresent dissipative processes enter the critical dynamics near a quantum critical point (QCP). Here we report a general approach enabling inclusion of both adiabatic and dissipative processes into the critical dynamics on the same footing. We reveal three distinct critical modes, the adiabatic quantum mode (AQM), the dissipative classical mode [classical critical dynamics mode (CCDM)], and the dissipative quantum critical mode (DQCM). We find that as a result of the transition from the regime dominated by thermal fluctuations to that governed by the quantum ones, the system acquires effective dimension d + zΛ(T), where z is the dynamical exponent, and temperature-depending parameter Λ(T) ∈ [0, 1] decreases with the temperature such that Λ(T = 0) = 1 and Λ(T → ∞) = 0. Our findings lead to a unified picture of quantum critical phenomena including both dissipation- and dissipationless quantum dynamic effects and offer a quantitative description of the quantum-to-classical crossover.
Dynamical response near quantum critical points
Lucas, Andrew; Podolsky, Daniel; Witczak-Krempa, William
2016-01-01
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 conformal 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.
Order parameter fluctuations at a buried quantum critical point.
Feng, Yejun; Wang, Jiyang; Jaramillo, R; van Wezel, Jasper; Haravifard, S; Srajer, G; Liu, Y; Xu, Z-A; Littlewood, P B; Rosenbaum, T F
2012-05-08
Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe(2) at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface.
Universal Postquench Prethermalization at a Quantum Critical Point.
Gagel, Pia; Orth, Peter P; Schmalian, Jörg
2014-11-28
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.
Partial dynamical symmetry at critical points of quantum phase transitions.
Leviatan, A
2007-06-15
We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.
Odd-Parity Superconductivity and the Ferromagnetic Quantum Critical Point
Huxley, A. D.; Yates, S. J. C.; Lévy, F.; Sheikin, I.
2007-05-01
The study of the emergence of superconductivity close to quantum critical points affords a powerful means to identify the mechanism that drives the formation of unconventional superconductivity in heavy fermion materials. The recent discovery of superconducting states close to quantum critical points in ferromagnets UGe2 and URhGe is reviewed in this light. For URhGe we examine whether the predominant type of magnetic excitations involved are longitudinal excitations, hitherto considered theoretically to be the most promising candidate to mediate equal-spin-paired superconductivity.
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.
Black holes as critical point of quantum phase transition
Energy Technology Data Exchange (ETDEWEB)
Dvali, Gia [Arnold Sommerfeld Center for Theoretical Physics, Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen (Germany); Max-Planck-Institut fuer Physik, Muenchen (Germany); CERN, Theory Department, Geneva 23 (Switzerland); New York University, Department of Physics, Center for Cosmology and Particle Physics, New York, NY (United States); Gomez, Cesar [Arnold Sommerfeld Center for Theoretical Physics, Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen (Germany); Universidad Autonoma de Madrid, Instituto de Fisica Teorica UAM-CSIC, C-XVI, Madrid (Spain)
2014-02-15
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. (orig.)
Black Holes as Critical Point of Quantum Phase Transition
Dvali, Gia
2014-01-01
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.
Black holes as critical point of quantum phase transition
Dvali, Gia; Gomez, Cesar
2014-02-01
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.
Thermal conductivity at a disordered quantum critical point
Hartnoll, Sean A; Santos, Jorge E
2015-01-01
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....
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
Experimental consequences of quantum critical points at high temperatures
Freitas, D. C.; Rodière, P.; Núñez, M.; Garbarino, G.; Sulpice, A.; Marcus, J.; Gay, F.; Continentino, M. A.; Núñez-Regueiro, M.
2015-11-01
We study the C r1 -xR ex phase diagram finding that its phase transition temperature towards an antiferromagnetic order TN follows a quantum [(xc-x ) /xc ] ψ law, with ψ =1 /2 , from the quantum critical point (QCP) at xc=0.25 up to TN≈600 K . We compare this system to others in order to understand why this elemental material is affected by the QCP up to such unusually high temperatures. We determine a general criterion for the crossover, as a function of an external parameter such as concentration, from the region controlled solely by thermal fluctuations to that where quantum effects become observable. The properties of materials with low coherence lengths will thus be altered far away from the QCP.
Impurities near an antiferromagnetic-singlet quantum critical point
Mendes-Santos, T.; Costa, N. C.; Batrouni, G.; Curro, N.; dos Santos, R. R.; Paiva, T.; Scalettar, R. T.
2017-02-01
Heavy-fermion systems and other strongly correlated electron materials often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact quantum Monte Carlo simulations, we examine the effect of impurities in the vicinity of such an AF-singlet quantum critical point (QCP), through an appropriately defined "impurity susceptibility" χimp. Our key finding is a connection within a single calculational framework between AF domains induced on the singlet side of the transition and the behavior of the nuclear magnetic resonance (NMR) relaxation rate 1 /T1 . We show that local NMR measurements provide a diagnostic for the location of the QCP, which agrees remarkably well with the vanishing of the AF order parameter and large values of χimp.
Universal Entanglement Entropy in 2D Conformal Quantum Critical Points
Energy Technology Data Exchange (ETDEWEB)
Hsu, Benjamin; Mulligan, Michael; Fradkin, Eduardo; Kim, Eun-Ah
2008-12-05
We study the scaling behavior of the entanglement entropy of two dimensional conformal quantum critical systems, i.e. systems with scale invariant wave functions. They include two-dimensional generalized quantum dimer models on bipartite lattices and quantum loop models, as well as the quantum Lifshitz model and related gauge theories. We show that, under quite general conditions, the entanglement entropy of a large and simply connected sub-system of an infinite system with a smooth boundary has a universal finite contribution, as well as scale-invariant terms for special geometries. The universal finite contribution to the entanglement entropy is computable in terms of the properties of the conformal structure of the wave function of these quantum critical systems. The calculation of the universal term reduces to a problem in boundary conformal field theory.
Zooming on the quantum critical point in Nd-LSCO
Energy Technology Data Exchange (ETDEWEB)
Cyr-Choiniere, Olivier, E-mail: olivier.cyr-choiniere@usherbrooke.c [Department de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada); Daou, R.; Chang, J.; Laliberte, Francis; Doiron-Leyraud, Nicolas; LeBoeuf, David [Department de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada); Jo, Y.J.; Balicas, L. [National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310-3706 (United States); Yan, J.-Q. [Ames Laboratory, Ames, IA 50011 (United States); Cheng, J.-G.; Zhou, J.-S.; Goodenough, J.B. [Texas Materials Institute, University of Texas at Austin, Austin, TX 78712 (United States); Taillefer, Louis, E-mail: louis.taillefer@physique.usherbrooke.c [Department de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Quebec, J1K 2R1 (Canada); Canadian Institute for Advanced Research, Toronto, Ontario, M5G 1Z8 (Canada)
2010-12-15
Recent studies of the high-T{sub c} superconductor La{sub 1.6-x}Nd{sub 0.4}Sr{sub x}CuO{sub 4} (Nd-LSCO) have found a linear-T in-plane resistivity {rho}{sub ab} and a logarithmic temperature dependence of the thermopower S/T at a hole doping p=0.24 and a Fermi-surface reconstruction just below p=0.24. These are typical signatures of a quantum critical point (QCP). Here we report data on the c-axis resistivity {rho}{sub c}(T) of Nd-LSCO measured as a function of temperature near this QCP, in a magnetic field large enough to entirely suppress superconductivity. Like {rho}{sub ab},{rho}{sub c} shows an upturn at low temperature, a signature of Fermi surface reconstruction caused by stripe order. Tracking the height of the upturn as it decreases with doping enables us to pin down the precise location of the QCP where stripe order ends, at p*=0.235{+-}0.005. We propose that the temperature T{sub {rho}} below which the upturn begins marks the onset of the pseudogap phase, found to be roughly twice as high as the stripe-ordering temperature in this material.
The critical point of quantum chromodynamics through lattice and experiment
Indian Academy of Sciences (India)
Sourendu Gupta
2011-05-01
This talk discusses methods of extending lattice computations at ﬁnite temperature into regions of ﬁnite chemical potential, and the conditions under which such results from the lattice may be compared to experiments. Such comparisons away from a critical point are absolutely essential for quantitative use of lattice QCD in heavy-ion physics. An outline of various arguments which can then be used to locate the critical point is also presented.
del Campo, Adolfo; Rams, Marek M; Zurek, Wojciech H
2012-09-14
The dynamics of a quantum phase transition is inextricably woven with the formation of excitations, as a result of critical slowing down in the neighborhood of the critical point. We design a transitionless quantum driving through a quantum critical point, allowing one to access the ground state of the broken-symmetry phase by a finite-rate quench of the control parameter. The method is illustrated in the one-dimensional quantum Ising model in a transverse field. Driving through the critical point is assisted by an auxiliary Hamiltonian, for which the interplay between the range of the interaction and the modes where excitations are suppressed is elucidated.
Fermi-surface collapse and dynamical scaling near a quantum-critical point.
Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao
2010-08-17
Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh(2)Si(2), a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.
The partition function zeroes of quantum critical points
Energy Technology Data Exchange (ETDEWEB)
Crompton, P.R. [Department of Applied Maths, School of Mathematics, University of Leeds, Leeds, LS2 9JT (United Kingdom)], E-mail: p.crompton@lancaster.ac.uk
2009-04-01
The Lee-Yang theorem for the zeroes of the partition function is not strictly applicable to quantum systems because the zeroes are defined in units of the fugacity e{sup h{delta}}{sup {tau}}, and the Euclidean-time lattice spacing {delta}{tau} can be divergent in the infrared (IR). We recently presented analytic arguments describing how a new space-Euclidean time zeroes expansion can be defined, which reproduces Lee and Yang's scaling but avoids the unresolved branch points associated with the breaking of nonlocal symmetries such as Parity. We now present a first numerical analysis for this new zeroes approach for a quantum spin chain system. We use our scheme to quantify the renormalization group flow of the physical lattice couplings to the IR fixed point of this system. We argue that the generic Finite-Size Scaling (FSS) function of our scheme is identically the entanglement entropy of the lattice partition function and, therefore, that we are able to directly extract the central charge, c, of the quantum spin chain system using conformal predictions for the scaling of the entanglement entropy.
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.
Fermionic quantum critical point of spinless fermions on a honeycomb lattice
Wang, L.; Corboz, P.; Troyer, M.
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
Superconductivity and non-Fermi liquid behavior near a nematic quantum critical point
Lederer, Samuel; Schattner, Yoni; Berg, Erez; Kivelson, Steven A.
2017-05-01
Using determinantal quantum Monte Carlo, we compute the properties of a lattice model with spin mn>1mn>mn>2mn>12 itinerant electrons tuned through a quantum phase transition to an Ising nematic phase. The nematic fluctuations induce superconductivity with a broad dome in the superconducting TcTc enclosing the nematic quantum critical point. For temperatures above TcTc, we see strikingly non-Fermi liquid behavior, including a “nodal-antinodal dichotomy” reminiscent of that seen in several transition metal oxides. In addition, the critical fluctuations have a strong effect on the low-frequency optical conductivity, resulting in behavior consistent with “bad metal” phenomenology.
Metamagnetic behavior near the quantum critical point in UGe 2
Huxley, A.; Sheikin, I.; Braithwaite, D.
2000-07-01
We have discovered a low-field metamagnetic transition in UGe 2 close to the critical pressure at which the Curie temperature is suppressed to zero. The systematic evolution of the transition with pressure provides a unique opportunity to test theoretical models of metamagnetism.
Łącki, Mateusz; Damski, Bogdan; Zakrzewski, Jakub
2016-12-02
We show that the critical point of the two-dimensional Bose-Hubbard model can be easily found through studies of either on-site atom number fluctuations or the nearest-neighbor two-point correlation function (the expectation value of the tunnelling operator). Our strategy to locate the critical point is based on the observation that the derivatives of these observables with respect to the parameter that drives the superfluid-Mott insulator transition are singular at the critical point in the thermodynamic limit. Performing the quantum Monte Carlo simulations of the two-dimensional Bose-Hubbard model, we show that this technique leads to the accurate determination of the position of its critical point. Our results can be easily extended to the three-dimensional Bose-Hubbard model and different Hubbard-like models. They provide a simple experimentally-relevant way of locating critical points in various cold atomic lattice systems.
Partial Dynamical Symmetry at Critical-Points of Quantum Phase Transitions
Leviatan, A
2007-01-01
We show that partial dynamical symmetries (PDS) can occur at critical-points of quantum phase transitions, in which case, underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of PDS are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape-phases in nuclei.
Athermal domain-wall creep near a ferroelectric quantum critical point.
Kagawa, Fumitaka; Minami, Nao; Horiuchi, Sachio; Tokura, Yoshinori
2016-02-16
Ferroelectric domain walls are typically stationary because of the presence of a pinning potential. Nevertheless, thermally activated, irreversible creep motion can occur under a moderate electric field, thereby underlying rewritable and non-volatile memory applications. Conversely, as the temperature decreases, the occurrence of creep motion becomes less likely and eventually impossible under realistic electric-field magnitudes. Here we show that such frozen ferroelectric domain walls recover their mobility under the influence of quantum fluctuations. Nonlinear permittivity and polarization-retention measurements of an organic charge-transfer complex reveal that ferroelectric domain-wall creep occurs via an athermal process when the system is tuned close to a pressure-driven ferroelectric quantum critical point. Despite the heavy masses of material building blocks such as molecules, the estimated effective mass of the domain wall is comparable to the proton mass, indicating the realization of a ferroelectric domain wall with a quantum-particle nature near the quantum critical point.
Influence of the ferroelectric quantum critical point on SrTiO3 interfaces
Atkinson, W. A.; Lafleur, P.; Raslan, A.
2017-02-01
We study a model SrTiO3 interface in which conduction t2 g electrons couple to the ferroelectric (FE) phonon mode. We treat the FE mode within a self-consistent phonon theory that captures its quantum critical behavior and show that proximity to the quantum critical point leads to universal tails in the electron density of the form n (z ) ˜(λ+z ) -2 , where λ ˜T2 -d /z , with d =3 the dimensionality and z =1 the dynamical critical exponent. Implications for the metal-insulator transition at low electron density are discussed.
Scaling of the magnetic Grüneisen ratio near quantum critical point
Tokiwa, Yoshi
2014-03-01
The magnetic Grüneisen ratio ΓH = (1/T)dT/dH is the most sensitive probe of quantum criticality. Its divergence signals the underlying instability. We have studied quantum criticality in the frustrated Kondo lattice system YbAgGe and the heavy fermion superconductor CeCoIn5 by high-precision magnetocaloric effect measurements. In the former, NFL behavior appears around a metamagnetic spin-flop transition between two symmetry broken phases. Previously, it was unclear how the two ordered phases are related to the NFL state. Here, we propose a novel quantum bicritical point (QBCP) scenario, which is distinct from either quantum critical end point or ordinary QCPs with single symmetry broken phase. The observed scaling behavior of ΓH and its characteristic asymmetry across the critical field are consistent with a QBCP scenario. We also report a possible violation of Wiedemann-Franz law at the QBCP in YbAgGe. In CeCoIn5 indications of a quantum critical field hidden inside the superconducting (SC) phase have been extensively debated. We show ΓH data and scaling analysis in the normal state, which surprisingly suggests a zero-field QCP. Anomalous behaviors of ΓH and specific heat within the SC state further support this conclusion.
Zhu, Lijun; Garst, Markus; Rosch, Achim; Si, Qimiao
2003-08-08
At a generic quantum critical point, the thermal expansion alpha is more singular than the specific heat c(p). Consequently, the "Grüneisen ratio," Gamma=alpha/c(p), diverges. When scaling applies, Gamma approximately T(-1/(nu z)) at the critical pressure p=p(c), providing a means to measure the scaling dimension of the most relevant operator that pressure couples to; in the alternative limit T-->0 and p not equal p(c), Gamma approximately 1/(p-p(c)) with a prefactor that is, up to the molar volume, a simple universal combination of critical exponents. For a magnetic-field driven transition, similar relations hold for the magnetocaloric effect (1/T) partial differential T/ partial differential H|(S). Finally, we determine the corrections to scaling in a class of metallic quantum critical points.
Duality between the Deconfined Quantum-Critical Point and the Bosonic Topological Transition
Qin, Yan Qi; He, Yuan-Yao; You, Yi-Zhuang; Lu, Zhong-Yi; Sen, Arnab; Sandvik, Anders W.; Xu, Cenke; Meng, Zi Yang
2017-07-01
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 CP1 model (NCCP1 ) and noncompact quantum electrodynamics (QED) with two flavors (N =2 ) of massless two-component Dirac fermions. The easy-plane NCCP1 model is the field theory of the putative deconfined quantum-critical point separating a planar (X Y ) 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 X Y model with additional multispin couplings) and show that it hosts a continuous transition between the X Y 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 quantum
Topology-induced anomalous defect production by crossing a quantum critical point.
Bermudez, A; Patanè, D; Amico, L; Martin-Delgado, M A
2009-04-03
We study the influence of topology on the quench dynamics of a system driven across a quantum critical point. We show how the appearance of certain edge states, which fully characterize the topology of the system, dramatically modifies the process of defect production during the crossing of the critical point. Interestingly enough, the density of defects is no longer described by the Kibble-Zurek scaling, but determined instead by the nonuniversal topological features of the system. Edge states are shown to be robust against defect production, which highlights their topological nature.
Regularity and chaos at critical points of first-order quantum phase transitions
Macek, Michal
2011-01-01
We study the interplay between regular and chaotic dynamics at the critical point of a first order quantum shape-phase transition in an interacting boson model of nuclei. A classical analysis reveals a distinct behavior of the coexisting phases in a broad energy range. The dynamics is completely regular in the deformed phase while it becomes strongly chaotic in the spherical phase. A quantum analysis of the spectra separates the regular states from the irregular ones, assigns them to particular phases and discloses persisting regular rotational bands in the deformed region.
Transport Properties near Quantum Critical Point in 2D Hubbard Model
Chen, Kuang-Shing; Pathak, Sandeep; Yang, Shuxiang; Su, Shi-Quan; Galanakis, Dimitris; Mikelsons, Karlis; Moreno, Juana; Jarrell, Mark
2011-03-01
We obtain high quality estimates of the self energy Σ (K , ω) by direct analytic continuation of Σ (K , iωn) obtained from Continuous-Time Quantum Monte Carlo. We use these results to investigate the transport properties near the quantum critical point found in the 2D Hubbard model at finite doping. Resistivity, thermal conductivity, Wiedemann-Franz Law, and thermopower are examined in the Fermi liquid, Marginal Fermi liquid (MFL), and pseudo-gap regions. Σ (k , ω) with k along the nodal direction displays temperature-dependent scaling similar to that seen in the experiment. A next-nearest neighbor hopping tOISE-0730290.
Kallin, Ann B; Hyatt, Katharine; Singh, Rajiv R P; Melko, Roger G
2013-03-29
We develop a method to calculate the bipartite entanglement entropy of quantum models, in the thermodynamic limit, using a numerical linked-cluster expansion (NLCE) involving only rectangular clusters. It is based on exact diagonalization of all n×m rectangular clusters at the interface between entangled subsystems A and B. We use it to obtain the Renyi entanglement entropy of the two-dimensional transverse field Ising model, for arbitrary real Renyi index α. Extrapolating these results as a function of the order of the calculation, we obtain universal pieces of the entanglement entropy associated with lines and corners at the quantum critical point. They show NLCE to be one of the few methods capable of accurately calculating universal properties of arbitrary Renyi entropies at higher dimensional critical points.
Itinerant Magnetism and the Ferromagnetic Quantum Critical Point in Fe(Ga,Ge)3
Singh, David J.
2014-03-01
FeGa3 is a tetragonal semiconductor with a band gap of ~0.5 eV and interesting thermoelectric properties. It shows diamagnetic behavior but when modestly electron doped by Ge, a ferromagnetic quantum critical point emerges and the ground state becomes a ferromagnetic metal. We present first-principles calculations showing that the magnetism can be readily explained in an itinerant picture without the need for preexisting moments in the semiconducting state and without the need for correlation terms. We also present Boltzmann transport calculations of the thermopower. Itinerant magnetism implies strong coupling between the electrons at the Fermi energy that control transport and the magnetism. Thus, FeGa3 may be a particularly interesting material near a quantum critical point. We find that the ferromagnetic state is half-metallic over a substantial composition range. Work supported by the Department of Energy, BES, Materials Sciences and Engineering Division.
Superconductivity near a Quantum-Critical Point: The Special Role of the First Matsubara Frequency.
Wang, Yuxuan; Abanov, Artem; Altshuler, Boris L; Yuzbashyan, Emil A; Chubukov, Andrey V
2016-10-07
Near a quantum-critical point in a metal strong fermion-fermion interaction mediated by a soft collective boson gives rise to incoherent, non-Fermi liquid behavior. It also often gives rise to superconductivity which masks the non-Fermi liquid behavior. We analyze the interplay between the tendency to pairing and fermionic incoherence for a set of quantum-critical models with effective dynamical interaction between low-energy fermions. We argue that superconducting T_{c} is nonzero even for strong incoherence and/or weak interaction due to the fact that the self-energy from dynamic critical fluctuations vanishes for the two lowest fermionic Matsubara frequencies ω_{m}=±πT. We obtain the analytic formula for T_{c}, which reproduces well earlier numerical results for the electron-phonon model at vanishing Debye frequency.
Theory of the nematic quantum critical point in a nodal superconductor
Kim, Eun-Ah
2008-03-01
In the last several years, experimental evidence has accumulated in a variety of highly correlated electronic systems of new quantum phases which (for purely electronic reasons) spontaneously break the rotational (point group) symmetry of the underlying crystal. Such electron ``nematic'' phases have been seen in quantum Hall systems[1], in the metamagnetic metal Sr3Ru2O7[2], and more recently in magnetic neutron scattering studies of the high temperature superconductor, YBCO[3]. In the case of a high Tc superconductor, the quantum dynamics of nematic order parameter naturally couples strongly to quasiparticle (qp) excitations. In this talk, I will discuss our recent results on the effects of the coupling between quantum critical nematic fluctuations and the nodal qp's of a d-wave superconductor in the vicinity of a putative quantum critical point inside the superconducting phase. We solve a model system with N flavors of quasiparticles in the large N limit[4]. To leading order in 1/N, quantum fluctuations enhance the dispersion anisotropy of the nodal excitations, and cause strong scattering which critically broadens the quasiparticle peaks in the spectral function, except in the vicinity of ``the tips of the banana,'' where the qp's remain sharp. We will discuss the possible implications of our results to ARPES and STM experiments. [1] M.P. Lilly, K.B. Cooper, J.P. Eisenstein, L.N. Pfeiffer, and K.W. West, PRL 83, 824 (1999). [2] R. A. Borzi and S. A. Grigera and J. Farrell and R. S. Perry and S. J. S. Lister and S. L. Lee and D. A. Tennant and Y. Maeno and A. P. Mackenzie, Science 315, 214 (2007). [3] V. Hinkov, D. Haug, B. Fauqu'e, P. Bourges, Y. Sidis, A. Ivanov, C. Bernhard, C. T. Lin, B. Keimer, unpublished. [4] E.-A. Kim, M. Lawler, P. Oreto, E. Fradkin, S. Kivelson, cond-mat/0705.4099.
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyun-Jung [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Bulla, Ralf [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Vojta, Matthias [Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, D-76128 Karlsruhe (Germany)
2005-11-02
The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra.
Lee, Hyun-Jung; Bulla, Ralf; Vojta, Matthias
2005-11-01
The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra.
Energy Technology Data Exchange (ETDEWEB)
Schlottmann, P. [Department of Physics, Florida State University, MC 4350-309 Keene Building, Tallahassee, FL 32306 (United States)]. E-mail: schlottm@martech.fsu.edu
2004-12-31
The nesting of the Fermi surfaces of an electron pocket and a hole pocket separated by a wave vector Q and the interaction between electrons gives rise to spin- and charge-density waves. The order can gradually be suppressed by mismatching the nesting and a quantum critical point is obtained as the critical temperature tends to zero. We calculate the quasi-particle damping close to the quantum critical point and discuss its consequences on the resistivity and Hall effect.
Lévy, F.; Sheikin, I.; Huxley, A.
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 0.5K, we find that it can survive in extremely high magnetic fields, exceeding 28T.
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)
The phase and critical point of quantum Einstein-Cartan gravity
Xue, She-Sheng
2012-05-01
By introducing diffeomorphism and local Lorentz gauge invariant holonomy fields, we study in the recent article [S.-S. Xue, Phys. Rev. D 82 (2010) 064039] the quantum Einstein-Cartan gravity in the framework of Regge calculus. On the basis of strong coupling expansion, mean-field approximation and dynamical equations satisfied by holonomy fields, we present in this Letter calculations and discussions to show the phase structure of the quantum Einstein-Cartan gravity, (i) the order phase: long-range condensations of holonomy fields in strong gauge couplings; (ii) the disorder phase: short-range fluctuations of holonomy fields in weak gauge couplings. According to the competition of the activation energy of holonomy fields and their entropy, we give a simple estimate of the possible ultra-violet critical point and correlation length for the second-order phase transition from the order phase to disorder one. At this critical point, we discuss whether the continuum field theory of quantum Einstein-Cartan gravity can be possibly approached when the macroscopic correlation length of holonomy field condensations is much larger than the Planck length.
The break-up of heavy electrons at a quantum critical point.
Custers, J; Gegenwart, P; Wilhelm, H; Neumaier, K; Tokiwa, Y; Trovarelli, O; Geibel, C; Steglich, F; Pépin, C; Coleman, P
2003-07-31
The point at absolute zero where matter becomes unstable to new forms of order is called a quantum critical point (QCP). The quantum fluctuations between order and disorder that develop at this point induce profound transformations in the finite temperature electronic properties of the material. Magnetic fields are ideal for tuning a material as close as possible to a QCP, where the most intense effects of criticality can be studied. A previous study on the heavy-electron material YbRh2Si2 found that near a field-induced QCP electrons move ever more slowly and scatter off one another with ever increasing probability, as indicated by a divergence to infinity of the electron effective mass and scattering cross-section. But these studies could not shed light on whether these properties were an artefact of the applied field, or a more general feature of field-free QCPs. Here we report that, when germanium-doped YbRh2Si2 is tuned away from a chemically induced QCP by magnetic fields, there is a universal behaviour in the temperature dependence of the specific heat and resistivity: the characteristic kinetic energy of electrons is directly proportional to the strength of the applied field. We infer that all ballistic motion of electrons vanishes at a QCP, forming a new class of conductor in which individual electrons decay into collective current-carrying motions of the electron fluid.
Keimer, Bernhard; Sachdev, Subir
2011-01-01
This is a review of the basic theoretical ideas of quantum criticality, and of their connection to numerous experiments on correlated electron compounds. A shortened, modified, and edited version appeared in Physics Today. This arxiv version has additional citations to the literature.
Strečka, Jozef; Verkholyak, Taras
2016-10-01
Magnetic properties of the ferrimagnetic mixed spin-(1/2,S) Heisenberg chains are examined using quantum Monte Carlo simulations for two different quantum spin numbers S=1 and 3/2. The calculated magnetization curves at finite temperatures are confronted with zero-temperature magnetization data obtained within the density matrix renormalization group method, which imply an existence of two quantum critical points determining a breakdown of the gapped Lieb-Mattis ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. While a square root behavior of the magnetization accompanying each quantum critical point is gradually smoothed upon rising temperature, the susceptibility and isothermal entropy change data at low temperatures provide a stronger evidence of the zero-temperature quantum critical points through marked local maxima and minima, respectively.
Candidate Elastic Quantum Critical Point in LaCu_{6-x}Au_{x}.
Poudel, L; May, A F; Koehler, M R; McGuire, M A; Mukhopadhyay, S; Calder, S; Baumbach, R E; Mukherjee, R; Sapkota, D; de la Cruz, C; Singh, D J; Mandrus, D; Christianson, A D
2016-12-02
The structural properties of LaCu_{6-x}Au_{x} are studied using neutron diffraction, x-ray diffraction, and heat capacity measurements. The continuous orthorhombic-monoclinic structural phase transition in LaCu_{6} is suppressed linearly with Au substitution until a complete suppression of the structural phase transition occurs at the critical composition x_{c}=0.3. Heat capacity measurements at low temperatures indicate residual structural instability at x_{c}. The instability is ferroelastic in nature, with density functional theory calculations showing negligible coupling to electronic states near the Fermi level. The data and calculations presented here are consistent with the zero temperature termination of a continuous structural phase transition suggesting that the LaCu_{6-x}Au_{x} series hosts an elastic quantum critical point.
Mapping the current–current correlation function near a quantum critical point
Energy Technology Data Exchange (ETDEWEB)
Prodan, Emil, E-mail: prodan@yu.edu [Department of Physics, Yeshiva University, New York, NY 10016 (United States); Bellissard, Jean [School of Mathematics and School of Physics, Georgia Institute of Technology, Atlanta, GA (United States)
2016-05-15
The current–current correlation function is a useful concept in the theory of electron transport in homogeneous solids. The finite-temperature conductivity tensor as well as Anderson’s localization length can be computed entirely from this correlation function. Based on the critical behavior of these two physical quantities near the plateau–insulator or plateau–plateau transitions in the integer quantum Hall effect, we derive an asymptotic formula for the current–current correlation function, which enables us to make several theoretical predictions about its generic behavior. For the disordered Hofstadter model, we employ numerical simulations to map the current–current correlation function, obtain its asymptotic form near a critical point and confirm the theoretical predictions.
Shear viscosity at the Ising-nematic quantum critical point in two dimensional metals
Patel, Aavishkar A; Sachdev, Subir
2016-01-01
In a strongly interacting quantum liquid without quasiparticles, general scaling arguments imply that the dimensionless ratio $(k_B /\\hbar)\\, \\eta/s$, where $\\eta$ is the shear viscosity and $s$ is the entropy density, is a universal number. We compute the shear viscosity of the Ising-nematic critical point of metals in spatial dimension $d=2$ by an expansion below $d=5/2$. The anisotropy associated with directions parallel and normal to the Fermi surface leads to a violation of the scaling expectations: $\\eta$ scales in the same manner as a chiral conductivity, and the ratio $\\eta/s$ diverges as $T^{-2/z}$, where $z$ is the dynamic critical exponent for fermionic excitations dispersing normal to the Fermi surface.
Gattenlöhner, S; Hannes, W-R; Ostrovsky, P M; Gornyi, I V; Mirlin, A D; Titov, M
2014-01-17
We explore the longitudinal conductivity of graphene at the Dirac point in a strong magnetic field with two types of short-range scatterers: adatoms that mix the valleys and "scalar" impurities that do not mix them. A scattering theory for the Dirac equation is employed to express the conductance of a graphene sample as a function of impurity coordinates; an averaging over impurity positions is then performed numerically. The conductivity σ is equal to the ballistic value 4e2/πh for each disorder realization, provided the number of flux quanta considerably exceeds the number of impurities. For weaker fields, the conductivity in the presence of scalar impurities scales to the quantum-Hall critical point with σ≃4×0.4e2/h at half filling or to zero away from half filling due to the onset of Anderson localization. For adatoms, the localization behavior is also obtained at half filling due to splitting of the critical energy by intervalley scattering. Our results reveal a complex scaling flow governed by fixed points of different symmetry classes: remarkably, all key manifestations of Anderson localization and criticality in two dimensions are observed numerically in a single setup.
Exotic quantum critical point on the surface of three-dimensional topological insulator
Bi, Zhen; You, Yi-Zhuang; Xu, Cenke
2016-07-01
In the last few years a lot of exotic and anomalous topological phases were constructed by proliferating the vortexlike topological defects on the surface of the 3 d topological insulator (TI) [Fidkowski et al., Phys. Rev. X 3, 041016 (2013), 10.1103/PhysRevX.3.041016; Chen et al., Phys. Rev. B 89, 165132 (2014), 10.1103/PhysRevB.89.165132; Bonderson et al., J. Stat. Mech. (2013) P09016, 10.1088/1742-5468/2013/09/P09016; Wang et al., Phys. Rev. B 88, 115137 (2013), 10.1103/PhysRevB.88.115137; Metlitski et al., Phys. Rev. B 92, 125111 (2015), 10.1103/PhysRevB.92.125111]. In this work, rather than considering topological phases at the boundary, we will study quantum critical points driven by vortexlike topological defects. In general, we will discuss a (2 +1 )d quantum phase transition described by the following field theory: L =ψ ¯γμ(∂μ-i aμ) ψ +| (∂μ-i k aμ) ϕ| 2+r|ϕ | 2+g |ϕ| 4 , with tuning parameter r , arbitrary integer k , Dirac fermion ψ , and complex scalar bosonic field ϕ , which both couple to the same (2 +1 )d dynamical noncompact U(1) gauge field aμ. The physical meaning of these quantities/fields will be explained in the text. Making use of the new duality formalism developed in [Metlitski et al., Phys. Rev. B 93, 245151 (2016), 10.1103/PhysRevB.93.245151; Wang et al., Phys. Rev. X 5, 041031 (2015), 10.1103/PhysRevX.5.041031; Wang et al., Phys. Rev. B 93, 085110 (2016), 10.1103/PhysRevB.93.085110; D. T. Son, Phys. Rev. X 5, 031027 (2015), 10.1103/PhysRevX.5.031027], we demonstrate that this quantum critical point has a quasi-self-dual nature. And at this quantum critical point, various universal quantities such as the electrical conductivity and scaling dimension of gauge-invariant operators, can be calculated systematically through a 1 /k2 expansion, based on the observation that the limit k →+∞ corresponds to an ordinary 3 d X Y transition.
Quantum criticality from Fisher information
Song, Hongting; Luo, Shunlong; Fu, Shuangshuang
2017-04-01
Quantum phase transition is primarily characterized by a qualitative sudden change in the ground state of a quantum system when an external or internal parameter of the Hamiltonian is continuously varied. Investigating quantum criticality using information-theoretic methods has generated fruitful results. Quantum correlations and fidelity have been exploited to characterize the quantum critical phenomena. In this work, we employ quantum Fisher information to study quantum criticality. The singular or extremal point of the quantum Fisher information is adopted as the estimated thermal critical point. By a significant model constructed in Quan et al. (Phys Rev Lett 96: 140604, 2006), the effectiveness of this method is illustrated explicitly.
Cai, Ang; Pixley, Jedediah; Si, Qimiao
Heavy fermion metals represent a canonical system to study superconductivity driven by quantum criticality. We are particularly motivated by the properties of CeRhIn5, which shows the characteristic features of a Kondo destruction quantum critical point (QCP) in its normal state, and has one of the highest Tc's among the heavy fermion superconductors. As a first step to study this problem within a cluster-EDMFT approach, we analyze a four-site Anderson impurity model with the antiferromagnetic spin component of the cluster coupled to a sub-Ohmic bosonic bath. We find a QCP that belongs to the same universality class as the single-site Bose-Fermi Anderson model. Together with previous work on a two-site model, our result suggests that the Kondo destruction QCP is robust as cluster size increases. More importantly, we are able to calculate the d-wave pairing susceptibility, which we find to be enhanced near the QCP. Using this model as the effective cluster model of the periodic Anderson model, we are also able to study the superconducting pairing near the Kondo-destruction QCP of the lattice model; preliminary results will be presented.
Magnetic and superconducting quantum critical points of heavy-fermion systems
Energy Technology Data Exchange (ETDEWEB)
Demuer, A.; Sheikin, I.; Braithwaite, D. E-mail: dbraithwaite@cea.fr; Faak, B.; Huxley, A.; Raymond, S.; Flouquet, J
2001-05-01
Two examples of heavy-fermion systems are presented : CePd{sub 2}Si{sub 2}, an antiferromagnet with a quantum critical point at P{sub C}=28 kbar and UGe{sub 2} an itinerant ferromagnet which transits in a paramagnetic phase above P{sub C}=16 kbar. In CePd{sub 2}Si{sub 2} the superconductivity domain is centered on P{sub C}. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Neel temperatures. In UGe{sub 2} superconductivity appears in 9 kbar at a temperature T{sub S}, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border (P
Magnetic and superconducting quantum critical points of heavy-fermion systems
Demuer, A.; Sheikin, I.; Braithwaite, D.; Fåk, B.; Huxley, A.; Raymond, S.; Flouquet, J.
2001-05-01
Two examples of heavy-fermion systems are presented : CePd 2Si 2, an antiferromagnet with a quantum critical point at PC=28 kbar and UGe 2 an itinerant ferromagnet which transits in a paramagnetic phase above PC=16 kbar. In CePd 2Si 2 the superconductivity domain is centered on PC. Special attention was given to the superconducting and magnetic anomalies at their superconducting and Néel temperatures. In UGe 2 superconductivity appears in 9 kbar at a temperature TS, more than two orders of magnitude lower than the Curie temperature; furthermore, it occurs only on the magnetic border ( P< PC). Another characteristic temperature TX is detected by resistivity; the zigzag uranium chain of the lattice may favor a supplementary nesting in the majority spin band.
New quantum-critical-point-related effects in Ce lattice systems
Energy Technology Data Exchange (ETDEWEB)
Sereni, J.G. [Division Bajas Temperaturas, Centro Atomico Bariloche (CNEA), 8400 S.C. de Bariloche (Argentina)]. E-mail: jsereni@cab.cnea.gov.ar
2004-12-31
Anomalous physical properties related to quantum critical points are investigated in Ce-systems whose magnetic phase boundaries, TN,C(x,p), can be traced for at least one decade of temperature. A change from the usual negative curvature to a linear concentration, x, dependence of TN,C(x) is observed at x*>=xcr/2 (xcr being the critical concentration). Within the x*xxcr region, the usual specific heat temperature dependence Cm/T{proportional_to}Ln(1/T) develops above TN,C, while a nearly constant value of Cm/T maximum is observed besides a scaling of Cm/T(T) with {delta}T=T-TN,C. Coincidentally, a significant increase of the zero-point entropy S0(x)(=RLn2-Sm(x,T)) occurs. Dimensionality and dynamics of the spin fluctuations can be analyzed computing the internal energy and entropy for T>=TN and AC-susceptibility results. Consequences for the free-energy evolution within this region and implications of the S0(x) increase are discussed.
Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.
2016-10-01
Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 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 TN. Isothermal measurements at T sound attenuation α reveal two closely spaced features of different characters on approaching the material's quantum-critical point (QCP) at Bs ≈ 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 TN(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/kB ≈ 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.
Uncovering the hidden quantum critical point in disordered massless Dirac and Weyl semimetals
Pixley, J. H.; Huse, David A.; Das Sarma, S.
2016-09-01
We study the properties of the avoided or hidden quantum critical point (AQCP) in three-dimensional Dirac and Weyl semimetals in the presence of short range potential disorder. By computing the averaged density of states (along with its second and fourth derivative at zero energy) with the kernel polynomial method (KPM) we systematically tune the effective length scale that eventually rounds out the transition and leads to an AQCP. We show how to determine the strength of the avoidance, establishing that it is not controlled by the long wavelength component of the disorder. Instead, the amount of avoidance can be adjusted via the tails of the probability distribution of the local random potentials. A binary distribution with no tails produces much less avoidance than a Gaussian distribution. We introduce a double Gaussian distribution to interpolate between these two limits. As a result we are able to make the length scale of the avoidance sufficiently large so that we can accurately study the properties of the underlying transition (that is eventually rounded out), unambiguously identify its location, and provide accurate estimates of the critical exponents ν =1.01 ±0.06 and z =1.50 ±0.04 . We also show that the KPM expansion order introduces an effective length scale that can also round out the transition in the scaling regime near the AQCP.
Kondo effect and quantum critical point in Mn(1-x)CoxSi
Teyssier, J.; Viennois, R.; Guritanu, V.; Giannini, E.; van der Marel, D.
2010-01-01
We report magnetic, transport and neutron diffraction studies of the solid solution Mn1-xCoxSi. For the Mn rich compounds, a sharp decrease of the Curie temperature is observed upon cobalt doping and neutron elastic scattering shows that the helimagnetic order of MnSi persists up to x = 0.06 with a shortening of the helix period. For higher Co concentrations (0.06 Weiss temperature changes sign and the system enters an antiferromagnetic state upon cooling (TN=9K for x = 0.50). In this doping range, the antiferromagnetic coupling leads to a Kondo effect marked by a minimum in the resistivity. This scenario is supported by the scaling of the magnetoresistance with a TK approx 6.5 K, close to the change in curvature of the resistivity and in agreement with the Weiss temperature from magnetic susceptibility. The sign change of the Weiss temperature and the transition from a helimagnetic to an antiferromagnetic ground state, with increasing the Co doping, point toward the existence of a quantum critical point at the composition Mn0.94Co0.06Si.
Coexistence of order and chaos at critical points of first-order quantum phase transitions in nuclei
Macek, M
2011-01-01
We study the interplay between ordered and chaotic dynamics at the critical point of a generic first-order quantum phase transition in the interacting boson model of nuclei. Classical and quantum analyses reveal a distinct behavior of the coexisting phases. While the dynamics in the deformed phase is robustly regular, the spherical phase shows strongly chaotic behavior in the same energy intervals. The effect of collective rotations on the dynamics is investigated.
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
2016-07-01
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 ≈0.17, 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.
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.
Quantum critical point for stripe order: An organizing principle of cuprate superconductivity
Energy Technology Data Exchange (ETDEWEB)
Doiron-Leyraud, Nicolas [Departement de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Canada Canadian Institute for Advanced Research, Toronto (Canada); Taillefer, Louis, E-mail: Louis.Taillefer@USherbrooke.ca [Departement de Physique and RQMP, Universite de Sherbrooke, Sherbrooke, Canada Canadian Institute for Advanced Research, Toronto (Canada)
2012-11-01
A spin density-wave quantum critical point (QCP) is the central organizing principle of organic, iron-pnictide, heavy-fermion and electron-doped cuprate superconductors. It accounts for the superconducting T{sub c} dome, the non-Fermi-liquid resistivity, and the Fermi-surface reconstruction. Outside the magnetically ordered phase above the QCP, scattering and pairing decrease in parallel as the system moves away from the QCP. Here we argue that a similar scenario, based on a stripe-order QCP, is a central organizing principle of hole-doped cuprate superconductors. Key properties of La{sub 1.8-x}Eu{sub 0.2}Sr{sub x}CuO{sub 4}, La{sub 1.6-x}Nd{sub 0.4}Sr{sub x}CuO{sub 4} and YBa{sub 2}Cu{sub 3}O{sub y} are naturally unified, including stripe order itself, its QCP, Fermi-surface reconstruction, the linear-T resistivity, and the nematic character of the pseudogap phase.
Is U3Ni3Sn4 best described as near a quantum critical point?
Energy Technology Data Exchange (ETDEWEB)
Booth, C.H.; Shlyk, L.; Nenkov, K.; Huber, J.G.; De Long, L.E.
2003-04-08
Although most known non-Fermi liquid (NFL) materials are structurally or chemically disordered, the role of this disorder remains unclear. In particular, very few systems have been discovered that may be stoichiometric and well ordered. To test whether U{sub 3}Ni{sub 3}Sn{sub 4} belongs in this latter class, we present measurements of the x-ray absorption fine structure (XAFS) of polycrystalline and single-crystal U{sub 3}Ni{sub 3}Sn{sub 4} samples that are consistent with no measurable local atomic disorder. We also present temperature-dependent specific heat data in applied magnetic fields as high as 8 T that show features that are inconsistent with the antiferromagnetic Griffiths' phase model, but do support the conclusion that a Fermi liquid/NFL crossover temperature increases with applied field. These results are inconsistent with theoretical explanations that require strong disorder effects, but do support the view that U{sub 3}Ni{sub 3}Sn{sub 4} is a stoichoiometric, ordered material that exhibits NFL behavior, and is best described as being near an antiferromagnetic quantum critical point.
Zero-point term and quantum effects in the Johnson noise of resistors: a critical appraisal
Kish, Laszlo B.; Niklasson, Gunnar A.; Granqvist, Claes G.
2016-05-01
There is a longstanding debate about the zero-point term in the Johnson noise voltage of a resistor. This term originates from a quantum-theoretical treatment of the fluctuation-dissipation theorem (FDT). Is the zero-point term really there, or is it only an experimental artifact, due to the uncertainty principle, for phase-sensitive amplifiers? Could it be removed by renormalization of theories? We discuss some historical measurement schemes that do not lead to the effect predicted by the FDT, and we analyse new features that emerge when the consequences of the zero-point term are measured via the mean energy and force in a capacitor shunting the resistor. If these measurements verify the existence of a zero-point term in the noise, then two types of perpetual motion machines can be constructed. Further investigation with the same approach shows that, in the quantum limit, the Johnson-Nyquist formula is also invalid under general conditions even though it is valid for a resistor-antenna system. Therefore we conclude that in a satisfactory quantum theory of the Johnson noise, the FDT must, as a minimum, include also the measurement system used to evaluate the observed quantities. Issues concerning the zero-point term may also have implications for phenomena in advanced nanotechnology.
Critically damped quantum search.
Mizel, Ari
2009-04-17
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we find that there is a critical damping value that divides between the quantum O(sqrt[N]) and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-point quantum search algorithm in which ignorance of the number of targets increases the number of oracle queries only by a factor of 1.5.
Superconductivity around quantum critical point in P-doped iron arsenides
Energy Technology Data Exchange (ETDEWEB)
Cao Guanghan, E-mail: ghcao@zju.edu.c [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Jiang Shuai; Wang Cao; Li Yuke; Ren Zhi; Tao Qian; Dai Jianhui; Xu Zhuan [Department of Physics, Zhejiang University, Hangzhou 310027 (China)
2010-12-15
We demonstrate that, by the P/As substitution-without doping of charge carriers-in a FeAs-layer-based parent compound, superconductivity can be universally introduced. The maximum superconducting critical temperature (T{sub c}) of BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2} achieves 30 K. The P doping in LnFeAsO system (Ln = La and Sm) produces superconductivity below 11 K. The normal-state resistivity obeys linear temperature dependence and the normal-state Hall coefficient shows strong temperature dependence. These non-Fermi liquid behaviors suggest magnetic quantum criticality. The maximum T{sub c} values in different systems correlates strongly with the diagonal bondangle of Fe-As-Fe, implying the important role of the next-nearest-neighbor magnetic exchange coupling in iron pnictide superconductors.
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.
3 d - 4 d hybridization anomaly in NixPd1-x alloys at quantum critical point
Swain, P.; Srivastava, Sanjeev K.; Srivastava, Suneel K.
2017-07-01
First-principles density functional theory computations of electronic structure and local magnetic properties of the non-fluctuating ground state of NixPd1-x alloy system around its quantum critical point xc=0.026 have been performed. The density of states at the Fermi energy and certain other parameters characterizing the Ni 3 d - Pd 4 d hybridization apparently follow power-laws with x similar to that obeyed by the reported ferromagnetic to paramagnetic transition temperature. The width of Pd 4 d density of states (DOS) and centroid of Ni 3 d DOS show peak-like anomalies in the neighbourhood of xc, and so indicate a possible scenario of the existence of a definite relation between the orbital hybridization and the emergence of quantum fluctuations in the system.
Evidence of a quantum critical point in Ce1-xYbxCoIn5 alloys at high Yb doping
Singh, Y. P.; Haney, D. J.; Huang, X. Y.; White, B. D.; Maple, M. B.; Dzero, M.; Almasan, C. C.
2015-03-01
We performed this study on single crystals of Ce1-xYbxCoIn5 alloys with the motivation to further explore some of the previously reported unusual behaviors such as robust coherence and superconductivity, non-Fermi liquid (NFL) behavior, and the possibility of quantum criticality in higher Yb doping. Our specific heat and electronic magneto-transport measurements on the alloy with x = 0.75 nominal doping down to temperatures (T) as low as 0.5 K and magnetic fields (H) as high as 14 T. Our analysis of both specific heat and resistivity data unveils the presence of a crossover from NFL behavior at high temperatures to Fermi-liquid (FL) behavior at lower temperatures. Our analysis also indicates that the origin of the NFL behavior is a result of quantum fluctuations of unknown origin. The H-T phase diagram extracted from resistivity and specific heat shows that the crossover from NFL to FL behavior at zero temperature occurs at H = 0. This implies that the alloy with x = 0.75 Yb concentration is quantum critical, i.e., xc = 0.75. This result of zero field quantum critical point at x = 0.75 is also confirmed from our analysis of magneto-resistance data. This work was supported by the National Science Foundation (Grant NSF DMR-1006606) and Ohio Board of Regents (Grant OBR-RIP-220573) at KSU, and by the U.S. Department of Energy (Grant DE-FG02- 04ER46105) at UCSD.
Finite-temperature scaling close to Ising-nematic quantum critical points in two-dimensional metals
Punk, Matthias
2016-11-01
We study finite-temperature properties of metals close to an Ising-nematic quantum critical point in two spatial dimensions. In particular we show that at any finite temperature there is a regime where order parameter fluctuations are characterized by a dynamical critical exponent z =2 , in contrast to z =3 found at zero temperature. Our results are based on a simple Eliashberg-type approach, which gives rise to a boson self-energy proportional to Ω /γ (T ) at small momenta, where γ (T ) is the temperature dependent fermion scattering rate. These findings might shed some light on recent Monte Carlo simulations at finite temperature, where results consistent with z =2 were found.
Schroeder, Almut; Ubaid-Kassis, Sara; Vojta, Thomas
2011-03-09
We report magnetization measurements close to the ferromagnetic quantum phase transition of the d-metal alloy Ni(1 - x)V(x) at a vanadium concentration of x(c)≈11.4%. In the diluted regime (x > x(c)), the temperature (T) and magnetic field (H) dependences of the magnetization are characterized by nonuniversal power laws and display H/T scaling in a wide temperature and field range. The exponents vary strongly with x and follow the predictions of a quantum Griffiths phase. We also discuss the deviations and limits of the quantum Griffiths phase as well as the phase boundaries due to bulk and cluster physics.
Sentís, Gael; Bagan, Emilio; Calsamiglia, John; Chiribella, Giulio; Muñoz-Tapia, Ramon
2016-10-01
Sudden changes are ubiquitous in nature. Identifying them is crucial for a number of applications in biology, medicine, and social sciences. Here we take the problem of detecting sudden changes to the quantum domain. We consider a source that emits quantum particles in a default state, until a point where a mutation occurs that causes the source to switch to another state. The problem is then to find out where the change occurred. We determine the maximum probability of correctly identifying the change point, allowing for collective measurements on the whole sequence of particles emitted by the source. Then, we devise online strategies where the particles are measured individually and an answer is provided as soon as a new particle is received. We show that these online strategies substantially underperform the optimal quantum measurement, indicating that quantum sudden changes, although happening locally, are better detected globally.
Quantum critical point of Dirac fermion mass generation without spontaneous symmetry breaking
He, Yuan-Yao; Wu, Han-Qing; You, Yi-Zhuang; Xu, Cenke; Meng, Zi Yang; Lu, Zhong-Yi
2016-12-01
We study a lattice model of interacting Dirac fermions in (2 +1 ) dimensions space-time with an SU(4) symmetry. While increasing the interaction strength, this model undergoes a continuous quantum phase transition from a weakly interacting Dirac semimetal to a fully gapped and nondegenerate phase without condensing any Dirac fermion bilinear mass operator. This unusual mechanism for mass generation is consistent with recent studies of interacting topological insulators/superconductors, and also consistent with recent progress in the lattice QCD community.
Quantum Critical Point, Scaling, and Universality in High Tc [CaxLa(1-x)][Ba(2-c-x)La(c+x)]Cu3Oy
2005-01-01
Using charge transport observations on sintered ceramic samples of CLBLCO, we failed to observe the Quantum Critical Point (QCP) where it is expected. Experimental data relating Cooper pair density, electrical conductivity, and superconductivity critical temperature suggest that Homes' relation might need a more specific definition of 'sigma'. Transport observations on YBCO single crystals will resolve this question.
Institute of Scientific and Technical Information of China (English)
崔珊; 何兰坡; 洪晓晨; 朱相德; Cedomir Petrovic; 李世燕
2016-01-01
It was found that selenium doping can suppress the charge-density-wave (CDW) order and induce bulk supercon-ductivity in ZrTe3. The observed superconducting dome suggests the existence of a CDW quantum critical point (QCP) in ZrTe3−x Sex near x≈0.04. To elucidate the superconducting state near the CDW QCP, we measure the thermal conductivity of two ZrTe3−x Sex single crystals (x=0.044 and 0.051) down to 80 mK. For both samples, the residual linear termκ0/T at zero field is negligible, which is a clear evidence for nodeless superconducting gap. Furthermore, the field dependence ofκ0/T manifests a multigap behavior. These results demonstrate multiple nodeless superconducting gaps in ZrTe3−x Sex , which indicates conventional superconductivity despite of the existence of a CDW QCP.
Energy Technology Data Exchange (ETDEWEB)
Kawasaki, S; Tabuchi, T; Zheng Guoqing [Department of Physics, Okayama University, Okayama 700-8530 (Japan); Wang, X F; Chen, X H [Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2010-05-15
{sup 75}As-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe{sub 2}As{sub 2} under pressure. At P = 4.7 and 10.8 kbar, the temperature dependencies of nuclear-spin-lattice relaxation rate (1/T{sub 1}) measured in the tetragonal phase show no coherence peak just below T{sub 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.
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.
Energy Technology Data Exchange (ETDEWEB)
Zuo, Zheng-Wei, E-mail: zuozw@163.com [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Kang, Da-wei [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); Wang, Zhao-Wu [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China); National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Li, Liben [School of Physics and Engineering, Henan University of Science and Technology, Luoyang 471003 (China)
2016-08-26
The tunneling junction between one-dimensional topological superconductor and integer (fractional) topological insulator (TI), realized via point contact, is investigated theoretically with bosonization technology and renormalization group methods. For the integer TI case, in a finite range of edge interaction parameter, there is a non-trivial stable fixed point which corresponds to the physical picture that the edge of TI breaks up into two sections at the junction, with one side coupling strongly to the Majorana fermion and exhibiting perfect Andreev reflection, while the other side decouples, exhibiting perfect normal reflection at low energies. This fixed point can be used as a signature of the Majorana fermion and tested by nowadays experiment techniques. For the fractional TI case, the universal low-energy transport properties are described by perfect normal reflection, perfect Andreev reflection, or perfect insulating fixed points dependent on the filling fraction and edge interaction parameter of fractional TI. - Highlights: • Tunneling junctions between topological superconductor and topological insulator are investigated. • There is a non-trivial stable fixed point in integer topological insulator case at low energies. • The edge of topological insulator breaks up into two sections at the junction. • One side couples strongly to the Majorana fermion and exhibits perfect Andreev reflection. • The other side decouples and exhibits perfect normal reflection.
Field and pressure response of Yb compounds close to a quantum critical point
Indian Academy of Sciences (India)
C Seuring; E W Scheidt; E Bauer
2002-05-01
YbCu5-Al provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic ﬁeld. Near to the critical concentration cr ≈ 1.5 non-Fermi-liquid properties (NFL) are obvious, obeying hyperscaling. If magnetic order sets in for >1.5, the application of moderate magnetic ﬁelds quenches order and again NFL features become evident. Hyperscaling in this case indicates strongly interacting spin ﬂuctuations.
Kleine, Christian; Mußhoff, Julian; Anders, Frithjof B.
2014-12-01
The energy-dependent scattering of fermions from a localized orbital at an energy-dependent rate Γ (ɛ ) ∝|ɛ| r gives rise to quantum critical points (QCPs) in the pseudogap single-impurity Anderson model separating a local moment phase with an unscreened spin moment from a strong-coupling phase which slightly deviates from the screened phase of standard Kondo problem. Using the time-dependent numerical renormalization group (TD-NRG) approach we show that local dynamic properties always equilibrate towards a steady-state value even for quenches across the QCP but with systematic deviations from the thermal equilibrium depending on the distance to the critical coupling. Local nonequilibrium properties are presented for interaction quenches and hybridization quenches. We augment our numerical data by an analytical calculation that becomes exact at short times and find excellent agreement between the numerics and the analytical theory. For interaction quenches within the screened phase we find a universal function for the time-dependent local double occupancy. We trace back the discrepancy between our results and the data obtained by a time-dependent Gutzwiller variational approach to restrictions of the wave-function ansatz in the Gutzwiller theory: while the NRG ground states properly account for the formation of an extended spin moment which decouples from the system in the unscreened phase, the Gutzwiller ansatz only allows the formation of the spin moment on the local impurity orbital.
Goh, S K; Tompsett, D A; Saines, P J; Chang, H C; Matsumoto, T; Imai, M; Yoshimura, K; Grosche, F M
2015-03-06
The quasiskutterudite superconductor Sr_{3}Rh_{4}Sn_{13} features a pronounced anomaly in electrical resistivity at T^{*}∼138 K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T^{*} as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., x_{c}=0.9). This establishes the (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures.
DEFF Research Database (Denmark)
Jensen, Ole B.; Morelli, Nicola
2011-01-01
where the networks meet and establish contact. Thus we argue for the usefulness of the notion of Critical Point of Contact (CPC) to deepen our understanding of the actual life within networks. En route to this notion we draw upon theories within as diverse realms such as interaction design, service...
DEFF Research Database (Denmark)
2012-01-01
In this brief article, we shall illustrate the application of the analytical and interventionist concept of ‘Critical Points of Contact’ (CPC) through a number of urban design studios. The notion of CPC has been developed over a span of the last three to four years and is reported in more detail...
Sentís, Gael; Calsamiglia, John; Chiribella, Giulio; Munoz-Tapia, Ramon
2016-01-01
Sudden changes are ubiquitous in nature. Identifying them is of crucial importance for a number of applications in medicine, biology, geophysics, and social sciences. Here we investigate the problem in the quantum domain, considering a source that emits particles in a default state, until a point where it switches to another state. Given a sequence of particles emitted by the source, the problem is to find out where the change occurred. For large sequences, we obtain an analytical expression for the maximum probability of correctly identifying the change point when joint measurements on the whole sequence are allowed. We also construct strategies that measure the particles individually and provide an online answer as soon as a new particle is emitted by the source. We show that these strategies substantially underperform the optimal strategy, indicating that quantum sudden changes, although happening locally, are better detected globally.
Critical-Point Structure in Finite Nuclei
Leviatan, A
2006-01-01
Properties of quantum shape-phase transitions in finite nuclei are considered in the framework of the interacting boson model. Special emphasis is paid to the dynamics at the critical-point of a general first-order phase transition.
Quantum Criticality via Magnetic Branes
D'Hoker, Eric; Kraus, Per
Holographic methods are used to investigate the low temperature limit, including quantum critical behavior, of strongly coupled 4-dimensional gauge theories in the presence of an external magnetic field, and finite charge density. In addition to the metric, the dual gravity theory contains a Maxwell field with Chern-Simons coupling. In the absence of charge, the magnetic field induces an RG flow to an infrared {AdS}3 × {R}2 geometry, which is dual to a 2-dimensional CFT representing strongly interacting fermions in the lowest Landau level. Two asymptotic Virasoro algebras and one chiral Kac-Moody algebra arise as emergent symmetries in the IR. Including a nonzero charge density reveals a quantum critical point when the magnetic field reaches a critical value whose scale is set by the charge density. The critical theory is probed by the study of long-distance correlation functions of the boundary stress tensor and current. All quantities of major physical interest in this system, such as critical exponents and scaling functions, can be computed analytically. We also study an asymptotically AdS 6 system whose magnetic field induced quantum critical point is governed by an IR Lifshitz geometry, holographically dual to a D=2+1 field theory. The behavior of these holographic theories shares important similarities with that of real world quantum critical systems obtained by tuning a magnetic field, and may be relevant to materials such as Strontium Ruthenates.
Isobe, Hiroki; Yang, Bohm-Jung; Chubukov, Andrey; Schmalian, Jörg; Nagaosa, Naoto
2016-02-19
We study the effects of Coulomb interaction between 2D Weyl fermions with anisotropic dispersion which displays relativistic dynamics along one direction and nonrelativistic dynamics along the other. Such a dispersion can be realized in phosphorene under electric field or strain, in TiO_{2}/VO_{2} superlattices, and, more generally, at the quantum critical point between a nodal semimetal and an insulator in systems with a chiral symmetry. Using the one-loop renormalization group approach in combination with the large-N expansion, we find that the system displays interaction-driven non-Fermi liquid behavior in a wide range of intermediate frequencies and marginal Fermi liquid behavior at the smallest frequencies. In the non-Fermi liquid regime, the quasiparticle residue Z at energy E scales as Z∝E^{a} with a>0, and the parameters of the fermionic dispersion acquire anomalous dimensions. In the marginal Fermi-liquid regime, Z∝(|logE|)^{-b} with universal b=3/2.
Rose, F.; Dupuis, N.
2017-01-01
Using a nonperturbative functional renormalization-group approach to the two-dimensional quantum O (N ) model, we compute the low-frequency limit ω →0 of the zero-temperature conductivity in the vicinity of the quantum critical point. Our results are obtained from a derivative expansion to second order of a scale-dependent effective action in the presence of an external (i.e., nondynamical) non-Abelian gauge field. While in the disordered phase the conductivity tensor σ (ω ) is diagonal, in the ordered phase it is defined, when N ≥3 , by two independent elements, σA(ω ) and σB(ω ) , respectively associated to SO (N ) rotations which do and do not change the direction of the order parameter. For N =2 , the conductivity in the ordered phase reduces to a single component σA(ω ) . We show that limω→0σ (ω ,δ ) σA(ω ,-δ ) /σq2 is a universal number, which we compute as a function of N (δ measures the distance to the quantum critical point, q is the charge, and σq=q2/h the quantum of conductance). On the other hand we argue that the ratio σB(ω →0 ) /σq is universal in the whole ordered phase, independent of N and, when N →∞ , equal to the universal conductivity σ*/σq at the quantum critical point.
Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K
2015-11-13
The family of the superconducting quasiskutterudites (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) features a structural quantum critical point at x(c)=0.9, around which a dome-shaped variation of the superconducting transition temperature T(c) is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x(c), which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2Δ/k(B)T(c) and ΔC/γT(c) beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13) thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity.
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.
Directory of Open Access Journals (Sweden)
Debra Lewis
2013-05-01
Full Text Available Relative equilibria of Lagrangian and Hamiltonian systems with symmetry are critical points of appropriate scalar functions parametrized by the Lie algebra (or its dual of the symmetry group. Setting aside the structures – symplectic, Poisson, or variational – generating dynamical systems from such functions highlights the common features of their construction and analysis, and supports the construction of analogous functions in non-Hamiltonian settings. If the symmetry group is nonabelian, the functions are invariant only with respect to the isotropy subgroup of the given parameter value. Replacing the parametrized family of functions with a single function on the product manifold and extending the action using the (coadjoint action on the algebra or its dual yields a fully invariant function. An invariant map can be used to reverse the usual perspective: rather than selecting a parametrized family of functions and finding their critical points, conditions under which functions will be critical on specific orbits, typically distinguished by isotropy class, can be derived. This strategy is illustrated using several well-known mechanical systems – the Lagrange top, the double spherical pendulum, the free rigid body, and the Riemann ellipsoids – and generalizations of these systems.
Lewis, Debra
2013-05-01
Relative equilibria of Lagrangian and Hamiltonian systems with symmetry are critical points of appropriate scalar functions parametrized by the Lie algebra (or its dual) of the symmetry group. Setting aside the structures - symplectic, Poisson, or variational - generating dynamical systems from such functions highlights the common features of their construction and analysis, and supports the construction of analogous functions in non-Hamiltonian settings. If the symmetry group is nonabelian, the functions are invariant only with respect to the isotropy subgroup of the given parameter value. Replacing the parametrized family of functions with a single function on the product manifold and extending the action using the (co)adjoint action on the algebra or its dual yields a fully invariant function. An invariant map can be used to reverse the usual perspective: rather than selecting a parametrized family of functions and finding their critical points, conditions under which functions will be critical on specific orbits, typically distinguished by isotropy class, can be derived. This strategy is illustrated using several well-known mechanical systems - the Lagrange top, the double spherical pendulum, the free rigid body, and the Riemann ellipsoids - and generalizations of these systems.
Finding critical points whose polarization is also a critical point
Squassina, Marco; Van Schaftingen, Jean
2011-01-01
We show that near any given minimizing sequence of paths for the mountain pass lemma, there exists a critical point whose polarization is also a critical point. This is motivated by the fact that if any polarization of a critical point is also a critical point and the Euler-Lagrange equation is a second-order semi-linear elliptic problem, T. Bartsch, T. Weth and M. Willem (J. Anal. Math., 2005) have proved that the critical point is axially symmetric.
DEFF Research Database (Denmark)
Jensen, Ole B.; Morelli, Nicola
2011-01-01
where the networks meet and establish contact. Thus we argue for the usefulness of the notion of Critical Point of Contact (CPC) to deepen our understanding of the actual life within networks. En route to this notion we draw upon theories within as diverse realms such as interaction design, service...... design, geography, and mobility studies. After the introduction in section we develop and define the notion of CPC based upon a broad set of disciplines and theories. We illustrate the usefulness of the notion within the field of mobility in the network city and within the field of service design...
Critically damped quantum search
Mizel, Ari
2008-01-01
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we have found that there is a critical damping value that divides between the quantum $O(\\sqrt{N})$ and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-poin...
Mielczarek, Jakub
2014-01-01
This essay addresses the issue of gravitational phase transitions in the early universe. We suggest that a second order phase transition observed in the Causal Dynamical Triangulations approach to quantum gravity may have a cosmological relevance. The phase transition interpolates between a non-geometric crumpled phase of gravity, and an extended phase with classical properties. Transitions of this kind have been postulated earlier in the context of geometrogenesis in Quantum Graphity. We show that critical behavior may also be associated with a signature change event in Loop Quantum Cosmology. In both cases, classical spacetime originates at the critical point associated with a second order phase transition.
Multidimensional entropy landscape of quantum criticality
Grube, K.; Zaum, S.; Stockert, O.; Si, Q.; Löhneysen, H. V.
2017-08-01
The third law of thermodynamics states that the entropy of any system in equilibrium has to vanish at absolute zero temperature. At nonzero temperatures, on the other hand, matter is expected to accumulate entropy near a quantum critical point, where it undergoes a continuous transition from one ground state to another. Here, we determine, based on general thermodynamic principles, the spatial-dimensional profile of the entropy S near a quantum critical point and its steepest descent in the corresponding multidimensional stress space. We demonstrate this approach for the canonical quantum critical compound CeCu 6-xAux near its onset of antiferromagnetic order. We are able to link the directional stress dependence of S to the previously determined geometry of quantum critical fluctuations. Our demonstration of the multidimensional entropy landscape provides the foundation to understand how quantum criticality nucleates novel phases such as high-temperature superconductivity.
Directory of Open Access Journals (Sweden)
Jakub Mielczarek
2017-01-01
Full Text Available This article addresses the issue of possible gravitational phase transitions in the early universe. We suggest that a second-order phase transition observed in the Causal Dynamical Triangulations approach to quantum gravity may have a cosmological relevance. The phase transition interpolates between a nongeometric crumpled phase of gravity and an extended phase with classical properties. Transition of this kind has been postulated earlier in the context of geometrogenesis in the Quantum Graphity approach to quantum gravity. We show that critical behavior may also be associated with a signature change in Loop Quantum Cosmology, which occurs as a result of quantum deformation of the hypersurface deformation algebra. In the considered cases, classical space-time originates at the critical point associated with a second-order phase transition. Relation between the gravitational phase transitions and the corresponding change of symmetry is underlined.
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.
Universality of quantum critical dynamics in a planar OPO
Drummond, P D; Drummond, Peter D.; Dechoum, Kaled
2005-01-01
We analyze the critical quantum fluctuations in a coherently driven planar optical parametric oscillator. We show that the presence of transverse modes combined with quantum fluctuations changes the behavior of the `quantum image' critical point. This zero-temperature non-equilibrium quantum system has the same universality class as a finite-temperature magnetic Lifshitz transition.
Critical dynamics near QCD critical point
Minami, Yuki
2012-01-01
In this thesis, we study the critical dynamics near the QCD critical point. Near the critical point, the relevant modes for the critical dynamics are identified as the hydrodynamic modes. Thus, we first study the linear dynamics of them by the relativistic hydrodynamics. We show that the thermal diffusion mode is the most relevant mode, whereas the sound mode is suppressed around the critical point. We also find that the Landau equation, which is believed to be an acausal hydrodynamic equation, has no problem to describe slowly varying fluctuations. Moreover, we find that the Israel-Stewart equation, which is a causal one, gives the same result as the Landau equation gives in the long-wavelength region. Next, we study the nonlinear dynamics of the hydrodynamic modes by the nonlinear Langevin equation and the dynamic renormalization group (RG). In the vicinity of the critical point, the usual hydrodynamics breaks down by large fluctuations. Thus, we must consider the nonlinear Langevin equation. We construct t...
QCD critical point: The race is on
Indian Academy of Sciences (India)
Rajiv V Gavai
2015-05-01
A critical point in the phase diagram of quantum chromodynamics (QCD), if established either theoretically or experimentally, would be as profound a discovery as the good-old gas–liquid critical point. Unlike the latter, however, first-principles-based approaches are being employed to locate it theoretically. Due to the short-lived nature of the concerned phases, novel experimental techniques are needed to search for it. The Relativistic Heavy Ion Collider (RHIC) in USA has an experimental programme to do so. This short review is an attempt to provide a glimpse of the race between the theorists and the experimentalists as well as the synergy between them.
Uranium Critical Point Location Problem
Iosilevskiy, Igor
2013-01-01
Significant uncertainty of our present knowledge for uranium critical point parameters is under consideration. Present paper is devoted to comparative analysis of possible resolutions for the problem of uranium critical point location, as well as to discussion of plausible scheme of decisive experiment, which could resolve existing uncertainty. New calculations of gas-liquid coexistence in uranium by modern thermodynamic code are included in the analysis.
Nonequilibrium critical scaling in quantum thermodynamics
Bayat, Abolfazl; Apollaro, Tony J. G.; Paganelli, Simone; De Chiara, Gabriele; Johannesson, Henrik; Bose, Sougato; Sodano, Pasquale
2016-05-01
The emerging field of quantum thermodynamics is contributing important results and insights into archetypal many-body problems, including quantum phase transitions. Still, the question whether out-of-equilibrium quantities, such as fluctuations of work, exhibit critical scaling after a sudden quench in a closed system has remained elusive. Here, we take a novel approach to the problem by studying a quench across an impurity quantum critical point. By performing density matrix renormalization group computations on the two-impurity Kondo model, we are able to establish that the irreversible work produced in a quench exhibits finite-size scaling at quantum criticality. This scaling faithfully predicts the equilibrium critical exponents for the crossover length and the order parameter of the model, and, moreover, implies an exponent for the rescaled irreversible work. By connecting the irreversible work to the two-impurity spin correlation function, our findings can be tested experimentally.
Quantum point contacts in quantum wire systems
Energy Technology Data Exchange (ETDEWEB)
Sternemann, E.; Buchholz, S.S.; Fischer, S.F.; Kunze, U. [Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum (Germany); Reuter, D.; Wieck, A.D. [Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum (Germany)
2010-07-01
Quantum point contacts (QPCs) attract high interest for applications as magnetic focussing, beam splitting (quantum Hall edge states), spin filtering and electron thermometry. Here, we investigate QPCs in complex quantum wire (QWR) systems such as quantum rings. The QPCs were realized by lithographical definition of a short (150 nm) constriction (170 nm width) in (a) a 540 nm wide QWR and (b) 520 nm wide QWR leads of a QWR ring as in. Nanogates on top of the constrictions allow for the control of occupied modes in the QPCs. The devices are based on a GaAs/AlGaAs heterostructure with a 2DEG 55 nm below the surface, patterned by electron beam lithography and wet-chemical etching. Two- and four-terminal conductance measurements at temperatures between 23 mK and 4.2 K were performed using lock-in technique. Our measurements reveal that QPCs in 1D nanostructures can be prepared to show subband separations of 6 meV, clear conductance quantization as well as the 0.7 anomaly. We further show that electron injection across a QPC into a QWR ring allows for electron interference (Aharonov-Bohm effect).
Quantum points/patterns, Part 2. From quantum points to quantum patterns via multiresolution
Fedorova, Antonina N
2011-01-01
It is obvious that we still have not any unified framework covering a zoo of interpretations of Quantum Mechanics, as well as satisfactory understanding of main ingredients of a phenomena like entanglement. The starting point is an idea to describe properly the key ingredient of the area, namely point/particle-like objects (physical quantum points/particles or, at least, structureless but quantum objects) and to change point (wave) functions by sheaves to the sheaf wave functions (Quantum Sheaves). In such an approach Quantum States are sections of the coherent sheaves or contravariant functors from the kinematical category describing space-time to other one, Quantum Dynamical Category, properly describing the complex dynamics of Quantum Patterns. The objects of this category are some filtrations on the functional realization of Hilbert space of Quantum States. In this Part 2, the sequel of Part 1, we present a family of methods which can describe important details of complex behaviour in quantum ensembles: t...
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.
Squire, Richard H.; March, Norman H.; Booth, Michael L.
There has been considerable effort expended toward understanding high temperature superconductors (HTSC), and more specifically the cuprate phase diagram as a function of doping level. Yet, the only agreement seems to be that HTSC is an example of a strongly correlated material where Coulomb repulsion plays a major role. This manuscript proposes a model based on a Feshbach resonance pairing mechanism and competing orders. An initial BCS-type superconductivity at high doping is suppressed in the two particle channel by a localized preformed pair (PP) (Nozieres and Schmitt-Rink, J Low Temp Phys, 1985, 59, 980) (circular density wave) creating a quantum critical point. As doping continues to diminish, the PP then participates in a Feshbach resonance complex that creates a new electron (hole) pair that delocalizes and constitutes HTSC and the characteristic dome (Squire and March, Int J Quantum Chem, 2007, 107, 3013; 2008, 108, 2819). The resonant nature of the new pair contributes to its short coherence length. The model we propose also suggests an explanation (and necessity) for an experimentally observed correlated lattice that could restrict energy dissipation to enable the resonant Cooper pair to move over several correlation lengths, or essentially free. The PP density wave is responsible for the pseudogap as it appears as a "localized superconductor" since its density of states and quasiparticle spectrum are similar to those of a superconductor (Peierls-Fröhlich theory), but with no phase coherence between the PP.
Rose, Félix
2016-01-01
Using a nonperturbative functional renormalization-group approach to the two-dimensional quantum O($N$) model, we compute the low-frequency limit $\\omega\\to 0$ of the zero-temperature conductivity in the vicinity of the quantum critical point. Our results are obtained from a derivative expansion to second order of a scale-dependent effective action in the presence of an external (i.e., non-dynamical) non-Abelian gauge field. While in the disordered phase the conductivity tensor $\\sigma(\\omega)$ is diagonal, in the ordered phase it is defined, when $N\\geq 3$, by two independent elements, $\\sigma_{\\rm A}(\\omega)$ and $\\sigma_{\\rm B}(\\omega)$, respectively associated to SO($N$) rotations which do and do not change the direction of the order parameter. For $N=2$, the conductivity in the ordered phase reduces to a single component $\\sigma_{\\rm A}(\\omega)$. We show that $\\lim_{\\omega\\to 0}\\sigma(\\omega,\\delta)\\sigma_{\\rm A}(\\omega,-\\delta)/\\sigma_q^2$ is a universal number which we compute as a function of $N$ ($\\d...
Shape phase mixing in critical point nuclei
Budaca, R
2016-01-01
Spectral properties of nuclei near the critical point of the quantum phase transition between spherical and axially symmetric shapes are studied in a hybrid collective model which combines the $\\gamma$-stable and $\\gamma$-rigid collective conditions through a rigidity parameter. The model in the lower and upper limits of the rigidity parameter recovers the X(5) and X(3) solutions respectively, while in the equally mixed case it corresponds to the X(4) critical point symmetry. Numerical applications of the model on nuclei from regions known for critical behavior reveal a sizable shape phase mixing and its evolution with neutron or proton numbers. The model also enables a better description of energy spectra and electromagnetic transitions for these nuclei.
Critical points of metal vapors
Energy Technology Data Exchange (ETDEWEB)
Khomkin, A. L., E-mail: alhomkin@mail.ru; Shumikhin, A. S. [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)
2015-09-15
A new method is proposed for calculating the parameters of critical points and binodals for the vapor–liquid (insulator–metal) phase transition in vapors of metals with multielectron valence shells. The method is based on a model developed earlier for the vapors of alkali metals, atomic hydrogen, and exciton gas, proceeding from the assumption that the cohesion determining the basic characteristics of metals under normal conditions is also responsible for their properties in the vicinity of the critical point. It is proposed to calculate the cohesion of multielectron atoms using well-known scaling relations for the binding energy, which are constructed for most metals in the periodic table by processing the results of many numerical calculations. The adopted model allows the parameters of critical points and binodals for the vapor–liquid phase transition in metal vapors to be calculated using published data on the properties of metals under normal conditions. The parameters of critical points have been calculated for a large number of metals and show satisfactory agreement with experimental data for alkali metals and with available estimates for all other metals. Binodals of metals have been calculated for the first time.
The critical end point through observables
Energy Technology Data Exchange (ETDEWEB)
Kozlov, G. [Joint Institute for Nuclear Research, Joliot-Curie st.6, Dubna, 141980 (Russian Federation)
2016-01-22
We develop the model of the critical phenomena of strongly interacting matter at high temperatures and baryon densities. The dual Yang-Mills theory with scalar degrees of freedom (the dilatons) is used. The dilatons are the consequence of a spontaneous breaking of a scale symmetry. The phase transitions are considered in systems where the field conjugate to the order parameter has the critical end mode. The critical end point (CEP) is a distinct singular feature existence of which is dictated by the chiral dynamics. The physical realization of CEP is via the influence quantum fluctuations of two-body Bose-Einstein correlations for observed particles to which the critical end mode couples.
Cheng, Jie; Dong, Peng; Xu, Wei; Liu, Shengli; Chu, Wangsheng; Chen, Xianhui; Wu, Ziyu
2015-07-01
Many researchers have pointed out that there is a quantum critical point (QCP) in the F-doped SmOFeAs system. In this paper, the electronic structure and local structure of the superconductive FeAs layer in SmO(1-x)FxFeAs as a function of the F-doping concentration have been investigated using Fe and As K-edge X-ray absorption spectroscopy. Experiments performed on the X-ray absorption near-edge structure showed that in the vicinity of the QCP the intensity of the pre-edge feature at the Fe-edge decreases continuously, while there is a striking rise of the shoulder-peak at the As edge, suggesting the occurrence of charge redistribution near the QCP. Further analysis on the As K-edge extended X-ray absorption fine structure demonstrated that the charge redistribution originates mostly from a shortening of the Fe-As bond at the QCP. An evident relationship between the mysterious QCP and the fundamental Fe-As bond was established, providing new insights on the interplay between QCP, charge dynamics and the local structural Fe-As bond in Fe-based superconductors.
The Critical Point Facility (CPF)
1992-01-01
The Critical Point Facility (CPF) is an ESA multiuser facility designed for microgravity research onboard Spacelab. It has been conceived and built to offer investigators opportunities to conduct research on critical point phenomena in microgravity. This facility provides the high precision and stability temperature standards required in this field of research. It has been primarily designed for the purpose of optical investigations of transparent fluids. During a Spacelab mission, the CPF automatically processes several thermostats sequentially, each thermostat corresponding to an experiment. The CPF is now integrated in Spacelab at Kennedy Space Center, in preparation for the International Microgravity Lab. mission. The CPF was designed to submit transparent fluids to an adequate, user defined thermal scenario, and to monitor their behavior by using thermal and optical means. Because they are strongly affected by gravity, a good understanding of critical phenomena in fluids can only be gained in low gravity conditions. Fluids at the critical point become compressed under their own weight. The role played by gravity in the formation of interfaces between distinct phases is not clearly understood.
Pole distribution of PVI transcendents close to a critical point
Guzzetti, Davide
2012-12-01
The distribution of the poles of Painlevé VI transcendents associated to semi-simple Frobenius manifolds is determined close to a critical point. It is shown that the poles accumulate at the critical point, asymptotically along two rays. As an example, the Frobenius manifold given by the quantum cohomology of CP2 is considered. The general PVI is also considered.
Quantum criticality of hot random spin chains.
Vasseur, R; Potter, A C; Parameswaran, S A
2015-05-29
We study the infinite-temperature properties of an infinite sequence of random quantum spin chains using a real-space renormalization group approach, and demonstrate that they exhibit nonergodic behavior at strong disorder. The analysis is conveniently implemented in terms of SU(2)_{k} anyon chains that include the Ising and Potts chains as notable examples. Highly excited eigenstates of these systems exhibit properties usually associated with quantum critical ground states, leading us to dub them "quantum critical glasses." We argue that random-bond Heisenberg chains self-thermalize and that the excited-state entanglement crosses over from volume-law to logarithmic scaling at a length scale that diverges in the Heisenberg limit k→∞. The excited state fixed points are generically distinct from their ground state counterparts, and represent novel nonequilibrium critical phases of matter.
QCD Critical Point in a Quasiparticle Model
Srivastava, P K; Singh, C P
2010-01-01
Recent theoretical investigations have unveiled a rich structure in the quantum chromodynamics (QCD) phase diagram which consists of quark gluon plasma (QGP) and the hadronic phases but also supports the existence of a cross-over transition ending at a critical end point (CEP). We find a too large variation in determination of the coordinates of the CEP in the temperature (T), baryon chemical potential ($\\mu_{B}$) plane and, therefore, its identification in the current heavy-ion experiments becomes debatable. Here we use an equation of state (EOS) for a deconfined QGP using a thermodynamically consistent quasiparticle model involving quarks and gluons having thermal masses. We further use a thermodynamically consistent excluded volume model for the hadron gas (HG) which was recently proposed by us. Using these equations of state, a first order deconfining phase transition is constructed using Gibbs' criteria. This leads to an interesting finding that the phase transition line ends at a critical point (CEP) be...
Energy Technology Data Exchange (ETDEWEB)
Nakanishi, Y; Kamiyama, T; Ito, K; Nakamura, M; Yoshizawa, M [Graduate School of Engineering, Iwate University, Morioka 020-8551 (Japan); Saiga, Y [Graduate School of Advanced Sciences of Matter, Hiroshima University, HigashiHiroshima 739-8530 (Japan); Kosaka, M [Department of Physics, Saitama University, Saitama 338-8570 (Japan); Uwatoko, Y, E-mail: yoshiki@iwate-u.ac.j [Institute for Solid State Physics, University of Tokyo, Kashiwa 227-8581 (Japan)
2010-01-15
We performed ultrasonic measurements on high quality single crystals of the Yb-based heavy fermion compounds YbTr{sub 2}Zn{sub 20} (Tr: Co, Rh and Ir) over a temperature range from 200 K to 0.5 K, which seem to be close to a quantum critical point (QCP). A sharp contrast of the temperature dependence of elastic constants was found at low temperature among the three compounds, reflecting the 4f electronic state stemmed from Yb ion. The results indicate that a crystalline electric field (CEF) effect seems to be dominant in the systems YbRh{sub 2}Zn{sub 20} and YbIr{sub 2}Zn{sub 20} at low temperatures. On the other hand, the CEF effect is much less, but an additional effect would be dominant which is most probably ascribable to non Fermi liquid characteristics formed close to the QCP. We discuss briefly each 4f electronic state developed at the low temperatures and physical parameters relating to a renormalized band model in YbTr{sub 2}Zn{sub 20} in the framework of a deformation potential approximation.
Indications of a Quantum Critical Point in Bi2Sr2CaCu2O8+δ Using a Local Kondo Effect
Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle
2014-03-01
A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By substituting Fe atoms for Cu atoms in the CuO plane of Bi2Sr2CaCu2O8+δ (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.
Quantum critical point in SmO(1-x)F(x)FeAs and oxygen vacancy induced by high fluorine dopant.
Cheng, Jie; Chu, Shengqi; Chu, Wangsheng; Xu, Wei; Zhou, Jing; Zhang, Linjuan; Zhao, Haifeng; Liu, Ronghua; Chen, Xianhui; Marcelli, Augusto; Wu, Ziyu
2011-09-01
The local lattice and electronic structure of the high-T(c) superconductor SmO(1-x)F(x)FeAs as a function of F-doping have been investigated by Sm L(3)-edge X-ray absorption near-edge structure and multiple-scattering calculations. Experiments performed at the L(3)-edge show that the white line (WL) is very sensitive to F-doping. In the under-doped region (x ≤ 0.12) the WL intensity increases with doping and then it suddenly starts decreasing at x = 0.15. Meanwhile, the trend of the WL linewidth versus F-doping levels is just contrary to that of the intensity. The phenomenon is almost coincident with the quantum critical point occurring in SmO(1-x)F(x)FeAs at x ≃ 0.14. In the under-doped region the increase of the intensity is related to the localization of Sm-5d states, while theoretical calculations show that both the decreasing intensity and the consequent broadening of linewidth at high F-doping are associated with the content and distribution of oxygen vacancies.
Interval Mathematics Applied to Critical Point Transitions
Stradi, Benito A.
2012-01-01
The determination of critical points of mixtures is important for both practical and theoretical reasons in the modeling of phase behavior, especially at high pressure. The equations that describe the behavior of complex mixtures near critical points are highly nonlinear and with multiplicity of solutions to the critical point equations. Interval arithmetic can be used to reliably locate all the critical points of a given mixture. The method also verifies the nonexistence of a critical point ...
Critical Point Symmetries in Nuclei
Bonatsos, D; Petrellis, D; Terziev, P A; Yigitoglu, I; Bonatsos, Dennis
2006-01-01
Critical Point Symmetries (CPS) appear in regions of the nuclear chart where a rapid change from one symmetry to another is observed. The first CPSs, introduced by F. Iachello, were E(5), which corresponds to the transition from vibrational [U(5)] to gamma-unstable [O(6)] behaviour, and X(5), which represents the change from vibrational [U(5)] to prolate axially deformed [SU(3)] shapes. These CPSs have been obtained as special solutions of the Bohr collective Hamiltonian. More recent special solutions of the same Hamiltonian, to be described here, include Z(5) and Z(4), which correspond to maximally triaxial shapes (the latter with ``frozen'' gamma=30 degrees), as well as X(3), which corresponds to prolate shapes with ``frozen'' gamma=0. CPSs have the advantage of providing predictions which are parameter free (up to overall scale factors) and compare well to experiment. However, their mathematical structure [with the exception of E(5)] needs to be clarified.
Correlations in avalanche critical points
Cerruti, Benedetta; Vives, Eduard
2009-07-01
Avalanche dynamics and related power-law statistics are ubiquitous in nature, arising in phenomena such as earthquakes, forest fires, and solar flares. Very interestingly, an analogous behavior is associated with many condensed-matter systems, such as ferromagnets and martensites. Bearing it in mind, we study the prototypical random-field Ising model at T=0 . We find a finite correlation between waiting intervals and the previous avalanche size. This correlation is not found in other models for avalanches but it is experimentally found in earthquakes and in forest fires. Our study suggests that this effect occurs in critical points that are at the end of a first-order discontinuity separating two regimes: one with high activity from another with low activity.
Multicritical point in a diluted bilayer Heisenberg quantum antiferromagnet.
Sandvik, Anders W
2002-10-21
The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed interlayer dimers is studied using quantum Monte Carlo simulations. A zero-temperature multicritical point (p(*),g(*)) at the classical percolation density p=p(*) and interlayer coupling g(*) approximately equal 0.16 is demonstrated. The quantum critical exponents of the percolating cluster are determined using finite-size scaling. It is argued that the associated finite-temperature quantum critical regime extends to zero interlayer coupling and could be relevant for antiferromagnetic cuprates doped with nonmagnetic impurities.
Quantum Point Cloud and its Compression
Jiang, Nan; Hu, Hao; Dang, Yijie; Zhang, Wenyin
2017-10-01
Quantum computation is becoming an important and effective tool to overcome the high real-time computational requirements of classical digital image processing. The quantum representations of two-dimensional images have been a lot of achievements. However, there are only few methods to express a three-dimensional image by quantum representation. In this paper, a three-dimensional quantum representation for digital images — quantum point cloud is proposed. Moreover, a lossy compression method is used to reduce the complexity of preparation.
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.)
Critical Casimir forces from the equation of state of quantum critical systems
Rançon, Adam; Henry, Louis-Paul; Rose, Félix; Cardozo, David Lopes; Dupuis, Nicolas; Holdsworth, Peter C. W.; Roscilde, Tommaso
2016-10-01
The mapping between a classical length and inverse temperature as imaginary time provides a direct equivalence between the Casimir force of a classical system in D dimensions and internal energy of a quantum system in d =D -1 dimensions. The scaling functions of the critical Casimir force of the classical system with periodic boundaries thus emerge from the analysis of the symmetry related quantum critical point. We show that both nonperturbative renormalization group and quantum Monte Carlo analysis of quantum critical points provide quantitative estimates for the critical Casimir force in the corresponding classical model, giving access to widely different aspect ratios for the geometry of confined systems. In light of these results, we propose protocols for the realization of critical Casimir forces for periodic boundaries through state-of-the-art cold-atom and solid-state experiments.
Generalized dynamic scaling for quantum critical relaxation in imaginary time.
Zhang, Shuyi; Yin, Shuai; Zhong, Fan
2014-10-01
We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.
Anatomy of quantum critical wave functions in dissipative impurity problems
Blunden-Codd, Zach; Bera, Soumya; Bruognolo, Benedikt; Linden, Nils-Oliver; Chin, Alex W.; von Delft, Jan; Nazir, Ahsan; Florens, Serge
2017-02-01
Quantum phase transitions reflect singular changes taking place in a many-body ground state; however, computing and analyzing large-scale critical wave functions constitutes a formidable challenge. Physical insights into the sub-Ohmic spin-boson model are provided by the coherent-state expansion (CSE), which represents the wave function by a linear combination of classically displaced configurations. We find that the distribution of low-energy displacements displays an emergent symmetry in the absence of spontaneous symmetry breaking while experiencing strong fluctuations of the order parameter near the quantum critical point. Quantum criticality provides two strong fingerprints in critical low-energy modes: an algebraic decay of the average displacement and a constant universal average squeezing amplitude. These observations, confirmed by extensive variational matrix-product-state (VMPS) simulations and field theory arguments, offer precious clues into the microscopics of critical many-body states in quantum impurity models.
Quantum criticality in Einstein-Maxwell-dilaton gravity
Energy Technology Data Exchange (ETDEWEB)
Wen, Wen-Yu, E-mail: steve.wen@gmail.com [California Institute of Technology, Pasadena, CA 91125 (United States); Department of Physics and Center for Theoretical Sciences and Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 106, Taiwan (China); Department of Physics, Chung Yuan Christian University, Chung Li 32023, Taiwan (China)
2012-02-01
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.
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.
Critical point wetting drop tower experiment
Kaukler, W. F.; Tcherneshoff, L. M.; Straits, S. R.
1984-01-01
Preliminary results for the Critical Point Wetting CPW Drop Tower Experiment are produced with immiscible systems. Much of the observed phenomena conformed to the anticipated behavior. More drops will be needed to test the CPW theory with these immiscible systems.
Correlation Probes of a QCD Critical Point
Csörgö, T
2009-01-01
Critical opalescence is a characteristic experimental signature of a second order phase transition in solid state physics. A new, experimentally accessible measure of opacity and of attenuation length in heavy ion reactions is suggested, as a combination of HBT radii and nuclear modification factors. This opacity is maximal when $\\sqrt{s_{NN}}$, the system size and centrality correspond to the critical point of QCD. To characterize the phase transition at this critical point, the critical exponent of the correlation function can be determined by measuring the L\\'evy index of stability of the Bose-Einstein or HBT correlations. The exponent of the correlation length can be determined from fits to the multiplicity distribution in various pseudorapidity intervals, also as a function of colliding energy, system size, centrality and (chemical) freeze-out temperature. These two critical exponents determine the remaining four critical exponents and the universality class of this second order phase transition. As a co...
Critical points in Lovelock Black Holes
Frassino, Antonia M; Simovic, Fil
2016-01-01
We review some of the results obtained by introducing a thermodynamic pressure via the cosmological constant in a class of higher curvature theories known as Lovelock gravity. In particular, we focus on a specific relation between the higher-order Lovelock couplings that introduces a peculiar isolated critical point for hyperbolic black holes characterized by non-standard critical exponents.
Can a quantum critical state represent a blackbody?
Chakravarty, Sudip
2016-01-01
The blackbody theory of Planck played a seminal role in the development of quantum theory at the turn of the past century. A blackbody cavity is generally thought to be a collection of photons in thermal equilibrium; the radiation emitted is at all wavelengths, and the intensity follows a scaling law, which is Planck's characteristic distribution law. These photons arise from non-interacting normal modes. Here we suggest that certain quantum critical states when heated emit "radiation" at all wavelengths and satisfy all the criteria of a blackbody. An important difference is that the "radiation" does not necessarily consist of non-interacting photons, but also emergent relativistic bosons or fermions. The examples we provide include emergent relativistic fermions at a topological quantum critical point. This perspective on a quantum critical state may be illuminating in many unforeseen ways.
Parity-time symmetric quantum critical phenomena
Ashida, Yuto; Ueda, Masahito
2016-01-01
Symmetry plays a central role in the theory of phase transitions. Parity-time (PT) symmetry is an emergent notion in synthetic nonconservative systems, where the gain-loss balance creates a threshold for spontaneous symmetry breaking across which spectral singularity emerges. Considerable studies on PT symmetry have been conducted in optics and weakly interacting open quantum systems. Here by extending the idea of PT symmetry to strongly correlated many-body systems, we discover unconventional quantum critical phenomena, where spectral singularity and quantum criticality conspire to yield an exotic universality class which has no counterpart in known critical phenomena. Moreover, we find that superfluid correlation is anomalously enhanced owing to winding renormalization group flows in a PT-symmetry-broken quantum critical phase. Our findings can experimentally be tested in ultracold atoms.
Nonlinear peltier effect in quantum point contacts
Bogachek, E. N.; Scherbakov, A. G.; Landman, Uzi
1998-11-01
A theoretical analysis of the Peltier effect in two-dimensional quantum point contacts, in field-free conditions and under the influence of applied magnetic fields, is presented. It is shown that in the nonlinear regime (finite applied voltage) new peaks in the Peltier coefficient appear leading to violation of Onsager's relation. Oscillations of the Peltier coefficient in a magnetic field are demonstrated.
Critical Points in Distance Learning System
Directory of Open Access Journals (Sweden)
Airina Savickaitė
2013-08-01
Full Text Available Purpose – This article presents the results of distance learning system analysis, i.e. the critical elements of the distance learning system. The critical points of distance learning are a part of distance education online environment interactivity/community process model. The most important is the fact that the critical point is associated with distance learning participants. Design/methodology/approach – Comparative review of articles and analysis of distance learning module. Findings – A modern man is a lifelong learner and distance learning is a way to be a modern person. The focus on a learner and feedback is the most important thing of learning distance system. Also, attention should be paid to the lecture-appropriate knowledge and ability to convey information. Distance system adaptation is the way to improve the learner’s learning outcomes. Research limitations/implications – Different learning disciplines and learning methods may have different critical points. Practical implications – The information of analysis could be important for both lecturers and students, who studies distance education systems. There are familiar critical points which may deteriorate the quality of learning. Originality/value – The study sought to develop remote systems for applications in order to improve the quality of knowledge. Keywords: distance learning, process model, critical points. Research type: review of literature and general overview.
Critical Point Theory for Lagrangian Systems
Mazzucchelli, Marco
2012-01-01
Lagrangian systems constitute a very important and old class in dynamics. Their origin dates back to the end of the eighteenth century, with Joseph-Louis Lagrange's reformulation of classical mechanics. The main feature of Lagrangian dynamics is its variational flavor: orbits are extremal points of an action functional. The development of critical point theory in the twentieth century provided a powerful machinery to investigate existence and multiplicity questions for orbits of Lagrangian systems. This monograph gives a modern account of the application of critical point theory, and more spec
Pions near the chiral critical point
Hippert, M.; Fraga, E. S.; Santos, E. M.
2016-04-01
It is an exciting possibility that the QCD critical point can be found in ultrarelativistic heavy-ion collision experiments (HICs). While quantities such as some event-by-event moments of specific observables should display strong non-monotonic behavior near the critical point and could, hence, be used as signatures of criticality, it is not clear that this behavior could effectively be observed in the highly non-ideal scenario of HICs. We here employ Monte Carlo simulations to test second-order moments of pion observables as possible signatures of the critical point while taking into account some realistic ingredients, similar to the ones found in HICs. We make use of simplified models to introduce spurious contributions and dynamical effects.
Fixed-point adiabatic quantum search
Dalzell, Alexander M.; Yoder, Theodore J.; Chuang, Isaac L.
2017-01-01
Fixed-point quantum search algorithms succeed at finding one of M target items among N total items even when the run time of the algorithm is longer than necessary. While the famous Grover's algorithm can search quadratically faster than a classical computer, it lacks the fixed-point property—the fraction of target items must be known precisely to know when to terminate the algorithm. Recently, Yoder, Low, and Chuang [Phys. Rev. Lett. 113, 210501 (2014), 10.1103/PhysRevLett.113.210501] gave an optimal gate-model search algorithm with the fixed-point property. Previously, it had been discovered by Roland and Cerf [Phys. Rev. A 65, 042308 (2002), 10.1103/PhysRevA.65.042308] that an adiabatic quantum algorithm, operating by continuously varying a Hamiltonian, can reproduce the quadratic speedup of gate-model Grover search. We ask, can an adiabatic algorithm also reproduce the fixed-point property? We show that the answer depends on what interpolation schedule is used, so as in the gate model, there are both fixed-point and non-fixed-point versions of adiabatic search, only some of which attain the quadratic quantum speedup. Guided by geometric intuition on the Bloch sphere, we rigorously justify our claims with an explicit upper bound on the error in the adiabatic approximation. We also show that the fixed-point adiabatic search algorithm can be simulated in the gate model with neither loss of the quadratic Grover speedup nor of the fixed-point property. Finally, we discuss natural uses of fixed-point algorithms such as preparation of a relatively prime state and oblivious amplitude amplification.
Quantum point contacts as heat engines
Pilgram, Sebastian; Sánchez, David; López, Rosa
2015-11-01
The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely.
Transport signatures of quantum critically in Cr at high pressure.
Energy Technology Data Exchange (ETDEWEB)
Jaramillo, R.; Feng, Y.; Wang, J.; Rosenbaum, T. F. (X-Ray Science Division); ( PSC-USR); (Harvard Univ.); (Univ. of Chicago)
2010-08-03
The elemental antiferromagnet Cr at high pressure presents a new type of naked quantum critical point that is free of disorder and symmetry-breaking fields. Here we measure magnetotransport in fine detail around the critical pressure, P{sub c} {approx} 10 GPa, in a diamond anvil cell and reveal the role of quantum critical fluctuations at the phase transition. As the magnetism disappears and T {yields} 0, the magntotransport scaling converges to a non-mean-field form that illustrates the reconstruction of the magnetic Fermi surface, and is distinct from the critical scaling measured in chemically disordered Cr:V under pressure. The breakdown of itinerant antiferromagnetism only comes clearly into view in the clean limit, establishing disorder as a relevant variable at a quantum phase transition.
Quantum critical metals in 4 -ɛ dimensions
Torroba, Gonzalo; Wang, Huajia
2014-10-01
We study the quantum theory of a Fermi surface coupled to a gapless boson scalar in D =4 -ɛ space-time dimensions as a simple model for non-Fermi liquids (NFL) near a quantum phase transition. Our analysis takes into account the full backreaction from Landau damping of the boson, and obtains an RG flow that proceeds through three distinct stages. Above the scale of Landau damping, the Fermi velocity flows to zero, while the coupling evolves according to its classical dimension. Once damping becomes important, its backreaction leads to a crossover regime where dynamic and static damping effects compete and the fermion self-energy does not respect scaling. Below this crossover and having tuned the boson to criticality, the theory flows to a z =3 scalar interacting with an NFL. We finally analyze the IR phases of the theory with arbitrary number of flavors Nc. When Nc is small, the superconducting dome covers the NFL behavior; strikingly, for moderately large Nc, we find that NFL effects become important first, before the onset of superconductivity. A generic prediction of the theory is that the Fermi velocity and quasiparticle residue vanish with a power law ωɛ as the fixed point is approached. These features may be useful for understanding some of the phenomenology of high-Tc materials in a systematic ɛ expansion.
Nonionic reverse micelles near the critical point.
Shrestha, Lok Kumar; Shrestha, Rekha Goswami
2013-01-01
We report shape, size, and internal cross-sectional structure of diglycerol monomyristate (C₁₄G₂) reverse micelles in n-hexadecane near the critical point using small-angle X-ray scattering (SAXS). Pair-distance distribution function, p(r), which gives structural information in real-space, was obtained by indirect Fourier transformation (IFT) method. The p(r) showed a clear picture of rodlike micelles at higher temperatures well above the critical point (micellar solution phase separates into two immiscible liquids at ~ 48°C). At a fixed surfactant concentration (5% C₁₄G₂), decrease in temperature increases the micellar size monotonously and surprisingly shape of the p(r) curve at 50°C; close to the critical point, mimics the shape of the two dimensional disk-like micelles indicating the onset of critical fluctuations (attractive interactions among rodlike micelles forming a weak network). A similar behavior has been observed with normal micelles in aqueous system near the critical point. When the system is heated to 60°C, shape of the p(r) curve regains rodlike structure. At fixed temperature of 60°C, increase in C₁₄G₂ concentration induced one dimensional micellar growth. Maximum length of micelles increases from ca. 23.5 to 46.0 nm upon increasing concentration from 1 to 12% keeping cross section diameter apparently unchanged at ca. 4.0 nm.
Macroscopic Quantum Phenomena from the Correlation, Coupling and Criticality Perspectives
Chou, C. H.; Hu, B. L.; Subaşi, Y.
2011-12-01
In this sequel paper we explore how macroscopic quantum phenomena can be measured or understood from the behavior of quantum correlations which exist in a quantum system of many particles or components and how the interaction strengths change with energy or scale, under ordinary situations and when the system is near its critical point. We use the nPI (master) effective action related to the Boltzmann-BBGKY / Schwinger-Dyson hierarchy of equations as a tool for systemizing the contributions of higher order correlation functions to the dynamics of lower order correlation functions. Together with the large N expansion discussed in our first paper [1] we explore 1) the conditions whereby an H-theorem is obtained, which can be viewed as a signifier of the emergence of macroscopic behavior in the system. We give two more examples from past work: 2) the nonequilibrium dynamics of N atoms in an optical lattice under the large Script N (field components), 2PI and second order perturbative expansions, illustrating how N and Script N enter in these three aspects of quantum correlations, coherence and coupling strength. 3) the behavior of an interacting quantum system near its critical point, the effects of quantum and thermal fluctuations and the conditions under which the system manifests infrared dimensional reduction. We also discuss how the effective field theory concept bears on macroscopic quantum phenomena: the running of the coupling parameters with energy or scale imparts a dynamical-dependent and an interaction-sensitive definition of 'macroscopia'.
Thermodynamic curvature from the critical point to the triple point.
Ruppeiner, George
2012-08-01
I evaluate the thermodynamic curvature R for fourteen pure fluids along their liquid-vapor coexistence curves, from the critical point to the triple point, using thermodynamic input from the NIST Chemistry WebBook. In this broad overview, R is evaluated in both the coexisting liquid and vapor phases. R is an invariant whose magnitude |R| is a measure of the size of mesoscopic organized structures in a fluid, and whose sign specifies whether intermolecular interactions are effectively attractive (R0). I discuss five principles for R in pure fluids: (1) Near the critical point, the attractive part of the interactions forms loose structures of size |R| proportional to the correlation volume ξ(3), and the sign of R is negative. (2) In the vapor phase, there are instances of compact clusters of size |R| formed by the attractive part of the interactions and prevented from collapse by the repulsive part of the interactions, and the sign of R is positive. (3) In the asymptotic critical point regime, the R's in the coexisting liquid and vapor phases are equal to each other, i.e., commensurate. (4) Outside the asymptotic critical-point regime incommensurate R's may be associated with metastability. (5) The compact liquid phase has |R| on the order of the volume of a molecule, with the sign of R being negative for a liquidlike state held together by attractive interactions and the sign of R being positive for a solidlike state held up by repulsive interactions. These considerations amplify and extend the application of thermodynamic curvature in pure fluids.
On the Quantum Geometry of Multi-critical CDT
Atkin, Max R
2012-01-01
We extend a recently introduced model of multi-critical CDT to higher multi-critical points. It is observed that the continuum limit can be taken on the level of the action and that the resulting continuum surface model is again described by a matrix model. The resolvent, a simple observable of the quantum geometry which is accessible from the matrix model is calculated for arbitrary multi-critical points. We go beyond the matrix model by determining the propagator using the peeling procedure which is used to extract the effective quantum Hamiltonian and the Hausdorff dimension. With this at hand a string field theory formalism for multi-critical CDT is introduced and it is shown that the Dyson-Schwinger equations match the loop equations of the matrix model. We conclude by commenting on how to formally obtain the sum over topologies and a relation to stochastic quantisation.
Holographic butterfly effect and diffusion in quantum critical region
Ling, Yi; Xian, Zhuo-Yu
2017-09-01
We investigate the butterfly effect and charge diffusion near the quantum phase transition in holographic approach. We argue that their criticality is controlled by the holographic scaling geometry with deformations induced by a relevant operator at finite temperature. Specifically, in the quantum critical region controlled by a single fixed point, the butterfly velocity decreases when deviating from the critical point. While, in the non-critical region, the behavior of the butterfly velocity depends on the specific phase at low temperature. Moreover, in the holographic Berezinskii-Kosterlitz-Thouless transition, the universal behavior of the butterfly velocity is absent. Finally, the tendency of our holographic results matches with the numerical results of Bose-Hubbard model. A comparison between our result and that in the O( N ) nonlinear sigma model is also given.
Hall effect in quantum critical charge-cluster glass.
Wu, Jie; Bollinger, Anthony T; Sun, Yujie; Božović, Ivan
2016-04-19
Upon doping, cuprates undergo a quantum phase transition from an insulator to a d-wave superconductor. The nature of this transition and of the insulating state is vividly debated. Here, we study the Hall effect in La2-xSrxCuO4(LSCO) samples doped near the quantum critical point atx∼ 0.06. Dramatic fluctuations in the Hall resistance appear belowTCG∼ 1.5 K and increase as the sample is cooled down further, signaling quantum critical behavior. We explore the doping dependence of this effect in detail, by studying a combinatorial LSCO library in which the Sr content is varied in extremely fine steps,Δx∼ 0.00008. We observe that quantum charge fluctuations wash out when superconductivity emerges but can be restored when the latter is suppressed by applying a magnetic field, showing that the two instabilities compete for the ground state.
Note on "Quantum superconducting criticality in graphene and topological insulators"
Roy, Bitan; Herbut, Igor F
2016-01-01
We correct our previous conclusion regarding the fate of a charged quantum critical point across the superconducting transition for two dimensional massless Dirac fermion. Within the leading order $\\epsilon$ expansion, we now find that the requisite number of four-component Dirac fermion flavors ($N_f$) for the continuous phase transition through a charged critical point is $N_f>18.2699$. For $N_f\\geq1/2$, the critical number of bosonic flavors for this transition is significantly reduced as compared to the value determined in the absence of the Dirac fermions in the theory.
The Critical Point Entanglement and Chaos in the Dicke Model
Directory of Open Access Journals (Sweden)
Lina Bao
2015-07-01
Full Text Available Ground state properties and level statistics of the Dicke model for a finite number of atoms are investigated based on a progressive diagonalization scheme (PDS. Particle number statistics, the entanglement measure and the Shannon information entropy at the resonance point in cases with a finite number of atoms as functions of the coupling parameter are calculated. It is shown that the entanglement measure defined in terms of the normalized von Neumann entropy of the reduced density matrix of the atoms reaches its maximum value at the critical point of the quantum phase transition where the system is most chaotic. Noticeable change in the Shannon information entropy near or at the critical point of the quantum phase transition is also observed. In addition, the quantum phase transition may be observed not only in the ground state mean photon number and the ground state atomic inversion as shown previously, but also in fluctuations of these two quantities in the ground state, especially in the atomic inversion fluctuation.
Critical point of view: a Wikipedia reader
Lovink, G.; Tkacz, N.
2011-01-01
For millions of internet users around the globe, the search for new knowledge begins with Wikipedia. The encyclopedia’s rapid rise, novel organization, and freely offered content have been marveled at and denounced by a host of commentators. Critical Point of View moves beyond unflagging praise, wel
A Holographic Model For Quantum Critical Responses
Myers, Robert C; Witczak-Krempa, William
2016-01-01
We analyze the dynamical response functions of strongly interacting quantum critical states described by conformal field theories (CFTs). We construct a self-consistent holographic model that incorporates the relevant scalar operator driving the quantum critical phase transition. Focusing on the finite temperature dynamical conductivity $\\sigma(\\omega,T)$, we study its dependence on our model parameters, notably the scaling dimension of the relevant operator. It is found that the conductivity is well-approximated by a simple ansatz proposed by Katz et al [1] for a wide range of parameters. We further dissect the conductivity at large frequencies $\\omega >> T$ using the operator product expansion, and show how it reveals the spectrum of our model CFT. Our results provide a physically-constrained framework to study the analytic continuation of quantum Monte Carlo data, as we illustrate using the O(2) Wilson-Fisher CFT. Finally, we comment on the variation of the conductivity as we tune away from the quantum cri...
Critical point fluctuations in supported lipid membranes.
Connell, Simon D; Heath, George; Olmsted, Peter D; Kisil, Anastasia
2013-01-01
In this paper, we demonstrate that it is possible to observe many aspects of critical phenomena in supported lipid bilayers using atomic force microscopy (AFM) with the aid of stable and precise temperature control. The regions of criticality were determined by accurately measuring and calculating phase diagrams for the 2 phase L(d)-L(o) region, and tracking how it moves with temperature, then increasing the sampling density around the estimated critical regions. Compositional fluctuations were observed above the critical temperature (T(c)) and characterised using a spatial correlation function. From this analysis, the phase transition was found to be most closely described by the 2D Ising model, showing it is a critical transition. Below T(c) roughening of the domain boundaries occurred due to the reduction in line tension close to the critical point. Smaller scale density fluctuations were also detected just below T(c). At T(c), we believe we have observed fluctuations on length scales greater than 10 microm. The region of critically fluctuating 10-100 nm nanodomains has been found to extend a considerable distance above T(c) to temperatures within the biological range, and seem to be an ideal candidate for the actual structure of lipid rafts in cell membranes. Although evidence for this idea has recently emerged, this is the first direct evidence for nanoscale domains in the critical region.
Abrahams, Elihu; Wölfle, Peter
2012-02-28
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 YbRh(2)Si(2), 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.
Correlated fluctuations near the QCD critical point
Jiang, Lijia; Song, Huichao
2015-01-01
In this paper, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy dependent cumulant $C_4$ and $\\kappa \\sigma^2$ of net protons through tuning the related parameters. However, the calculated $C_2$ and $C_3$ with both Poisson and Binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. In order to qualitatively and quantitatively describe the experimental data, the dynamical critical fluctuations and more realistic non-critical fluctuation baselines should be investigated in the near future.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
2016-02-01
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as a control parameter driving the second-order critical end point Tc of the metal-insulator transition down to zero at t⊥c/t ≃0.2 . Below t⊥c, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far.
Critical point anomalies include expansion shock waves
Energy Technology Data Exchange (ETDEWEB)
Nannan, N. R., E-mail: ryan.nannan@uvs.edu [Mechanical Engineering Discipline, Anton de Kom University of Suriname, Leysweg 86, PO Box 9212, Paramaribo, Suriname and Process and Energy Department, Delft University of Technology, Leeghwaterstraat 44, 2628 CA Delft (Netherlands); Guardone, A., E-mail: alberto.guardone@polimi.it [Department of Aerospace Science and Technology, Politecnico di Milano, Via La Masa 34, 20156 Milano (Italy); Colonna, P., E-mail: p.colonna@tudelft.nl [Propulsion and Power, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands)
2014-02-15
From first-principle fluid dynamics, complemented by a rigorous state equation accounting for critical anomalies, we discovered that expansion shock waves may occur in the vicinity of the liquid-vapor critical point in the two-phase region. Due to universality of near-critical thermodynamics, the result is valid for any common pure fluid in which molecular interactions are only short-range, namely, for so-called 3-dimensional Ising-like systems, and under the assumption of thermodynamic equilibrium. In addition to rarefaction shock waves, diverse non-classical effects are admissible, including composite compressive shock-fan-shock waves, due to the change of sign of the fundamental derivative of gasdynamics.
Correlated fluctuations near the QCD critical point
Jiang, Lijia; Li, Pengfei; Song, Huichao
2016-08-01
In this article, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy-dependent cumulant C4 and κ σ2 of net protons through tuning the related parameters. However, the calculated C2 and C3 with both Poisson and binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. To qualitatively and quantitatively describe all the related experimental data, the dynamical critical fluctuations and more realistic noncritical fluctuation baselines should be investigated in the near future.
Tuning the quantum critical crossover in quantum dots
Murthy, Ganpathy
2005-03-01
Quantum dots with large Thouless number g embody a regime where both disorder and interactions can be treated nonperturbatively using large-N techniques (with N=g) and quantum phase transitions can be studied. Here we focus on dots where the noninteracting Hamiltonian is drawn from a crossover ensemble between two symmetry classes, where the crossover parameter introduces a new, tunable energy scale independent of and much smaller than the Thouless energy. We show that the quantum critical regime, dominated by collective critical fluctuations, can be accessed at the new energy scale. The nonperturbative physics of this regime can only be described by the large-N approach, as we illustrate with two experimentally relevant examples. G. Murthy, PRB 70, 153304 (2004). G. Murthy, R. Shankar, D. Herman, and H. Mathur, PRB 69, 075321 (2004)
Sensitive chemical compass assisted by quantum criticality
Cai, C. Y.; Ai, Qing; Quan, H. T.; Sun, C. P.
2012-02-01
A radical-pair-based chemical reaction might be used by birds for navigation via the geomagnetic direction. The inherent physical mechanism is that the quantum coherent transition from a singlet state to triplet states of the radical pair could respond to a weak magnetic field and be sensitive to the direction of such a field; this then results in different photopigments to be sensed by the avian eyes. Here, we propose a quantum bionic setup, inspired by the avian compass, as an ultrasensitive probe of a weak magnetic field based on the quantum phase transition of the environments of the two electrons in the radical pair. We prove that the yield of the chemical products via recombination from the singlet state is determined by the Loschmidt echo of the environments with interacting nuclear spins. Thus quantum criticality of environments could enhance the sensitivity of detection of weak magnetic fields.
Sensitive Chemical Compass Assisted by Quantum Criticality
Cai, C Y; Quan, H T; Sun, C P
2011-01-01
The radical-pair-based chemical reaction could be used by birds for the navigation via the geomagnetic direction. An inherent physical mechanism is that the quantum coherent transition from a singlet state to triplet states of the radical pair could response to the weak magnetic field and be sensitive to the direction of such a field and then results in different photopigments in the avian eyes to be sensed. Here, we propose a quantum bionic setup for the ultra-sensitive probe of a weak magnetic field based on the quantum phase transition of the environments of the two electrons in the radical pair. We prove that the yield of the chemical products via the recombination from the singlet state is determined by the Loschmidt echo of the environments with interacting nuclear spins. Thus quantum criticality of environments could enhance the sensitivity of the detection of the weak magnetic field.
Hammerath, F.; Bonfà, P.; Sanna, S.; Prando, G.; De Renzi, R.; Kobayashi, Y.; Sato, M.; Carretta, P.
2014-04-01
A superconducting-to-magnetic transition is reported for LaFeAsO0.89F0.11 where a per-thousand amount of Mn impurities is dispersed. By employing local spectroscopic techniques like muon spin rotation (μSR) and nuclear quadrupole resonance (NQR) on compounds with Mn contents ranging from x =0.025% to x =0.75%, we find that the electronic properties are extremely sensitive to the Mn impurities. In fact, a small amount of Mn as low as 0.2% suppresses superconductivity completely. Static magnetism, involving the FeAs planes, is observed to arise for x >0.1% and becomes further enhanced upon increasing Mn substitution. Also a progressive increase of low-energy spin fluctuations, leading to an enhancement of the NQR spin-lattice relaxation rate T1-1, is observed upon Mn substitution. The analysis of T1-1 for the sample closest to the crossover between superconductivity and magnetism (x =0.2%) points toward the presence of an antiferromagnetic quantum critical point around that doping level.
Chemically mediated quantum criticality in NbFe2.
Alam, Aftab; Johnson, D D
2011-11-11
Laves-phase Nb(1+c)Fe(2-c) is a rare itinerant intermetallic compound exhibiting magnetic quantum criticality at c(cr)∼1.5%Nb excess; its origin, and how alloying mediates it, remains an enigma. For NbFe(2), we show that an unconventional band critical point above the Fermi level E(F) explains most observations and that chemical alloying mediates access to this unconventional band critical point by an increase in E(F) with decreasing electrons (increasing %Nb), counter to rigid-band concepts. We calculate that E(F) enters the unconventional band critical point region for c(cr) > 1.5%Nb and by 1.74%Nb there is no Nb site-occupation preference between symmetry-distinct Fe sites, i.e., no electron-hopping disorder, making resistivity near constant as observed. At larger Nb (Fe) excess, the ferromagnetic Stoner criterion is satisfied.
Quantum criticality and DBI magneto-resistance
Kiritsis, Elias; Li, Li
2017-03-01
We use the DBI action from string theory and holography to study the magneto-resistance at quantum criticality with hyperscaling violation. We find and analyze a rich class of scaling behaviors for the magneto-resistance. A special case describes the scaling results found in pnictides by Hayers et al in 2014 (arXiv:1412.6484).
Critical Opalescence: An Optical Signature for a QCD Critical Point
Csorgo, T
2009-01-01
Four possible scenarios are considered for a transition from a quark-gluon matter to hadronic matter, and their corresponding correlation signatures are discussed. Four criteria are highlighted for a definitive experimental search for a QCD critical point. An old-new experimental measure, the optical opacity (or its inverse the nuclear attenuation length) is determined, in terms of a combination of nuclear suppression factors and a measurement of the relevant fireball length scales. Length scale estimates using either the Hanbury Brown -- Twiss radii or that of the initial nuclear geometry for measurements of optical opacity with respect to the reaction plane yield, somewhat surprizingly, nearly the same nuclear attenuation lenght in 0-5 % most central 200 GeV Au+Au collisions, corresponding to 2.9 $\\pm$ 0.3 fm. The necessity and the possibility of measuring critical exponents is also discussed in the context of determination of the universality class of the QCD critical point. Critical opalescence is propose...
Complex Critical Exponents in Diluted Systems of Quantum Rotors
Fernandes, Rafael; Schmalian, Jörg
2011-03-01
In this work, we investigate the effects of the Berry phase 2 πρ on the critical properties of XY quantum-rotors that undergo a percolation transition. This model describes a variety of randomly-diluted quantum systems, such as interacting bosons coupled to a particle reservoir, quantum planar antiferromagnets under a perpendicular magnetic field, and Josephson-junction arrays with an external bias-voltage. Focusing on the quantum critical point at the percolation threshold, we find that, for rational ρ , one recovers the power-law behavior with the same critical exponents as in the case with no Berry phase. However, for irrational ρ , the low-energy excitations change completely and are given by emergent spinless fermions with fractal spectrum. As a result, critical properties that cannot be described by the usual Ginzburg-Landau-Wilson theory of phase transitions emerge, such as complex critical exponents, log-periodic oscillations, and dynamically-broken scale invariance. Research supported by the U.S. DOE, Office of BES, Materials Science and Engineering Division.
Macroscopic Quantum Criticality in a Circuit QED
Wang, Y D; Nori, F; Quan, H T; Sun, C P; Liu, Yu-xi; Nori, Franco
2006-01-01
Cavity quantum electrodynamic (QED) is studied for two strongly-coupled charge qubits interacting with a single-mode quantized field, which is provided by a on-chip transmission line resonator. We analyze the dressed state structure of this superconducting circuit QED system and the selection rules of electromagnetic-induced transitions between any two of these dressed states. Its macroscopic quantum criticality, in the form of ground state level crossing, is also analyzed, resulting from competition between the Ising-type inter-qubit coupling and the controllable on-site potentials.
High critical temperature superconductor Josephson junctions for quantum circuit applications
Energy Technology Data Exchange (ETDEWEB)
Bauch, T; Gustafsson, D; Cedergren, K; Nawaz, S; Mumtaz Virk, M; Lombardi, F [Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, Goeteborg (Sweden); Pettersson, H; Olsson, E [Department of Applied Physics, Chalmers University of Technology, Goeteborg (Sweden)], E-mail: bauch@chalmers.se
2009-12-15
Recent findings of macroscopic quantum properties in high critical temperature superconductor (HTS) Josephson junctions (JJs) point toward the need to revise the role of zero energy quasi-particles in this novel superconductor. We will discuss the possibility of designing superconducting artificial atoms in a transmon configuration to study the low energy excitation spectra of HTS. We have engineered high quality grain boundary JJs on low dielectric constant substrates. By fabricating submicron junctions, we extract values of capacitance and Josephson critical current densities that satisfy the main transmon design requirements. Moreover, the measured critical current noise power extrapolated at 1 Hz gives a dephasing time of 25 ns, which indicates that the observation of macroscopic quantum coherent effects in HTS JJ is a feasible task.
Energy Technology Data Exchange (ETDEWEB)
Jiang Shuai; Xing Hui; Xuan Guofang; Wang Cao; Ren Zhi; Dai Jianhui; Xu Zhu' an; Cao Guanghan [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Feng, Chunmu, E-mail: ghcao@zju.edu.c [Test and Analysis Center, Zhejiang University, Hangzhou 310027 (China)
2009-09-23
We report bulk superconductivity induced by an isovalent doping of phosphorus in BaFe{sub 2}(As{sub 1-x}P{sub x}){sub 2}. The P-for-As substitution results in shrinkage of the lattice, especially for the FeAs block layers. The resistivity anomaly associated with the spin-density-wave (SDW) transition in the undoped compound is gradually suppressed by the P doping. Superconductivity with a maximum T{sub c} of 30 K emerges at x = 0.32, coinciding with a magnetic quantum critical point (QCP) which is shown by the disappearance of SDW order and the linear temperature-dependent resistivity in the normal state. The T{sub c} values were found to decrease with further P doping and no superconductivity was observed down to 2 K for x>=0.77. The appearance of superconductivity in the vicinity of QCP hints at the superconductivity mechanism in iron-based arsenides. (fast track communication)
Kondo Effect at a Quantum Critical Point
Ramazashvili, Revaz; Coleman, Piers
1998-03-01
The Kondo effect in a metal on the verge of a zero-temperature magnetic instability provides a fascinating example of interference between local and long-range correlations. (A. I. Larkin and V. I. Mel'nikov, Sov. Phys. JETP 34, 656 (1972)) (P. Coleman and A. M. Tsvelik, cond-mat/9707003) (A. Sengupta, cond-mat/9707316) We discuss possible consequences of this interference, including the breakdown of the Fermi liquid state.
Fixing the quantum three-point function
Energy Technology Data Exchange (ETDEWEB)
Jiang, Yunfeng; Kostov, Ivan [Institut de Physique Théorique, DSM, CEA, URA2306 CNRS,Saclay, F-91191 Gif-sur-Yvette (France); Loebbert, Florian [School of Natural Sciences, Institute for Advanced Study,Einstein Drive, Princeton, NJ 08540 (United States); Niels Bohr International Academy & Discovery Center, Niels Bohr Institute,Blegdamsvej 17, 2100 Copenhagen (Denmark); Serban, Didina [Institut de Physique Théorique, DSM, CEA, URA2306 CNRS,Saclay, F-91191 Gif-sur-Yvette (France)
2014-04-03
We propose a new method for the computation of quantum three-point functions for operators in su(2) sectors of N=4 super Yang-Mills theory. The method is based on the existence of a unitary transformation relating inhomogeneous and long-range spin chains. This transformation can be traced back to a combination of boost operators and an inhomogeneous version of Baxter’s corner transfer matrix. We reproduce the existing results for the one-loop structure constants in a simplified form and indicate how to use the method at higher loop orders. Then we evaluate the one-loop structure constants in the quasiclassical limit and compare them with the recent strong coupling computation.
Critical Points of the Electric Field from a Collection of Point Charges
Energy Technology Data Exchange (ETDEWEB)
Max, N; Weinkauf, T
2007-02-16
The electric field around a molecule is generated by the charge distribution of its constituents: positively charged atomic nuclei, which are well approximated by point charges, and negatively charged electrons, whose probability density distribution can be computed from quantum mechanics. For the purposes of molecular mechanics or dynamics, the charge distribution is often approximated by a collection of point charges, with either a single partial charge at each atomic nucleus position, representing both the nucleus and the electrons near it, or as several different point charges per atom. The critical points in the electric field are useful in visualizing its geometrical and topological structure, and can help in understanding the forces and motion it induces on a charged ion or neutral dipole. Most visualization tools for vector fields use only samples of the field on the vertices of a regular grid, and some sort of interpolation, for example, trilinear, on the grid cells. There is less risk of missing or misinterpreting topological features if they can be derived directly from the analytic formula for the field, rather than from its samples. This work presents a method which is guaranteed to find all the critical points of the electric field from a finite set of point charges. To visualize the field topology, we have modified the saddle connector method to use the analytic formula for the field.
Universal thermodynamics at the liquid-vapor critical point.
Sanchez, Isaac C; Boening, Kevin L
2014-11-26
For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that defines the residual chemical potential adopts a near universal value of 2/3 at the critical point. More precisely, the reciprocal of the fugacity coefficient equals 1.52 ± 0.02 and includes fluids as diverse as helium (1.50), dodecafluoropentane (1.50), and water (1.53). For 65 classical fluids, a dimensionless thermal pressure coefficient and internal pressure attain critical values of 1.88 ± 0.11 and 1.61 ± 0.11, respectively. From equations of state, values of these new critical constants have been calculated and agree favorably with experimental values. Specifically, for the critical fugacity coefficient, the following results were obtained for its reciprocal: van der Waals (1.44), lattice gas (1.43), scaled particle theory (1.46), and the Redlich-Kwong eq (1.50). The semiempirical Redlich-Kwong equation is also the most accurate for the thermal pressure coefficient (1.86) and internal pressure (1.53). Physical interpretations of these results are discussed as well as their implications for other critical phenomena.
Viscoelasticity of Xenon near the Critical Point
Berg, Robert F.; Moldover, Michael R.; Zimmerli, Gregory A.
1999-01-01
Using a novel, overdamped, oscillator flown aboard the Space Shuttle, we measured the viscosity of xenon near the liquid-vapor critical point in the frequency range 2 Hz less than or equal to f less than or equal to 12 Hz. The measured viscosity divergence is characterized by the exponent z(sub eta) = 0.0690 +/- 0.0006, in agreement with the value z(sub eta) = 0.067 +/- 0.002 calculated from a two-loop perturbation expansion. Viscoelastic behavior was evident when t = (T - T(sub c))/T(sub c) less than 10(exp -5) and dominant when t less than 10(exp -6), further from T(sub c) than predicted. Viscoelastic behavior scales as Af(tau) where tau is the fluctuation decay time. The measured value of A is 2.0 +/- 0.3 times the result of a one-loop calculation. (Uncertainties stated are one standard uncertainty.)
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
2015-01-01
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping $t_{\\perp}$ acts as a control parameter driving the second-order critical end point $T_c$ of the metal-insulator transition down to zero at $t_{\\perp}^{c}/t\\simeq 0.2$. Below $t_{\\perp}^{c}$, the volume of the hole and electron Fermi p...
Zero-point quantum fluctuations in cosmology
Hollenstein, Lukas; Maggiore, Michele; Mitsou, Ermis
2011-01-01
We re-examine the classic problem of the renormalization of zero-point quantum fluctuations in a Friedmann-Robertson-Walker background. We discuss a number of issues that arise when regularizing the theory with a momentum-space cutoff, and show explicitly how introducing non-covariant counter-terms allows to obtain covariant results for the renormalized vacuum energy-momentum tensor. We clarify some confusion in the literature concerning the equation of state of vacuum fluctuations. Further, we point out that the general structure of the effective action becomes richer if the theory contains a scalar field phi with mass m smaller than the Hubble parameter H(t). Such an ultra-light particle cannot be integrated out completely to get the effective action. Apart from the volume term and the Einstein-Hilbert term, that are reabsorbed into renormalizations of the cosmological constant and Newton's constant, the effective action in general also has a term proportional to F(phi)R, for some function F(phi). As a resu...
Edge Quantum Criticality and Emergent Supersymmetry in Topological Phases
Li, Zi-Xiang; Jiang, Yi-Fan; Yao, Hong
2017-09-01
Proposed as a fundamental symmetry describing our Universe, spacetime supersymmetry (SUSY) has not been discovered yet in nature. Nonetheless, it has been predicted that SUSY may emerge in low-energy physics of quantum materials such as topological superconductors and Weyl semimetals. Here, by performing state-of-the-art sign-problem-free quantum Monte Carlo simulations of an interacting two-dimensional topological superconductor, we show convincing evidence that the N =1 SUSY emerges at its edge quantum critical point (EQCP) while its bulk remains gapped and topologically nontrivial. Remarkably, near the EQCP, we find that the edge Majorana fermion acquires a mass that is identical with that of its bosonic superpartner. To the best of our knowledge, this is the first observation that fermions and bosons have equal dynamically generated masses, a hallmark of emergent SUSY. We further discuss experimental signatures of such EQCP and associated SUSY.
Nambu-Goldstone Effective Theory of Information at Quantum Criticality
Dvali, Gia; Gomez, Cesar; Wintergerst, Nico
2015-01-01
We establish a fundamental connection between quantum criticality of a many-body system, such as Bose-Einstein condensates, and its capacity of information-storage and processing. For deriving the effective theory of modes in the vicinity of the quantum critical point we develop a new method by mapping a Bose-Einstein condensate of $N$-particles onto a sigma model with a continuous global (pseudo)symmetry that mixes bosons of different momenta. The Bogolyubov modes of the condensate are mapped onto the Goldstone modes of the sigma model, which become gapless at the critical point. These gapless Goldstone modes are the quantum carriers of information and entropy. Analyzing their effective theory, we observe the information-processing properties strikingly similar to the ones predicted by the black hole portrait. The energy cost per qubit of information-storage vanishes in the large-$N$ limit and the total information-storage capacity increases with $N$ either exponentially or as a power law. The longevity of i...
Entanglement in Nonunitary Quantum Critical Spin Chains
Couvreur, Romain; Jacobsen, Jesper Lykke; Saleur, Hubert
2017-07-01
Entanglement entropy has proven invaluable to our understanding of quantum criticality. It is natural to try to extend the concept to "nonunitary quantum mechanics," which has seen growing interest from areas as diverse as open quantum systems, noninteracting electronic disordered systems, or nonunitary conformal field theory (CFT). We propose and investigate such an extension here, by focusing on the case of one-dimensional quantum group symmetric or supergroup symmetric spin chains. We show that the consideration of left and right eigenstates combined with appropriate definitions of the trace leads to a natural definition of Rényi entropies in a large variety of models. We interpret this definition geometrically in terms of related loop models and calculate the corresponding scaling in the conformal case. This allows us to distinguish the role of the central charge and effective central charge in rational minimal models of CFT, and to define an effective central charge in other, less well-understood cases. The example of the s l (2 |1 ) alternating spin chain for percolation is discussed in detail.
Eigenvalues of a diffusion process with a critical point
Dekker, H.; Kampen, N.G. van
1979-01-01
The eigenvalues of a Fokker-Planck equation involving a critical point have been computed by means of a simple discretization technique. The results smoothly connect the monostable case above the critical point with the bistable case below it.
Quantum chaos on a critical Fermi surface
Patel, Aavishkar A
2016-01-01
We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of $N$ species of fermions at non-zero density coupled to a $U(1)$ gauge field in two spatial dimensions, and determine the Lyapunov rate and the butterfly velocity in an extended RPA approximation. The thermal diffusivity is found to be universally related to these chaos parameters, i.e. the relationship is independent of $N$, the gauge coupling constant, the Fermi velocity, the Fermi surface curvature, and high energy details.
Quantum criticality in the 2D Hubbard: from weak to strong coupling
Galanakis, Dimitrios; Mikelsons, Karlis; Khatami, Ehsan; Zhang, Peng; Xu, Zhaoxin; Moreno, Juana; Jarrell, Mark
2010-03-01
We study the phase diagram of the two-dimensional Hubbard model in the vicinity of the quantum critical point which separates the fermi liquid from the pseudogap region. We use the Dynamical Cluster Approximation (DCA) in conjunction with the weak-coupling continuous time quantum Monte Carlo (CTQMC) cluster solver. We measure the filling nc and the density of states at the critical point as a function of the Coulomb interaction U. We observe a change in behavior when the Coulomb interaction is of the order of the bandwidth. We also evaluate the temperature range in which the system is under the influence of the quantum critical point and compare it with the effective spin coupling Jeff. We discuss the consistency of these results with various mechanisms of quantum criticality. This research is supported by NSF DMR-0706379 and OISE-0952300.
Quantum Criticality in YFe2Al10
Gannon, William; Wu, Liusuo; Zaliznyak, Igor; Qiu, Yiming; Rodriguez-Rivera, Jose; Aronson, Meigan
Quantum criticality has been studied in many systems, but there are few systems where observed scaling can be unified with a critical free energy F, or where the critical exponents form the basis for QC universality classes. We have identified a new layered material YFe2Al10 that shows remarkably strong QC behavior, where the scaling properties of the magnetic susceptibility and specific heat are consistent with the same F. Recent neutron scattering results paint a remarkable picture of the QC fluctuations in YFe2Al10. In contrast to classical transitions, where fluctuations are relatively long ranged and inelastic scattering is observed at a magnetic zone center, in YFe2Al10 the scattering is independent of wave vector in the critical plane, indicating that the fluctuations are spatially localized, while out of plane scattering indicates that the interplaner interactions are restricted to nearest neighbors. The dynamical susceptibility χ'' ~=E-2 , and is wholly temperature independent, indicating that E/T scaling is present, the signature of QC fluctuations. These results hint that the the criticality in YFe2Al10 is local, which until now has only been found in a few f-electron based compounds.
Dynamic universality class of the QCD critical point
Son, D. T.; Stephanov, M. A.
2004-01-01
We show that the dynamic universality class of the QCD critical point is that of model H and discuss the dynamic critical exponents. We show that the baryon diffusion rate vanishes at the critical point. The dynamic critical index $z$ is close to 3.
Dormedy, E S; Brashears, M M; Cutter, C N; Burson, D E
2000-12-01
A 2% lactic acid wash used in a large meat-processing facility was validated as an effective critical control point (CCP) in a hazard analysis and critical control point (HACCP) plan. We examined the microbial profiles of beef carcasses before the acid wash, beef carcasses immediately after the acid wash, beef carcasses 24 h after the acid wash, beef subprimal cuts from the acid-washed carcasses, and on ground beef made from acid-washed carcasses. Total mesophilic, psychrotrophic, coliforms, generic Escherichia coli, lactic acid bacteria, pseudomonads, and acid-tolerant microorganisms were enumerated on all samples. The presence of Salmonella spp. was also determined. Acid washing significantly reduced all counts except for pseudomonads that were present at very low numbers before acid washing. All other counts continued to stay significantly lower (P HACCP plans and can significantly reduce the total number of microorganisms present on the carcass and during further processing.
Quantum superconductor-insulator transition: implications of BKT critical behavior.
Schneider, T; Weyeneth, S
2013-07-31
We explore the implications of Berezinskii-Kosterlitz-Thouless (BKT) critical behavior on the two-dimensional (2D) quantum superconductor-insulator (QSI) transition driven by the tuning parameter x. Concentrating on the sheet resistance R(x,T) BKT behavior implies: an explicit quantum scaling function for R(x,T) along the superconducting branch ending at the nonuniversal critical value Rc = R(xc); a BKT-transition line T(c)(x) [proportionality] (x - x(c))(zν[overline]), where z is the dynamic exponent and ν[overline] the exponent of the zero-temperature correlation length; independent estimates of zν[overline], z and ν[overline] from the x dependence of the nonuniversal parameters entering the BKT expression for the sheet resistance. To illustrate the potential and the implications of this scenario we analyze the data of Bollinger et al (2011 Nature 472 458) taken on gate voltage tuned epitaxial films of La2-xSrxCuO4 that are one unit cell in thickness. The resulting estimates, z ~/= 3.1 and ν[overline] ~/= 0.52, indicate a clean 2D-QSI critical point where hyperscaling, the proportionality between d/λ(2)(0) and Tc, and the correspondence between the quantum phase transitions in D dimensions and the classical ones in (D + z) dimensions are violated.
Quantum critical transport at a continuous metal-insulator transition
Haldar, P.; Laad, M. S.; Hassan, S. R.
2016-01-01
In contrast to the first-order correlation-driven Mott metal-insulator transition (MIT), contin- uous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the "strong disorder" category. Employing cluster-dynamical mean-field theory (CDMFT), we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on b...
Poran, S; Nguyen-Duc, T; Auerbach, A; Dupuis, N; Frydman, A; Bourgeois, Olivier
2017-02-22
The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition.
Poran, S.; Nguyen-Duc, T.; Auerbach, A.; Dupuis, N.; Frydman, A.; Bourgeois, Olivier
2017-01-01
The superconductor–insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition. PMID:28224994
Degenerate optomechanical parametric oscillators: cooling in the vicinity of a critical point
Degenfeld-Schonburg, Peter; Hartmann, Michael J; Navarrete-Benlloch, Carlos
2015-01-01
Degenerate optomechanical parametric oscillators are optical resonators in which a mechanical degree of freedom is coupled to a cavity mode that is nonlinearly amplified via parametric down-conversion of an external pumping laser. Below a critical pumping power the down-converted field is purely quantum-mechanical, making the theoretical description of such systems very challenging. Here we introduce a theoretical approach that is capable of describing this regime, even at the critical point itself. We find that the down-converted field can induce significant mechanical cooling and identify the process responsible of this as a "cooling by heating" mechanism. Moreover, we show that, contrary to naive expectations and semi-classical predictions, cooling is not optimal at the critical point, where the photon number is largest. Our approach opens the possibility for analyzing further hybrid dissipative quantum systems in the vicinity of critical points.
Superconducting quantum criticality of topological surface states at three loops
Zerf, Nikolai; Maciejko, Joseph
2016-01-01
The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent $\\mathcal{N}=2$ supersymmetry, based on a renormalization group (RG) analysis at one-loop order in the $\\epsilon$ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order $\\epsilon^3$, obtaining the more accurate value $\
Quantum coordinated multi-point communication based on entanglement swapping
Du, Gang; Shang, Tao; Liu, Jian-wei
2017-05-01
In a quantum network, adjacent nodes can communicate with each other point to point by using pre-shared Einsten-Podolsky-Rosen (EPR) pairs, and furthermore remote nodes can establish entanglement channels by using quantum routing among intermediate nodes. However, with the rapid development of quantum networks, the demand of various message transmission among nodes inevitably emerges. In order to realize this goal and extend quantum networks, we propose a quantum coordinated multi-point communication scheme based on entanglement swapping. The scheme takes full advantage of EPR pairs between adjacent nodes and performs multi-party entanglement swapping to transmit messages. Considering various demands of communication, all nodes work cooperatively to realize different message transmission modes, including one to many, many to one and one to some. Scheme analysis shows that the proposed scheme can flexibly organize a coordinated group and efficiently use EPR resources, while it meets basic security requirement under the condition of coordinated communication.
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...
Echo State Condition at the Critical Point
Directory of Open Access Journals (Sweden)
Norbert Michael Mayer
2016-12-01
Full Text Available Recurrent networks with transfer functions that fulfil the Lipschitz continuity with K = 1 may be echo state networks if certain limitations on the recurrent connectivity are applied. It has been shown that it is sufficient if the largest singular value of the recurrent connectivity is smaller than 1. The main achievement of this paper is a proof under which conditions the network is an echo state network even if the largest singular value is one. It turns out that in this critical case the exact shape of the transfer function plays a decisive role in determining whether the network still fulfills the echo state condition. In addition, several examples with one-neuron networks are outlined to illustrate effects of critical connectivity. Moreover, within the manuscript a mathematical definition for a critical echo state network is suggested.
Percolation systems away from the critical point
Indian Academy of Sciences (India)
Deepak Dhar
2002-02-01
This article reviews some effects of disorder in percolation systems away from the critical density c. For densities below c, the statistics of large clusters deﬁnes the animals problem. Its relation to the directed animals problem and the Lee–Yang edge singularity problem is described. Rare compact clusters give rise to Grifﬁths singularities in the free energy of diluted ferromagnets, and lead to a very slow relaxation of magnetization. In biased diffusion on percolation clusters, trapping in dead-end branches leads to asymptotic drift velocity becoming zero for strong bias, and very slow relaxation of velocity near the critical bias ﬁeld.
Imprints of a critical point on photon emission
Energy Technology Data Exchange (ETDEWEB)
Wunderlich, F.; Kaempfer, B. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Technische Universitaet Dresden, Institut fuer Theoretische Physik, Dresden (Germany)
2016-08-15
The linear sigma model with linearized fluctuations of all involved fields facilitates the onset of a sequence of first-order phase transitions at a critical point. This phase structure has distinctive imprints on the photon emission rates. We argue that analogously a critical point in the QCD phase diagram manifests itself by peculiarities of the photon spectra, in particular when the dynamical expansion path of matter crosses the phase transition curve in the vicinity of the critical point. (orig.)
Nagy, D.; Domokos, P.
2015-07-01
We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N spin couple to independent reservoirs at zero temperature. The critical exponent, which is 1 if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.
Critical Point Dryer: Tousimis 916B Series C
Federal Laboratory Consortium — Description: CORAL Name: Critical Point Dryer This system utilizes CO 2to dry fragile suspended and floating structures Specifications / Capabilities: Wafer size up...
Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry
Coldea, R.; Tennant, D. A.; Wheeler, E M; Wawrzynska, E.; Prabhakaran, D.; Telling, M; Habicht, K.; Smeibidl, P; Kiefer, K.
2011-01-01
Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E8 Lie group with a spectrum of 8 particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by tuning the quasi-one-dimensional Ising ferromagnet CoNb2O6 through its critical point using strong transv...
Entropy Flow in Near-Critical Quantum Circuits
Friedan, Daniel
2017-05-01
Near-critical quantum circuits close to equilibrium are ideal physical systems for asymptotically large-scale quantum computers, because their low energy collective excitations evolve reversibly, effectively isolated from microscopic environmental fluctuations by the renormalization group. Entropy flows in near-critical quantum circuits near equilibrium as a locally conserved quantum current, obeying circuit laws analogous to the electric circuit laws. These "Kirchhoff laws" for entropy flow are the fundamental design constraints for asymptotically large-scale quantum computers. A quantum circuit made from a near-critical system (of conventional type) is described by a relativistic 1+1 dimensional relativistic quantum field theory on the circuit. The quantum entropy current near equilibrium is just the energy current divided by the temperature. The universal properties of the energy-momentum tensor constrain the entropy flow characteristics of the circuit components: the entropic conductivity of the quantum wires and the entropic admittance of the quantum circuit junctions. For example, near-critical quantum wires are always resistanceless inductors for entropy. A universal formula is derived for the entropic conductivity: σ S(ω ) = iv2 S/ω T , where ω is the frequency, T the temperature, S the equilibrium entropy density and v the velocity of "light". The thermal conductivity is Re(Tσ S(ω ))=π v2 S δ (ω ). The thermal Drude weight is, universally, v2S. This gives a way to measure the entropy density directly.
Molina-Vilaplana, Javier; Sodano, Pasquale
2011-10-01
In ( d + 1) dimensional Multiscale Entanglement Renormalization Ansatz (MERA) networks, tensors are connected so as to reproduce the discrete, ( d + 2) holographic geometry of Anti de Sitter space (AdS d+2) with the original system lying at the boundary. We analyze the MERA renormalization flow that arises when computing the quantum correlations between two disjoint blocks of a quantum critical system, to show that the structure of the causal cones characteristic of MERA, requires a transition between two different regimes attainable by changing the ratio between the size and the separation of the two disjoint blocks. We argue that this transition in the MERA causal developments of the blocks may be easily accounted by an AdS d+2 black hole geometry when the mutual information is computed using the Ryu-Takayanagi formula. As an explicit example, we use a BTZ AdS3 black hole to compute the MI and the quantum correlations between two disjoint intervals of a one dimensional boundary critical system. Our results for this low dimensional system not only show the existence of a phase transition emerging when the conformal four point ratio reaches a critical value but also provide an intuitive entropic argument accounting for the source of this instability. We discuss the robustness of this transition when finite temperature and finite size effects are taken into account.
Nussinov, Zohar; Johnson, Patrick; Graf, Matthias J.; Balatsky, Alexander V.
2013-05-01
Many electronic systems (e.g., the cuprate superconductors and heavy fermions) exhibit striking features in their dynamical response over a prominent range of experimental parameters. While there are some empirical suggestions of particular increasing length scales that accompany such transitions in some cases, this identification is not universal and in numerous instances no large correlation length is evident. To better understand, as a matter of principle, such behavior in quantum systems, we extend a known mapping (earlier studied in stochastic or supersymmetric quantum mechanics) between finite temperature classical Fokker-Planck systems and related quantum systems at zero temperature to include general nonequilibrium dynamics. Unlike Feynman mappings or stochastic quantization methods in field theories (as well as more recent holographic type dualities), the classical systems that we consider and their quantum duals reside in the same number of space-time dimensions. The upshot of our very broad and rigorous result is that a Wick rotation exactly relates (i) the dynamics in general finite temperature classical dissipative systems to (ii) zero temperature dynamics in the corresponding dual many-body quantum systems. Using this correspondence, we illustrate that, even in the absence of imposed disorder, many continuum quantum fluid systems (and possible lattice counterparts) may exhibit a zero-point “quantum dynamical heterogeneity” wherein the dynamics, at a given instant, is spatially nonuniform. While the static length scales accompanying this phenomenon do not seem to exhibit a clear divergence in standard correlation functions, the length scale of the dynamical heterogeneities can increase dramatically. We further study “quantum jamming” and illustrate how a hard-core bosonic system can undergo a zero temperature quantum critical metal-to-insulator-type transition with an extremely large effective dynamical exponent z>4 that is consistent with
Ding, L. J.; Zhong, Y.
2017-07-01
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∗ denoting the gapless phase crossover into quantum critical regimes, smoothly connects near the critical fields to the universal linear line T∗ ∼ (h - hc,s), and ends at hc,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 Γh, 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.
Entropy landscape of phase formation associated with quantum criticality in Sr3Ru2O7.
Rost, A W; Perry, R S; Mercure, J-F; Mackenzie, A P; Grigera, S A
2009-09-11
Low-temperature phase transitions and the associated quantum critical points are a major field of research, but one in which experimental information about thermodynamics is sparse. Thermodynamic information is vital for the understanding of quantum many-body problems. We show that combining measurements of the magnetocaloric effect and specific heat allows a comprehensive study of the entropy of a system. We present a quantitative measurement of the entropic landscape of Sr3Ru2O7, a quantum critical system in which magnetic field is used as a tuning parameter. This allows us to track the development of the entropy as the quantum critical point is approached and to study the thermodynamic consequences of the formation of a novel electronic liquid crystalline phase in its vicinity.
On the critical point of a Malthus-Verhulst process
Dekker, H.
1980-01-01
The master equation for the Malthus-Verhulst process including spontaneous generation will be re-examined in the light of an extended version of Van Kampen's method at the critical point. The Malthus-Verhulst process turns out to be a remarkable special case as the standard scaling property is left untouched at the critical point.
Macroscopic Quantum Phenomena from the Correlation, Coupling and Criticality Perspectives
Chou, C H; Subasi, Y
2011-01-01
In this sequel paper we explore how macroscopic quantum phenomena can be measured or understood from the behavior of quantum correlations which exist in a quantum system of many particles or components and how the interaction strengths change with energy or scale, under ordinary situations and when the system is near its critical point. We use the nPI (master) effective action related to the Boltzmann-BBGKY / Schwinger-Dyson hierarchy of equations as a tool for systemizing the contributions of higher order correlation functions to the dynamics of lower order correlation functions. Together with the large N expansion discussed in our first paper(MQP1) we explore 1) the conditions whereby an H-theorem is obtained, which can be viewed as a signifier of the emergence of macroscopic behavior in the system. We give two more examples from past work: 2) the nonequilibrium dynamics of N atoms in an optical lattice under the large $\\cal N$ (field components), 2PI and second order perturbative expansions, illustrating h...
The location of critical points of analytic and harmonic functions
Walsh, J L
1950-01-01
This book is concerned with the critical points of analytic and harmonic functions. A critical point of an analytic function means a zero of its derivative, and a critical point of a harmonic function means a point where both partial derivatives vanish. The analytic functions considered are largely polynomials, rational functions, and certain periodic, entire, and meromorphic functions. The harmonic functions considered are largely Green's functions, harmonic measures, and various linear combinations of them. The interest in these functions centers around the approximate location of their crit
Direct Observation of Critical Point Wetting in Microgravity
Kaukler, W. F.
1985-01-01
The objective of this program is to observe the interface shape in single and multicomponent systems at the onset of critical wetting in microgravity using the MSFC drop tower and KC-135 aircraft. Test cells for the drop facility were built and tested up to critical point of CCl. Low temperature drops were conducted for two-component systems near the critical consolute point. Contact angle seems to approach 90 deg near the critical consolute temperature contrary to expectations. It is suspected that since the interfacial energy becomes vanishingly small at the critical consolute temperature, the interface shape has not reached equilibrium in the available low-gravity time.
Has the QCD critical point been observed at RHIC?
Antoniou, N G; Diakonos, F K
2016-01-01
The experimental search for the location of the QCD critical point in the phase diagram is of primary importance. In a recent publication it is claimed that measurements at RHIC lead not only to the location of the critical point ($\\mu_{cep}=95$ MeV, $T_{cep}=165$ MeV) but also to the verification of its universality class ($3d$ Ising system) by extracting the values of the critical exponents ($\\gamma=1.2$, $\
A Fast Measurement based fixed-point Quantum Search Algorithm
Mani, Ashish
2011-01-01
Generic quantum search algorithm searches for target entity in an unsorted database by repeatedly applying canonical Grover's quantum rotation transform to reach near the vicinity of the target entity represented by a basis state in the Hilbert space associated with the qubits. Thus, when qubits are measured, there is a high probability of finding the target entity. However, the number of times quantum rotation transform is to be applied for reaching near the vicinity of the target is a function of the number of target entities present in the unsorted database, which is generally unknown. A wrong estimate of the number of target entities can lead to overshooting or undershooting the targets, thus reducing the success probability. Some proposals have been made to overcome this limitation. These proposals either employ quantum counting to estimate the number of solutions or fixed point schemes. This paper proposes a new scheme for stopping the application of quantum rotation transformation on reaching near the ...
Excitation-Gap Scaling near Quantum Critical Three-Dimensional Antiferromagnets.
Lohöfer, M; Wessel, S
2017-04-07
By means of large-scale quantum Monte Carlo simulations, we examine the quantum critical scaling of the magnetic excitation gap (the triplon gap) in a three-dimensional dimerized quantum antiferromagnet, the bicubic lattice, and identify characteristic multiplicative logarithmic scaling corrections atop the leading mean-field behavior. These findings are in accord with field-theoretical predictions that are based on an effective description of the quantum critical system in terms of an asymptotically free field theory, which exhibits a logarithmic decay of the renormalized interaction strength upon approaching the quantum critical point. Furthermore, using bond-based singlet spectroscopy, we identify the amplitude (Higgs) mode resonance within the antiferromagnetic region. We find a Higgs mass scaling in accord with field-theoretical predictions that relate it by a factor of sqrt[2] to the corresponding triplon gap in the quantum disordered regime. In contrast to the situation in lower-dimensional systems, we observe in this three-dimensional coupled-dimer system a distinct signal from the amplitude mode also in the dynamical spin structure factor. Its width is observed to vanish proportional to the Higgs mass in the accessible proximity to the quantum critical point.
Floating point representations in quantum circuit synthesis
Wiebe, Nathan; Kliuchnikov, Vadym
2013-09-01
We provide a non-deterministic quantum protocol that approximates the single qubit rotations Rx(2ϕ21ϕ22) using Rx(2ϕ1) and Rx(2ϕ2) and a constant number of Clifford and T operations. We then use this method to construct a ‘floating point’ implementation of a small rotation wherein we use the aforementioned method to construct the exponent part of the rotation and also to combine it with a mantissa. This causes the cost of the synthesis to depend more strongly on the relative (rather than absolute) precision required. We analyze the mean and variance of the T-count required to use our techniques and provide new lower bounds for the T-count for ancilla free synthesis of small single-qubit axial rotations. We further show that our techniques can use ancillas to beat these lower bounds with high probability. We also discuss the T-depth of our method and see that the vast majority of the cost of the resultant circuits can be shifted to parallel computation paths.
Emergent Lorentz symmetry with vanishing velocity in a critical two-subband quantum wire.
Sitte, M; Rosch, A; Meyer, J S; Matveev, K A; Garst, M
2009-05-01
We consider a quantum wire with two subbands of spin-polarized electrons in the presence of strong interactions. We focus on the quantum phase transition when the second subband starts to get filled as a function of gate voltage. Performing a one-loop renormalization group analysis of the effective Hamiltonian, we identify the critical fixed-point theory as a conformal field theory having an enhanced SU(2) symmetry and central charge 3/2. While the fixed point is Lorentz invariant, the effective "speed of light" nevertheless vanishes at low energies due to marginally irrelevant operators leading to a diverging critical specific heat coefficient.
Collectivity, Phase Transitions and Exceptional Points in Open Quantum Systems
Heiss, W D; Rotter, I
1998-01-01
Phase transitions in open quantum systems, which are associated with the formation of collective states of a large width and of trapped states with rather small widths, are related to exceptional points of the Hamiltonian. Exceptional points are the singularities of the spectrum and eigenfunctions, when they are considered as functions of a coupling parameter. In the present paper this parameter is the coupling strength to the continuum. It is shown that the positions of the exceptional points (their accumulation point in the thermodynamical limit) depend on the particular type and energy dependence of the coupling to the continuum in the same way as the transition point of the corresponding phase transition.
X(5) Critical-Point Structure in a Finite System
Leviatan, A
2005-01-01
X(5) is a paradigm for the structure at the critical point of a particular first-order phase transition for which the intrinsic energy surface has two degenerate minima separated by a low barrier. For a finite system, we show that the dynamics at such a critical point can be described by an effective deformation determined by minimizing the energy surface after projection onto angular momentum zero, and combined with two-level mixing. Wave functions of a particular analytic form are used to derive estimates for energies and quadrupole rates at the critical point.
Critical-point symmetry in a finite system.
Leviatan, A; Ginocchio, J N
2003-05-30
At a critical point of a second-order phase transition the intrinsic energy surface is flat and there is no stable minimum value of the deformation. However, for a finite system, we show that there is an effective deformation which can describe the dynamics at the critical point. This effective deformation is determined by minimizing the energy surface after projection onto the appropriate symmetries. We derive analytic expressions for energies and quadrupole rates which provide good estimates for these observables at the critical point.
Critical-Point Symmetry in a Finite System
Leviatan, A
2003-01-01
At a critical point of a second order phase transition the intrinsic energy surface is flat and there is no stable minimum value of the deformation. However, for a finite system, we show that there is an effective deformation which can describe the dynamics at the critical point. This effective deformation is determined by minimizing the energy surface after projection onto the appropriate symmetries. We derive analytic expressions for energies and quadrupole rates which provide good estimates for these observables at the critical point.
Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots
Institute of Scientific and Technical Information of China (English)
ZHU Fei-Yun; TU Tao; HAO Xiao-Jie; GUO Guang-Can; GUO Guo-Ping
2009-01-01
We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact (QPC) as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.
Ultimate quantum limit on resolution of two thermal point sources
Nair, Ranjith
2016-01-01
We obtain the fundamental quantum limit for resolving two thermal point sources using an imaging system with limited spatial bandwidth. Using the quantum Cram\\'er-Rao bound, we show that the standard Rayleigh limit is not fundamental and can be surpassed by concrete coherent measurement techniques. Our results are valid for all values of the source strength, all ranges of the electromagnetic spectrum, and for any imaging system with an inversion-symmetric point-spread function. Our findings have applications to many areas of metrology including microscopy, astronomy, and standoff target sensing.
Odd viscosity in the quantum critical region of a holographic Weyl semimetal
Landsteiner, Karl; Sun, Ya-Wen
2016-01-01
We study odd viscosity in a holographic model of a Weyl semimetal. The model is characterised by a quantum phase transition from a topological semimetal to a trivial semimetal state. Since the model is axisymmetric in three spatial dimensions there are two independent odd viscosities. Both odd viscosity coefficients are non-vanishing in the quantum critical region and non-zero only due to the mixed axial gravitational anomaly. It is therefore a novel example in which the mixed axial gravitational anomaly gives rise to a transport coefficient at first order in derivatives at finite temperature. We also compute anisotropic shear viscosities and show that one of them violates the KSS bound. In the quantum critical region, the physics of viscosities as well as conductivities is governed by the quantum critical point.
Quantum critical transport at a continuous metal-insulator transition
Haldar, P.; Laad, M. S.; Hassan, S. R.
2016-08-01
In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.
Critical Point Dryer: Tousimis 916B Series C
Federal Laboratory Consortium — Description:CORAL Name: Critical Point DryerThis system utilizes CO 2to dry fragile suspended and floating structures Specifications / Capabilities:Wafer size up to...
Cubic Polynomials with Rational Roots and Critical Points
Gupta, Shiv K.; Szymanski, Waclaw
2010-01-01
If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.
Critical Point Theorems and Applications to Differential Equations
Institute of Scientific and Technical Information of China (English)
A. R. EL AMROUSS
2005-01-01
This paper contains a generalization of the well-known Palais-Smale and Cerami compactness conditions. The compactness condition introduced is used to prove some general existence theorems for critical points. Some applications are given to differential equations.
Critical points and dynamic systems with planar hexagonal symmetry
Energy Technology Data Exchange (ETDEWEB)
Chen Ning [Faculty of Information and Control Engineering, Shenyang Jianzhu University, Shenyang 110168 (China)]. E-mail: n_chen@126.com; Meng Fan Yu [Faculty of Information and Control Engineering, Shenyang Jianzhu University, Shenyang 110168 (China)
2007-05-15
In this investigation, we detect and utilize critical points of functions with hexagonal symmetry in order to study their dynamics. The asymmetric unit in a parallelogram lattice is chosen as the initial searching region for a critical point set in a dynamic plane. The accelerated direct search algorithm is used within the parallelogram lattice to search for the critical points. Parameter space is separated into regions (chaotic, periodic or mixed) by the Ljapunov exponents of the critical points. Then the generalized Mandelbrot set (M-set), which is a cross-section of the parameter space, is constructed. Many chaotic attractors and filled-in Julia sets can be generated by using parameters from this kind of M-sets.
Critical Missing Equation of Quantum Physics for Understanding Atomic Structures
Huang, Xiaofei
2013-01-01
This paper presents an optimization approach to explain why and how a quantum system evolves from an arbitrary initial state to a stationary state, satisfying the time-independent Schr\\"{o}dinger equation. It also points out the inaccuracy of this equation, which is critial important in quantum mechanics and quantum chemistry, due to a fundamental flaw in it conflicting with the physical reality. The some directions are suggested on how to modify the equation to fix the problem
Critical Missing Equation of Quantum Physics for Understanding Atomic Structures
Huang, Xiaofei
2015-01-01
This paper presents an optimization approach to explain why and how a quantum system evolves from an arbitrary initial state to a stationary state, satisfying the time-independent Schr\\"{o}dinger equation. It also points out the inaccuracy of this equation, which is critial important in quantum mechanics and quantum chemistry, due to a fundamental flaw in it conflicting with the physical reality. The some directions are suggested on how to modify the equation to fix the problem
Binary Colloidal Alloy Test-3 and 4: Critical Point
Weitz, David A.; Lu, Peter J.
2007-01-01
Binary Colloidal Alloy Test - 3 and 4: Critical Point (BCAT-3-4-CP) will determine phase separation rates and add needed points to the phase diagram of a model critical fluid system. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.
Inherently unstable networks collapse to a critical point.
Sheinman, M; Sharma, A; Alvarado, J; Koenderink, G H; MacKintosh, F C
2015-07-01
Nonequilibrium systems that are driven or drive themselves towards a critical point have been studied for almost three decades. Here we present a minimalist example of such a system, motivated by experiments on collapsing active elastic networks. Our model of an unstable elastic network exhibits a collapse towards a critical point from any macroscopically connected initial configuration. Taking into account steric interactions within the network, the model qualitatively and quantitatively reproduces results of the experiments on collapsing active gels.
Search for the QCD critical point at SPS energies
Anticic, T; Barna, D; Bartke, J; Betev, L; Bialkowska, H; Blume, C; Boimska, B; Botje, M; Bracinik, J; Buncic, P; Cerny, V; Christakoglou, P; Chung, P; Chvala, O; Cramer, J G; Csato, P; Dinkelaker, P; Eckardt, V; Fodor, Z; Foka, P; Friese, V; Gal, J; Gazdzicki, M; Genchev, V; Gladysz, E; Grebieszkow, K; Hegyi, S; Hohne, C; Kadija, K; Karev, A; Kikola, D; Kolesnikov, V I; Kornas, E; Korus, R; Kowalski, M; Kreps, M; Laszlo, A; Lacey, R; van Leeuwen, M; Levai, P; Litov, L; Lungwitz, B; Makariev, M; Malakhov, A I; Mateev, M; Melkumov, G L; Mischke, A; Mitrovski, M; Mrowczynski, St; Nicolic, V; Palla, G; Panagiotou, A D; Petridis, A; Peryt, W; Pikna, M; Pluta, J; Prindle, D; Puhlhofer, F; Renfordt, R; Roland, C; Roland, G; Rybczynski, M; Rybicki, A; Sandoval, A; Schmitz, N; Schuster, T; Seyboth, P; Sikler, F; Sitar, B; Skrzypczak, E; Slodkowski, M; Stefanek, G; Stock, R; Strabel, C; Strobele, H; Susa, T; Szentpetery, I; Sziklai, J; Szuba, M; Szymanski, P; Trubnikov, V; Utvic, M; Varga, D; Vassiliou, M; Veres, G I; Vesztergombi, G; Vranic, D; Wlodarczyk, Z; Wojtaszek-Szwarc, A; Yoo, I K; Abgrall, N; Aduszkiewicz, A; Andrieu, B; Anticic, T; Antoniou, N; Argyriades, J; Asryan, A G; Baatar, B; Blondel, A; Blumer, J; Boldizsar, L; Bravar, A; Brzychczyk, J; Bubak, A; Bunyatov, S A; Choi, K.-U; Christakoglou, P; Chung, P; Cleymans, J; Derkach, D A; Diakonos, F; Dominik, W; Dumarchez, J; Engel, R; Ereditato, A; Feofilov, G A; Fodor, Z; Ferrero, A; Gazdzicki, M; Golubeva, M; Grebieszkow, K; Grzeszczuk, A; Guber, F; Hasegawa, T; Haungs, A; Igolkin, S; Ivanov, A S; Ivashkin, A; Kadija, K; Katrynska, N; Kielczewska, D; Kikola, D; Kisiel, J; Kobayashi, T; Kolesnikov, V I; Kolev, D; Kolevatov, R S; Kondratiev, V P; Kowalski, S; Kurepin, A; Lacey, R; Laszlo, A; Lyubushkin, V V; Majka, Z; Malakhov, A I; Marchionni, A; Marcinek, A; Maris, I; Matveev, V; Melkumov, G L; Meregaglia, A; Messina, M; Mijakowski, P; Mitrovski, M; Montaruli, T; Mrowczynski, St; Murphy, S; Nakadaira, T; Naumenko, P A; Nikolic, V; Nishikawa, K; Palczewski, T; Palla, G; Panagiotou, A D; Peryt, W; Planeta, R; Pluta, J; Popov, B A; Posiadala, M; Przewlocki, P; Rauch, W; Ravonel, M; Renfordt, R; Rohrich, D; Rondio, E; Rossi, B; Roth, M; Rubbia, A; Rybczynski, M; Sadovsky, A; Sakashita, K; Schuster, T; Sekiguchi, T; Seyboth, P; Shibata, M; Sissakian, A N; Skrzypczak, E; Slodkowski, M; Sorin, A S; Staszel, P; Stefanek, G; Stepaniak, J; Strabel, C; Stroebele, H; Susa, T; Szentpetery, I; Szuba, M; Tada, M; Taranenko, A; Tsenov, R; Ulrich, R; Unger, M; Vassiliou, M; Vechernin, V V; Vesztergombi, G; Wlodarczyk, Z; Wojtaszek-Szwarc, A; Zipper, W
2009-01-01
Lattice QCD calculations locate the QCD critical point at energies accessible at the CERN Super Proton Synchrotron (SPS). We present average transverse momentum and multiplicity fluctuations, as well as baryon and anti-baryon transverse mass spectra which are expected to be sensitive to effects of the critical point. The future CP search strategy of the NA61/SHINE experiment at the SPS is also discussed.
Implementation of hazard analysis critical control point in jameed production.
Al-Saed, A K; Al-Groum, R M; Al-Dabbas, M M
2012-06-01
The average of standard plate count and coliforms, Staphylococcus aureus and Salmonella counts for three home-made jameed samples, a traditional fermented dairy product, before applying hazard analysis critical control point system were 2.1 × 10(3), 8.9 × 10(1), 4 × 10(1) and less than 10 cfu/g, respectively. The developed hazard analysis critical control point plan resulted in identifying ten critical control points in the flow chart of jameed production. The critical control points included fresh milk receiving, pasteurization, addition of starter, water and salt, straining, personnel hygiene, drying and packaging. After applying hazard analysis critical control point system, there was significant improvement in the microbiological quality of the home-made jameed. The standard plate count was reduced to 3.1 × 10(2) cfu/g whereas coliform and Staphylococcus aureus counts were less than 10 cfu/g and Salmonella was not detected. Sensory evaluation results of color and flavor of sauce prepared from jameed showed a significant increase in the average scores given after hazard analysis critical control point application.
Enhanced protein crystallization around the metastable critical point
Wolde, P.R. ten; Frenkel, D.
1999-01-01
We report on a computer-simulation study of homogeneous crystal nucleation in a model for globular proteins. We find that the presence of a metastable vapour-liquid critical point drastically changes the pathway for the formation of a critical nucleus. But what is more important, the large density f
Two-point functions in (loop) quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Calcagni, Gianluca; Gielen, Steffen; Oriti, Daniele, E-mail: calcagni@aei.mpg.de, E-mail: gielen@aei.mpg.de, E-mail: doriti@aei.mpg.de [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany)
2011-06-21
The path-integral formulation of quantum cosmology with a massless scalar field as a sum-over-histories of volume transitions is discussed, with particular but non-exclusive reference to loop quantum cosmology. Exploiting the analogy with the relativistic particle, we give a complete overview of the possible two-point functions, pointing out the choices involved in their definitions, deriving their vertex expansions and the composition laws they satisfy. We clarify the origin and relations of different quantities previously defined in the literature, in particular the tie between definitions using a group averaging procedure and those in a deparametrized framework. Finally, we draw some conclusions about the physics of a single quantum universe (where there exist superselection rules on positive- and negative-frequency sectors and different choices of inner product are physically equivalent) and multiverse field theories where the role of these sectors and the inner product are reinterpreted.
Two-point functions in (loop) quantum cosmology
Energy Technology Data Exchange (ETDEWEB)
Calcagni, Gianluca; Oriti, Daniele [Max-Planck-Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany); Gielen, Steffen [Max-Planck-Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, D-14476 Golm (Germany); DAMTP, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)
2011-07-01
We discuss the path-integral formulation of quantum cosmology with a massless scalar field as a sum-over-histories of volume transitions, with particular but non-exclusive reference to loop quantum cosmology (LQC). Exploiting the analogy with the relativistic particle, we give a complete overview of the possible two-point functions, pointing out the choices involved in their definitions, deriving their vertex expansions and the composition laws they satisfy. We clarify the origin and relations of different quantities previously defined in the literature, in particular the tie between definitions using a group averaging procedure and those in a deparametrized framework. Finally, we draw some conclusions about the physics of a single quantum universe (where there exist superselection rules on positive- and negative-frequency sectors and different choices of inner product are physically equivalent) and multiverse field theories where the role of these sectors and the inner product are reinterpreted.
On the critical temperatures of superconductors: a quantum gravity approach
Gregori, Andrea
2010-01-01
We consider superconductivity in the light of the quantum gravity theoretical framework introduced in [1]. In this framework, the degree of quantum delocalization depends on the geometry of the energy distribution along space. This results in a dependence of the critical temperature characterizing the transition to the superconducting phase on the complexity of the structure of a superconductor. We consider concrete examples, ranging from low to high temperature superconductors, and discuss how the critical temperature can be predicted once the quantum gravity effects are taken into account.
Superconducting quantum criticality of topological surface states at three loops
Zerf, Nikolai; Lin, Chien-Hung; Maciejko, Joseph
2016-11-01
The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent N =2 supersymmetry, based on a one-loop renormalization group (RG) analysis in the ɛ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order ɛ3, obtaining the more accurate value ν ≈0.985 for the correlation length exponent and confirming that the fermion and boson anomalous dimensions remain unchanged beyond one loop, as expected from non-renormalization theorems in supersymmetric theories. We further couple the system to a dynamical U(1) gauge field, and argue that the transition becomes fluctuation-induced first order in an appropriate type-I regime. We discuss implications of this result for quantum phase transitions between certain symmetry-preserving correlated surface states of 3D topological insulators.
Phase diagram and critical end point for strongly interacting quarks.
Qin, Si-xue; Chang, Lei; Chen, Huan; Liu, Yu-xin; Roberts, Craig D
2011-04-29
We introduce a method based on chiral susceptibility, which enables one to draw a phase diagram in the chemical-potential-temperature plane for strongly interacting quarks whose interactions are described by any reasonable gap equation, even if the diagrammatic content of the quark-gluon vertex is unknown. We locate a critical end point at (μ(E),T(E))∼(1.0,0.9)T(c), where T(c) is the critical temperature for chiral-symmetry restoration at μ=0, and find that a domain of phase coexistence opens at the critical end point whose area increases as a confinement length scale grows.
Identification of critical points of thermal environment in broiler production
Directory of Open Access Journals (Sweden)
AG Menezes
2010-03-01
Full Text Available This paper describes an exploratory study carried out to determine critical control points and possible risks in hatcheries and broiler farms. The study was based in the identification of the potential hazards existing in broiler production, from the hatchery to the broiler farm, identifying critical control points and defining critical limits. The following rooms were analyzed in the hatchery: egg cold storage, pre-heating, incubator, and hatcher rooms. Two broiler houses were studied in two different farms. The following data were collected in the hatchery and broiler houses: temperature (ºC and relative humidity (%, air velocity (m s-1, ammonia levels, and light intensity (lx. In the broiler house study, a questionnaire using information of the Broiler Production Good Practices (BPGP manual was applied, and workers were interviewed. Risk analysis matrices were build to determine Critical Control Points (CCP. After data collection, Statistical Process Control (SPC was applied through the analysis of the Process Capacity Index, using the software program Minitab15®. Environmental temperature and relative humidity were the critical points identified in the hatchery and in both farms. The classes determined as critical control points in the broiler houses were poultry litter, feeding, drinking water, workers' hygiene and health, management and biosecurity, norms and legislation, facilities, and activity planning. It was concluded that CCP analysis, associated with SPC control tools and guidelines of good production practices, may contribute to improve quality control in poultry production.
Possible signal for critical point in hadronization process
Rybczynski, M; Wlodarczyk, Z.; Wilk, G.
2003-01-01
We argue that recent data on fluctuations observed in heavy ion collisions show non-monotonic behaviour as function of number of participants (or "wounded nucleons") N_W. When interpreted in thermodynamical approach this result can be associated with a possible structure occuring in the corresponding equation of state (EoS). This in turn could be further interpreted as due to the occurence of some characteristic points (like "softest point" or "critical point") of EoS discussed in the literat...
Characterizing variable for the critical point in momentum space
Institute of Scientific and Technical Information of China (English)
DU Jia-Xin; KE Hong-Wei; XU Ming-Mei; LIU Lian-Shou
2009-01-01
The possible experimentally observable signal in momentum space for the critical point, which is free from the contamination of statistical fluctuations, is discussed. It is shown that the higher order scaled moment of transverse momentum can serve as an appropriate signal for the critical point, provided the transverse momentum distribution has a sudden change when energy increases passing through this point. A 2-D percolation model with a linear temperature gradient is constructed to check this suggestion. A sudden change of third order scaled moment of transverse momentum is observed.
Critical Brownian sheet does not have double points
Dalang, Robert C; Nualart, Eulalia; Wu, Dongsheng; Xiao, Yimin
2010-01-01
We derive a decoupling formula for the Brownian sheet which has the following ready consequence: An $N$-parameter Brownian sheet in $\\R^d$ has double points if and only if $2(d-2N)
The QCD critical point: an exciting Odyssey in the Femto-world
Gavai, Rajiv V.
2016-07-01
Strongly interacting matter, which makes up the nuclei of atoms, is described by a theory called quantum chromodynamics (QCD). A critical point in the phase diagram of QCD, if established either theoretically or experimentally, would be as profound a discovery as the familiar gas-liquid critical point discovered in the nineteenth century. Due to the extremely short-lived nature of the concerned phases, novel experimental techniques are needed to search for it. The Relativistic Heavy Ion Collider (RHIC) in USA has an experimental programme which can fit the bill to do so. Theoretical techniques of Lattice QCD, which is QCD defined on a discrete space-time lattice, have provided glimpses into where the QCD critical point may be, and how to search for it in the experimental data. A brief overview of the theoretical and experimental attempts is provided.
Random matrix theory and critical phenomena in quantum spin chains
Hutchinson, J.; Keating, J. P.; Mezzadri, F.
2015-09-01
We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups $U(N)$, $O(N)$ and $Sp(2N)$. In particular we calculate critical exponents $s$, $\
Candidate Elastic Quantum Critical Point in {\mathrm{LaCu}}_{6-x}{\mathrm{Au}}_{x}
Energy Technology Data Exchange (ETDEWEB)
Poudel, L.; May, A. F.; Koehler, M. R.; McGuire, M. A.; Mukhopadhyay, S.; Calder, S.; Baumbach, R. E.; Mukherjee, R.; Sapkota, D.; de la Cruz, C.; Singh, D. J.; Mandrus, D.; Christianson, A. D.
2016-11-01
The structural properties of LaCu _{6-x} Au _{x} are studied using neutron diffraction, x-ray diffraction, and heat capacity measurements. The continuous orthorhombic-monoclinic structural phase transition in LaCu_{ 6} is suppressed linearly with Au substitution until a complete suppression of the structural phase transition occurs at the critical composition x _{c} = 0.3 . Heat capacity measurements at low temperatures indicate residual structural instability at x_{ c} . The instability is ferroelastic in nature, with density functional theory calculations showing negligible coupling to electronic states near the Fermi level. The data and calculations presented here are consistent with the zero temperature termination of a continuous structural phase transition suggesting that the LaCu _{6-x} Au _{x} series hosts an elastic quantum critical point.
Critical Dynamics : The Expansion of the Master Equation Including a Critical Point
Dekker, H.
1980-01-01
In this thesis it is shown how to solve the master equation for a Markov process including a critical point by means of successive approximations in terms of a small parameter. A critical point occurs if, by adjusting an externally controlled quantity, the system shows a transition from normal monos
Quantum Limits to Optical Point-Source Localization
Tsang, Mankei
2014-01-01
Many superresolution microscopic techniques rely on the accurate localization of optical point sources from far field. To investigate the fundamental limits to their resolution, here I derive measurement-independent quantum lower bounds on the error of locating point sources in free space, taking full account of the quantum, nonparaxial, and vectoral nature of photons. To arrive at analytic results, I focus mainly on the cases of one and two classical monochromatic sources with an initial vacuum optical state. For one source, a lower bound on the root-mean-square position estimation error is on the order of $\\lambda_0/\\sqrt{N}$, where $\\lambda_0$ is the free-space wavelength and $N$ is the average number of radiated photons. For two sources, owing to a nuisance parameter effect, the error bound diverges when their radiated fields overlap significantly. The use of squeezed light to further enhance the accuracy of locating one point source is also discussed.
Reprint of : Quantum point contacts as heat engines
Pilgram, Sebastian; Sánchez, David; López, Rosa
2016-08-01
The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely.
Behavior of the dielectric constant of Ar near the critical point.
Hidalgo, Marcelo; Coutinho, Kaline; Canuto, Sylvio
2015-03-01
The fundamental question of the behavior of the dielectric constant near the critical point is addressed using Ar as the probe system. The neighborhood of the liquid-vapor critical point of Ar is accessed by classical Monte Carlo simulation and then explicit quantum mechanics calculations are performed to study the behavior of the dielectric constant. The theoretical critical temperature is determined by calculating the position of the discontinuity of the specific heat and is found to be at T(c)Theor=148.7K, only 2 K below the experimental value. The large fluctuations and the inhomogeneity of the density that characterize the critical point rapidly disappear and are not seen at T=T(c)Theor+2K. The structure of Ar obtained by the radial distribution function is found to be in very good agreement with experiment both in the liquid phase and 2 K above the critical temperature. The behavior of the dielectric constant is then analyzed after calculating the static dipole polarizability and using a many-body Clausius-Mossotti equation. The dielectric constant shows a density-independent behavior around the critical density, 2 K above the critical temperature. At this point, the calculated value of the dielectric constant is 1.173±0.005 in excellent agreement with the experimental value of 1.179.
An N/4 fixed-point duality quantum search algorithm
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Here a fixed-point duality quantum search algorithm is proposed.This algorithm uses iteratively non-unitary operations and measurements to search an unsorted database.Once the marked item is found,the algorithm stops automatically.This algorithm uses a constant non-unitary operator,and requires N/4 steps on average(N is the number of data from the database) to locate the marked state.The implementation of this algorithm in a usual quantum computer is also demonstrated.
Gradient terms in quantum-critical theories of itinerant fermions
Maslov, Dmitrii L.; Sharma, Prachi; Torbunov, Dmitrii; Chubukov, Andrey V.
2017-08-01
We investigate the origin and renormalization of the gradient (Q2) term in the propagator of soft bosonic fluctuations in theories of itinerant fermions near a quantum critical point (QCP) with ordering wavevector Q0=0 . A common belief is that (i) the Q2 term comes from fermions with high energies (roughly of order of the bandwidth) and, as such, should be included into the bare bosonic propagator of the effective low-energy model, and (ii) fluctuations within the low-energy model generate Landau damping of soft bosons, but affect the Q2 term only weakly. We argue that the situation is in fact more complex. First, we found that the high- and low-energy contributions to the Q2 term are of the same order. Second, we computed the high-energy contributions to the Q2 term in two microscopic models (a Fermi gas with Coulomb interaction and the Hubbard model) and found that in all cases these contributions are numerically much smaller than the low-energy ones, especially in 2D. This last result is relevant for the behavior of observables at low energies, because the low-energy part of the Q2 term is expected to flow when the effective mass diverges near QCP. If this term is the dominant one, its flow has to be computed self-consistently, which gives rise to a novel quantum-critical behavior. Following up on these results, we discuss two possible ways of formulating the theory of a QCP with Q0=0 .
Dynamical net-proton fluctuations near a QCD critical point
Herold, Christoph; Yan, Yupeng; Kobdaj, Chinorat
2016-01-01
We investigate the evolution of the net-proton kurtosis and the kurtosis of the chiral order parameter near the critical point in the model of nonequilibrium chiral fluid dynamics. The order parameter is propagated explicitly and coupled to an expanding fluid of quarks and gluons in order to describe the dynamical situation in a heavy-ion collision. We study the critical region near the critical point on the crossover side. There are two sources of fluctuations: non-critical initial event-by-event fluctuations and critical fluctuations. These fluctuations can be distinguished by comparing a mean-field evolution of averaged thermodynamic quantities with the inclusion of fluctuations at the phase transition. We find that while the initial state fluctuations give rise to flat deviations from statistical fluctuations, critical fluctuations reveal a clear structure of the phase transition. The signals of the critical point in the net-proton and sigma field kurtosis are affected by the nonequilibrium dynamics and t...
Unconventional critical activated scaling of two-dimensional quantum spin glasses
Matoz-Fernandez, D. A.; Romá, F.
2016-07-01
We study the critical behavior of two-dimensional short-range quantum spin glasses by numerical simulations. Using a parallel tempering algorithm, we calculate the Binder cumulant for the Ising spin glass in a transverse magnetic field with two different short-range bond distributions, the bimodal and the Gaussian ones. Through an exhaustive finite-size analysis, we show that the cumulant probably follows an unconventional activated scaling, which we interpret as new evidence supporting the hypothesis that the quantum critical behavior is governed by an infinite randomness fixed point.
Energy Technology Data Exchange (ETDEWEB)
Jaramillo, R.; Feng, Y.; Rosenbaum, T. F.; Harvard Univ.; Univ. of Chicago
2010-05-01
We explore the behavior of the nested bandstructure of chromium as a function of temperature and pressure to the point where magnetism disappears. X-ray diffraction measurements of the charge order parameter suggest that the nesting condition is maintained at high pressure, where the spin density wave ground state is destabilized by a continuous quantum phase transition. By comparing diffraction line-shapes measured throughout the temperature-pressure phase diagram we are able to identify and describe three regimes: thermal near-critical, weak coupling ground state, and quantum critical.
Critical Care Glucose Point-of-Care Testing.
Narla, S N; Jones, M; Hermayer, K L; Zhu, Y
Maintaining blood glucose concentration within an acceptable range is a goal for patients with diabetes mellitus. Point-of-care glucose meters initially designed for home self-monitoring in patients with diabetes have been widely used in the hospital settings because of ease of use and quick reporting of blood glucose information. They are not only utilized for the general inpatient population but also for critically ill patients. Many factors affect the accuracy of point-of-care glucose testing, particularly in critical care settings. Inaccurate blood glucose information can result in unsafe insulin delivery which causes poor glucose control and can be fatal. Healthcare professionals should be aware of the limitations of point-of-care glucose testing. This chapter will first introduce glucose regulation in diabetes mellitus, hyperglycemia/hypoglycemia in the intensive care unit, importance of glucose control in critical care patients, and pathophysiological variables of critically ill patients that affect the accuracy of point-of-care glucose testing. Then, we will discuss currently available point-of-care glucose meters and preanalytical, analytical, and postanalytical sources of variation and error in point-of-care glucose testing.
Quantum Algorithms with Fixed Points: The Case of Database Search
Grover, L K; Tulsi, T; Grover, Lov K.; Patel, Apoorva; Tulsi, Tathagat
2006-01-01
The standard quantum search algorithm lacks a feature, enjoyed by many classical algorithms, of having a fixed-point, i.e. a monotonic convergence towards the solution. Here we present two variations of the quantum search algorithm, which get around this limitation. The first replaces selective inversions in the algorithm by selective phase shifts of $\\frac{\\pi}{3}$. The second controls the selective inversion operations using two ancilla qubits, and irreversible measurement operations on the ancilla qubits drive the starting state towards the target state. Using $q$ oracle queries, these variations reduce the probability of finding a non-target state from $\\epsilon$ to $\\epsilon^{2q+1}$, which is asymptotically optimal. Similar ideas can lead to robust quantum algorithms, and provide conceptually new schemes for error correction.
Quantum theory of superresolution for two incoherent optical point sources
Tsang, Mankei; Lu, Xiaoming
2015-01-01
We prove that Rayleigh's criterion is fundamentally irrelevant to the localization of two incoherent point sources in far-field optical imaging. This is done in two ways: (1) We derive the quantum Cram\\'er-Rao error bound for the problem under standard assumptions for thermal optical sources, and the bound shows little sign of the accuracy degradation that plagues conventional imaging when Rayleigh's criterion is violated. (2) We propose a linear optical measurement method called spatial-mode demultiplexing (SPADE) that can attain the quantum bound for separation estimation regardless of the distance between the sources, a task conventional methods perform poorly for close sources. These results demonstrate that Rayleigh's criterion is nothing but a technicality specific to conventional imaging, and cleverer quantum measurements can locate two incoherent sources with arbitrary separation almost as accurately as conventional methods do for isolated sources.
Detection of Majorana Kramers pairs using a quantum point contact
Li, Jian; Pan, Wei; Bernevig, B. Andrei; Lutchyn, Roman
We propose a setup that integrates a quantum point contact (QPC) and a Josephson junction on a quantum spin Hall sample, experimentally realizable in InAs/GaSb quantum wells. The confinement due to both the QPC and the superconductor results in a Kramers pair of Majorana zero-energy bound states when the superconducting phases in the two arms differ by an odd multiple of π across the Josephson junction. We investigate the detection of these Majorana pairs with the integrated QPC, and find a robust switching from normal to Andreev scattering across the edges due to the presence of Majorana Kramers pairs. This transport signature is expected to be exhibited in measurements of differential conductance and/or current cross-correlation at low bias. This work was supported by ONR-N00014-14-1-0330.
Qin, Yanqi; Normand, Bruce; Sandvik, Anders; Meng, Zi Yang
We investigate the quantum phase transition in an S=1/2 dimerized Heisenberg antiferromagnet in three spatial dimensions. By means of quantum Monte Carlo simulations and finite-size scaling analyses, we get high-precision results for the quantum critical properties at the transition from the magnetically disordered dimer-singlet phase to the ordered Neel phase. This transition breaks O(N) symmetry with N=3 in D=3+1 dimensions. This is the upper critical dimension, where multiplicative logarithmic corrections to the leading mean-field critical properties are expected; we extract these corrections, establishing their precise forms for both the zero-temperature staggered magnetization, ms, and the Neel temperature, TN. We present a scaling ansatz for TN, including logarithmic corrections, which agrees with our data and indicates exact linearity with ms, implying a complete decoupling of quantum and thermal fluctuation effects close to the quantum critical point. These logarithmic scaling forms have not previously identified or verified by unbiased numerical methods and we discuss their relevance to experimental studies of dimerized quantum antiferromagnets such as TlCuCl3. Ref.: arXiv:1506.06073
Critical points for finite Fibonacci chains of point delta-interactions and orthogonal polynomials
Energy Technology Data Exchange (ETDEWEB)
De Prunele, E, E-mail: eprunele@univ-fcomte.fr [Institut UTINAM, UMR CNRS 6213, Universite de Franche-Comte, 16 route de Gray, 25030 Besancon Cedex (France)
2011-10-21
For a one-dimensional Schroedinger operator with a finite number n of point delta-interactions with a common intensity, the parameters are the intensity, the n - 1 intercenter distances and the mass. Critical points are points in the parameters space of the Hamiltonian where one bound state appears or disappears. The study of critical points for Hamiltonians with point delta-interactions arranged along a Fibonacci chain is shown to be closely related to the study of the so-called Fibonacci operator, a discrete one-dimensional Schroedinger-type operator, which occurs in the context of tight binding Hamiltonians. These critical points are the zeros of orthogonal polynomials previously studied in the context of special diatomic linear chains with elastic nearest-neighbor interaction. Properties of the zeros (location, asymptotic behavior, gaps, ...) are investigated. The perturbation series from the solvable periodic case is determined. The measure which yields orthogonality is investigated numerically from the zeros. It is shown that the transmission coefficient at zero energy can be expressed in terms of the orthogonal polynomials and their associated polynomials. In particular, it is shown that when the number of point delta-interactions is equal to a Fibonacci number minus 1, i.e. when the intervals between point delta-interactions form a palindrome, all the Fibonacci chains at critical points are completely transparent at zero energy. (paper)
Gate-controlled Kondo screening in graphene: Quantum criticality and electron-hole asymmetry
Vojta, M.; Fritz, L.; Bulla, R.
2010-04-01
Magnetic impurities in neutral graphene provide a realization of the pseudogap Kondo model, which displays a quantum phase transition between phases with screened and unscreened impurity moment. Here, we present a detailed study of the pseudogap Kondo model with finite chemical potential μ. While carrier doping restores conventional Kondo screening at lowest energies, properties of the quantum critical fixed point turn out to influence the behavior over a large parameter range. Most importantly, the Kondo temperature TK shows an extreme asymmetry between electron and hole doping. At criticality, depending on the sign of μ, TK follows either the scaling prediction TK~|μ| with a universal prefactor, or TK~|μ|x with x≈2.6. This asymmetry between electron and hole doping extends well outside the quantum critical regime and also implies a qualitative difference in the shape of the tunneling spectra for both signs of μ.
Far from equilibrium energy flow in quantum critical systems
Bhaseen, M J; Lucas, Andrew; Schalm, Koenraad
2013-01-01
We investigate far from equilibrium energy transport in strongly coupled quantum critical systems. Combining results from gauge-gravity duality, relativistic hydrodynamics, and quantum field theory, we argue that long-time energy transport occurs via a universal steady-state for any spatial dimensionality. This is described by a boosted thermal state. We determine the transport properties of this emergent steady state, including the average energy flow and its long-time fluctuations.
On the critical temperatures of superconductors: a quantum gravity approach
Gregori, Andrea
2010-01-01
We consider superconductivity in the light of the quantum gravity theoretical framework introduced in [1]. In this framework, the degree of quantum delocalization depends on the geometry of the energy distribution along space. This results in a dependence of the critical temperature characterizing the transition to the superconducting phase on the complexity of the structure of a superconductor. We consider concrete examples, ranging from low to high temperature superconductors, and discuss h...
Critical points of multidimensional random Fourier series: Variance estimates
Nicolaescu, Liviu I.
2016-08-01
We investigate the number of critical points of a Gaussian random smooth function uɛ on the m-torus Tm ≔ ℝm/ℤm approximating the Gaussian white noise as ɛ → 0. Let N(uɛ) denote the number of critical points of uɛ. We prove the existence of constants C, C' such that as ɛ goes to zero, the expectation of the random variable ɛmN(uɛ) converges to C, while its variance is extremely small and behaves like C'ɛm.
Critical Points in Nuclei and Interacting Boson Model Intrinsic States
Ginocchio, J N; Ginocchio, Joseph N.
2003-01-01
We consider properties of critical points in the interacting boson model, corresponding to flat-bottomed potentials as encountered in a second-order phase transition between spherical and deformed $\\gamma$-unstable nuclei. We show that intrinsic states with an effective $\\beta$-deformation reproduce the dynamics of the underlying non-rigid shapes. The effective deformation can be determined from the the global minimum of the energy surface after projection onto the appropriate symmetry. States of fixed $N$ and good O(5) symmetry projected from these intrinsic states provide good analytic estimates to the exact eigenstates, energies and quadrupole transition rates at the critical point.
Komnik, A.; Saleur, H.
2011-09-01
We verify the validity of the Cohen-Gallavotti fluctuation theorem for the strongly correlated problem of charge transfer through an impurity in a chiral Luttinger liquid, which is realizable experimentally as a quantum point contact in a fractional quantum Hall edge state device. This is accomplished via the development of an analytical method to calculate the full counting statistics of the problem in all the parameter regimes involving the temperature, the Hall voltage, and the gate voltage.
Diagnosis as the First Critical Point in the Treatment Trajectory
DEFF Research Database (Denmark)
Missel, Malene; Pedersen, Jesper H; Hendriksen, Carsten
2015-01-01
of patients with operable lung cancer in order to identify their needs for care interventions from the point of diagnosis to hospitalization. METHODS: We investigated patients' lived experiences from a longitudinal perspective at 4 critical time points during the treatment trajectory; we present here...... the patient to face a new life situation, and demands one-on-one supportive care. CONCLUSIONS: Diagnosis is the first critical point for patients with operable lung cancer and disrupts their daily life. Patients need psychosocial support during the period from diagnosis to surgical intervention and patient...... the findings from the first time point, diagnosis. Data were collected through interviews conducted 7 to 10 days following diagnosis of lung cancer. Data from 19 patients are included, and the analysis is based on Ricoeur's interpretation theory. The study framework is inspired by Schutz's phenomenological...
Gate-defined graphene quantum point contact in the quantum Hall regime.
Nakaharai, S; Williams, J R; Marcus, C M
2011-07-15
We investigate transport in a gate-defined graphene quantum point contact in the quantum Hall regime. Edge states confined to the interface of p and n regions in the graphene sheet are controllably brought together from opposite sides of the sample and allowed to mix in this split-gate geometry. Among the expected quantum Hall features, an unexpected additional plateau at 0.5h/e2 is observed. We propose that chaotic mixing of edge channels gives rise to the extra plateau.
Hazard Analysis and Critical Control Point Program for Foodservice Establishments.
Control Point ( HACCP ) inspections in foodservice operations throughout the state. The HACCP system , which first emerged in the late 1960s, is a rational...has been adopted for use in the foodservice industry. The HACCP system consists of three main components which are the: (1) Assessment of the hazards...to monitor critical control points. This system has shown promise as a tool to reduce the frequency of foodborne disease outbreaks in foodservice
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.
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.
A critical evaluation of Quintner et al: missing the point.
Dommerholt, Jan; Gerwin, Robert D
2015-04-01
The objective of this article is to critically analyze a recent publication by Quinter, Bove and Cohen, published in Rheumatology, about myofascial pain syndrome and trigger points (Quintner et al., 2014). The authors concluded that the leading trigger point hypothesis is flawed in reasoning and in science. They claimed to have refuted the trigger point hypothesis. The current paper demonstrates that the Quintner et al. paper is a biased review of the literature replete with unsupported opinions and accusations. In summary, Quintner et al. have not presented any convincing evidence to believe that the Integrated TrP Hypothesis should be laid to rest.
Oscillatory integrals for phase functions having certain degenerate critical points
Institute of Scientific and Technical Information of China (English)
Jinmyong KIM; ZHENG Quan
2008-01-01
The paper is concerned with oscillatory integrals for phase functions having certain de-generate critical points. Under a finite type condition of phase functions we show the estimate of oscillatory integrals of the first kind. The decay of the oscillatory integral depends on indices of the finite type, the spatial dimension and the symbol.
Oscillatory integrals for phase functions having certain degenerate critical points
Institute of Scientific and Technical Information of China (English)
Jinmyong; KIM
2008-01-01
The paper is concerned with oscillatory integrals for phase functions having certain de- generate critical points. Under a finite type condition of phase functions we show the estimate of oscillatory integrals of the first kind. The decay of the oscillatory integral depends on indices of the finite type, the spatial dimension and the symbol.
Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.
Dong, J K; Zhou, S Y; Guan, T Y; Zhang, H; Dai, Y F; Qiu, X; Wang, X F; He, Y; Chen, X H; Li, S Y
2010-02-26
The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.
Peculiar thermodynamics of the second critical point in supercooled water.
Bertrand, C E; Anisimov, M A
2011-12-08
On the basis of the principle of critical-point universality, we examine the peculiar thermodynamics of the liquid-liquid critical point in supercooled water. We show that the liquid-liquid criticality in water represents a special kind of critical behavior in fluids, intermediate between two limiting cases: the lattice gas, commonly used to model liquid-vapor transitions, and the lattice liquid, a weakly compressible liquid with an entropy-driven phase separation. While the ordering field in the lattice gas is associated with the chemical potential and the order parameter with the density, in the lattice liquid the ordering field is the temperature and the order parameter is the entropy. The behavior of supercooled water is much closer to lattice-liquid behavior than to lattice-gas behavior. Using new experimental data recently obtained by Mishima [J. Chem. Phys. 2010, 133, 144503], we have revised the parametric scaled equation of state, previously suggested by Fuentevilla and Anisimov [Phys. Rev. Lett. 2006, 97, 195702], and obtain a consistent description of the thermodynamic anomalies of supercooled water by adjusting linear backgrounds, one critical amplitude, and the critical pressure. We also show how the lattice-liquid description affects the finite-size scaling description of supercooled water in confined media.
Scanning gate imaging of a disordered quantum point contact.
Aoki, N; da Cunha, C R; Akis, R; Ferry, D K; Ochiai, Y
2014-05-14
Scanning gate microscopy (SGM) is a novel technique that has been used to image characteristic features related to the coherent electron flow in mesoscopic structures. For instance, SGM has successfully been applied to study peculiar electron transport properties that arise due to small levels of disorder in a system. The particular case of an InGaAs quantum well layer in a heterostructure, which is dominated by a quasi-ballistic regime, was analyzed. A quantum point contact fabricated onto this material exhibits conduction fluctuations that are not expected in typical high-mobility heterostructures such as AlGaAs/GaAs. SGM revealed not only interference patterns corresponding to specific conductance fluctuations but also mode-dependent resistance peaks corresponding to the first and second quantum levels of conductance (2e(2)/h) at zero magnetic field. On the other hand, clear conductance plateaus originating from the integer quantum Hall effect were observed at high magnetic fields. The physical size of incompressible edge channels was estimated from cross-sectional analysis of these images.
Universal short-time quantum critical dynamics in imaginary time
Yin, Shuai; Mai, Peizhi; Zhong, Fan
2014-04-01
We propose a scaling theory for the universal imaginary-time quantum critical dynamics for both short and long times. We discover that there exists a universal critical initial slip related to a small initial order parameter M0. In this stage, the order parameter M increases with the imaginary time τ as M ∝M0τθ with a universal initial-slip exponent θ. For the one-dimensional transverse-field Ising model, we estimate θ to be 0.373, which is markedly distinct from its classical counterpart. Apart from the local order parameter, we also show that the entanglement entropy exhibits universal behavior in the short-time region. As the critical exponents in the early stage and in equilibrium are identical, we apply the short-time dynamics method to determine quantum critical properties. The method is generally applicable in both the Landau-Ginzburg-Wilson paradigm and topological phase transitions.
Quantum Critical Behaviour of Semisimple Gauge Theories
DEFF Research Database (Denmark)
Esbensen, Jacob Kamuk; Ryttov, Thomas A.; Sannino, Francesco
2016-01-01
(M)_R \\times U(1) $ of the theory. To avoid gauge anomalies we add lepton-like particles. At the two-loops level an intriguing phase diagram appears. We uncover phases in which one, two or three fixed points exist and discuss the associated flows of the coupling constants. We discover a phase featuring...... complete asymptotic freedom and simultaneously an interacting infrared fixed point in both couplings. The analysis further reveals special renormalisation group trajectories along which one coupling displays asymptotic freedom and the other asymptotic safety, while both flowing in the infrared...... to an interacting fixed point. These are \\emph{safety free} trajectories. We briefly sketch out possible phenomenological implications, among which an independent way to generate near-conformal dynamics a l\\'a walking is investigated....
Black Hole Type Quantum Computing in Critical Bose-Einstein Systems
Dvali, Gia
2015-01-01
Recent ideas about understanding physics of black hole information-processing in terms of quantum criticality allow us to implement black hole mechanisms of quantum computing within critical Bose-Einstein systems. The generic feature, uncovered both by analytic and numeric studies, is the emergence at the critical point of gapless weakly-interacting modes, which act as qubits for information-storage at a very low energy cost. These modes can be effectively described in terms of either Bogoliubov or Goldstone degrees of freedom. The ground-state at the critical point is maximally entangled and far from being classical. We confirm this near-critical behavior by a new analytic method. We compute growth of entanglement and show its consistency with black hole type behavior. On the other hand, in the over-critical regime the system develops a Lyapunov exponent and scrambles quantum information very fast. By, manipulating the system parameters externally, we can put it in and out of various regimes and in this way ...
Chiral symmetry breaking in three-dimensional quantum electrodynamics as fixed point annihilation
Herbut, Igor F
2016-01-01
Spontaneous chiral symmetry breaking in three dimensional ($d=3$) quantum electrodynamics is understood as annihilation of an infrared-stable fixed point that describes the large-N conformal phase by another unstable fixed point at a critical number of fermions $N=N_c$. We discuss the root of universality of $N_c$ in this picture, together with some features of the phase boundary in the $(d,N)$ plane. In particular, it is shown that as $d\\rightarrow 4$, $N_c\\rightarrow 0$ with a constant slope, our best estimate of which suggests that $N_c = 2.89$ in $d=3$.
Energy Technology Data Exchange (ETDEWEB)
Mukherjee, K; Iyer, Kartik K; Patil, Swapnil; Maiti, K; Sampathkumaran, E V, E-mail: kmukherjee@tifr.res.in, E-mail: sampath@tifr.res.in [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005 (India)
2011-01-01
We report the influence of external pressure on the temperature dependence of magnetization and electrical resistivity as well as high-resolution photoemission studies for an alloy, Ce{sub 2}Rh{sub 0.7}Co{sub 0.3}Si{sub 3}, ordering magnetically below 3 K. It is found that external pressure has the same effect as that induced by (further) Co substitution for Rh in the series, Ce{sub 2}Rh{sub 1-x}Co{sub x}Si{sub 3}, resulting in qualitative changes in the features in the magnetic and transport data, with a suppression of magnetic ordering followed by quantum critical point effect. The high-resolution photo-emission spectra reveal signature of Kondo feature even at ambient pressure. These findings support the validity of spin-density-wave picture in this series.
Hydrodynamical Evolution near the QCD Critical End Point
Nonaka, Chiho; Asakawa, Masayuki
2003-10-01
Recently, the possibility of the existence of a critical end point (CEP) in the QCD phase diagram has attracted a lot of attention and several experimental signatures have been proposed for it^1. Berdnikov and Rajagopal discussed the growth of the correlation length near the critical end point in heavy-ion collision from the schematic argument^2. However, there has seen, so far, no quantitative study on the hydrodynamic evolution near CEP. Here we quantitatively evaluate the effect of the critical end point on the observables using the hydrodynamical model. First, we construct an equation of state (EOS) that includes critical behavior of CEP. Here we assume that the singular part of EOS near CEP belongs to the same universality class as the 3-d Ising model. Then we match the singular part of EOS with known QGP and hadronic EOS. We found the strong focusing effect near the critical end point in n_B/s trajectories in T-μ plane. This behavior is very different from an EOS of Bag model which is used in usual hydrodynamical models. This suggests that the effect of CEP appears strongly in the time evolution of system and the experimental observables. Next we investigate the time evolution and the behavior of correlation length near CEP along n_B/s trajectories. In addition, we also discuss the consequences of CEP in experimental results such as fluctuations and the kinetic freeze-out temperature. ^1M. Stephanov, K. Rajagopal, and E. Shuryak, Phys. Rev. Lett. 81 (1998) 4816. ^2B. Berdnikov and K. Rajagopal, Phys. Rev. D61 (2000) 105017.
Critical fluctuations for quantum mean-field models
Energy Technology Data Exchange (ETDEWEB)
Fannes, M.; Kossakowski, A.; Verbeure, A. (Univ. Louvain (Belgium))
1991-11-01
A Ginzburg-Landau-type approximation is proposed for the local Gibbs states for quantum mean-field models that leads to the exact thermodynamics. Using this approach, the spin fluctuations are computed for some spin-1/2 models. At the critical temperature, the distribution function showing abnormal fluctuations is found explicitly.
Entanglement dynamics in critical random quantum Ising chain with perturbations
Huang, Yichen
2017-05-01
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.
Current-voltage curves of gold quantum point contacts revisited
DEFF Research Database (Denmark)
Hansen, K.; Nielsen, S K.; Brandbyge, Mads;
2000-01-01
We present measurements of current-voltage (I-V) curves on gold quantum point contacts (QPCs) with a conductance up to 4 G(0) (G(0) = 2e(2)/h is the conductance quantum) and voltages up to 2 V. The QPCs are formed between the gold tip of a scanning tunneling microscope and a Au(110) surface under...... clean ultra-high-vacuum conditions at room temperature. The I - V curves are found to he almost linear in contrast to previous reports. Tight-binding calculations of I - V curves for one- and two-atom contacts are in excellent agreement with our measurements. On the other hand, clearly nonlinear I - V...
Dynamic nature at the QCD Critical End Point
Ohnishi, K; Ohnishi, Kazuaki; Teiji Kunihiro
2005-01-01
We discuss the dynamic nature of the critical end point (CEP) which is the end point of the first order chiral phase transition. In the earlier work, Son and Stephanov analyzed the Langevin equation for CEP taking care of the mixing effect between the chiral condensate and the baryon number density and showed that the dynamic universality class of CEP is the model H, the same as that of the end point of the liquid-gas transition. We point out a difficulty in their treatment that the theory does not correctly reduce to CEP in the limiting situation where the mixing effect disappears. We give a reanalysis of the Langevin equation to conclude that CEP belongs to the model C apart from the energy and momentum densities, which is the same conclusion as given by Berdnikov and Rajagopal. We also propose a new signal for CEP in the heavy-ion collision experiments.
Critical exponents and scaling invariance in the absence of a critical point.
Saratz, N; Zanin, D A; Ramsperger, U; Cannas, S; Pescia, D; Vindigni, A
2016-12-05
The paramagnetic-to-ferromagnetic phase transition is classified as a critical phenomenon due to the power-law behaviour shown by thermodynamic observables when the Curie point is approached. Here we report the observation of such a behaviour over extraordinarily many decades of suitable scaling variables in ultrathin Fe films, for certain ranges of temperature T and applied field B. This despite the fact that the underlying critical point is practically unreachable because protected by a phase with a modulated domain structure, induced by the dipole-dipole interaction. The modulated structure has a well-defined spatial period and is realized in a portion of the (T, B) plane that extends above the putative critical temperature, where thermodynamic quantities do not display any singularity. Our results imply that scaling behaviour of macroscopic observables is compatible with an avoided critical point.
Critical behaviors near the (tri-)critical end point of QCD within the NJL model
Lu, Ya; Cui, Zhu-Fang; Zong, Hong-Shi
2015-01-01
We investigate the dynamical chiral symmetry breaking and its restoration at finite density and temperature within the two-flavor Nambu-Jona-Lasinio model, and mainly focus on the critical behaviors near the critical end point (CEP) and tricritical point (TCP) of QCD. The co-existence region of the Wigner and Nambu phase is determined in the phase diagram for the massive and massless current quark, respectively. We use the various susceptibilities to locate the CEP/TCP and then extract the critical exponents near them. Our calculations reveal that the various susceptibilities share the same critical behaviors for the physical current quark mass, while they show different features in the chiral limit. Furthermore the critical exponent of order parameter at the TCP, $\\beta$=1/4, differs from that on the $O(4)$ line, $\\beta$=1/2, which indicates a change in the universality class.
124Te and the E(5) Critical Point Symmetry
Ghiţă, D. G.; Căta-Danil, G.; Bucurescu, D.; Căta-Danil, I.; Ivascu, M.; Mihai, C.; Suliman, G.; Stroe, L.; Sava, T.; Zamfir, N. V.
We present a new study of the low-lying states in 124Te nucleus by γ-ray spectroscopy following 124I β+/ɛ decay. The β radioactive sources were produced in the 124Te(p, n)124I reaction induced by 11 MeV protons, delivered by the Bucharest FN Tandem Accelerator. The γ-rays were measured in a low background area with three large volume HPGe detectors. A total number of 276 milion double coincidence events were recorded in a six-day run. Most of the gamma line intensities previously measured were confirmed with improved accuracy and several gamma lines were obtained for the first time. Our results, combined with those from a recent (n, γ) study are compared with the predictions of the E(5) critical point symmetry model and numerical IBA-1 model calculations at the critical point of the U(5)-O(6) phase transition.
Identification of Critical Points in the Quality Management System
Directory of Open Access Journals (Sweden)
Tünde SZABÓ
2011-10-01
Full Text Available Creating a quality management system can help organizations and other stakeholders in satisfying customer needs and expectations. Moreover, a well-implemented quality management ensures the organization a capable structure to make continuous improvement actions. Thus, after the evaluation of the quality management system elements, the identification of critical points is a very important element. There are several ways of assessing and identifying these critical points; in this case, identification will be done by questionnaire survey carried out at the Székely National Museum in Saint George. The questionnaire aimed to assess the whole system of management and staff attitudes towards some considerations established by international standard ISO 9001:2008.
Quantum clock: A critical discussion on spacetime
Burderi, Luciano; Iaria, Rosario
2016-01-01
We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval $\\Delta t$ that this clock can measure scales as the inverse of its size $\\Delta r$. This implies an uncertainty relation between space and time: $\\Delta r$ $\\Delta t$ $> G \\hbar / c^4$; where G, $\\hbar$ and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.
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.
2015-04-01
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.
QCD Critical Point and Complex Chemical Potential Singularities
Stephanov, M A
2006-01-01
The thermodynamic singularities of QCD in the plane of complex baryo-chemical potential mu are studied. Predictions are made using scaling and universality arguments in the vicinity of the massless quark limit. The results are illustrated by a calculation of complex mu singularities in a random matrix model at finite temperature. Implications for lattice QCD simulations aimed at locating the QCD critical point are discussed.
Nonlinear Seebeck and Peltier effects in quantum point contacts
Energy Technology Data Exchange (ETDEWEB)
Cipiloglu, M.A.; Turgut, S.; Tomak, M. [Department of Physics, Middle East Technical University, Ankara (Turkey)
2004-09-01
The charge and entropy currents across a quantum point contact are expanded as a series in powers of the applied bias voltage and the temperature difference. After that, the expansions of the Seebeck voltage in temperature difference and the Peltier heat in current are obtained. With a suitable choice of the average temperature and chemical potential, the lowest order nonlinear term in both cases appear to be of third order. The behavior of the third-order coefficients in both cases are then investigated for different contact parameters. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Nonlinear Seebeck and Peltier effects in quantum point contacts
Çipilolu, M. A.; Turgut, S.; Tomak, M.
2004-09-01
The charge and entropy currents across a quantum point contact are expanded as a series in powers of the applied bias voltage and the temperature difference. After that, the expansions of the Seebeck voltage in temperature difference and the Peltier heat in current are obtained. With a suitable choice of the average temperature and chemical potential, the lowest order nonlinear term in both cases appear to be of third order. The behavior of the third-order coefficients in both cases are then investigated for different contact parameters.
Point form relativistic quantum mechanics and relativistic SU(6)
Klink, W. H.
1993-01-01
The point form is used as a framework for formulating a relativistic quantum mechanics, with the mass operator carrying the interactions of underlying constituents. A symplectic Lie algebra of mass operators is introduced from which a relativistic harmonic oscillator mass operator is formed. Mass splittings within the degenerate harmonic oscillator levels arise from relativistically invariant spin-spin, spin-orbit, and tensor mass operators. Internal flavor (and color) symmetries are introduced which make it possible to formulate a relativistic SU(6) model of baryons (and mesons). Careful attention is paid to the permutation symmetry properties of the hadronic wave functions, which are written as polynomials in Bargmann spaces.
Pezzini, S.; Cobaleda, C.; Piot, B. A.; Bellani, V.; Diez, E.
2014-09-01
We report on magnetotransport measurements up to 30 T performed on a bilayer graphene Hall bar, enclosed by two thin hexagonal boron nitride flakes. In the quantum Hall regime, our high-mobility sample exhibits an insulating state at the neutrality point which evolves into a metallic phase when a strong in-plane field is applied, as expected for a transition from a canted antiferromagnetic to a ferromagnetic spin-ordered phase. We individuate a temperature-independent crossing in the four-terminal resistance as a function of the total magnetic field, corresponding to the critical point of the transition. We show that the critical field scales linearly with the perpendicular component of the field, as expected from the underlying competition between the Zeeman energy and interaction-induced anisotropies. A clear scaling of the resistance is also found and a universal behavior is proposed in the vicinity of the transition.
Symmetry relations for multifractal spectra at random critical points
Monthus, Cécile; Berche, Bertrand; Chatelain, Christophe
2009-12-01
Random critical points are generically characterized by multifractal properties. In the field of Anderson localization, Mirlin et al (2006 Phys. Rev. Lett. 97 046803) have proposed that the singularity spectrum f(α) of eigenfunctions satisfies the exact symmetry f(2d-α) = f(α)+d-α. In the present paper, we analyze the physical origin of this symmetry in relation to the Gallavotti-Cohen fluctuation relations of large deviation functions that are well known in the field of non-equilibrium dynamics: the multifractal spectrum of the disordered model corresponds to the large deviation function of the rescaling exponent γ = (α-d) along a renormalization trajectory in the effective time t = lnL. We conclude that the symmetry discovered for the specific example of Anderson transitions should actually be satisfied at many other random critical points after an appropriate translation. For many-body random phase transitions, where the critical properties are usually analyzed in terms of the multifractal spectrum H(a) and of the moment exponents X(N) of the two-point correlation function (Ludwig 1990 Nucl. Phys. B 330 639), the symmetry becomes H(2X(1)-a) = H(a)+a-X(1), or equivalently Δ(N) = Δ(1-N) for the anomalous parts \\Delta (N) \\equiv X(N)-NX(1) . We present numerical tests favoring this symmetry for the 2D random Q-state Potts model with varying Q.
Ion exchange at the critical point of solution.
Savoy, J D; Baird, J K; Lang, J R
2016-03-11
A mixture of isobutyric acid (IBA)+water has an upper critical point of solution at 26.7°C and an IBA concentration of 4.40M. We have determined the Langmuir isotherms for the hydroxide form of Amberlite IRN-78 resin in contact with mixtures of IBA+water at temperatures, 27.0, 29.0, 31.0 and 38.0°C, respectively. The Langmuir plot at 38.0°C forms a straight line. At the three lower temperatures, however, a peak in the Langmuir plot is observed for IBA concentrations in the vicinity of 4.40M. We regard this peak to be a critical effect not only because it is located close to 4.40M, but also because its height becomes more pronounced as the temperature of the isotherm approaches the critical temperature. For concentrations in the vicinity of the peak, the data indicate that the larger isobutyrate ion is rejected by the resin in favor of the smaller hydroxide ion. This reversal of the expected ion exchange reaction might be used to separate ions according to size. Using the Donnan theory of ion exchange equilibrium, we link the swelling pressure to the osmotic pressure. We show that the peak in the Langmuir plot is associated with a maximum in the "osmotic" energy. This maximum has its origin in the concentration derivative of the osmotic pressure, which goes to zero as the critical point is approached.
Quantum Critical Behaviour of Semisimple Gauge Theories
DEFF Research Database (Denmark)
Kamuk Esbensen, Jacob; Ryttov, Thomas A.; Sannino, Francesco
2016-01-01
We study the perturbative phase diagram of semi-simple fermionic gauge theories resembling the Standard Model. We investigate an $SU(N)$ gauge theory with $M$ Dirac flavors where we gauge first an $SU(M)_L$ and then an $SU(2)_L \\subset SU(M)_L$ of the original global symmetry $SU(M)_L\\times SU......(M)_R \\times U(1) $ of the theory. To avoid gauge anomalies we add lepton-like particles. At the two-loops level an intriguing phase diagram appears. We uncover phases in which one, two or three fixed points exist and discuss the associated flows of the coupling constants. We discover a phase featuring...
Detection of Majorana Kramers Pairs Using a Quantum Point Contact
Li, Jian; Pan, Wei; Bernevig, B. Andrei; Lutchyn, Roman M.
2016-07-01
We propose a setup that integrates a quantum point contact (QPC) and a Josephson junction on a quantum spin Hall sample, experimentally realizable in InAs/GaSb quantum wells. The confinement due to both the QPC and the superconductor results in a Kramers pair of Majorana zero-energy bound states when the superconducting phases in the two arms differ by an odd multiple of π across the Josephson junction. We investigate the detection of these Majorana pairs with the integrated QPC, and find a robust switching from normal to Andreev scattering across the edges due to the presence of Majorana Kramers pairs. Such a switching of the current represents a qualitative signature where multiterminal differential conductances oscillate with alternating signs when the external magnetic field is tuned. We show that this qualitative signature is also present in current cross-correlations. Thus, the change of the backscattering current nature affects both conductance and shot noise, the measurement of which offers a significant advantage over quantitative signatures such as conductance quantization in realistic measurements.
Disorder-driven itinerant quantum criticality of three-dimensional massless Dirac fermions
Pixley, J. H.; Goswami, Pallab; Das Sarma, S.
2016-02-01
Progress in the understanding of quantum critical properties of itinerant electrons has been hindered by the lack of effective models which are amenable to controlled analytical and numerically exact calculations. Here we establish that the disorder-driven semimetal to metal quantum phase transition of three-dimensional massless Dirac fermions could serve as a paradigmatic toy model for studying itinerant quantum criticality, which is solved in this work by exact numerical and approximate field-theoretic calculations. As a result, we establish the robust existence of a non-Gaussian universality class, and also construct the relevant low-energy effective field theory that could guide the understanding of quantum critical scaling for many strange metals. Using the kernel polynomial method (KPM), we provide numerical results for the calculated dynamical exponent (z ) and correlation length exponent (ν ) for the disorder-driven semimetal (SM) to diffusive metal (DM) quantum phase transition at the Dirac point for several types of disorder, establishing its universal nature and obtaining the numerical scaling functions in agreement with our field-theoretical analysis.
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.
Possible Signal for Critical Point in Hadronization Process
Rybczynski, M.; Wlodarczyk, Z.; Wilk, G.
2004-02-01
We argue that recent data on fluctuations observed in heavy ion collisions show non-monotonic behaviour as function of number of participants (or ''wounded nucleons'') NW. When interpreted in thermodynamical approach this result can be associated with a possible structure occurring in the corresponding equation of state (EoS). This in turn could be further interpreted as due to the occurrence of some characteristic points (like softest point or critical point) of EoS discussed in the literature and therefore be regarded as a possible signal of the QGP formation in such collisions. We show, however, that the actual situation is still far from being clear and calls for more investigations of fluctuation phenomena in multiparticle production processes to be performed.
Delirium in Critically Ill Children: An International Point Prevalence Study.
Traube, Chani; Silver, Gabrielle; Reeder, Ron W; Doyle, Hannah; Hegel, Emily; Wolfe, Heather A; Schneller, Christopher; Chung, Melissa G; Dervan, Leslie A; DiGennaro, Jane L; Buttram, Sandra D W; Kudchadkar, Sapna R; Madden, Kate; Hartman, Mary E; deAlmeida, Mary L; Walson, Karen; Ista, Erwin; Baarslag, Manuel A; Salonia, Rosanne; Beca, John; Long, Debbie; Kawai, Yu; Cheifetz, Ira M; Gelvez, Javier; Truemper, Edward J; Smith, Rebecca L; Peters, Megan E; O'Meara, A M Iqbal; Murphy, Sarah; Bokhary, Abdulmohsen; Greenwald, Bruce M; Bell, Michael J
2017-04-01
To determine prevalence of delirium in critically ill children and explore associated risk factors. Multi-institutional point prevalence study. Twenty-five pediatric critical care units in the United States, the Netherlands, New Zealand, Australia, and Saudi Arabia. All children admitted to the pediatric critical care units on designated study days (n = 994). Children were screened for delirium using the Cornell Assessment of Pediatric Delirium by the bedside nurse. Demographic and treatment-related variables were collected. Primary study outcome measure was prevalence of delirium. In 159 children, a final determination of mental status could not be ascertained. Of the 835 remaining subjects, 25% screened positive for delirium, 13% were classified as comatose, and 62% were delirium-free and coma-free. Delirium prevalence rates varied significantly with reason for ICU admission, with highest delirium rates found in children admitted with an infectious or inflammatory disorder. For children who were in the PICU for 6 or more days, delirium prevalence rate was 38%. In a multivariate model, risk factors independently associated with development of delirium included age less than 2 years, mechanical ventilation, benzodiazepines, narcotics, use of physical restraints, and exposure to vasopressors and antiepileptics. Delirium is a prevalent complication of critical illness in children, with identifiable risk factors. Further multi-institutional, longitudinal studies are required to investigate effect of delirium on long-term outcomes and possible preventive and treatment measures. Universal delirium screening is practical and can be implemented in pediatric critical care units.
Bhole, Gaurav; Anjusha, V. S.; Mahesh, T. S.
2016-04-01
A robust control over quantum dynamics is of paramount importance for quantum technologies. Many of the existing control techniques are based on smooth Hamiltonian modulations involving repeated calculations of basic unitaries resulting in time complexities scaling rapidly with the length of the control sequence. Here we show that bang-bang controls need one-time calculation of basic unitaries and hence scale much more efficiently. By employing a global optimization routine such as the genetic algorithm, it is possible to synthesize not only highly intricate unitaries, but also certain nonunitary operations. We demonstrate the unitary control through the implementation of the optimal fixed-point quantum search algorithm in a three-qubit nuclear magnetic resonance (NMR) system. Moreover, by combining the bang-bang pulses with the crusher gradients, we also demonstrate nonunitary transformations of thermal equilibrium states into effective pure states in three- as well as five-qubit NMR systems.
Observability of quantum criticality and a continuous supersolid in atomic gases.
Diehl, S; Baranov, M; Daley, A J; Zoller, P
2010-04-23
We analyze the Bose-Hubbard model with a three-body hard-core constraint by mapping the system to a theory of two coupled bosonic degrees of freedom. We find striking features that could be observable in experiments, including a quantum Ising critical point on the transition from atomic to dimer superfluidity at unit filling, and a continuous supersolid phase for strongly bound dimers.
Piazza, Francesco; Zwerger, Wilhelm; Strack, Philipp
2016-02-01
Increasing the spin imbalance in superconductors can spatially modulate the gap by forming Cooper pairs with finite momentum. For large imbalances compared to the Fermi energy, the inhomogeneous FFLO superconductor ultimately becomes a normal metal. There is mounting experimental evidence for this scenario in two-dimensional (2D) organic superconductors in large in-plane magnetic fields; this is complemented by ongoing efforts to realize this scenario in coupled tubes of atomic Fermi gases with spin imbalance. Yet, a theory for the phase transition from a metal to an FFLO superconductor has not been developed so far and the universality class has remained unknown. Here we propose and analyze a spin imbalance driven quantum critical point between a 2D metal and an FFLO phase in anisotropic electron systems. We derive the effective action for electrons and bosonic FFLO pairs at this quantum phase transition. Using this action, we predict non-Fermi-liquid behavior and the absence of quasiparticles at a discrete set of hot spots on the Fermi surfaces. This results in strange power laws in thermodynamics and response functions, which are testable with existing experimental setups on 2D organic superconductors and may also serve as signatures of the elusive FFLO phase itself. The proposed universality class is distinct from previously known quantum critical metals and, because its critical fluctuations appear already in the pairing channel, a promising candidate for naked metallic quantum criticality over extended temperature ranges.
Zhang, L.X.; Leburton, J.P.; Hanson, R.; Kouwenhoven, L.P.
2004-01-01
We show that the design of a quantum point contact adjacent to a quantum dot can be optimized to produce maximum sensitivity to single-electron charging in the quantum dot. Our analysis is based on the self-consistent solution of coupled three-dimensional Kohn-Sham and Poisson equations for the
Dynamical eigenfunctions and critical density in loop quantum cosmology
Craig, David A
2012-01-01
We offer a new, physically transparent argument for the existence of the critical, universal maximum matter density in loop quantum cosmology for the case of a flat Friedmann-Lemaitre-Robertson-Walker cosmology with scalar matter. The argument is based on the existence of a sharp exponential ultraviolet cutoff in momentum space on the eigenfunctions of the quantum cosmological dynamical evolution operator (the gravitational part of the Hamiltonian constraint), attributable to the fundamental discreteness of spatial volume in loop quantum cosmology. The existence of the cutoff is proved directly from recently found exact solutions for the eigenfunctions for this model. As a consequence, the operators corresponding to the momentum of the scalar field and the spatial volume approximately commute. The ultraviolet cutoff then implies that the scalar momentum, though not a bounded operator, is in effect bounded on subspaces of constant volume, leading to the upper bound on the expectation value of the matter densit...
LEARNING THE CRITICAL POINTS FOR ADDITION IN MATEMATIKA GASING
Directory of Open Access Journals (Sweden)
Johannes Hamonangan Siregar
2014-07-01
Full Text Available We propose learning Matematika GASING to help students better understand the addition material. Matematika GASING is a way of learning mathematics in an easy, fun and enjoyable fashion. GASING is short for GAmpang, aSyIk, and menyenaNGkan (Bahasa Indonesia for easy, fun and enjoyable. It was originally developed by Prof. Yohanes Surya at the Surya Institute in Indonesia to improve the mathematics education in Indonesia. In Matematika GASING, there is a step called “the critical point” that needs to be mastered for each topic. The focus of our research is the critical point for addition, that is addition of two numbers between 1 − 10 with a sum less than 20. The subject is a matriculation class at STKIP Surya and the research method used is Classroom Action Research. The statistics obtained is described using Qualitative Descriptive Statistics.Keyword: Matematika GASING, Addition, Critical Points, Classroom Action Research. DOI: http://dx.doi.org/10.22342/jme.5.2.1500.160-169
Critical versus spurious fluctuations in the search for the QCD critical point
Hippert, M.; Fraga, E. S.; Santos, E. M.
2016-01-01
The neighborhood of the QCD chiral critical point is characterized by intense fluctuations of the chiral field which could, in principle, generate pronounced experimental signatures. However, experimental uncertainties which are inherent to heavy-ion collisions, as well as the modest size and duration of the formed plasma, will severely attenuate these signatures. Using Monte Carlo techniques, we study second-order event-by-event moments of pions as a prototype for signatures of the chiral critical point based on the enhancement of the correlation length and event-by-event analysis. We test their viability against some realistic ingredients, similar to the ones found in the RHIC beam energy scan program.
Critical versus spurious fluctuations in the search for the QCD critical point
Hippert, Maurício; Santos, Edivaldo M
2015-01-01
The neighborhood of the QCD chiral critical point is characterized by intense fluctuations of the chiral field which could, in principle, generate pronounced experimental signatures. However, experimental uncertainties which are inherent to heavy ion collisions, as well as the modest size and duration of the formed plasma, will severely attenuate these signatures. Using Monte Carlo techniques, we study second-order event-by-event moments of pions as a prototype for signatures of the chiral critical point based on the enhancement of the correlation length and event-by-event analysis. We test their viability against some realistic ingredients, similar to the ones found in the RHIC Beam Energy Scan program.
Quantum criticality in an Ising chain: experimental evidence for emergent E8 symmetry.
Coldea, R; Tennant, D A; Wheeler, E M; Wawrzynska, E; Prabhakaran, D; Telling, M; Habicht, K; Smeibidl, P; Kiefer, K
2010-01-08
Quantum phase transitions take place between distinct phases of matter at zero temperature. Near the transition point, exotic quantum symmetries can emerge that govern the excitation spectrum of the system. A symmetry described by the E8 Lie group with a spectrum of eight particles was long predicted to appear near the critical point of an Ising chain. We realize this system experimentally by using strong transverse magnetic fields to tune the quasi-one-dimensional Ising ferromagnet CoNb2O6 (cobalt niobate) through its critical point. Spin excitations are observed to change character from pairs of kinks in the ordered phase to spin-flips in the paramagnetic phase. Just below the critical field, the spin dynamics shows a fine structure with two sharp modes at low energies, in a ratio that approaches the golden mean predicted for the first two meson particles of the E8 spectrum. Our results demonstrate the power of symmetry to describe complex quantum behaviors.
Bulk and boundary critical behavior at Lifshitz points
Indian Academy of Sciences (India)
H W Diehl
2005-05-01
Lifshitz points are multicritical points at which a disordered phase, a homogeneous ordered phase, and a modulated ordered phase meet. Their bulk universality classes are described by natural generalizations of the standard 4 model. Analyzing these models systematically via modern field-theoretic renormalization group methods has been a long-standing challenge ever since their introduction in the middle of 1970s. We survey the recent progress made in this direction, discussing results obtained via dimensionality expansions, how they compare with Monte Carlo results, and open problems. These advances opened the way towards systematic studies of boundary critical behavior at -axial Lifshitz points. The possible boundary critical behavior depends on whether the surface plane is perpendicular to one of the modulation axes or parallel to all of them. We show that the semi-infinite field theories representing the corresponding surface universality classes in these two cases of perpendicular and parallel surface orientation differ crucially in their Hamiltonian's boundary terms and the implied boundary conditions, and explain recent results along with our current understanding of this matter.
Functional renormalization group analysis of the soft mode at the QCD critical point
Yokota, Takeru; Kunihiro, Teiji; Morita, Kenji
2016-07-01
We make an intensive investigation of the soft mode at the quantum chromodynamics (QCD) critical point on the basis of the functional renormalization group (FRG) method in the local potential approximation. We calculate the spectral functions ρ_{σ, π}(ω, p) in the scalar (σ) and pseudoscalar (π) channels beyond the random phase approximation in the quark-meson model. At finite baryon chemical potential μ with a finite quark mass, the baryon-number fluctuation is coupled to the scalar channel and the spectral function in the σ channel has a support not only in the time-like (ω > p) but also in the space-like (ω position of the latter becomes vanishingly small with the height being enhanced as the system approaches the QCD critical point, which is a manifestation of the fact that the phonon mode is the soft mode associated with the second-order transition at the QCD critical point, as has been suggested by some authors. Moreover, our extensive calculation of the spectral function in the (ω, p) plane enables us to see that the mesonic and phonon modes have the respective definite dispersion relations ω_{σ.ph}(p), and it turns out that ω_{σ}(p) crosses the light-cone line into the space-like region, and then eventually merges into the phonon mode as the system approaches the critical point more closely. This implies that the sigma-mesonic mode also becomes soft at the critical point. We also provide numerical stability conditions that are necessary for obtaining the accurate effective potential from the flow equation.
Hawking Radiation and Nonequilibrium Quantum Critical Current Noise
Sonner, Julian; Green, A. G.
2012-08-01
The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady state, leading to universal out-of-equilibrium behavior. This attractive notion has been demonstrated in just a few cases. We demonstrate how holography—a mapping between the quantum critical system and a gravity dual—provides an illuminating perspective and new results. Nontrivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system. We calculate this in a two-dimensional system driven by a strong in-plane electric field and deduce a universal scaling function interpolating between previously established equilibrium and far-from-equilibrium current noise. Since this applies at all fields, out-of-equilibrium experiments no longer require very high fields for comparison with theory.
Nontrivial Critical Fixed Point for Replica-Symmetry-Breaking Transitions
Charbonneau, Patrick; Yaida, Sho
2017-05-01
The transformation of the free-energy landscape from smooth to hierarchical is one of the richest features of mean-field disordered systems. A well-studied example is the de Almeida-Thouless transition for spin glasses in a magnetic field, and a similar phenomenon—the Gardner transition—has recently been predicted for structural glasses. The existence of these replica-symmetry-breaking phase transitions has, however, long been questioned below their upper critical dimension, du=6 . Here, we obtain evidence for the existence of these transitions in d
Learning the Critical Points for Addition in Matematika GASING
Directory of Open Access Journals (Sweden)
Johannes Hamonangan Siregar
2014-07-01
Full Text Available We propose learning Matematika GASING to help students better understand the addition material. Matematika GASING is a way of learning mathematics in an easy, fun and enjoyable fashion. GASING is short for GAmpang, aSyIk, and menyenaNGkan (Bahasa Indonesia for easy, fun and enjoyable. It was originally developed by Prof. Yohanes Surya at the Surya Institute in Indonesia to improve the mathematics education in Indonesia. In Matematika GASING, there is a step called “the critical point” that needs to be mastered for each topic. The focus of our research is the critical point for addition, that is addition of two numbers between 1 − 10 with a sum less than 20. The subject is a matriculation class at STKIP Surya and the research method used is Classroom Action Research. The statistics obtained is described using Qualitative Descriptive Statistics.
Shear Thinning Near the Critical Point of Xenon
Zimmerli, Gregory A.; Berg, Robert F.; Moldover, Michael R.; Yao, Minwu
2008-01-01
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span a wide range of reduced shear rate: 10(exp -3) critical fluctuations. The measurements had a temperature resolution of 0.01 mK and were conducted in microgravity aboard the Space Shuttle Columbia to avoid the density stratification caused by Earth's gravity. The viscometer measured the drag on a delicate nickel screen as it oscillated in the xenon at amplitudes 3 mu,m 430 mu, and frequencies 1 Hz critical scaling. At high frequencies, (omega tau)(exp 2) > gamma-dot tau, C(sub gamma) depends also on both x(sub 0) and omega. The data were compared with numerical calculations based on the Carreau-Yasuda relation for complex fluids: eta(gamma-dot)/eta(0)=[1+A(sub gamma)|gamma-dot tau|](exp - chi(sub eta)/3+chi(sub eta)), where chi(sub eta) =0.069 is the critical exponent for viscosity and mode-coupling theory predicts A(sub gamma) =0.121. For xenon we find A(sub gamma) =0.137 +/- 0.029, in agreement with the mode coupling value. Remarkably, the xenon data close to the critical temperature T(sub c) were independent of the cooling rate (both above and below T(sub c) and these data were symmetric about T(sub c) to within a temperature scale factor. The scale factors for the magnitude of the oscillator s response differed from those for the oscillator's phase; this suggests that the surface tension of the two-phase domains affected the drag on the screen below T(sub c).
Has the QCD critical point been observed at RHIC? - A Rebuttal
Lacey, Roy A
2016-01-01
This note rebuts an old, but recurring claim by Antoniou, Davis and Diakonos [1] that the critical point and associated critical exponents reported in Ref. [2], is based on an erroneous treatment of scaling relations near the critical point.
Liquid-Vapor Argon Isotope Fractionation from the Triple Point to the Critical Point
DEFF Research Database (Denmark)
Phillips, J. T.; Linderstrøm-Lang, C. U.; Bigeleisen, J.
1972-01-01
are compared at the same molar volume. The isotope fractionation factor α for 36Ar∕40Ar between liquid and vapor has been measured from the triple point to the critical temperature. The results are compared with previous vapor pressure data, which cover the range 84–102°K. Although the agreement is within....... The fractionation factor approaches zero at the critical temperature with a nonclassical critical index equal to 0.42±0.02.〈∇2Uc〉/ρc in liquid argon is derived from the experimental fractionation data and calculations of 〈∇2Ug〉/ρg for a number of potential functions for gaseous argon....
Giant acoustoelectric current in suspended quantum point contacts
Kreft, Dustin J.; Mourokh, Lev G.; Shin, Hyuncheol; Bichler, Max; Wegscheider, Werner; Blick, Robert H.
2016-12-01
We present results on the acoustoelectric current driven through a quantum point contact (QPC) placed on a suspended nanobridge, which is subject to surface acoustic waves (SAWs). The magnitude of this current is much larger than that of a two-dimensional gas, and the system has enhanced sensitivity to perturbations. In particular, the current oscillations as a function of magnetic field exhibit additional features associated with the spin splitting. Furthermore, the negative voltage applied to the QPC gates induces the oscillations revealing the subband structure not seen in transport measurements at the elevated temperatures of our experiment. Near the pinch off conditions, the acoustoelectric current becomes negative which we attribute to the enhanced backscattering caused by the SAW-phonons' absorption and emission.
Critical point drying: contamination in transitional fluid supply cylinders.
Hoagland, K D; Rosowski, J R; Cohen, A L
1980-01-01
We call attention to the occurrence of an oily residue in the CPD bomb after critical point drying, as well as the presence of rust, dirt, and an oily residue in CO2 and Freon supply cylinders. Bottled gas is often tested for purity once after manufacturing and then is pumped and stored, perhaps several times, before the consumer's cylinders are filled. The cylinders may be in use for over 40 years, and may never be chemically cleaned, although they are hydrostatically pressure tested every five years, with the date of each test stamped on the cylinder. To the bottled gas industry we recommend regular inspection of tanks for bottom contamination, and vacuum and chemical cleaning when contamination is found. To users of bottled gas for critical point drying, we recommend becoming aware of the procedures of cylinder inspection, cleaning, and circulation among users. We suggest reporting to the gas supplier any contamination produced by inadvertently backfilling the supply cylinder. Although a common awareness of the problem of supply cylinder residues should lead to failures, the best assurance of clean, oil-free, dry liquid CO2 and other transitional fluids may be in the development of in-line filters which would remove particles, oil and moisture between the supply cylinder and the CPD bomb. We also suggest the use of gas grades higher than commercial, such as welding anhydrous (CO2) or specialty gases.
Critical Point on the QCD Deconfining Phase Boundary
Srivastava, P K
2012-01-01
Ambiguities regarding the physics and the existence of the critical point (CP) on the QCD phase boundary still exist and the mist regarding the conjectured QCD phase boundary has not yet cleared. In this paper we extend our earlier study where we constructed a deconfining phase boundary using Gibbs' equilibrium conditions after using a quasiparticle equation of state (EOS) for quark gluon plasma (QGP) and an excluded volume EOS for the hadron gas (HG) and find the presence of a critical point on this phase boundary where the first order phase transition terminates. In this paper, we plot the difference in the normalized entropy density ($s/T^{3}$) between HG and QGP phases along the deconfining phase boundary and find that it vanishes at CP. Further we have shown the variation of the square of speed of sound ($c_{s}^{2}$) for the HG and QGP separately and find that the difference ($\\Delta c_{s}^{2}$) between them along the deconfining phase boundary again vanishes at the CP of the boundary. We also plot the v...
Measurement of Critical Adsorption of Nitrogen near Its Liquid-vapor Critical Point
Chan, Moses
2003-01-01
The density profile of a critical fluid near a solid surface is expected to show an universal shape. This is known as critical adsorption. The measurement of this effect, especially close to the critical point, is often obscured by gravity. We were able to separate the gravitational effect from critical adsorption by using two capacitors, one with a large gap and one with a small gap of approximately 2 m. Within the uncertainty in the measurement, our data, which ranges between 10(exp -3) to 2 x 10(exp -6) in reduced temperatures, is consistent with the predicted power law dependence. This work is carried out in collaboration with Rafael Garcia, Sarah Scheidemantel and Klaus Knorr. It is funded by NASA's office of Biological and Physical Researchunder.
Criticality in Two-Dimensional Quantum Systems: Tensor Network Approach
Ran, Shi-Ju; Li, Wei; Lewenstein, Maciej; Su, Gang
2016-01-01
Determination and characterization of criticality in two-dimensional (2D) quantum many-body systems belong to the most important challenges and problems of quantum physics. In this paper we propose an efficient scheme to solve this problem by utilizing the infinite projected entangled pair state (iPEPS), and tensor network (TN) representations. We show that the criticality of a 2D state is faithfully reproduced by the ground state (dubbed as boundary state) of a one-dimensional effective Hamiltonian constructed from its iPEPS representation. We demonstrate that for a critical state the correlation length and the entanglement spectrum of the boundary state are essentially different from those of a gapped iPEPS. This provides a solid indicator that allows to identify the criticality of the 2D state. Our scheme is verified on the resonating valence bond (RVB) states on kagom\\'e and square lattices, where the boundary state of the honeycomb RVB is found to be described by a $c=1$ conformal field theory. We apply ...
Quantum Criticality Beneath the Superconducting Dome in β-YbAlB4
Tomita, T.; Kuga, K.; Uwatoko, Y.; Nakatsuji, S.
2016-02-01
Yb-based heavy fermion superconductor β-YbAlB4 at 0 K and 0 T at ambient pressure is located near the quantum critical point with strong mixed valiancy. In this type of Yb electron system, we expect that the magnetic order connected to the quantum critical point derives from the applied pressure. We built a pressure-temperature phase diagram for β-YbAlB4 by measuring the electrical resistivity of high quality single crystal at temperatures down to 40 mK under an applied pressure. A strange metal region appeared, showing non-Fermi liquid ρab α T1.5 behavior, which is stable with applied pressure up to 0.4 GPa, even when below the superconducting dome excluded by a magnetic field of 0.1 T. By increasing of pressure above 2.5 GPa, a magnetic order is first generated. Such ambient quantum criticality/superconductivity is unconventional and is detached from the magnetic order.
Gauge-field-assisted Kekul\\'e quantum criticality
Scherer, Michael M
2016-01-01
We study the quantum phase transition of $U(1)$ - charged Dirac fermions Yukawa-coupled to the Kekul\\'e valence bond solid order parameter with $Z_3$ symmetry of the honeycomb lattice. The symmetry allows for the presence of the term in the action which is cubic in the Kekul\\'e order parameter, and which is expected to prevent the quantum phase transition in question from being continuous. The Gross-Neveu-Yukawa theory for the transition is investigated using a perturbative renormalization group and within the $\\epsilon$ expansion close to four space-time dimensions. For a vanishing $U(1)$ charge we show that quantum fluctuations may render the phase transition continuous only sufficiently far away from 3+1 dimensions, where the validity of the conclusions based on the leading order $\\epsilon$ expansion appear questionable. In the presence of a fluctuating gauge field, on the other hand, we find quantum critical behavior even at weak coupling to appear close to 3+1 dimensions, that is, within the domain of va...
Random matrix theory and critical phenomena in quantum spin chains.
Hutchinson, J; Keating, J P; Mezzadri, F
2015-09-01
We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups U(N),O(N), and Sp(2N). In particular we calculate critical exponents s,ν, and z, corresponding to the energy gap, correlation length, and dynamic exponent, respectively. We also compute the ground state correlators 〈σ_{i}^{x}σ_{i+n}^{x}〉_{g},〈σ_{i}^{y}σ_{i+n}^{y}〉_{g}, and 〈∏_{i=1}^{n}σ_{i}^{z}〉_{g}, all of which display quasi-long-range order with a critical exponent dependent upon system parameters. Our approach establishes universality of the exponents for the class of systems in question.
Quantum transport of disordered Weyl semimetals at the nodal point.
Sbierski, Björn; Pohl, Gregor; Bergholtz, Emil J; Brouwer, Piet W
2014-07-11
Weyl semimetals are paradigmatic topological gapless phases in three dimensions. We here address the effect of disorder on charge transport in Weyl semimetals. For a single Weyl node with energy at the degeneracy point and without interactions, theory predicts the existence of a critical disorder strength beyond which the density of states takes on a nonzero value. Predictions for the conductivity are divergent, however. In this work, we present a numerical study of transport properties for a disordered Weyl cone at zero energy. For weak disorder, our results are consistent with a renormalization group flow towards an attractive pseudoballistic fixed point with zero conductivity and a scale-independent conductance; for stronger disorder, diffusive behavior is reached. We identify the Fano factor as a signature that discriminates between these two regimes.
On Locating the Critical End Point in QCD Phase Diagram
Srivastava, P K; Singh, C P
2011-01-01
We use the available two different self-consistent formulations of quasiparticle models and extend their applications for the description of quark gluon plasma (QGP) at non-vanishing baryon chemical potentials. The thermodynamical quantities calculated from these models are compared with the values obtained from lattice simulations and a good agreement between theoretical calculations and lattice QCD data suggests that the values of the parameters used in the paper are consistent. A new equation of state (EOS) for a gas of extended baryons and pointlike mesons is presented here which incorporates the repulsive hard-core interactions arising due to geometrical size of baryons. A first order deconfining phase transition is constructed using Gibb's equilibrium criteria between the hadron gas EOS and quasiparticle model EOS for the weakly interacting quark matter. This leads to an interesting finding that the phase transition line ends at a critical end point beyond which a crossover region exists in the phase di...
Influence of intermolecular forces at critical-point wedge filling.
Malijevský, Alexandr; Parry, Andrew O
2016-04-01
We use microscopic density functional theory to study filling transitions in systems with long-ranged wall-fluid and short-ranged fluid-fluid forces occurring in a right-angle wedge. By changing the strength of the wall-fluid interaction we can induce both wetting and filling transitions over a wide range of temperatures and study the order of these transitions. At low temperatures we find that both wetting and filling transitions are first order in keeping with predictions of simple local effective Hamiltonian models. However close to the bulk critical point the filling transition is observed to be continuous even though the wetting transition remains first order and the wetting binding potential still exhibits a small activation barrier. The critical singularities for adsorption for the continuous filling transitions depend on whether retarded or nonretarded wall-fluid forces are present and are in excellent agreement with predictions of effective Hamiltonian theory even though the change in the order of the transition was not anticipated.
Critical sampling points methodology: case studies of geographically diverse watersheds.
Strobl, Robert O; Robillard, Paul D; Debels, Patrick
2007-06-01
Only with a properly designed water quality monitoring network can data be collected that can lead to accurate information extraction. One of the main components of water quality monitoring network design is the allocation of sampling locations. For this purpose, a design methodology, called critical sampling points (CSP), has been developed for the determination of the critical sampling locations in small, rural watersheds with regard to total phosphorus (TP) load pollution. It considers hydrologic, topographic, soil, vegetative, and land use factors. The objective of the monitoring network design in this methodology is to identify the stream locations which receive the greatest TP loads from the upstream portions of a watershed. The CSP methodology has been translated into a model, called water quality monitoring station analysis (WQMSA), which integrates a geographic information system (GIS) for the handling of the spatial aspect of the data, a hydrologic/water quality simulation model for TP load estimation, and fuzzy logic for improved input data representation. In addition, the methodology was purposely designed to be useful in diverse rural watersheds, independent of geographic location. Three watershed case studies in Pennsylvania, Amazonian Ecuador, and central Chile were examined. Each case study offered a different degree of data availability. It was demonstrated that the developed methodology could be successfully used in all three case studies. The case studies suggest that the CSP methodology, in form of the WQMSA model, has potential in applications world-wide.
Influence of intermolecular forces at critical-point wedge filling
Malijevský, Alexandr; Parry, Andrew O.
2016-04-01
We use microscopic density functional theory to study filling transitions in systems with long-ranged wall-fluid and short-ranged fluid-fluid forces occurring in a right-angle wedge. By changing the strength of the wall-fluid interaction we can induce both wetting and filling transitions over a wide range of temperatures and study the order of these transitions. At low temperatures we find that both wetting and filling transitions are first order in keeping with predictions of simple local effective Hamiltonian models. However close to the bulk critical point the filling transition is observed to be continuous even though the wetting transition remains first order and the wetting binding potential still exhibits a small activation barrier. The critical singularities for adsorption for the continuous filling transitions depend on whether retarded or nonretarded wall-fluid forces are present and are in excellent agreement with predictions of effective Hamiltonian theory even though the change in the order of the transition was not anticipated.
Nonuniversal Finite-Size Effects Near Critical Points
Dohm, V.
2008-11-01
We study the finite-size critical behavior of the anisotropic φ4 lattice model with periodic boundary conditions in a d-dimensional hypercubic geometry above, at, and below Tc. Our perturbation approach at fixed d = 3 yields excellent agreement with the Monte Carlo (MC) data for the finite-size amplitude of the free energy of the three-dimensional Ising model at Tc by Mon [Phys. Rev. Lett. 54, 2671 (1985)]. Below Tc a minimum of the scaling function of the excess free energy is found. We predict a measurable dependence of this minimum on the anisotropy parameters. Our theory agrees quantitatively with the non-monotonic dependence of the Binder cumulant on the ferromagnetic next-nearest neighbor (NNN) coupling of the two-dimensional Ising model found by MC simulations of Selke and Shchur [J. Phys. A 38, L739 (2005)]. Our theory also predicts a non-monotonic dependence for small values of the anti-ferromagnetic NNN coupling and the existence of a Lifshitz point at a larger value of this coupling. The tails of the large-L behavior at T ≠ Tc violate both finite-size scaling and universality even for isotropic systems as they depend on the bare four-point coupling of the φ4 theory, on the cutoff procedure, and on subleading long-range interactions.
Local quantum criticality of an iron-pnictide tetrahedron.
Ong, T Tzen; Coleman, Piers
2012-03-01
Motivated by the close correlation between transition temperature (T(c)) and the tetrahedral bond angle of the As-Fe-As layer observed in the iron-based superconductors, we study the interplay between spin and orbital physics of an isolated iron-arsenide tetrahedron embedded in a metallic environment. Whereas the spin-Kondo effect is suppressed to low temperatures by Hund's coupling, the orbital degrees of freedom are expected to quantum mechanically quench at high temperatures, giving rise to an overscreened, non-Fermi liquid ground state. Translated into a dense environment, this critical state may play an important role in the superconductivity of these materials.
On Prop erties of p-critical Points of Convex Bo dies
Institute of Scientific and Technical Information of China (English)
Huang Xing; Guo Qi
2015-01-01
Properties of the p-measures of asymmetry and the corresponding aﬃne equivariant p-critical points, defined recently by the second author, for convex bodies are discussed in this article. In particular, the continuity of p-critical points with respect to p on (1,+∞) is confirmed, and the connections between general p-critical points and the Minkowski-critical points (∞-critical points) are investigated. The behavior of p-critical points of convex bodies approximating a convex bodies is studied as well.
Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors.
Shibauchi, Takasada; Krusin-Elbaum, Lia; Hasegawa, Masashi; Kasahara, Yuichi; Okazaki, Ryuji; Matsuda, Yuji
2008-05-20
In high-transition-temperature (T(c)) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above T(c), the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T(2)) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a transformation from the non-Fermi-liquid state to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-T(c) superconductor Tl(2)Ba(2)CuO(6+x). From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field that decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field-with the Fermi-liquid coefficient of the T(2) dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two-dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations.
Quantum critical properties of a metallic spin-density-wave transition
Gerlach, Max H.; Schattner, Yoni; Berg, Erez; Trebst, Simon
2017-01-01
We report on numerically exact determinantal quantum Monte Carlo simulations of the onset of spin-density-wave (SDW) order in itinerant electron systems captured by a sign-problem-free two-dimensional lattice model. Extensive measurements of the SDW correlations in the vicinity of the phase transition reveal that the critical dynamics of the bosonic order parameter are well described by a dynamical critical exponent z =2 , consistent with Hertz-Millis theory, but are found to follow a finite-temperature dependence that does not fit the predicted behavior of the same theory. The presence of critical SDW fluctuations is found to have a strong impact on the fermionic quasiparticles, giving rise to a dome-shaped superconducting phase near the quantum critical point. In the superconducting state we find a gap function that has an opposite sign between the two bands of the model and is nearly constant along the Fermi surface of each band. Above the superconducting Tc, our numerical simulations reveal a nearly temperature and frequency independent self-energy causing a strong suppression of the low-energy quasiparticle weight in the vicinity of the hot spots on the Fermi surface. This indicates a clear breakdown of Fermi liquid theory around these points.
Scaling dimensions of higher-charge monopoles at deconfined critical points
Sreejith, G. J.; Powell, Stephen
2015-11-01
The classical cubic dimer model has a columnar ordering transition that is continuous and described by a critical Anderson-Higgs theory containing an SU (2 ) -symmetric complex field minimally coupled to a noncompact U (1 ) gauge theory. Defects in the dimer constraints correspond to monopoles of the gauge theory, with charge determined by the deviation from unity of the dimer occupancy. By introducing such defects into Monte Carlo simulations of the dimer model at its critical point, we determine the scaling dimensions y2=1.48 ±0.07 and y3=0.20 ±0.03 for the operators corresponding to defects of charge q =2 and 3, respectively. These results, which constitute the first direct determination of the scaling dimensions, shed light on the deconfined critical point of spin-1/2 quantum antiferromagnets, thought to belong to the same universality class. In particular, the positive value of y3 implies that the transition in the J Q model on the honeycomb lattice is of first order.
Microscopic Current Flow Patterns in Nanoscale Quantum Point Contacts
Sai, Na; Bushong, Neil; Hatcher, Ryan; di Ventra, Massimiliano
2006-03-01
Transport in nanoscale conductors has been studied extensively mainly using the stationary scattering approach. However, the dynamical nature of transport, and in particular, the flow patterns of the microscopic current through a nanoscale junction, have remained poorly understood. We apply a novel time-dependent transport approach [1], which combines closed and finite geometries with time-dependent density functional theory,to study current flow patterns in nanoscale quantum point contacts [2]. The results of both atomistic and jellium calculations show that surface charges form dynamically at the junction-electrode interfaces in both abrupt and adiabatic junctions. The curr ent exhibits some characteristics of a classical hydrodynamic liquid but also displays unique patterns arising from the interaction with the surface charges. We also investigate the effect of the flow velocity, charge density, and lattice structures on the electron dynamics. If time permits we also discuss the effects of the viscosity of the electron liquid [3]. Work supported by DOE (DE-FG02-05ER46204). [1] M. Di Ventra and T.N. Todorov, J. Phys. Cond. Matt. 16, 8025 (2004). [2] N. Bushong, N. Sai and, M. Di Ventra, Nano Lett. (in press). [3] N. Sai, M. Zwolak, G. Vignale, and M. Di Ventra, Phys. Rev. Lett. 94, 186810 (2005 ).
Crystal Power: Piezo Coupling to the Quantum Zero Point
November, Laurence J
2011-01-01
We consider electro-optical constructions in which the Casimir force is modulated in opposition to piezo-crystal elasticity, as in a stack of alternating tunably conductive and piezo layers. Adjacent tunably conducting layers tuned to conduct, attract by the Casimir force compressing the intermediate piezo, but when subsequently detuned to insulate, sandwiched piezo layers expand elastically to restore their original dimension. In each cycle some electrical energy is made available from the quantum zero point (zp). We estimate that the maximum power that could be derived at semiconductor THz modulation rates is megawatts/cm3. Similarly a permittivity wave generated by a THz acoustic wave in a single crystal by the acousto-optic effect produces multiple coherent Casimir wave mode overtones and a bulk mode. We model the Casimir effect in a sinusoidally graded medium finding it to be very enhanced over what is found in a multilayer stack for the equivalent permittivity contrast, and more slowly decreasing with s...
Quantum Spacetime, from a Practitioner's Point of View
Ambjorn, J; Jurkiewicz, J; Loll, R
2013-01-01
We argue that theories of quantum gravity constructed with the help of (Causal) Dynamical Triangulations have given us the most informative, quantitative models to date of quantum spacetime. Most importantly, these are derived dynamically from nonperturbative and background-independent quantum theories of geometry. In the physically relevant case of four spacetime dimensions, the ansatz of Causal Dynamical Triangulations produces - from a fairly minimal set of quantum field-theoretic inputs - an emergent spacetime which macroscopically looks like a de Sitter universe, and on Planckian scales possesses unexpected quantum properties. Important in deriving these results are a regularized version of the theory, in which the quantum dynamics is well defined, can be studied with the help of numerical Monte Carlo methods and extrapolated to infinite lattice volumes.
Strain-Driven Approach to Quantum Criticality in AFe_{2}As_{2} with A=K, Rb, and Cs.
Eilers, Felix; Grube, Kai; Zocco, Diego A; Wolf, Thomas; Merz, Michael; Schweiss, Peter; Heid, Rolf; Eder, Robert; Yu, Rong; Zhu, Jian-Xin; Si, Qimiao; Shibauchi, Takasada; Löhneysen, Hilbert V
2016-06-10
The iron-based superconductors AFe_{2}As_{2} with A=K, Rb, Cs exhibit large Sommerfeld coefficients approaching those of heavy-fermion systems. We have investigated the magnetostriction and thermal expansion of this series to shed light on this unusual behavior. Quantum oscillations of the magnetostriction allow identifying the band-specific quasiparticle masses which by far exceed the band-structure derived masses. The divergence of the Grüneisen ratio derived from thermal expansion indicates that with increasing volume along the series a quantum critical point is approached. The critical fluctuations responsible for the enhancement of the quasiparticle masses appear to weaken the superconducting state.
Institute of Scientific and Technical Information of China (English)
Shuxiang YU
2006-01-01
Using the concept of an isolated invariant set, some existence criteria of orbits connecting two critical points bifurcating from a single critical point for ordinary differential equations depending on a parameter are given.
A critical appraisal of point-of-care coagulation testing in critically ill patients.
Levi, M; Hunt, B J
2015-11-01
Derangement of the coagulation system is a common phenomenon in critically ill patients, who may present with severe bleeding and/or conditions associated with a prothrombotic state. Monitoring of this coagulopathy can be performed with conventional coagulation assays; however, point-of-care tests have become increasingly attractive, because not only do they yield a more rapid result than clinical laboratory testing, but they may also provide a more complete picture of the condition of the hemostatic system. There are many potential areas of study and applications of point-of-care hemostatic testing in critical care, including patients who present with massive blood loss, patients with a hypercoagulable state (such as in disseminated intravascular coagulation), and monitoring of antiplatelet treatment for acute arterial thrombosis, mostly acute coronary syndromes. However, the limitations of near-patient hemostatic testing has not been fully appreciated, and are discussed here. The currently available evidence indicates that point-of-care tests may be applied to guide appropriate blood product transfusion and the use of hemostatic agents to correct the hemostatic defect or to ameliorate antithrombotic treatment. Disappointingly, however, only in cardiac surgery is there adequate evidence to show that application of near-patient thromboelastography leads to an improvement in clinically relevant outcomes, such as reductions in bleeding-related morbidity and mortality, and cost-effectiveness. More research is required to validate the utility and cost-effectiveness of near-patient hemostatic testing in other areas, especially in traumatic bleeding and postpartum hemorrhage.
Critical relaxation with overdamped quasiparticles in open quantum systems
Lang, Johannes; Piazza, Francesco
2016-09-01
We study the late-time relaxation following a quench in an open quantum many-body system. We consider the open Dicke model, describing the infinite-range interactions between N atoms and a single, lossy electromagnetic mode. We show that the dynamical phase transition at a critical atom-light coupling is characterized by the interplay between reservoir-driven and intrinsic relaxation processes in the absence of number conservation. Above the critical coupling, small fluctuations in the occupation of the dominant quasiparticle mode start to grow in time, while the quasiparticle lifetime remains finite due to losses. Near the critical interaction strength, we observe a crossover between exponential and power-law 1 /τ relaxation, the latter driven by collisions between quasiparticles. For a quench exactly to the critical coupling, the power-law relaxation extends to infinite times, but the finite lifetime of quasiparticles prevents aging from appearing in two-times response and correlation functions. We predict our results to be accessible to quench experiments with ultracold bosons in optical resonators.
Mukherjee, Swagato; Yin, Yi
2015-01-01
We report on recent progress in the study of the evolution of non-Gaussian cumulants of critical fluctuations. We explore the implications of non-equilibrium effects on the search for the QCD critical point.
Critical point of the solar wind by radio sounding data
Lotova, N. A.; Oraevsky, V. N.; Pisarenko, Ya. V.; Vladimirskii, K. V.
1995-01-01
Results of the close-to-Sun plasmas sounding at the transonic region of the solar wind, where the sub-to supersonic flow transition proceeds (at 10 to 40 solar radii from the Sun), are presented. Natural sources of two types were used, water vapour maser sources at 1.35 cm and guasars at 2.9 m wavelength. scattering observations cover the period of 1986 to 1993, Russian Academy of Sciences telescopes RT-22 and DCR-1000 were used, IPS index and scattering angle being the immediate results of observations. Extensive studies of the scintillation index and scattering angle radial profiles reveal a remarkable structural detail, 'transonic region forrunner'-narrow region of diminished scattering close to the internal border of the extended transonic region with its characteristic enhanced scattering. Comparisons of the scattering and plasma velocity profiles let it possible to determine the critical point positions by the comparatively simple scattering observations. This new possibility widely improves the process of the basic data accumulation in the fundamental problem of the solar wind acceleration mechanism.
Baryon-Size Dependent Location of QCD Critical Point
Srivastava, P K; Singh, C P
2011-01-01
The physics regarding the existence of the critical end point (CEP) on the QCD phase boundary still remains unclear and its precise location is quite uncertain. In this paper we propose that the hard-core size of the baryons used in the description of the hot and dense hadron gas (HG) plays a decisive role in the existence of CEP. Here we construct a deconfining phase transition using Gibbs' equilibrium conditions after using a quasiparticle equation of state (EOS) for QCD plasma and excluded-volume EOS for the HG. We find that the first order transition results only when we assign a hard-core size to each baryon in the description of HG and the phase boundary thus obtained terminates at CEP beyond which a cross-over region occurs. The mean field approach for the HG lends support to this finding where unless we include an excluded-volume effect in the approach, CEP does not materialize on the QCD boundary. This investigation provides an intuitive reasoning regarding the origin of CEP and the cross-over transi...
Directory of Open Access Journals (Sweden)
L. S. Campana
2012-01-01
Full Text Available We explore the low-temperature thermodynamic properties and crossovers of a d-dimensional classical planar Heisenberg ferromagnet in a longitudinal magnetic field close to its field-induced zero-temperature critical point by employing the two-time Green’s function formalism in classical statistical mechanics. By means of a classical Callen-like method for the magnetization and the Tyablikov-like decoupling procedure, we obtain, for any d, a low-temperature critical scenario which is quite similar to the one found for the quantum counterpart. Remarkably, for d>2 the discrimination between the two cases is found to be related to the different values of the shift exponent which governs the behavior of the critical line in the vicinity of the zero-temperature critical point. The observation of different values of the shift-exponent and of the related critical exponents along thermodynamic paths within the typical V-shaped region in the phase diagram may be interpreted as a signature of emerging quantum critical fluctuations.
Steppke, Alexander
In a number of strongly correlated electron systems quantum phase transitions can be observed by the suppression of antiferromagnetic order. In contrast the prototypical continuous quantum phase transition of a metallic ferromagnet is often preempted by a first-order transition or a superconducting state. We show that the Kondo lattice system YbNi4P2 exhibits a ferromagnetically ordered phase with a very low Curie temperature of 0.15K. The compound can be tuned to a ferromagnetic quantum critical point by substitution of phosphorus by arsenic. With thermodynamic studies of specific heat, ac susceptibility and thermal expansion we show strong evidence for the ferromagnetic order and the quantum criticality in the YbNi4(P 1-x As x)2 doping series and the existence of a ferromagnetic quantum critical point at zero applied field for small substitutions.
Picture change error in quasirelativistic electron/spin density, Laplacian and bond critical points
Bučinský, Lukáš
2014-06-01
The change of picture of the quasirelativistic Hartree-Fock wave functions is considered for electron/spin densities, the negative Laplacian of electron density and the appropriate bond critical point characteristics from the Quantum Theory of Atoms In Molecules (QTAIM). [OsCl5(Hpz)]- and [RuCl5(NO)]2- transition metal complexes are considered. Both, scalar relativistic and spin-orbit effects have been accounted for using the Infinite Order Two Component (IOTC) Hamiltonian. Picture change error (PCE) correction in the electron and spin densities and the Laplacian of electron density are treated analytically. Generally, PCE is found significant only in the core region of the atoms for the electron/spin density as well as Laplacian.©2014 Elsevier B.V. All rights reserved.
21 CFR 120.8 - Hazard Analysis and Critical Control Point (HACCP) plan.
2010-04-01
... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Hazard Analysis and Critical Control Point (HACCP... SERVICES (CONTINUED) FOOD FOR HUMAN CONSUMPTION HAZARD ANALYSIS AND CRITICAL CONTROL POINT (HACCP) SYSTEMS General Provisions § 120.8 Hazard Analysis and Critical Control Point (HACCP) plan. (a) HACCP plan....
Quantum-ring spin interference device tuned by quantum point contacts
Energy Technology Data Exchange (ETDEWEB)
Diago-Cisneros, Leo [Facultad de Física, Universidad de La Habana, C.P.10400, La Habana (Cuba); Mireles, Francisco [Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, C.P. 22800 Ensenada, Baja California, México (Mexico)
2013-11-21
We introduce a spin-interference device that comprises a quantum ring (QR) with three embedded quantum point contacts (QPCs) and study theoretically its spin transport properties in the presence of Rashba spin-orbit interaction. Two of the QPCs conform the lead-to-ring junctions while a third one is placed symmetrically in the upper arm of the QR. Using an appropriate scattering model for the QPCs and the S-matrix scattering approach, we analyze the role of the QPCs on the Aharonov-Bohm (AB) and Aharonov-Casher (AC) conductance oscillations of the QR-device. Exact formulas are obtained for the spin-resolved conductances of the QR-device as a function of the confinement of the QPCs and the AB/AC phases. Conditions for the appearance of resonances and anti-resonances in the spin-conductance are derived and discussed. We predict very distinctive variations of the QR-conductance oscillations not seen in previous QR proposals. In particular, we find that the interference pattern in the QR can be manipulated to a large extend by varying electrically the lead-to-ring topological parameters. The latter can be used to modulate the AB and AC phases by applying gate voltage only. We have shown also that the conductance oscillations exhibits a crossover to well-defined resonances as the lateral QPC confinement strength is increased, mapping the eigenenergies of the QR. In addition, unique features of the conductance arise by varying the aperture of the upper-arm QPC and the Rashba spin-orbit coupling. Our results may be of relevance for promising spin-orbitronics devices based on quantum interference mechanisms.
Dairy production system type and critical points of contamination
Directory of Open Access Journals (Sweden)
Gilberto Henrique Simões
2015-12-01
Full Text Available Current milk production includes a large diversity between systems, which generates difficulties in defining a microbiological standard. The adapted practical and hygienic-sanitary management methods are diverse and introduce great complexity into the production systems. Based on this scenario, the objective of this study was to evaluate the types of dairy production systems of western Parana and to quantify Staphylococcus sp in three critical points in the dairy cattle production systems: the milking machines, milkers’ hands, the cooling tanks and raw milk. A total of 35 samples of refrigerated raw milk were collected, and a questionnaire referring to hygienic and sanitary management was administered. All of the data were collected during the period from September to October 2012 and involved 35 properties in the municipality of Marechal Cândido Rondon – PR. From these data, five groups were formed based on cluster analysis (CHA. The multiple correspondence analysis (MCA presented in the first two dimensions, CP1 (81.43% and CP2 (36.87%, showed the relevance of the variables used, which are sanitary and production management methods, and contamination and control of mastitis, respectively (CP1 and CP2. We found average contamination with 9.9 x 101 CFU/cm2, 2.2x104 CFU/cm2, 28 CFU/ cm2 and 3.8x103 CFU/mL; for milking machines, milkers’ hands, cooling tanks and milk, respectively. The results reveal the presence of staphylococcal agent in dairy production systems regardless of the adopted hygiene and health management protocols. The guidance, planning and adaptation of hygiene and health management systems can significantly improve the microbiological quality of the milk produced, both qualitatively and quantitatively.
Information processing and integration with intracellular dynamics near critical point.
Kamimura, Atsushi; Kobayashi, Tetsuya J
2012-01-01
Recent experimental observations suggest that cells can show relatively precise and reliable responses to external signals even though substantial noise is inevitably involved in the signals. An intriguing question is the way how cells can manage to do it. One possible way to realize such response for a cell is to evolutionary develop and optimize its intracellular signaling pathways so as to extract relevant information from the noisy signal. We recently demonstrated that certain intracellular signaling reactions could actually conduct statistically optimal information processing. In this paper, we clarify that such optimal reaction operates near bifurcation point. This result suggests that critical-like phenomena in the single-cell level may be linked to efficient information processing inside a cell. In addition, improving the performance of response in the single-cell level is not the only way for cells to realize reliable response. Another possible strategy is to integrate information of individual cells by cell-to-cell interaction such as quorum sensing. Since cell-to-cell interaction is a common phenomenon, it is equally important to investigate how cells can integrate their information by cell-to-cell interaction to realize efficient information processing in the population level. In this paper, we consider roles and benefits of cell-to-cell interaction by considering integrations of obtained information of individuals with the other cells from the viewpoint of information processing. We also demonstrate that, by introducing cell movement, spatial organizations can spontaneously emerge as a result of efficient responses of the population to external signals.
On the theory of quantum quenches in near-critical systems
Delfino, Gesualdo; Viti, Jacopo
2017-02-01
The theory of quantum quenches in near-critical one-dimensional systems formulated in Delfino (2014 J. Phys. A: Math. Theor. 402001) yields analytic predictions for the dynamics, unveils a qualitative difference between non-interacting and interacting systems, with undamped oscillations of one-point functions occurring only in the latter case, and explains the presence and role of different time scales. Here we examine additional aspects, determining in particular the relaxation value of one-point functions for small quenches. For a class of quenches we relate this value to the scaling dimensions of the operators. We argue that the E 8 spectrum of the Ising chain can be more accessible through a quench than at equilibrium, while for a quench of the plane anisotropy in the XYZ chain we obtain that the one-point function of the quench operator switches from damped to undamped oscillations at Δ =1/2 .
On the theory of quantum quenches in near-critical systems
Delfino, Gesualdo
2016-01-01
The theory of quantum quenches in near-critical one-dimensional systems formulated in [J. Phys. A 47 (2014) 402001] yields analytic predictions for the dynamics, unveils a qualitative difference between non-interacting and interacting systems, with undamped oscillations of one-point functions occurring only in the latter case, and explains the presence of different time scales. Here we examine additional aspects, obtaining in particular the expression for the relaxation value of one-point functions for small quenches. We argue that the $E_8$ spectrum of the Ising chain is more accessible through a quench than at equilibrium, while for a quench of the plane anisotropy in the XYZ chain we obtain that the one-point function of the quench operator switches from damped to undamped oscillations at $\\Delta=1/2$.
Theory of center-focus for a class of higher-degree critical points and infinite points
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
For the real planar autonomous differential system, the questionsof detection between center and focus, successor function, formal series, central integration, integration factor, focal values, values of singular point and bifurcation of limit cycles for a class of higher-degree critical points and infinite points are expounded.
Bhattacharyya, Sirshendu; Dasgupta, Subinay; Das, Arnab
2015-11-16
Understanding phase transitions in quantum matters constitutes a significant part of present day condensed matter physics. Quantum phase transitions concern ground state properties of many-body systems, and hence their signatures are expected to be pronounced in low-energy states. Here we report signature of a quantum critical point manifested in strongly out-of-equilibrium states with finite energy density with respect to the ground state and extensive (subsystem) entanglement entropy, generated by an external pulse. These non-equilibrium states are evidently completely disordered (e.g., paramagnetic in case of a magnetic ordering transition). The pulse is applied by switching a coupling of the Hamiltonian from an initial value (λI) to a final value (λF) for sufficiently long time and back again. The signature appears as non-analyticities (kinks) in the energy absorbed by the system from the pulse as a function of λF at critical-points (i.e., at values of λF corresponding to static critical-points of the system). As one excites higher and higher eigenstates of the final Hamiltonian H(λF) by increasing the pulse height (|λF - λI|), the non-analyticity grows stronger monotonically with it. This implies adding contributions from higher eigenstates help magnifying the non-analyticity, indicating strong imprint of the critical-point on them. Our findings are grounded on exact analytical results derived for Ising and XY chains in transverse field.
Third-order gas-liquid phase transition and the nature of Andrews critical point
Directory of Open Access Journals (Sweden)
Tian Ma
2011-12-01
Full Text Available The main objective of this article is to study the nature of the Andrews critical point in the gas-liquid transition in a physical-vapor transport (PVT system. A dynamical model, consistent with the van der Waals equation near the Andrews critical point, is derived. With this model, we deduce two physical parameters, which interact exactly at the Andrews critical point, and which dictate the dynamic transition behavior near the Andrews critical point. In particular, it is shown that 1 the gas-liquid co-existence curve can be extended beyond the Andrews critical point, and 2 the transition is first order before the critical point, second-order at the critical point, and third order beyond the Andrews critical point. This clearly explains why it is hard to observe the gas-liquid phase transition beyond the Andrews critical point. Furthermore, the analysis leads naturally the introduction of a general asymmetry principle of fluctuations and the preferred transition mechanism for a thermodynamic system. The theoretical results derived in this article are in agreement with the experimental results obtained in (K. Nishikawa and T. Morita, Fluid behavior at supercritical states studied by small-angle X-ray scattering, Journal of Supercritical Fluid, 13 (1998, pp. 143-148. Also, the derived second-order transition at the critical point is consistent with the result obtained in (M. Fisher, Specific heat of a gas near the critical point, Physical Review, 136:6A (1964, pp. A1599-A1604.
Magnon-induced nuclear relaxation in the quantum critical region of a Heisenberg linear chain
Hoch, M. J. R.
2017-07-01
The low-temperature properties of spin-1/2 one-dimensional (1D) Heisenberg antiferromagnetic (HAF) chains which have relatively small exchange couplings between the spins can be tuned using laboratory-scale magnetic fields. Magnetization measurements, made as a function of temperature, provide phase diagrams for these systems and establish the quantum critical point (QCP). The evolution of the spin dynamics behavior with temperature and applied field in the quantum critical (QC) region, near the QCP, is of particular interest and has been experimentally investigated in a number of 1D HAFs using neutron scattering and nuclear magnetic resonance as the preferred techniques. In the QC phase both quantum and thermal spin fluctuations are present. As a result of extended spin correlations in the chains, magnon excitations are important at finite temperatures. An expression for the NMR spin-lattice relaxation rate 1 /T1 of probe nuclei in the QC phase of 1D HAFs is obtained by considering Raman scattering processes which induce nuclear spin flips. The relaxation rate expression, which involves the temperature and the chemical potential, predicts scaling behavior of 1 /T1 consistent with recent experimental findings for quasi-1D HAF systems. A simple relationship between 1 /T1 and the deviation of the magnetization from saturation (MS-M ) is predicted for the QC region.
DEFF Research Database (Denmark)
Cismondi, Martin; Michelsen, Michael Locht
2007-01-01
of critical lines. Each calculated point is analysed for stability by means of the tangent plane distance, and the occurrence of an unstable point is used to determine a critical endpoint (CEP). The critical endpoint, in turn, is used as the starting point for constructing the three-phase line. The equations...... for the critical endpoint, as well as for points on the three-phase line, are also solved using Newton's method with temperature, molar volume and composition as the independent variables. The different calculations are integrated into a general procedure that allows us to automatically trace critical lines......, critical endpoints and three-phase lines for binary mixtures with phase diagrams of types from I to V without advance knowledge of the type of phase diagram. The procedure requires a thermodynamic model in the form of a pressure-explicit EOS but is not specific to a particular equation of state. (C) 2006...
Quantum criticality in an organic spin-liquid insulator κ-(BEDT-TTF)2Cu2(CN)3
Isono, Takayuki; Terashima, Taichi; Miyagawa, Kazuya; Kanoda, Kazushi; Uji, Shinya
2016-11-01
A quantum spin-liquid state, an exotic state of matter, appears when strong quantum fluctuations enhanced by competing exchange interactions suppress a magnetically ordered state. Generally, when an ordered state is continuously suppressed to 0 K by an external parameter, a quantum phase transition occurs. It exhibits critical scaling behaviour, characterized only by a few basic properties such as dimensions and symmetry. Here we report the low-temperature magnetic torque measurements in an organic triangular-lattice antiferromagnet, κ-(BEDT-TTF)2Cu2(CN)3, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. It is found that the magnetic susceptibilities derived from the torque data exhibit a universal critical scaling, indicating the quantum critical point at zero magnetic field, and the critical exponents, γ=0.83(6) and νz=1.0(1). These exponents greatly constrain the theoretical models for the quantum spin liquid, and at present, there is no theory to explain the values, to the best of our knowledge.
Overcoming Critical Slowing Down in Quantum Monte Carlo Simulations
Evertz, Hans Gerd; Marcu, Mihai
The classical d+1-dimensional spin systems used for the simulation of quantum spin systems in d dimensions are, quite generally, vertex models. Standard simulation methods for such models strongly suffer from critical slowing down. Recently, we developed the loop algorithm, a new type of cluster algorithm that to a large extent overcomes critical slowing down for vertex models. We present the basic ideas on the example of the F model, a special case of the 6-vertex model. Numerical results clearly demonstrate the effectiveness of the loop algorithm. Then, using the framework for cluster algorithms developed by Kandel and Domany, we explain how to adapt our algorithm to the cases of the 6-vertex model and the 8-vertex model, which are relevant for spin 1/2 systems. The techniqes presented here can be applied without modification to 2-dimensional spin 1/2 systems, provided that in the Suzuki-Trotter formula the Hamiltonian is broken up into 4 sums of link terms. Generalizations to more complicated situations (higher spins, different uses of the Suzuki-Trotter formula) are, at least in principle, straightforward.
Local Classical and Quantum Criticality due to Electron-Vibration Interaction
2009-01-01
We study the local classical and quantum critical properties of electron-vibration interaction, represented by the Yu-Anderson model. It exhibits an instability, similar to the Wentzel-Bardeen singularity, whose nature resembles to weakly first order quantum phase transitions at low temperatures, and crosses over to Gaussian behaviour with increasing temperature. We determine the dominant energy scale separating the quantum from classical criticality, study the effect of dissipation and analy...
Anomalous discontinuity at the percolation critical point of active gels.
Sheinman, M; Sharma, A; Alvarado, J; Koenderink, G H; MacKintosh, F C
2015-03-06
We develop a percolation model motivated by recent experimental studies of gels with active network remodeling by molecular motors. This remodeling was found to lead to a critical state reminiscent of random percolation (RP), but with a cluster distribution inconsistent with RP. Our model not only can account for these experiments, but also exhibits an unusual type of mixed phase transition: We find that the transition is characterized by signatures of criticality, but with a discontinuity in the order parameter.
Phase structure, critical points and susceptibilities in Nambu-Jona-Lasinio type models
De Sousa, C A; Ruivo, M C
2008-01-01
We investigate the chiral phase transition at finite temperature and chemical potential within SU(2) and SU(3) Nambu-Jona-Lasinio type models. The behavior of the baryon number susceptibility and the specific heat, in the vicinity of the critical end point, is studied. The class of the critical points is analyzed by calculating critical exponents.
Field-induced quadrupolar quantum criticality in PrV2Al20
Shimura, Yasuyuki; Tsujimoto, Masaki; Zeng, Bin; Balicas, Luis; Sakai, Akito; Nakatsuji, Satoru
2015-06-01
PrV2Al20 is a heavy-fermion superconductor based on the cubic Γ3 doublet that exhibits nonmagnetic quadrupolar ordering below ˜0.6 K. Our magnetotransport study on PrV2Al20 reveals field-induced quadrupolar quantum criticality at μ0Hc˜11 T applied along the [111] direction. Near the critical field μ0Hc required to suppress the quadrupolar state, we find a marked enhancement of the resistivity ρ (H ,T ) , a divergent quasiparticle effective mass and concomitant non-Fermi-liquid (NFL) behavior [i.e., ρ (T ) ∝Tn with n ≤0.5 ]. We also observe the Shubnikov-de Haas effect above μ0Hc , indicating effective mass enhancement or m*/m0˜10 . This reveals the competition between the nonmagnetic Kondo effect and the intersite quadrupolar coupling which leads to pronounced NFL behavior in an extensive region of T and μ0H emerging from the quantum-critical point.
SU(3) quantum critical model emerging from a spin-1 topological phase
Rao, Wen-Jia; Zhu, Guo-Yi; Zhang, Guang-Ming
2016-04-01
Different from the spin-1 Haldane gapped phase, we propose an SO(3) spin-1 matrix product state (MPS), whose parent Hamiltonian includes three-site spin interactions. From the entanglement spectrum of a single block with l sites, an enlarged SU(3) symmetry is identified in the edge states, which are conjugate to each other for the l =even block but identical for the l =odd block. By blocking this state, the blocked MPS explicitly displays the SU(3) symmetry with two distinct structures. Under a symmetric bulk bipartition with a sufficient large block length l =even , the entanglement Hamiltonian (EH) of the reduced system characterizes a spontaneous dimerized phase with twofold degeneracy. However, for the block length l =odd , the corresponding EH represents an SU(3) quantum critical point with delocalized edge quasiparticles, and the critical field theory is described by the SU(3) level-1 Wess-Zumino-Witten conformal field theory.
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
Apfelbaum, E M
2012-12-20
The critical-point coordinates of Beryllium have been calculated by means of recently found similarity relations between the Zeno-line and the critical-point parameters. We have used the NVT MC simulations and pseudopotential theory to calculate the Zeno-line parameters together with the data of isobaric measurements to construct the liquid branch of Beryllium binodal. The critical-point coordinates, determined this way, are lower than earlier estimates. We have shown that these previous estimates are in evident contradiction with available measurements data. Present investigation can resolve this contradiction if the measurements data are supposed to be reliable.
On the value of the critical point in fractal percolation
White, D.G.
1999-01-01
We derive a new lower bound pc > 0:8107 for the critical value of Mandelbrot's dyadic fractal percolation model. This is achieved by taking the random fractal set (to be denoted A 1) and adding to it a countable number of straight line segments, chosen in a certain (non-random) way as to simplify
Quantum Brownian motion near a point-like reflecting boundary
De Lorenci, V A; Silva, M M
2014-01-01
The Brownian motion of a test particle interacting with a quantum scalar field in the presence of a perfectly reflecting boundary is studied in (1 + 1)-dimensional flat spacetime. Particularly, the expressions for dispersions in velocity and position of the particle are explicitly derived and their behaviors examined. The results are similar to those corresponding to an electric charge interacting with a quantum electromagnetic field near a reflecting plane boundary, mainly regarding the divergent behavior of the dispersions at the origin (where the boundary is placed), and at the time interval corresponding to a round trip of a light pulse between the particle and the boundary. We close by addressing some effects of allowing the position of the particle to fluctuate.
Superconductivity versus quantum criticality: what can we learn from heavy fermions?
Steglich, F; Arndt, J; Friedemann, S; Krellner, C; Tokiwa, Y; Westerkamp, T; Brando, M; Gegenwart, P; Geibel, C; Wirth, S; Stockert, O
2010-04-28
Two quantum critical point (QCP) scenarios are being discussed for different classes of antiferromagnetic (AF) heavy-fermion (HF) systems. In the itinerant one, where AF order is of the spin-density wave (SDW) type, the heavy 'composite' charge carriers keep their integrity at the QCP. The second one implies a breakdown of the Kondo effect and a disintegration of the composite fermions at the AF QCP. We discuss two isostructural compounds as exemplary materials for these two different scenarios: CeCu(2)Si(2) exhibits a three-dimensional (3D) SDW QCP and superconductivity, presumably mediated by SDW fluctuations, as strongly suggested by recent inelastic neutron scattering experiments. In Y bRh(2)Si(2), the AF QCP is found to coincide with a Kondo-destroying one. However, in the latter compound these two QCPs can be detached by varying the average unit-cell volume, e.g. through the application of chemical pressure, as realized by partial substitution of either Ir or Co for Rh. A comparison of CeCu(2)Si(2) and Y bRh(2)Si(2) indicates that the apparent differences in quantum critical behaviour go along with disparate behaviour concerning the (non-) existence of superconductivity (SC). No sign of SC could be detected in Y bRh(2)Si(2) down to mK temperatures. A potential correlation between the specific nature of the QCP and the occurrence of SC, however, requires detailed studies on further quantum critical HF superconductors, e.g. on β-Y bAlB(4), UBe(13), CeCoIn(5) and CeRhIn(5).
Critical-point analysis of the liquid-vapor interfacial surface tension
Salvino, R. E.
1990-01-01
The interfacial surface tension of the liquid-vapor system is analyzed near the critical point in a manner similar to bulk thermodynamic critical-point analyses. This is accomplished by a critical-point analysis of the single-phase hard-wall surface tension. Both a Landau expansion and a scaling theory equation of state are investigated. Some general exponent relations are derived and, in addition, some thermodynamically defined correlation lengths are discussed.
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.
Rigidity of critical points for a nonlocal Ohta-Kawasaki energy
Dipierro, Serena; Novaga, Matteo; Valdinoci, Enrico
2017-04-01
We investigate the shape of critical points for a free energy consisting of a nonlocal perimeter plus a nonlocal repulsive term. In particular, we prove that a volume-constrained critical point is necessarily a ball if its volume is sufficiently small with respect to its isodiametric ratio, thus extending a result previously known only for global minimizers. We also show that, at least in one-dimension, there exist critical points with arbitrarily small volume and large isodiametric ratio. This example shows that a constraint on the diameter is, in general, necessary to establish the radial symmetry of the critical points.
Semi-local quantum criticality in string/M-theory
Donos, Aristomenis; Pantelidou, Christiana
2012-01-01
Semi-local quantum critical behaviour in $D-1$ spacetime dimensions can be holographically described by metrics that are conformal to $AdS_2\\times\\mathbb{R}^{D-2}$, with the conformal factor characterised by a parameter $\\eta$. We analyse such "$\\eta$-geometries" in a top-down setting by focussing on the $U(1)^4$ truncation of D=4 N=8 gauged supergravity. The model has extremal black hole solutions carrying three non-zero electric or magnetic charges which approach $AdS_4$ in the UV and an $\\eta=1$ geometry in the IR. Adding a fourth charge provides a mechanism to resolve the singularity of the $\\eta$-geometry, replacing it with an $AdS_2\\times\\mathbb{R}^2$ factor in the IR, while maintaining a large region where the $\\eta$-geometry scaling is approximately valid. Some of the magnetically charged black hole solutions preserve supersymmetry while others just preserve it in the IR. Finally, we show that $\\eta$-geometries, with various values of $\\eta$, can be obtained from the dimensional reduction of geometrie...
Criticality without Frustration for Quantum Spin-1 Chains
Bravyi, Sergey; Caha, Libor; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter W.
2012-11-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right brackets separated by empty spaces. Entanglement entropy of one half of the chain scales as (1)/(2)logn+O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
Criticality without frustration for quantum spin-1 chains
Bravyi, Sergey; Movassagh, Ramis; Nagaj, Daniel; Shor, Peter
2012-01-01
Frustration-free (FF) spin chains have a property that their ground state minimizes all individual terms in the chain Hamiltonian. We ask how entangled the ground state of a FF quantum spin-s chain with nearest-neighbor interactions can be for small values of s. While FF spin-1/2 chains are known to have unentangled ground states, the case s=1 remains less explored. We propose the first example of a FF translation-invariant spin-1 chain that has a unique highly entangled ground state and exhibits some signatures of a critical behavior. The ground state can be viewed as the uniform superposition of balanced strings of left and right parentheses separated by empty spaces. Entanglement entropy of one half of the chain scales as log(n)/2 + O(1), where n is the number of spins. We prove that the energy gap above the ground state is polynomial in 1/n. The proof relies on a new result concerning statistics of Dyck paths which might be of independent interest.
Discrete Holomorphicity at Two-Dimensional Critical Points
Cardy, John
2009-12-01
After a brief review of the historical role of analyticity in the study of critical phenomena, an account is given of recent discoveries of discretely holomorphic observables in critical two-dimensional lattice models. These are objects whose correlation functions satisfy a discrete version of the Cauchy-Riemann relations. Their existence appears to have a deep relation with the integrability of the model, and they are presumably the lattice versions of the truly holomorphic observables appearing in the conformal field theory (CFT) describing the continuum limit. This hypothesis sheds light on the connection between CFT and integrability, and, if verified, can also be used to prove that the scaling limit of certain discrete curves in these models is described by Schramm-Loewner evolution (SLE).
Point of View Speech (A Speech Assignment in Critical Thinking).
Brydges, Michael E.
This paper delineates an exercise where students are encouraged to give their point of view to a quotation received (the activity is an adaptation from the Impromptu Speaking event in Competitive Forensics). The paper states that students are to explain the meaning of a quotation (topic themes may be from ecology, education, environment, life,…
Exceptional points for parameter estimation in open quantum systems: Analysis of the Bloch equations
Am-Shallem, Morag; Moiseyev, Nimrod
2014-01-01
The dynamics of open quantum systems is typically described by a quantum dynamical semigroup generator ${\\cal L}$. The eigenvalues of ${\\cal L}$ are complex, reflecting unitary as well as dissipative dynamics. For certain values of parameters defining ${\\cal L}$, non-hermitian degeneracies emerge, i.e. exceptional points ($EP$). We study the implications of such points in the open system dynamics of a two-level-system described by the Bloch equation. This open system has become the paradigm of diverse fields in physics, from NMR to quantum information and elementary particles. We find as a function of detuning and driving amplitude a continuous line of exceptional points merging into two cusps of triple degeneracy. The dynamical signature of these $EP$ points is a unique time evolution. This unique feature can be employed experimentally to locate the $EP$ points and thereby to determine the intrinsic system parameters for any desired accuracy.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2-δAs2.
Luo, Yongkang; Ronning, F; Wakeham, N; Lu, Xin; Park, Tuson; Xu, Z-A; Thompson, J D
2015-11-03
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2-δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ~0.032 E-/formular unit in CeNi2-δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.
Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2
Luo, Yongkang; Ronning, F.; Wakeham, N.; Lu, Xin; Park, Tuson; Xu, Z.-A.; Thompson, J. D.
2015-01-01
The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening. PMID:26483465
The features of ballistic electron transport in a suspended quantum point contact
Energy Technology Data Exchange (ETDEWEB)
Shevyrin, A. A., E-mail: shevandrey@isp.nsc.ru; Budantsev, M. V.; Bakarov, A. K.; Toropov, A. I. [Rzhanov Institute of Semiconductor Physics, SB RAS, 630090 Novosibirsk (Russian Federation); Pogosov, A. G. [Rzhanov Institute of Semiconductor Physics, SB RAS, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, 630090 Novosibirsk (Russian Federation); Ishutkin, S. V.; Shesterikov, E. V. [Tomsk State University of Control Systems and Radioelectronics, 634050 Tomsk (Russian Federation)
2014-05-19
A suspended quantum point contact and the effects of the suspension are investigated by performing identical electrical measurements on the same experimental sample before and after the suspension. In both cases, the sample demonstrates conductance quantization. However, the suspended quantum point contact shows certain features not observed before the suspension, namely, plateaus at the conductance values being non-integer multiples of the conductance quantum, including the “0.7-anomaly.” These features can be attributed to the strengthening of electron-electron interaction because of the electric field confinement within the suspended membrane. Thus, the suspended quantum point contact represents a one-dimensional system with strong electron-electron interaction.
Fixed points and infrared completion of quantum gravity
Christiansen, Nicolai; Pawlowski, Jan M; Rodigast, Andreas
2012-01-01
The phase diagram of four-dimensional Einstein-Hilbert gravity is studied using Wilson's renormalization group. Smooth trajectories connecting the ultraviolet fixed point at short distances with attractive infrared fixed points at long distances are derived from the non-perturbative graviton propagator. Implications for the asymptotic safety conjecture and further results are discussed.
Phenomenological consequences of enhanced bulk viscosity near the QCD critical point
Monnai, Akihiko; Mukherjee, Swagato; Yin, Yi
2017-03-01
In the proximity of the QCD critical point the bulk viscosity of quark-gluon matter is expected to be proportional to nearly the third power of the critical correlation length, and become significantly enhanced. This work is the first attempt to study the phenomenological consequences of enhanced bulk viscosity near the QCD critical point. For this purpose, we implement the expected critical behavior of the bulk viscosity within a non-boost-invariant, longitudinally expanding 1 +1 dimensional causal relativistic hydrodynamical evolution at nonzero baryon density. We demonstrate that the critically enhanced bulk viscosity induces a substantial nonequilibrium pressure, effectively softening the equation of state, and leads to sizable effects in the flow velocity and single-particle distributions at the freeze-out. The observable effects that may arise due to the enhanced bulk viscosity in the vicinity of the QCD critical point can be used as complementary information to facilitate searches for the QCD critical point.
Dynamical Crossing of an Infinitely Degenerate Critical Point
Bachmann, Sven; Fraas, Martin; Graf, Gian Michele
2017-05-01
We study the evolution of a driven harmonic oscillator with a time-dependent frequency $\\omega_t \\propto |t|$. At time $t=0$ the Hamiltonian undergoes a point of infinite spectral degeneracy. If the system is initialized in the instantaneous vacuum in the distant past then the asymptotic future state is a squeezed state whose parameters are explicitly determined. We show that the squeezing is independent on the sweeping rate. This manifests the failure of the adiabatic approximation at points where infinitely many eigenvalues collide. We extend our analysis to the situation where the gap at $t=0$ remains finite. We also discuss the natural geometry of the manifold of squeezed states. We show that it is realized by the Poincar\\'e disk model viewed as a K\\"ahler manifold.
Susceptibilities from a black hole engineered EoS with a critical point
Portillo, Israel
2016-01-01
Currently at the Beam Energy Scan at RHIC experimental efforts are being made to find the QCD critical point. On the theoretical side, the behavior of higher-order susceptibilities of the net-baryon charge from Lattice QCD at $\\mu_{_B}\\!=\\!0$ may allow us to estimate the position of the critical point in the QCD phase diagram. However, even if the series expansion continues to higher-orders, there is always the possibility to miss the critical point behavior due to truncation errors. An alternative approach is to use a black hole engineered holographic model, which displays a critical point at large densities and matches lattice susceptibilities at $\\mu_{_B}\\!=\\!0$. Using the thermodynamic data from this black hole model, we obtain the freeze-out points extracted from the net-protons distribution measured at STAR and explore higher order fluctuations at the lowest energies at the beam energy scan to investigate signatures of the critical point.
Critical Point of Ising Films with Different Growth Directions
Institute of Scientific and Technical Information of China (English)
WANG Huai-yu; ZHOU Yun-song; D.L.Lin
2000-01-01
The critical temperature Tc of a spin-l/2 Ising film of cubic structures is calculated by the variational cumulant expansion method for three directions of growth. The results from different growth directions are analysed and compared with each other. In the present model, the Tc values depend largely on the number of nearest neighbors in a monolayer for films with the same number of monolayers but grown in different directions. For sc, bcc and fcc structures, the highest Tc is found along the (100), (110), and (111) direction, respectively.
Quantum Gravity from the Point of View of Locally Covariant Quantum Field Theory
Brunetti, Romeo; Fredenhagen, Klaus; Rejzner, Katarzyna
2016-08-01
We construct perturbative quantum gravity in a generally covariant way. In particular our construction is background independent. It is based on the locally covariant approach to quantum field theory and the renormalized Batalin-Vilkovisky formalism. We do not touch the problem of nonrenormalizability and interpret the theory as an effective theory at large length scales.
Universal crossover from ground-state to excited-state quantum criticality
Kang, Byungmin; Potter, Andrew C.; Vasseur, Romain
2017-01-01
We study the nonequilibrium properties of a nonergodic random quantum chain in which highly excited eigenstates exhibit critical properties usually associated with quantum critical ground states. The ground state and excited states of this system belong to different universality classes, characterized by infinite-randomness quantum critical behavior. Using strong-disorder renormalization group techniques, we show that the crossover between the zero and finite energy density regimes is universal. We analytically derive a flow equation describing the unitary dynamics of this isolated system at finite energy density from which we obtain universal scaling functions along the crossover.
Near-critical point phenomena in fluids (19-IML-1)
Beysens, D.
1992-01-01
Understanding the effects of gravity is essential if the behavior of fluids is to be predicted in spacecraft and orbital stations, and, more generally, to give a better understanding of the hydrodynamics in these systems. An understanding is sought of the behavior of fluids in space. What should emerge from the International Microgravity Lab (IML-1) mission is a better understanding of the kinetics of growth in off-critical conditions, in both liquid mixtures and pure fluids. This complex phenomenon is the object of intensive study in physics and materials sciences area. It is also expected that the IML-1 flight will procure key results to provide a better understanding of how a pure fluid can be homogenized without gravity induced convections, and to what extent the 'Piston Effect' is effective in thermalizing the compressible fluids.
Hydrogen bond breaking in aqueous solutions near the critical point
Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming
2001-01-01
The nature of water-anion bonding is examined using X-ray absorption fine structure spectroscopy on a 1mZnBr2/6m NaBr aqueous solution, to near critical conditions. Analyses show that upon heating the solution from 25??C to 500??C, a 63% reduction of waters occurs in the solvation shell of ZnBr42-, which is the predominant complex at all pressure-temperature conditions investigated. A similar reduction in the hydration shell of waters in the Br- aqua ion was found. Our results indicate that the water-anion and water-water bond breaking mechanisms occurring at high temperatures are essentially the same. This is consistent with the hydration waters being weakly hydrogen bonded to halide anions in electrolyte solutions. ?? 2001 Elsevier Science B.V.
Area law for fixed points of rapidly mixing dissipative quantum systems
Energy Technology Data Exchange (ETDEWEB)
Brandão, Fernando G. S. L. [Quantum Architectures and Computation Group, Microsoft Research, Redmond, Washington 98052 (United States); Department of Computer Science, University College London, Gower Street, London WC1E 6BT (United Kingdom); Cubitt, Toby S. [Department of Computer Science, University College London, Gower Street, London WC1E 6BT (United Kingdom); DAMTP, University of Cambridge, Cambridge (United Kingdom); Lucia, Angelo, E-mail: anlucia@ucm.es [Departamento de Análisis Matemático, Universidad Complutense de Madrid, Madrid (Spain); Michalakis, Spyridon [Institute for Quantum Information and Matter, Caltech, California 91125 (United States); Perez-Garcia, David [Departamento de Análisis Matemático, Universidad Complutense de Madrid, Madrid (Spain); IMI, Universidad Complutense de Madrid, Madrid (Spain); ICMAT, C/Nicolás Cabrera, Campus de Cantoblanco, 28049 Madrid (Spain)
2015-10-15
We prove an area law with a logarithmic correction for the mutual information for fixed points of local dissipative quantum system satisfying a rapid mixing condition, under either of the following assumptions: the fixed point is pure or the system is frustration free.
Isotope quantum effects in water around the freezing point.
Hart, R T; Mei, Q; Benmore, C J; Neuefeind, J C; Turner, J F C; Dolgos, M; Tomberli, B; Egelstaff, P A
2006-04-07
We have measured the difference in electronic structure factors between liquid H(2)O and D(2)O at temperatures of 268 and 273 K with high energy x-ray diffraction. These are compared to our previously published data measured from 279 to 318 K. We find that the total structural isotope effect increases by a factor of 3.5 over the entire range, as the temperature is decreased. Structural isochoric temperature differential and isothermal density differential functions have been used to compare these data to a thermodynamic model based upon a simple offset in the state function. The model works well in describing the magnitude of the structural differences above approximately 310 K, but fails at lower temperatures. The experimental results are discussed in light of several quantum molecular dynamics simulations and are in good qualitative agreement with recent temperature dependent, rotationally quantized rigid molecule simulations.
Holographic aspects of black holes, matrix models and quantum criticality
Papadoulaki, Olga
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
Garrabos, Yves; Palencia, Fabien; Lecoutre, Carole; Erkey, Can; Le Neindre, Bernard
2006-02-01
We present the master (i.e., unique) behavior of the correlation length, as a function of the thermal field along the critical isochore, asymptotically close to the gas-liquid critical point of xenon, krypton, argon, helium-3, sulfur hexafluoride, carbon dioxide, and heavy water. It is remarkable that this unicity extends to the correction-to-scaling terms. The critical parameter set, which contains all the needed information to reveal the master behavior, is composed of four thermodynamic coordinates of the critical point and one adjustable parameter which accounts for quantum effects in the helium-3 case. We use a scale dilatation method applied to the relevant physical variables of the one-component fluid subclass, in analogy with the basic hypothesis of the renormalization theory. This master behavior for the correlation length satisfies hyperscaling. We finally estimate the thermal field extent where the critical crossover of the singular thermodynamic and correlation functions deviates from the theoretical crossover function obtained from field theory.
Phenomenological Consequences of Enhanced Bulk Viscosity Near the QCD Critical Point
Monnai, Akihiko; Yin, Yi
2016-01-01
In the proximity of the QCD critical point the bulk viscosity of quark-gluon matter is expected to be proportional to nearly the third power of the critical correlation length, and become significantly enhanced. This work is the first attempt to study the phenomenological consequences of enhanced bulk viscosity near the QCD critical point. For this purpose, we implement the expected critical behavior of the bulk viscosity within a non-boost-invariant, longitudinally expanding $1+1$ dimensional causal relativistic hydrodynamical evolution at non-zero baryon density. We demonstrate that the critically-enhanced bulk viscosity induces a substantial non-equilibrium pressure, effectively softening the equation of state, and leads to sizable effects in the flow velocity and single particle distributions at the freeze-out. The observable effects that may arise due to the enhanced bulk viscosity in the vicinity of the QCD critical point can be used as complimentary information to facilitate searches for the QCD critic...
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.
Quantum fixed-point search algorithm with general phase shifts
Institute of Scientific and Technical Information of China (English)
2008-01-01
Grover presented the Phase-π/3 search by replacing the selective inversions by selective phase shifts of π/3.In this paper,we review and discuss the fixed-point search with general but equal phase shifts and the fixedpoint search with general but different phase shifts.
Whole wafer critical point drying of MEMS devices
Resnick, Paul J.; Clews, Peggy J.
2001-10-01
Stiction induced by capillary forces during the post-release drying step of MEMS fabrication can substantially limit the functional yield of complex devices. Supercritical CO2 drying provides a method to remove liquid from the device surface without creating a liquid/vapor interface, thereby mitigating stiction. We show that a continuous stirred-tank reactor (CSTR) model can be applied as a method to estimate the volume of liquid CO2 required to effectively displace the post release solvent. The CSTR model predicts that about 8 volume exchanges is sufficient to effectively displace the methanol to a concentration below the saturation point. Experimental data indicate that about 10 exchanges are adequate for repeatable drying of complex devices, which is in reasonable agreement to the model prediction. In addition to drying devices without inducing stiction, the process must be inherently non-contaminating. Data indicate that the majority of contaminants deposited during the drying process can be attributed to contaminants originating in the post-release solvent, rather than the supercritical CO2 process.
Grüneisen parameter studies on heavy fermion quantum criticality
Gegenwart, Philipp
2016-11-01
The Grüneisen parameter, experimentally determined from the ratio of thermal expansion to specific heat, quantifies the pressure dependence of characteristic energy scales of matter. It is highly enhanced for Kondo lattice systems, whose properties are strongly dependent on the pressure sensitive antiferromagnetic exchange interaction between f- and conduction electrons. In this review, we focus on the divergence of the Grüneisen parameter and its magnetic analogue, the adiabatic magnetocaloric effect, for heavy-fermion metals near quantum critical points. We compare experimental results with current theoretical models, including the effect of strong geometrical frustration. We also discuss the possibility of using materials with the divergent magnetic Grüneisen parameter for adiabatic demagnetization cooling to very low temperatures.
Band structure and itinerant magnetism in quantum critical NbFe2
Energy Technology Data Exchange (ETDEWEB)
Subedi, A. P. [University of Tennessee, Knoxville (UTK); Singh, David J [ORNL
2010-01-01
We report first-principles calculations of the band structure and magnetic ordering in the C14 Laves phase compound NbFe{sub 2}. The magnetism is itinerant in the sense that the moments are highly dependent on ordering. We find an overestimation of the magnetic tendency within the local spin-density approximation, similar to other metals near magnetic quantum critical points. We also find a competition between different magnetic states due to band-structure effects. These lead to competing magnetic tendencies due to competing interlayer interactions, one favoring a ferrimagnetic solution and the other an antiferromagnetic state. While the structure contains Kagome lattice sheets, which could, in principle, lead to strong magnetic frustration, the calculations do not show dominant nearest-neighbor antiferromagnetic interactions within these sheets. These results are discussed in relation to experimental observations.
Combining general relativity and quantum theory points of conflict and contact
Padmanabhan, T
2001-01-01
The issues related to bringing together the principles of general relativity and quantum theory are discussed. After briefly summarising the points of conflict between the two formalisms I focus on four specific themes in which some contact has been established in the past between GR and quantum field theory: (i) The role of planck length in the microstructure of spacetime (ii) The role of quantum effects in cosmology and origin of the universe (iii) The thermodynamics of spacetimes with horizons and especially the concept of entropy related to spacetime geometry (iv) The problem of the cosmological constant.
Frequency-Dependent Viscosity of Xenon Near the Critical Point
Berg, Robert F.; Moldover, Michael R.; Zimmerli, Gregory A.
1999-01-01
We used a novel, overdamped oscillator aboard the Space Shuttle to measure the viscosity eta of xenon near its critical density rho(sub c), and temperature T(sub c). In microgravity, useful data were obtained within 0.1 mK of T(sub c), corresponding to a reduced temperature t = (T -T(sub c))/T(sub c) = 3 x 10(exp -7). The data extend two decades closer to T(sub c) than the best ground measurements, and they directly reveal the expected power-law behavior eta proportional to t(sup -(nu)z(sub eta)). Here nu is the correlation length exponent, and our result for the small viscosity exponent is z(sub eta) = 0.0690 +/- 0.0006. (All uncertainties are one standard uncertainty.) Our value for z(sub eta) depends only weakly on the form of the viscosity crossover function, and it agrees with the value 0.067 +/- 0.002 obtained from a recent two-loop perturbation expansion. The measurements spanned the frequency range 2 Hz less than or equal to f less than or equal to 12 Hz and revealed viscoelasticity when t less than or equal to 10(exp -1), further from T(sub c) than predicted. The viscoelasticity scales as Af(tau), where tau is the fluctuation-decay time. The fitted value of the viscoelastic time-scale parameter A is 2.0 +/- 0.3 times the result of a one-loop perturbation calculation. Near T(sub c), the xenon's calculated time constant for thermal diffusion exceeded days. Nevertheless, the viscosity results were independent of the xenon's temperature history, indicating that the density was kept near rho(sub c), by judicious choices of the temperature vs. time program. Deliberately bad choices led to large density inhomogeneities. At t greater than 10(exp -5), the xenon approached equilibrium much faster than expected, suggesting that convection driven by microgravity and by electric fields slowly stirred the sample.
DEFF Research Database (Denmark)
Schwahn, D.; Mortensen, K.; Janssen, S.
1994-01-01
The critical behavior of a polymer blend was measured by small-angle neutron scattering above and below the critical temperature T-c, i.e., outside and inside the unstable region. The critical exponents and the amplitudes of the susceptibility and the correlation length were determined. For T > T......-c the critical exponents gamma and nu are consistent with the renormalization-group predictions. Below T-c, however, deviations from the expected values were observed. Also experimental critical amplitude ratios (20-30)% smaller than predicted were found....
Criticality, factorization and Wigner-Yanase skew information in quantum spin chains
Cheng, W. W.; Li, J. X.; Shan, C. J.; Gong, L. Y.; Zhao, S. M.
2015-07-01
We apply the Wigner-Yanase skew information approach to analyze criticality and factorization phenomenon in the one-dimensional anisotropy model with uniform coupling interaction and periodic-two one. Based on the exact solutions of the ground states, the Wigner-Yanase skew information between two nearest-neighbor lattices is obtained. For the uniform case, the first-order derivative of the Wigner-Yanase skew information is non-analytically around the critical point. The scaling behavior and the universality are verified numerically. In particular, such skew information can also detect the factorization transition in this model. For the periodic-two case, it is found that there exist more than one phase-transition point in some parameter region due to the competition between periodicity and anisotropy. Furthermore, two kinds of phase transitions, i.e., the Ising and anisotropy transitions, driven by external field and the anisotropy parameter , are investigated carefully by the skew information. Our results state that quantum phase transition driven by the anisotropy parameter can belong to the same universality class as the one driven by external field.
Hybrid Quantum Point Contact-Superconductor Devices Using InSb Nanowires
Gill, Stephen; Damasco, John Jeffrey; Car, Diana; Bakkers, Erik; Mason, Nadya
Recent experiments using hybrid nanowire (NW)-superconductor (SC) devices have provided evidence for Majorana quasiparticles in tunneling experiments. However, these tunneling experiments are marked by a soft superconducting gap, which likely originates from disorder at the NW-SC interface. Hence, clean NW-SC interfaces are important for future Majorana studies. By carefully processing the NW-SC interface, we have realized quantized conductance steps in quantum point contacts fabricated from InSb NWs and superconducting contacts. We study the length dependence of ballistic behavior and the induced superconductivity in InSb NWs by quantum point contact spectroscopy. Additionally, we discuss how the transport in InSb NW-SC quantum point contacts evolves in magnetic field.
Universal Critical Behavior at a Phase Transition to Quantum Turbulence
Takahashi, Masahiro; Takeuchi, Kazumasa A
2016-01-01
Turbulence is one of the most prototypical phenomena of systems driven out of equilibrium. While turbulence has been studied mainly with classical fluids like water, considerable attention is now drawn to quantum turbulence (QT), observed in quantum fluids such as superfluid helium and Bose-Einstein condensates. A distinct feature of QT is that it consists of quantum vortices, by which turbulent circulation is quantized. Yet, under strong forcing, characteristic properties of developed classical turbulence such as Kolmogorov's law have also been identified in QT. Here, we study the opposite limit of weak forcing, i.e., the onset of QT, numerically, and find another set of universal scaling laws known for classical non-equilibrium systems. Specifically, we show that the transition belongs to the directed percolation universality class, known to arise generically in transitions into an absorbing state, including transitions to classical shear-flow turbulence after very recent studies. We argue that quantum vort...
Liu, Bao; Zhang, Feng-Yang; Song, Jie; Song, He-Shan
2015-01-01
We propose a direct measurement scheme to read out the geometric phase of a coupled double quantum dot system via a quantum point contact(QPC) device. An effective expression of the geometric phase has been derived, which relates the geometric phase of the double quantum dot qubit to the current through QPC device. All the parameters in our expression are measurable or tunable in experiment. Moreover, since the measurement process affects the state of the qubit slightly, the geometric phase can be protected. The feasibility of the scheme has been analyzed. Further, as an example, we simulate the geometrical phase of a qubit when the QPC device is replaced by a single electron transistor(SET). PMID:26121538
Baird, James K; Baker, Jonathan D; Hu, Baichuan; Lang, Joshua R; Joyce, Karen E; Sides, Alison K; Richey, Randi D
2015-03-12
Binary liquid mixtures having a consolute point can be used as solvents for chemical reactions. When excess cerium(IV) oxide is brought into equilibrium with a mixture of isobutyric acid + water, and the concentration of cerium in the liquid phase is plotted in van't Hoff form, a straight line results for temperatures sufficiently in excess of the critical solution temperature. Within 1 K of the critical temperature, however, the concentration becomes substantially suppressed, and the van't Hoff slope diverges toward negative infinity. According to the phase rule, one mole fraction can be fixed. Given this restriction, the temperature behavior of the data is in exact agreement with the predictions of both the principle of critical point isomorphism and the Gibbs-Helmholtz equation. In addition, we have determined the concentration of lead in the liquid phase when crystalline lead(II) sulfate reacts with potassium iodide in isobutyric acid + water. When plotted in van't Hoff form, the data lie on a straight line for all temperatures including the critical region. The phase rule indicates that two mole fractions can be fixed. With this restriction, the data are in exact agreement with the principle of critical point isomorphism.
Energy Technology Data Exchange (ETDEWEB)
Khelalfa, R.; Durastanti, J.F. [Centre d' Etudes et de Recherche en Thermique, Environnement et Systemes, Paris 12, 61 avenue du General de Gaulle, 94010 Creteil Cedex (France); Darrozes, J.S. [Institut Jean Le Rond d' Alembert, Paris 6, 4 place Jussieu, 75252 Paris Cedex 05 (France)
2011-07-01
The assembly of metal parts that may be encountered in industry (nuclear, space, ...), creates frequently a path of leakage which can let a fluid pass. In this following study, we aim at understanding the phenomenology of a confined flow through the vicinity of critical point and its influence on the leakage rate. This sealing problem was limited to stationary and viscous situations. The leakage geometry has been assimilated to a capillary tube whose the wall temperature is fixed at the fluid critical value. A difference of pressure was imposed between a supercritical inlet and a subcritical outlet. The phenomenological approach has led to highlight the existence of a transition zone crossing the critical point. In this region of strong expansion, has shown the existence of a thermo-mechanical coupling and be taken a into account by the thermal convection joined the conduction to transport heat. It shows that the progression in fluid outwards is slowed by that cap effect. (authors)
Institute of Scientific and Technical Information of China (English)
Feng LI; Yin Lai JIN
2011-01-01
In this paper,center conditions and bifurcation of limit cycles at the nilpotent critical point in a class of quintic polynomial differential system are investigated.With the help of computer algebra system MATHEMATICA,the first 8 quasi Lyapunov constants are deduced.As a result,the necessary and sufficient conditions to have a center are obtained.The fact that there exist 8 small amplitude limit cycles created from the three-order nilpotent critical point is also proved.Henceforth we give a lower bound of cyclicity of three-order nilpotent critical point for quintic Lyapunov systems.
Measurements of the Coexistence Curve near the Liquid-Gas Critical Point
Hahn, Inseob
2003-01-01
The shape of the liquid-gas coexistence curve of He-3 very near the critical point (-2x10(exp -6) critical point was strongly affected by the gravitational field. Away from the critical point, the coexistence curve obtained using this technique was also consistent with the earlier work using the local density measurements of Pittman et al. The recent crossover parametric model of the equation-of-state are used to analyze the height-dependent measured coexistence curves. Data analyses have indicated that microgravity will permit measurements within two additional decades in reduced temperatures beyond the best gravity-free data obtained in Earth-bound experiments.
Evidence for a Disordered Critical Point in a Glass-Forming Liquid.
Berthier, Ludovic; Jack, Robert L
2015-05-22
Using computer simulations of an atomistic glass-forming liquid, we investigate the fluctuations of the overlap between a fluid configuration and a quenched reference system. We find that large fluctuations of the overlap develop as temperature decreases, consistent with the existence of the random critical point that is predicted by effective field theories. We discuss the scaling of fluctuations near the presumed critical point, comparing the observed behavior with that of the random-field Ising model. We argue that this critical point directly reveals the existence of an interfacial tension between amorphous metastable states, a quantity relevant both for equilibrium relaxation and for nonequilibrium melting of stable glass configurations.
Quantum point contacts and resistive switching in Ni/NiO nanowire junctions
Oliver, Sean M.; Fairfield, Jessamyn A.; Bellew, Allen T.; Lee, Sunghun; Champlain, James G.; Ruppalt, Laura B.; Boland, John J.; Vora, Patrick M.
2016-11-01
Metal oxide devices that exhibit resistive switching are leading candidates for non-volatile memory applications due to their potential for fast switching, low-power operation, and high device density. It is widely accepted in many systems that two-state resistive behavior arises from the formation and rupture of conductive filaments spanning the oxide layer. However, means for controlling the filament geometry, which critically influences conduction, have largely been unexamined. Here, we explore the connection between filament geometry and conductance in a model resistive switching system based on the junction of two nickel/nickel oxide core/shell nanowires. Variable temperature current-voltage measurements indicate that either wide metallic filaments or narrow semiconducting filaments can be preferentially formed by varying the current compliance during electroformation. Metallic filaments behave as a conventional metallic resistance in series with a small barrier, while semiconducting filaments behave as quantum point contacts. The ability to tune filament geometry and behavior through the electroforming process may open avenues for enhanced functionality in nanoscale memristive systems.
The phase transition and classification of critical points in the multistability chemical reactions
Institute of Scientific and Technical Information of China (English)
ChunhuaZHANG; FugenWU; ChunyanWU; FaOU
2000-01-01
In this paper, we study the phase transition and classification of critical points in multistability chemical reaction systems. Referring to the spirit of Landau's theory of phase transitions, this paper deals with the varied transitions and critical phenomena in multistable chemical systems. It is demonstrated that the higher the order of the multistability,the wider the variety of phase transitions will be. A classification scheme of critical points according to the stability criterion and the thermodynamic potential continuity is suggested.It is useful for us to study critical phenomena especially in the non-equilibrium systems including the multi-stable chemical ones.
Vapor-like liquid coexistence densities affect the extension of the critical point's influence zone
Rivera, Jose Luis; Guerra-Gonzalez, Roberto
2015-01-01
The critical point affects the coexistence behavior of the vapor-liquid equilibrium densities. The length of the critical influence zone is under debate because for some properties, like shear viscosity, the extension is only a few degrees, while for others, such as the density order parameter, the critical influence zone range covers up to hundreds of degrees below the critical temperature. Here we show that for a simple molecular potential of ethane, the critical influence zone covers a wide zone of tens of degrees (below the critical temperature) down to a transition temperature, at which the apparent critical influence zone vanishes and the transition temperature can be predicted through a pressure analysis of the coexisting bulk liquid phase. The liquid phases within the apparent critical influence zone show low densities, making them behave internally like their corresponding vapor phases. Therefore, the experimentally observed wide extension of the critical influence zone is due to a vapor-like effect ...
Tirrito, Emanuele; Ran, Shi-Ju
2016-01-01
We demonstrate an efficient method that allows for simultaneous determination of the ground state, low energy excitation properties and excitation gap in quantum many body systems. To this aim we first use the \\textit{ab-initio} optimization principle of tensor networks (TN), to show that the infinite density matrix renormalization group (iDMRG) in the real space is associated in a natural manner to the infinite time-evolving block decimation (iTEBD) implemented on a continuous matrix product state (MPS), and defined in imaginary time. We illustrate this association showing that the (imaginary) time matrix product state (MPS) in iTEBD reproduces accurately the properties of the two-dimensional (2D) classical Ising model, verifying in this way that the time MPS corresponds to a well-defined physical state. We apply then our scheme to the one-dimensional (1D) quantum Ising chain, where the time MPS is defined in continuous imaginary time. It is found that the time MPS at or close to the critical point is always...
Visualizing Robustness of Critical Points for 2D Time-Varying Vector Fields
Wang, B.
2013-06-01
Analyzing critical points and their temporal evolutions plays a crucial role in understanding the behavior of vector fields. A key challenge is to quantify the stability of critical points: more stable points may represent more important phenomena or vice versa. The topological notion of robustness is a tool which allows us to quantify rigorously the stability of each critical point. Intuitively, the robustness of a critical point is the minimum amount of perturbation necessary to cancel it within a local neighborhood, measured under an appropriate metric. In this paper, we introduce a new analysis and visualization framework which enables interactive exploration of robustness of critical points for both stationary and time-varying 2D vector fields. This framework allows the end-users, for the first time, to investigate how the stability of a critical point evolves over time. We show that this depends heavily on the global properties of the vector field and that structural changes can correspond to interesting behavior. We demonstrate the practicality of our theories and techniques on several datasets involving combustion and oceanic eddy simulations and obtain some key insights regarding their stable and unstable features. © 2013 The Author(s) Computer Graphics Forum © 2013 The Eurographics Association and Blackwell Publishing Ltd.
Variation of critical point of aging transition in a networked oscillators system.
Huang, Wenwen; Zhang, Xiyun; Hu, Xin; Zou, Yong; Liu, Zonghua; Guan, Shuguang
2014-06-01
In this work, we study the variation of critical point in aging transition in a networked system consisting of both active and inactive oscillators. By theoretical analysis and numerical simulations, we show that the critical point of aging transition actually is determined by the (normalized) cross links between active and inactive subpopulations of oscillators. This reveals how specific configuration of active and inactive oscillators in the network can lead to the variation of transition point. In particular, we investigate how different strategies of targeted inactivation influence the transition point based on the theory. Our results theoretically explain why the low-degree nodes are crucial regarding dynamical robustness in such systems.
Spectral analysis of growing graphs a quantum probability point of view
Obata, Nobuaki
2017-01-01
This book is designed as a concise introduction to the recent achievements on spectral analysis of graphs or networks from the point of view of quantum (or non-commutative) probability theory. The main topics are spectral distributions of the adjacency matrices of finite or infinite graphs and their limit distributions for growing graphs. The main vehicle is quantum probability, an algebraic extension of the traditional probability theory, which provides a new framework for the analysis of adjacency matrices revealing their non-commutative nature. For example, the method of quantum decomposition makes it possible to study spectral distributions by means of interacting Fock spaces or equivalently by orthogonal polynomials. Various concepts of independence in quantum probability and corresponding central limit theorems are used for the asymptotic study of spectral distributions for product graphs. This book is written for researchers, teachers, and students interested in graph spectra, their (asymptotic) spectr...
Quantum and classical statistics of the electromagnetic zero-point field
Ibison, M
1996-01-01
A classical electromagnetic zero-point field (ZPF) analogue of the vacuum of quantum field theory has formed the basis for theoretical investigations in the discipline known as random or stochastic electrodynamics (SED) wherein quantum measurements are imitated by the introduction of a stochastic classical background EM field. Random EM fluctuations are assumed to provide perturbations which can mimic some quantum phenomena while retaining a purely classical basis, e.g. the Casimir force, the Van-der-Waals force, the Lamb shift, spontaneous emission, the RMS radius of the harmonic oscillator, and the radius of the Bohr atom. This classical ZPF is represented as a homogeneous, isotropic ensemble of plane waves with fixed amplitudes and random phases. Averaging over the random phases is assumed to be equivalent to taking the ground-state expectation values of the corresponding quantum operator. We demonstrate that this is not precisely correct by examining the statistics of the classical ZPF in contrast to that...
Schreiber, K. A.; Samkharadze, N.; Gardner, G. C.; Biswas, Rudro R.; Manfra, M. J.; Csáthy, G. A.
2017-07-01
Under hydrostatic pressure, the ground state of a two-dimensional electron gas at ν =5 /2 changes from a fractional quantum Hall state to the stripe phase. By measuring the energy gap of the fractional quantum Hall state and of the onset temperature of the stripe phase, we mapped out a phase diagram of these competing phases in the pressure-temperature plane. Our data highlight the dichotomy of two descriptions of the half-filled Landau level near the quantum critical point: one based on electrons and another on composite fermions.
Is the critical point for aperture crossing adapted to the person-plus-object system?
Hackney, Amy L; Cinelli, Michael E; Frank, Jim S
2014-01-01
When passing through apertures, individuals scale their actions to their shoulder width and rotate their shoulders or avoid apertures that are deemed too small for straight passage. Carrying objects wider than the body produces a person-plus-object system that individuals must account for in order to pass through apertures safely. The present study aimed to determine whether individuals scale their critical point to the widest horizontal dimension (shoulder or object width). Two responses emerged: Fast adapters adapted to the person-plus-object system by maintaining a consistent critical point regardless of whether the object was carried while slow adapters initially increased their critical point (overestimated) before adapting back to their original critical point. The results suggest that individuals can account for increases in body width by scaling actions to the size of the object width but people adapt at different rates.
Signatures of quantum chaos in nodal points and streamlines in electron transport through billiards
Berggren, K F; Sadreev, A F; Starikov, A A; Berggren, Karl-Fredrik; Pichugin, Konstantin N.; Sadreev, Almas F.; Starikov, Anton
1999-01-01
Streamlines and distributions of nodal points are used as signatures of chaos in coherent electron transport through three types of billiards, Sinai, Bunimovich and rectangular. Numerical averaged distribution functions of nearest distances between nodal points are presented. We find the same form for the Sinai and Bunimovich billiards and suggest that there is a universal form that can be used as a signature of quantum chaos for electron transport in open billiards. The universal distribution function is found to be insensitive to the way avaraging is performed (over positions of leads, over an energy interval with a few conductance fluctuations, or both). The integrable rectangular billiard, on the other hand, displays nonuniversal distribution with a central peak related to partial order of nodal points for the case of symmetric attachment of leads. However cases with nonsymmetric leads tend to the universal form. Also it is shown how nodal points in rectangular billiard can lead to "channeling of quantum ...
Quantum limit for two-dimensional resolution of two incoherent optical point sources
Ang, Shan Zheng; Tsang, Mankei
2016-01-01
We obtain the multiple-parameter quantum Cram\\'er-Rao bound for estimating the Cartesian components of the centroid and separation of two incoherent optical point sources using an imaging system with finite spatial bandwidth. Under quite general and realistic assumptions on the point-spread function of the imaging system, and for weak source strengths, we show that the Cram\\'er-Rao bounds for the x and y components of the separation are independent of the values of those components, which may be well-below the conventional Rayleigh resolution limit. We also propose two linear optics-based measurement methods that approach the quantum bound for the estimation of the Cartesian components of the separation once the centroid has been located. One of the methods is an interferometric scheme that approaches the quantum bound for sub-Rayleigh separations. The other method uses fiber coupling to attain the bound regardless of the distance between the two sources.
The thermodynamics and transport properties of transition metals in critical point
Khomkin, Alexander L
2016-01-01
A new method for calculating the critical point parameters (density, temperature, pressure and electrical conductivity) and binodal of vapor-liquid (dielectric-metal) phase transition is proposed. It is based on the assumption that cohesion, which determines the main properties of solid state, also determines the properties in the vicinity of the critical point. Comparison with experimental and theoretical data available for transition metals is made.
Critical point quantities and integrability conditions for a class of quintic systems
Institute of Scientific and Technical Information of China (English)
刘一戎; 肖萍
2004-01-01
For a class of quintic systems, the first 16 critical point quantities are obtained by computer algebraic system Mathematica, and the necessary and sufficient conditions that there exists an exact integral in a neighborhood of the origin are also given. The technique employed is essentially different from usual ones. The recursive formula for computation of critical point quantities is linear and then avoids complex integral operations. Some results show an interesting contrast with the related results on quadratic systems.
Leherte, L; Meurice, N; Vercauteren, D P
2000-01-01
A procedure for the comparison of three-dimensional electron density distributions is proposed for similarity searches between pharmacological ligands at various levels of crystallographic resolution. First, a graph representation of molecular electron density distributions is generated using a critical point analysis approach. Pairwise as well as multiple comparisons between the obtained graphs of critical points are then carried out using a Monte Carlo/simulated annealing technique, and results are compared with genetic algorithm solutions.
Dalmonte, M.; Lechner, W.; Cai, Zi; Mattioli, M.; Läuchli, A. M.; Pupillo, G.
2015-07-01
We investigate the quantum phases of hard-core bosonic atoms in an extended Hubbard model where particles interact via soft-shoulder potentials in one dimension. Using a combination of field-theoretical methods and strong-coupling perturbation theory, we demonstrate that the low-energy phase can be a conformal cluster Luttinger liquid (CLL) phase with central charge c =1 , where the microscopic degrees of freedom correspond to mesoscopic ensembles of particles. Using numerical density-matrix renormalization-group methods, we demonstrate that the CLL phase [first predicted in M. Mattioli et al., Phys. Rev. Lett. 111, 165302 (2013), 10.1103/PhysRevLett.111.165302] is separated from a conventional Tomonaga-Luttinger liquid by an exotic critical point with central charge c =3/2 . The latter is expression of an emergent conformal supersymmetry, which is not present in the original Hamiltonian. We discuss the observability of the CLL phase in realistic experimental settings with weakly dressed Rydberg atoms confined to optical lattices. Using quantum Monte Carlo simulations, we show that the typical features of CLLs are stable up to comparatively high temperatures. Using exact diagonalizations and quantum trajectory methods, we provide a protocol for adiabatic state preparation as well as quantitative estimates on the effects of particle losses.
Bulk singularities at critical end points: a field-theory analysis
Diehl, H. W.; Smock, M.
2001-06-01
A class of continuum models with a critical end point is considered whose Hamiltonian [φ,ψ] involves two densities: a primary order-parameter field, φ, and a secondary (noncritical) one, ψ. Field-theoretic methods (renormalization group results in conjunction with functional methods) are used to give a systematic derivation of singularities occurring at critical end points. Specifically, the thermal singularity | t|2 - α of the first-order line on which the disordered or ordered phase coexists with the noncritical spectator phase, and the coexistence singularity | t|1 - α or | t|β of the secondary density are derived. It is clarified how the renormalization group (RG) scenario found in position-space RG calculations, in which the critical end point and the critical line are mapped onto two separate fixed points CEP* and λ*, translates into field theory. The critical RG eigenexponents of CEP* and λ* are shown to match. CEP* is demonstrated to have a discontinuity eigenperturbation (with eigenvalue y = d), tangent to the unstable trajectory that emanates from CEP* and leads to λ*. The nature and origin of this eigenperturbation as well as the role redundant operators play are elucidated. The results validate that the critical behavior at the end point is the same as on the critical line.
Peltier Coefficient and Photon-Assisted Tunnelling in Quantum Point Contact
H. Aly, Arafa
2008-12-01
We present the Peltier coefficient and thermal transport in quantum point contact (QPC), under the influence of external fields and different temperatures. Also we obtain the oscillations of the Peltier coefficient in external fields. Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes and temperatures. The obtained results are consistent with the experimental data in the literature.
Conductance enhancement in quantum-point-contact semiconductor-superconductor devices
DEFF Research Database (Denmark)
Mortensen, Asger; Jauho, Antti-Pekka; Flensberg, Karsten;
1999-01-01
We present numerical calculations of the conductance of an interface between a phase-coherent two-dimensional electron gas and a superconductor with a quantum point contact in the normal region. Using a scattering matrix approach we reconsider the geometry of De Raedt, Michielsen, and Klapwijk [P...
Long-term mortality after critical care: what is the starting point?
Ranzani, Otavio T.; Zampieri, Fernando G; Park, Marcelo; Salluh, Jorge IF
2013-01-01
Mortality is still the most assessed outcome in the critically ill patient and is routinely used as the primary end-point in intervention trials, cohort studies, and benchmarking analysis. Despite this, interest in patient-centered prognosis after ICU discharge is increasing, and several studies report quality of life and long-term outcomes after critical illness. In a recent issue of Critical Care, Cuthbertson and colleagues reported interesting results from a cohort of 439 patients with sep...
Long-term mortality after critical care: what is the starting point?
Ranzani, Otavio T; Zampieri, Fernando G; Park, Marcelo; Salluh, Jorge IF
2013-01-01
Mortality is still the most assessed outcome in the critically ill patient and is routinely used as the primary end-point in intervention trials, cohort studies, and benchmarking analysis. Despite this, interest in patient-centered prognosis after ICU discharge is increasing, and several studies report quality of life and long-term outcomes after critical illness. In a recent issue of Critical Care, Cuthbertson and colleagues reported interesting results from a cohort of 439 patients with sep...
Lee, Sang-Hee; Kang, Seung-Ho
2016-10-01
In previous studies, we showed that the branch length similarity (BLS) entropy profile could be used successfully for the recognition of shapes such as battle tanks, facial expressions, and butterflies. In the present study, we introduce critical points defined as a set of distinguishing points with high curvature to the BLS entropy profile in order to improve the shape recognition. In order to generate a given number of critical points from the shape, we propose a critical point detection method. Furthermore, we show the invariant properties of the BLS entropy descriptor. To evaluate the effects of critical points on the shape recognition of the BLS entropy descriptor, we performed a butterfly classification experiment against a real image data set, and we conducted performance comparisons with other point detection methods. In addition, the performance of the BLS entropy descriptor computed using the critical points was compared with those of other well-known descriptors such as the Fourier descriptor using three machine learning techniques, the Bayesian classifier, the multi-layer perceptron and the support vector machine. The results show that the BLS entropy descriptor outperforms other well-known descriptors.
Energy Technology Data Exchange (ETDEWEB)
Zozoulenko, I V; Ihnatsenka, S [Solid State Electronics, Department of Science and Technology (ITN), Linkoeping University, 60174 Norrkoeping (Sweden)
2008-04-23
We have developed a mean-field first-principles approach for studying electronic and transport properties of low dimensional lateral structures in the integer quantum Hall regime. The electron interactions and spin effects are included within the spin density functional theory in the local density approximation where the conductance, the density, the effective potentials and the band structure are calculated on the basis of the Green's function technique. In this paper we present a systematic review of the major results obtained on the energetics, spin polarization, effective g factor, magnetosubband and edge state structure of split-gate and cleaved-edge overgrown quantum wires as well as on the conductance of quantum point contacts (QPCs) and open quantum dots. In particular, we discuss how the spin-resolved subband structure, the current densities, the confining potentials, as well as the spin polarization of the electron and current densities in quantum wires and antidots evolve when an applied magnetic field varies. We also discuss the role of the electron interaction and spin effects in the conductance of open systems focusing our attention on the 0.7 conductance anomaly in the QPCs. Special emphasis is given to the effect of the electron interaction on the conductance oscillations and their statistics in open quantum dots as well as to interpretation of the related experiments on the ultralow temperature saturation of the coherence time in open dots.
Quantum Discord for Investigating Quantum Correlations without Entanglement in Solids
Rong, Xing; Jin, Fangzhou; Geng, Jianpei; Feng, Pengbo; Xu, Nanyang; Wang, Ya; Ju, Chenyong; Shi, Mingjun; Du, Jiangfeng
2012-01-01
Quantum systems unfold diversified correlations which have no classical counterparts. These quantum correlations have various different facets. Quantum entanglement, as the most well known measure of quantum correlations, plays essential roles in quantum information processing. However, it has recently been pointed out that quantum entanglement cannot describe all the nonclassicality in the correlations. Thus the study of quantum correlations in separable states attracts widely attentions. Herein, we experimentally investigate the quantum correlations of separable thermal states in terms of quantum discord. The sudden change of quantum discord is observed, which captures ambiguously the critical point associated with the behavior of Hamiltonian. Our results display the potential applications of quantum correlations in studying the fundamental properties of quantum system, such as quantum criticality of non-zero temperature.
Long-term mortality after critical care: what is the starting point?
Ranzani, Otavio T; Zampieri, Fernando G; Park, Marcelo; Salluh, Jorge If
2013-09-27
Mortality is still the most assessed outcome in the critically ill patient and is routinely used as the primary end-point in intervention trials, cohort studies, and benchmarking analysis. Despite this, interest in patient-centered prognosis after ICU discharge is increasing, and several studies report quality of life and long-term outcomes after critical illness. In a recent issue of Critical Care, Cuthbertson and colleagues reported interesting results from a cohort of 439 patients with sepsis, who showed high ongoing long-term mortality rates after severe sepsis, reaching 61% at 5 years (from a starting point of ICU admission). Follow-up may start at ICU admission, after ICU discharge, or after hospital discharge. Using ICU admission as a starting point will include patients with a wide range of illness severities and reasons for ICU admission. As a result, important consequences of the ICU, such as rehabilitation and reduced quality of life, may be diluted in an unselected population. ICU discharge is another frequently used starting point. ICU discharge is a marker of better outcome and reduced risk for acute deterioration, making this an interesting starting point for studying long-term mortality, need for ICU readmission, and critical illness rehabilitation. Finally, using hospital discharge as the starting point will include patients with the minimal requirements to sustain an adequate condition in a non-monitored environment but will add a ?survivors bias?; that is, patients who survive critical illness are a special group among the critically ill. In this commentary, we discuss the heterogeneity in long-term mortality from recent studies in critical care medicine ? heterogeneity that may be a consequence simply of changing the follow-up starting point ? and propose a standardized follow-up starting point for future studies according to the outcome of interest.
THE UNIQUENESS OF LIMIT CYCLE AND CRITICAL POINT FOR A CLASS OF CUBIC SYSTEM
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
In this paper,we consider an accompany system concerning some class of cubic system. We then prove that the system has at most one limit cycle. Finally,we obtain the topological structure of both the critical points at infinity and the singular points lying on invariant lines.
Nonthermal Fixed Points in Quantum Field Theory Beyond the Weak-Coupling Limit
Berges, Jürgen
2016-01-01
Quantum systems in extreme conditions can exhibit universal behavior far from equilibrium associated to nonthermal fixed points, with a wide range of topical applications from early-universe inflaton dynamics and heavy-ion collisions to strong quenches in ultracold quantum gases. So far, most studies rely on a mapping of the quantum dynamics onto a classical-statistical theory that can be simulated on a computer. However, the mapping is based on a weak-coupling limit while phenomenological applications often require moderate values of couplings. We report on the observation of nonthermal fixed points directly in quantum field theory beyond the weak-coupling limit. For the example of a relativistic scalar \\mathrm{O}(N) symmetric quantum field theory, we numerically solve the nonequilibrium dynamics employing a 1/N expansion to next-to-leading order, which does not rely on a small coupling parameter. Starting from two different sets of (a) over-occupied and (b) strong-field initial conditions, we find that nont...
Molecular dynamics simulation of a binary mixture near the lower critical point.
Pousaneh, Faezeh; Edholm, Olle; Maciołek, Anna
2016-07-07
2,6-lutidine molecules mix with water at high and low temperatures but in a wide intermediate temperature range a 2,6-lutidine/water mixture exhibits a miscibility gap. We constructed and validated an atomistic model for 2,6-lutidine and performed molecular dynamics simulations of 2,6-lutidine/water mixture at different temperatures. We determined the part of demixing curve with the lower critical point. The lower critical point extracted from our data is located close to the experimental one. The estimates for critical exponents obtained from our simulations are in a good agreement with the values corresponding to the 3D Ising universality class.
Tensor RG calculations and quantum simulations near criticality
Meurice, Y; Tsai, Shan-Wen; Unmuth-Yockey, J; Yang, Li-Ping; Zhang, Jin
2016-01-01
We discuss the reformulation of the O(2) model with a chemical potential and the Abelian Higgs model on a 1+1 dimensional space-time lattice using the Tensor Renormalization Group (TRG) method. The TRG allows exact blocking and connects smoothly the classical Lagrangian approach to the quantum Hamiltonian approach. We calculate the entanglement entropy in the superfluid phase of the O(2) model and show that it approximately obeys the logarithmic Calabrese-Cardy scaling obtained from Conformal Field Theory (CFT). We calculate the Polyakov loop in the Abelian Higgs model and discuss the possibility of a deconfinement transition at finite volume. We propose Bose-Hubbard Hamiltonians implementable on optical lattices as quantum simulators for CFT models.
Can we approach the gas-liquid critical point using slab simulations of two coexisting phases?
Goujon, Florent; Ghoufi, Aziz; Malfreyt, Patrice; Tildesley, Dominic J
2016-09-28
In this paper, we demonstrate that it is possible to approach the gas-liquid critical point of the Lennard-Jones fluid by performing simulations in a slab geometry using a cut-off potential. In the slab simulation geometry, it is essential to apply an accurate tail correction to the potential energy, applied during the course of the simulation, to study the properties of states close to the critical point. Using the Janeček slab-based method developed for two-phase Monte Carlo simulations [J. Janec̆ek, J. Chem. Phys. 131, 6264 (2006)], the coexisting densities and surface tension in the critical region are reported as a function of the cutoff distance in the intermolecular potential. The results obtained using slab simulations are compared with those obtained using grand canonical Monte Carlo simulations of isotropic systems and the finite-size scaling techniques. There is a good agreement between these two approaches. The two-phase simulations can be used in approaching the critical point for temperatures up to 0.97 TC(∗) (T(∗) = 1.26). The critical-point exponents describing the dependence of the density, surface tension, and interfacial thickness on the temperature are calculated near the critical point.
Can we approach the gas-liquid critical point using slab simulations of two coexisting phases?
Goujon, Florent; Ghoufi, Aziz; Malfreyt, Patrice; Tildesley, Dominic J.
2016-09-01
In this paper, we demonstrate that it is possible to approach the gas-liquid critical point of the Lennard-Jones fluid by performing simulations in a slab geometry using a cut-off potential. In the slab simulation geometry, it is essential to apply an accurate tail correction to the potential energy, applied during the course of the simulation, to study the properties of states close to the critical point. Using the Janeček slab-based method developed for two-phase Monte Carlo simulations [J. Janec̆ek, J. Chem. Phys. 131, 6264 (2006)], the coexisting densities and surface tension in the critical region are reported as a function of the cutoff distance in the intermolecular potential. The results obtained using slab simulations are compared with those obtained using grand canonical Monte Carlo simulations of isotropic systems and the finite-size scaling techniques. There is a good agreement between these two approaches. The two-phase simulations can be used in approaching the critical point for temperatures up to 0.97 TC ∗ (T∗ = 1.26). The critical-point exponents describing the dependence of the density, surface tension, and interfacial thickness on the temperature are calculated near the critical point.
Quantum creation and inflationary universes a critical appraisal
Coule, D H
2000-01-01
We contrast the possibility of inflation starting a) from the universe's inception or b) from an earlier non-inflationary state. Neither case is ideal since a) assumes quantum mechanical reasoning is straightforwardly applicable to the early universe; while case b) requires that a singularity still be present. Further, in agreement with Vachaspati and Trodden [1] case b) can only solve the horizon problem if the non-inflationary phase has equation of state $\\gamma<4/3$.
Reprint of : Dynamics of a quantum wave emitted by a decaying and evanescent point source
Delgado, F.; Muga, J. G.
2016-08-01
We put forward a model that describes a decaying and evanescent point source of non-interacting quantum waves in 1D. This point-source assumption allows for a simple description that captures the essential aspects of the dynamics of a wave traveling through a classically forbidden region without the need to specify the details of the inner region. The dynamics of the resulting wave is examined and several characteristic times are identified. One of them generalizes the tunneling time-scale introduced by Büttiker and Landauer and it characterizes the arrival of the maximum of the wave function. Diffraction in time and deviations from exponential decay are also studied. Here we show that there exists an optimal injection frequency and detection point for the observation of these two quantum phenomena.
On the Critical Behaviour, Crossover Point and Complexity of the Exact Cover Problem
Morris, Robin D.; Smelyanskiy, Vadim N.; Shumow, Daniel; Koga, Dennis (Technical Monitor)
2003-01-01
Research into quantum algorithms for NP-complete problems has rekindled interest in the detailed study a broad class of combinatorial problems. A recent paper applied the quantum adiabatic evolution algorithm to the Exact Cover problem for 3-sets (EC3), and provided an empirical evidence that the algorithm was polynomial. In this paper we provide a detailed study of the characteristics of the exact cover problem. We present the annealing approximation applied to EC3, which gives an over-estimate of the phase transition point. We also identify empirically the phase transition point. We also study the complexity of two classical algorithms on this problem: Davis-Putnam and Simulated Annealing. For these algorithms, EC3 is significantly easier than 3-SAT.
Fluctuation theorem for a double quantum dot coupled to a point-contact electrometer
Energy Technology Data Exchange (ETDEWEB)
Golubev, D. [Institut für Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe (Germany); Utsumi, Y. [Department of Physics Engineering, Faculty of Engineering, Mie University, Tsu, Mie, 514-8507 (Japan); Marthaler, M. [Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76128 Karlsruhe (Germany); Schön, G. [Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany and Institut für Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe (Germany)
2013-12-04
Motivated by recent experiments on the real-time single-electron counting through a semiconductor GaAs double quantum dot (DQD) by a nearby quantum point contact (QPC), we develop the full-counting statistics of coupled DQD and QPC system. By utilizing the time-scale separation between the dynamics of DQD and QPC, we derive the modified master equation with tunneling rates depending on the counting fields, which fulfill the detailed fluctuation theorem. Furthermore, we derive universal relations between the non-linear corrections to the current and noise, which can be verified in experiments.
The repulsive nature of naked singularities from the point of view of quantum mechanics
Energy Technology Data Exchange (ETDEWEB)
Batic, D.; Chin, D. [University of West Indies, Department of Mathematics, Kingston 6 (Jamaica); Nowakowski, M. [Universidad de los Andes, Departamento de Fisica, Cra. 1E No. 18A-10, Bogota (Colombia)
2011-04-15
We use the Dirac equation coupled to a background metric to examine what happens to quantum-mechanical observables like the probability density and the radial current in the vicinity of a naked singularity of the Reissner-Nordstroem type. We find that the wave function of the Dirac particle is regular in the point of the singularity. We show that the probability density is exactly zero at the singularity reflecting quantum-mechanically the repulsive nature of the naked singularity. Furthermore, the surface integral of the radial current over a sphere in the vicinity of the naked singularity turns out to be also zero. (orig.)
On the Origins of the Planck Zero Point Energy in Relativistic Quantum Field Theory
Widom, A; Srivastava, Y N
2015-01-01
It is argued that the zero point energy in quantum field theory is a reflection of the particle anti-particle content of the theory. This essential physical content is somewhat disguised in electromagnetic theory wherein the photon is its own anti-particle. To illustrate this point, we consider the case of a charged Boson theory $(\\pi^+,\\pi^-)$ wherein the particle and anti-particle can be distinguished by the charge $\\pm e$. Starting from the zero point energy, we derive the Boson pair production rate per unit time per unit volume from the vacuum in a uniform external electric field. The result is further generalized for arbitrary spin $s$.
Konno, Kohkichi; Nagasawa, Tomoaki; Takahashi, Rohta
2017-10-01
We discuss the scattering of a quantum particle by two independent successive point interactions in one dimension. The parameter space for two point interactions is given by U(2) × U(2) , which is described by eight real parameters. We perform an analysis of perfect resonant transmission on the whole parameter space. By investigating the effects of the two point interactions on the scattering matrix of plane wave, we find the condition under which perfect resonant transmission occurs. We also provide the physical interpretation of the resonance condition.
The Unicellular State as a Point Source in a Quantum Biological System
Directory of Open Access Journals (Sweden)
John S. Torday
2016-05-01
Full Text Available A point source is the central and most important point or place for any group of cohering phenomena. Evolutionary development presumes that biological processes are sequentially linked, but neither directed from, nor centralized within, any specific biologic structure or stage. However, such an epigenomic entity exists and its transforming effects can be understood through the obligatory recapitulation of all eukaryotic lifeforms through a zygotic unicellular phase. This requisite biological conjunction can now be properly assessed as the focal point of reconciliation between biology and quantum phenomena, illustrated by deconvoluting complex physiologic traits back to their unicellular origins.
Green, A G; Sondhi, S L
2005-12-31
Scaling arguments imply that quantum-critical points exhibit universal nonlinear responses to external probes. We investigate the origins of such nonlinearities in transport, which is especially problematic since the system is necessarily driven far from equilibrium. We argue that for a wide class of systems the new ingredient that enters is the Schwinger mechanism--the production of carriers from the vacuum by the applied field--which is then balanced against a scattering rate that is itself set by the field. We show by explicit computation how this works for the case of the symmetric superfluid-Mott insulator transition of bosons.
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.
Scrutinizing Hall Effect in Mn1 -xFex Si : Fermi Surface Evolution and Hidden Quantum Criticality
Glushkov, V. V.; Lobanova, I. I.; Ivanov, V. Yu.; Voronov, V. V.; Dyadkin, V. A.; Chubova, N. M.; Grigoriev, S. V.; Demishev, S. V.
2015-12-01
Separating between the ordinary Hall effect and anomalous Hall effect in the paramagnetic phase of Mn1 -xFex Si reveals an ordinary Hall effect sign inversion associated with the hidden quantum critical (QC) point x*˜0.11 . The effective hole doping at intermediate Fe content leads to verifiable predictions in the field of fermiology, magnetic interactions, and QC phenomena in Mn1 -xFex Si . The change of electron and hole concentrations is considered as a "driving force" for tuning the QC regime in Mn1 -xFex Si via modifying the Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism.
Two mode photon bunching effect as witness of quantum criticality in circuit QED
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
We suggest a scheme to probe critical phenomena at a quantum phase transition (QPT) using the quantum correlation of two photonic modes simultaneously coupled to a critical system. As an experimentally accessible physical implementation,a circuit QED system is formed by a capacitively coupled Josephson junction qubit array interacting with one superconducting transmission line resonator (TLR). It realizes an Ising chain in the transverse field (ICTF) which interacts with the two magnetic modes propagating in the TLR. We demonstrate that in the vicinity of criticality the originally independent fields tend to display photon bunching effects due to their interaction with the ICTF. Thus,the occurrence of the QPT is reflected by the quantum characteristics of the photonic fields.
Two mode photon bunching effect as witness of quantum criticality in circuit QED
Institute of Scientific and Technical Information of China (English)
AI Qing; WANG YingDan; LONG GuiLu; SUN ChangPu
2009-01-01
We suggest a scheme to probe critical phenomena at a quantum phase transition (OPT) using the quantum correlation of two photonic modes simultaneously coupled to a critical system. As an experimentally accessible physical implementation, a circuit QED system is formed by a capsciUvely coupled Josephson junction qubit array interacting with one superconducting transmission line resonator (TLR). It realizes an Ising chain in the transverse field (ICTF) which interacts with the two magnetic modes propagating in the TLR. We demonstrate that in the vicinity of criticality the originally independent fields tend to display photon bunching effects due to their interaction with the ICTF. Thus,the occurrence of the QPT is reflected by the quantum characteristics of the photonic fields.
Critical points in the 16-moment approximation. [plasma flow in laboratory and space plasmas study
Yasseen, F.; Retterer, J. M.
1991-01-01
The singular points in steady state, field-aligned plasma transport models based on velocity moment theory are examined. In particular, two separate singular points in the equations obtained from the 16-moment approximation are identified. These equations are presented in a form that makes the singularities apparent, and they are solved in a simple illustrative case. The singular points, one occurring at the sonic point and the other at a critical value of the parallel heat flux, give rise to different outflow regimes, characterized generically by different asymptotic behavior. The existence of the different outflow regimes separated by the heat flux critical point has been only hinted at in previous discussions of numerical simulation of the polar wind.
Measurement Back-Action in Quantum Point-Contact Charge Sensing
Directory of Open Access Journals (Sweden)
Bruno Küng
2010-06-01
Full Text Available Charge sensing with quantum point-contacts (QPCs is a technique widely used in semiconductor quantum-dot research. Understanding the physics of this measurement process, as well as finding ways of suppressing unwanted measurement back-action, are therefore both desirable. In this article, we present experimental studies targeting these two goals. Firstly, we measure the effect of a QPC on electron tunneling between two InAs quantum dots, and show that a model based on the QPC’s shot-noise can account for it. Secondly, we discuss the possibility of lowering the measurement current (and thus the back-action used for charge sensing by correlating the signals of two independent measurement channels. The performance of this method is tested in a typical experimental setup.
Theoretical Analysis of Thermodynamic Measurements near a Liquid-Gas Critical Point
Barmatz, M.; Zhong, Fang; Hahn, Inseob
2003-01-01
Over the years, many ground-based studies have been performed near liquid-gas critical points to elucidate the expected divergences in thermodynamic quantities. The unambiguous interpretation of these studies very near the critical point is hindered by a gravity-induced density stratification. However, these ground-based measurements can give insight into the crossover behavior between the asymptotic critical region near the transition and the mean field region farther away. We have completed a detailed analysis of heat capacity, susceptibility and coexistence curve measurements near the He-3 liquid-gas critical point using the minimal-subtraction renormalization (MSR) scheme within the phi(exp 4) model. This MSR scheme, using only two adjustable parameters, provides a reasonable global fit to all of these experimental measurements in the gravity-free region out to a reduced temperature of |t| approx. 2x10(exp -2). Recently this approach has also been applied to the earlier microgravity measurements of Haupt and Straub in SF(sub 6) with surprising results. The conclusions drawn from the MSR analyses will be presented. Measurements in the gravity-affected region closer to the He-3 critical point have also been analyzed using the recent crossover parametric model (CPM) of the equation-of-state. The results of fitting heat capacity measurements to the CPM model along the He-3 critical isochore in the gravity-affected region will also be presented.
Sandvik, Anders W
2007-06-01
Using ground-state projector quantum Monte Carlo simulations in the valence-bond basis, it is demonstrated that nonfrustrating four-spin interactions can destroy the Néel order of the two-dimensional S=1/2 Heisenberg antiferromagnet and drive it into a valence-bond solid (VBS) phase. Results for spin and dimer correlations are consistent with a single continuous transition, and all data exhibit finite-size scaling with a single set of exponents, z=1, nu=0.78+/-0.03, and eta=0.26+/-0.03. The unusually large eta and an emergent U(1) symmetry, detected using VBS order parameter histograms, provide strong evidence for a deconfined quantum critical point.
Critical Point Cancellation in 3D Vector Fields: Robustness and Discussion.
Skraba, Primoz; Rosen, Paul; Wang, Bei; Chen, Guoning; Bhatia, Harsh; Pascucci, Valerio
2016-02-29
Vector field topology has been successfully applied to represent the structure of steady vector fields. Critical points, one of the essential components of vector field topology, play an important role in describing the complexity of the extracted structure. Simplifying vector fields via critical point cancellation has practical merit for interpreting the behaviors of complex vector fields such as turbulence. However, there is no effective technique that allows direct cancellation of critical points in 3D. This work fills this gap and introduces the first framework to directly cancel pairs or groups of 3D critical points in a hierarchical manner with a guaranteed minimum amount of perturbation based on their robustness, a quantitative measure of their stability. In addition, our framework does not require the extraction of the entire 3D topology, which contains non-trivial separation structures, and thus is computationally effective. Furthermore, our algorithm can remove critical points in any subregion of the domain whose degree is zero and handle complex boundary configurations, making it capable of addressing challenging scenarios that may not be resolved otherwise. We apply our method to synthetic and simulation datasets to demonstrate its effectiveness.
Hazard analysis and critical control point (HACCP) history and conceptual overview.
Hulebak, Karen L; Schlosser, Wayne
2002-06-01
The concept of Hazard Analysis and Critical Control Point (HACCP) is a system that enables the production of safe meat and poultry products through the thorough analysis of production processes, identification of all hazards that are likely to occur in the production establishment, the identification of critical points in the process at which these hazards may be introduced into product and therefore should be controlled, the establishment of critical limits for control at those points, the verification of these prescribed steps, and the methods by which the processing establishment and the regulatory authority can monitor how well process control through the HACCP plan is working. The history of the development of HACCP is reviewed, and examples of practical applications of HACCP are described.
Completely mixed state is a critical point for three-qubit entanglement
Energy Technology Data Exchange (ETDEWEB)
Tamaryan, Sayatnova, E-mail: sayat@mail.yerphi.am [Department of Theoretical Physics, A. Alikhanyan National Laboratory, Yerevan (Armenia)
2011-06-06
Pure three-qubit states have five algebraically independent and one algebraically dependent polynomial invariants under local unitary transformations and an arbitrary entanglement measure is a function of these six invariants. It is shown that if the reduced density operator of a some qubit is a multiple of the unit operator, than the geometric entanglement measure of the pure three-qubit state is absolutely independent of the polynomial invariants and is a constant for such tripartite states. Hence a one-particle completely mixed state is a critical point for the geometric measure of entanglement. -- Highlights: → Geometric measure of pure three-qubits is expressed in terms of polynomial invariants. → When one Bloch vector is zero the measure is independent of the remaining invariants. → Hence a one-particle completely mixed state is a critical point for the geometric measure. → The existence of the critical points is an inherent feature of the entanglement.
Determination of liquid-liquid critical point composition using 90∘ laser light scattering
Williamson, J. Charles; Brown, Allison M.; Helvie, Elise N.; Dean, Kevin M.
2016-04-01
Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90∘ light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90∘ light scattering are precise to the parts-per-thousand level and show long-term reproducibility.
Determination of liquid-liquid critical point composition using 90^{∘} laser light scattering.
Williamson, J Charles; Brown, Allison M; Helvie, Elise N; Dean, Kevin M
2016-04-01
Despite over a century of characterization efforts, liquid-liquid critical point compositions are difficult to identify with good accuracy. Reported values vary up to 10% for even well-studied systems. Here, a technique is presented for high-precision determination of the critical composition of a partially miscible binary liquid system. Ninety-degree laser light-scattering intensities from single-phase samples are analyzed using an equation derived from nonclassical power laws and the pseudospinodal approximation. Results are reported for four liquid-liquid systems (aniline + hexane, isobutyric acid + water, methanol + cyclohexane, and methanol + carbon disulfide). Compared to other methods, the 90^{∘} light-scattering approach has a strong dependence on composition near the critical point, is less affected by temperature fluctuations, and is insensitive to the presence of trace impurities in the samples. Critical compositions found with 90^{∘} light scattering are precise to the parts-per-thousand level and show long-term reproducibility.
Anomalous conductance of a strongly interacting Fermi gas through a quantum point contact
Liu, Boyang; Zhai, Hui; Zhang, Shizhong
2017-01-01
In this work we study the particle conductance of a strongly interacting Fermi gas through a quantum point contact. With an atom-molecule two-channel model, we compute the contribution to particle conductance by both the fermionic atoms and the bosonic molecules using the Keldysh formalism. Focusing on the regime above the Fermi superfluid transition temperature, we find that the fermionic contribution to the conductance is reduced by interaction compared with the quantized value for the noninteracting case; while the bosonic contribution to the conductance exhibits a plateau with nonuniversal values that is larger than the quantized conductance. This feature is particularly profound at temperature close to the superfluid transition. We emphasize that the enhanced conductance arises because of the bosonic nature of closed channel molecules and the low dimensionality of the quantum point contact.
Ortmann, Frank; Roche, Stephan
2013-02-22
We report on robust features of the longitudinal conductivity (σ(xx)) of the graphene zero-energy Landau level in the presence of disorder and varying magnetic fields. By mixing an Anderson disorder potential with a low density of sublattice impurities, the transition from metallic to insulating states is theoretically explored as a function of Landau-level splitting, using highly efficient real-space methods to compute the Kubo conductivities (both σ(xx) and Hall σ(xy)). As long as valley degeneracy is maintained, the obtained critical conductivity σ(xx) =/~ 1.4e(2)/h is robust upon an increase in disorder (by almost 1 order of magnitude) and magnetic fields ranging from about 2 to 200 T. When the sublattice symmetry is broken, σ(xx) eventually vanishes at the Dirac point owing to localization effects, whereas the critical conductivities of pseudospin-split states (dictating the width of a σ(xy) = 0 plateau) change to σ(xx) =/~ e(2)/h, regardless of the splitting strength, superimposed disorder, or magnetic strength. These findings point towards the nondissipative nature of the quantum Hall effect in disordered graphene in the presence of Landau level splitting.
Barlow, Nathaniel S; Schultz, Andrew J; Weinstein, Steven J; Kofke, David A
2015-08-21
The mathematical structure imposed by the thermodynamic critical point motivates an approximant that synthesizes two theoretically sound equations of state: the parametric and the virial. The former is constructed to describe the critical region, incorporating all scaling laws; the latter is an expansion about zero density, developed from molecular considerations. The approximant is shown to yield an equation of state capable of accurately describing properties over a large portion of the thermodynamic parameter space, far greater than that covered by each treatment alone.
Time-Averaged Behaviour at the Critical Parameter Point of Transition to Spatiotemporal Chaos
Institute of Scientific and Technical Information of China (English)
贺凯芬
2001-01-01
A time-averaged behaviour is found to be important for investigating the critical behaviour in parameter space for the transition from temporal chaos to spatiotemporal chaos by using an energy representation. Considering any wave solution as a superposition of the steady wave with its perturbation wave, we find that when approaching the critical parameter point the averaged positive interaction energy for the k = 1 mode becomes competitive with the negative one, with the summation displaying a scaling behaviour of power law.
Peltier Coefficient and Photon-Assisted Tunneling in Quantum Point Contact
Institute of Scientific and Technical Information of China (English)
Arafa H. Aly
2008-01-01
@@ We present the Peltier coefficient and thermal transport in quantum point contact (QPC), under the influence of external fields and different temperatures.Also we obtain the oscillations of the Peltier coeffffcient in external fields.Numerical calculations of the Peltier coefficient are performed at different applied voltages, amplitudes and temperatures.The obtained results are cons/stent with the experimental data in the literature.
Indian Academy of Sciences (India)
Ghasem A Afrouzi; Mohammad B Ghaemi; Shirin Mir
2015-11-01
A variety of three-critical-point theorems have been established for nonsmooth functionals, based on a minimax inequality. In this paper, a generalized form of a recent result due to Ricceri is introduced for non-smooth functionals and by a few hypotheses, without any minimax inequality, the existence of at least three critical points with a uniform bound on the norms of solutions, is obtained. Also, as an application, our main theorem is used to obtain at least three anti-periodic solutions for a second order differential inclusion.
Z(5): critical point symmetry for the prolate to oblate nuclear shape phase transition
Energy Technology Data Exchange (ETDEWEB)
Bonatsos, Dennis; Lenis, D.; Petrellis, D.; Terziev, P.A
2004-05-27
A critical point symmetry for the prolate to oblate shape phase transition is introduced, starting from the Bohr Hamiltonian and approximately separating variables for {gamma}=30 deg. Parameter-free (up to overall scale factors) predictions for spectra and B(E2) transition rates are found to be in good agreement with experimental data for {sup 194}Pt, which is supposed to be located very close to the prolate to oblate critical point, as well as for its neighbours ({sup 192}Pt, {sup 196}Pt)
Z(5): Critical point symmetry for the prolate to oblate nuclear shape phase transition
Bonatsos, D; Petrellis, D; Terziev, P A; Bonatsos, Dennis
2004-01-01
A critical point symmetry for the prolate to oblate shape phase transition is introduced, starting from the Bohr Hamiltonian and approximately separating variables for $\\gamma=30^{\\rm o}$. Parameter-free (up to overall scale factors) predictions for spectra and B(E2) transition rates are found to be in good agreement with experimental data for 194-Pt, which is supposed to be located very close to the prolate to oblate critical point, as well as for its neighbours (192-Pt, 196-Pt).
Anomalous waves in gas-liquid mixtures near gas critical point in Gardner equation approximation
Gasenko, V. G.
2016-10-01
The waves in a bubbled incompressible liquid with Van der Waals gas in a bubbles being near critical points is considered in a frame of Gardner equation. It is shown that both coefficients on quadratic and cubic nonlinear terms in Gardner equation change the sign near gas critical point and it results the anomalous waves: negative and limited solitons, kinks, antikinks and breathers. The dynamics and interactions of these waves was studied numerically by high accuracy Fourier methods with periodically boundary conditions. In particular it is revealed that limited solitons always arise from initial distribution with a few identical soliton's pair and stand stable in their form after numerous interactions.
Volume of supercooled water under pressure and the liquid-liquid critical point.
Mishima, Osamu
2010-10-14
The volume of water (H(2)O) was obtained at about 200-275 K and 40-400 MPa by using emulsified water. The plot of volume against temperature showed slightly concave-downward curvature at pressures higher than ≈200 MPa. This is compatible with the liquid-liquid critical-point hypothesis, but hardly with the singularity-free scenario. When the critical point is assumed to exist at ≈50 MPa and ≈223 K, the experimental volume and the derived compressibility are qualitatively described by the modified Fuentevilla-Anisimov scaling equation.
Recognition as a reference point for a concept of progress in critical theory
DEFF Research Database (Denmark)
Hansen, Ejvind
2009-01-01
Honneth’s reflections on the importance of recognitive structures still may be of value in critical discussions. Even though it may be granted that a certain notion of progress is inevitable in critical discussions, it does not follow that it has to be a robust notion. I suggest that recognitive...... structures may serve as a universal reference point that can be used to locate disagreement (recognitive structures are always at play), rather than a robust universal starting point that can be used solve disagreement (it is not given that we agree upon which recognitive structures should be furthered)....
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.
2016-07-01
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 used as fundamental building blocks for the realization of textbook many-body quantum models, illustrating key concepts such as quantum phase transitions, topological order or frustration as a function of system size. Here, we use low-temperature scanning tunnelling microscopy to construct arrays of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg chains in a transverse field, for which a quantum phase transition from an antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic limit. Site-resolved measurements on these finite-size realizations reveal a number of sudden ground state changes when the field approaches the critical value, each corresponding to a new domain wall entering the chains. We observe that these state crossings become closer for longer chains, suggesting the onset of critical behaviour. Our results present opportunities for further studies on quantum behaviour of many-body systems, as a function of their size and structural complexity.
Pasteurised milk and implementation of HACCP (Hazard Analysis Critical Control Point
Directory of Open Access Journals (Sweden)
T.B Murdiati
2004-10-01
Full Text Available The purpose of pasteurisation is to destroy pathogen bacteria without affecting the taste, flavor, and nutritional value. A study on the implementation of HACCP (Hazard Analysis Critical Control Point in producing pasteurized milk was carried out in four processing unit of pasteurised milk, one in Jakarta, two in Bandung and one in Bogor. The critical control points in the production line were identified. Milk samples were collected from the critical points and were analysed for the total number of microbes. Antibiotic residues were detected on raw milks. The study indicated that one unit in Bandung dan one unit in Jakarta produced pasteurized milk with lower number of microbes than the other units, due to better management and control applied along the chain of production. Penisilin residues was detected in raw milk used by unit in Bogor. Six critical points and the hazard might arise in those points were identified, as well as how to prevent the hazards. Quality assurance system such as HACCP would be able to produce high quality and safety of pasteurised milk, and should be implemented gradually.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-29
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}.
Noise levels at critical points in the municipality of Guadalajara, Jalisco, Mexico
Figueroa, Arturo; Garcia, Jesus; Macias, Jorge; Orozco, Martha; Garcia, Javier; Delgadillo, Alan
2002-11-01
Studies of acoustic conditions are planning tools on which we can diagnose the problem of noise pollution in the cities. The first study on noise pollution made in the city was made by the University of Guadalajara in 1995 and updated in 1998 covering with measuring points the city center. This paper discusses the problem of noise pollution by motor vehicles at critical points and covers a total of 105 points. The study also analyzes the problem of noise pollution base on the community annoyance from which a regulation policy should derive. Results of the study show that the most critical points are located within zone 1 (center) where Leq levels within the range of 70-85 dB were found. Such levels exceed by far the international standard of 65 dB as recommended for ambient noise by the World Health Organization.
Universal free-energy distribution in the critical point of a random Ising ferromagnet.
Dotsenko, Victor; Holovatch, Yurij
2014-11-01
We discuss the non-self-averaging phenomena in the critical point of weakly disordered Ising ferromagnet. In terms of the renormalized replica Ginzburg-Landau Hamiltonian in dimensions Dcritical free-energy fluctuations. In particular, using known fixed-point values for the renormalized coupling parameters, we obtain the universal curve for such PDF in the dimension D=3. It is demonstrated that this function is strongly asymmetric: its left tail is much slower than the right one.
Universal Organization of Resting Brain Activity at the Thermodynamic Critical Point
Yu, Shan; Shriki, Oren; Plenz, Dietmar
2013-01-01
Thermodynamic criticality describes emergent phenomena in a wide variety of complex systems. In the mammalian brain, the complex dynamics that spontaneously emerge from neuronal interactions have been characterized as neuronal avalanches, a form of critical branching dynamics. Here, we show that neuronal avalanches also reflect that the brain dynamics are organized close to a thermodynamic critical point. We recorded spontaneous cortical activity in monkeys and humans at rest using high-density intracranial microelectrode arrays and magnetoencephalography, respectively. By numerically changing a control parameter equivalent to thermodynamic temperature, we observed typical critical behavior in cortical activities near the actual physiological condition, including the phase transition of an order parameter, as well as the divergence of susceptibility and specific heat. Finite-size scaling of these quantities allowed us to derive robust critical exponents highly consistent across monkey and humans that uncover ...