Integer quantum hall effect

We study the quantum dynamics of a particle bound on a torus in the presence of an external magnetic field. We derive and discuss the effective Schrödinger equation for the surface eigenmodes and the corresponding quantum effective potential which is periodic and exhibits quantum anti-centrifugal force for nonvanishing angular momentum quantum numbers. An energy band structure of pure geometrical origin emerges naturally which can be tested experimentally in semiconducting as well as carbon nanotori.

Quantum Zakharov equations are obtained to describe the nonlinear interaction between quantum Langmuir waves and quantum ion-acoustic waves. These quantum Zakharov equations are applied to two model cases, namely the four-wave interaction and the decay instability. In the case of the four-wave instability, sufficiently large quantum effects tend to suppress the instability.

We investigate the formation of transverse patterns in a doubly resonant degenerate optical parametric oscillator. Extending previous work, we treat the more realistic case of a spherical mirror cavity with a finite-sized input pump field. Using numerical simulations in real space, we determine the conditions on the cavity geometry, pump size and detunings for which pattern formation occurs; we find multistability of different types of optical patterns. Below threshold, we analyze the dependence of the quantum image on the width of the input field, in the near and in the far field.

We suggest a procedure for calculating correlation functions of the local densities of states (DOS) at the plateau transitions in the integer quantum Hall effect (IQHE). We argue that their correlation functions are appropriately described in terms of the SL( )/SU(2) WZNW model (at the usual Kač–Moody point and with the level 6≤k≤8 ). In this model we have identified the operators corresponding to the local DOS, and derived the partial differential equation determining their correlation functions. The OPEs for powers of the local DOS obtained from this equation are in agreement with available results.

The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic

We have measured the current-voltage (I-V ) characteristics of small-capacitance single Josephson junctions at low temperatures (T = 0.02 − 0.6 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc superconducting quantum interference devices (SQUIDs). The single-junction I-V curve is sensitive to the impedance of the environment, which can be tuned in situ. We have observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance R ′ 0 of the SQUID arrays is much higher than the quantum resistance RK ≡ h/e 2 ≈ 26 kΩ. The negative differential resistance is evidence of the coherent single-Cooperpair tunneling within the theory of current-biased single Josephson junctions. Based on this theory, we have calculated the I-V curves numerically in order to compare them with the experimental ones at R ′ 0 ≫ RK . The numerical calculation agrees with the experiments qualitatively. We also discuss the R ′ 0 dependence of the single-Josephson-junction I-V curve in terms of the superconductorinsulator transition driven by changing the coupling to the environment.

Under strict neutrality conditions the number N e 0 of electrons in a 2DEG is constant at any perpendicular magnetic field B. Therefore, the standard explanation of the de Haas-van Alphen-(dHvA)-effect has to be modified. It is shown that the spin-dependent total energy of a 2DEG is at the origin of the dHvA-effect. The spin-polarization can show up at extreme conditions. Only when the effective g-factor g*=2 or 0 the resulting 1/B-periods are the same as earlier deduced from the orbital motion of the electrons. For all other g* the observed magnetizations have more complex 1/B-dependences. 1) Introduction In text books [1, 2] the de Haas-van Alphen-(dHvA)-effect is often introduced with the help of a 2-Dimensional Electron Gas (2DEG). The full three-dimensional solid has then to be considered as composed of a huge number of such 2DEG's (of the order of 10 7) with different values of discrete kz. This is justified by the physics of the dHvA which essentially takes place in a plane perpendicular to the external magnetic field B. In all textbooks [1-4], in Onsager's original paper [5], and in a book of reference [6] the explanation of the dHvA-effect relies dominantly on changing populations of the Landau-ensembles as a function of the magnetic field B. It is assumed that these changing populations are responsible for variations of the total energy TE of the electrons. Variations of the magnetization Me=−(1/V)dTE/dB are then described for the 2DEG(kz=0) and for the sum of all 2DEG(kz). It is, however, obvious that neutrality imposes the total number of electrons N e 0 in the 2DEG to stay constant for all magnetic fields. This situation has already been treated in chapter 2.3.3 of Ref.[6] as a digression from the above description. For N e 0(B)=const this digression will become the only contribution to Me while the above description has to be discarded. Unfortunately, this treatment was restricted to a spin g-factor of gs=2.00. It will be extended here to the general case of gs=|g*| with |g*|>0. The result will be compared to the spin-polarization of the Landau ensembles LE still under the condition of N e 0(B)=const. It turns out that every second spin-resolved LE creates a net spin-polarization of the 2DEG. It corresponds to a net magnetization Ms proportional to |g*|. The comparison between Me and Ms clearly establishes a dominance of Me over Ms. This improved approach considerably simplifies the explanation of the dHvA-effect.

We have developed a model of the high-current breakdown of the integer quantum Hall effect, as measured in contactless experiments using a highly-sensitive torsion balance magnetometer. The model predicts that, for empirically "low-mobility" samples ͑ Ͻ 75 m 2 V −1 s −1 ͒, the critical current for breakdown should decrease with, and have a linear dependence on, temperature. This prediction is verified experimentally with the addition of a low-temperature saturation of the critical current at a temperature that depends on both sample number density and filling factor. It is shown that this saturation is consistent with quasielastic inter-Landau-level scattering when the maximum electric field in the sample reaches a large enough value. In addition we show how this model can be extended to give qualitative agreement with experiments on high-mobility samples.

The nanocomposite energy applications for plasma reactor produced nanoparticles are reviewed. Nanoparticles are commonly defined as particles less than 100 nm in diameter. Due to this small size, nanoparticles have a high surface-to-volume ratio. This increases the surface energy compared to the bulk material. The high surface-to-volume ratio and size effects (quantum effects) give nanoparticles distinctive chemical, electronic, optical, magnetic and mechanical properties from those of the bulk material. Nanoparticles synthesis can be grouped into 3 broad approaches. The first one is wet phase synthesis (sol-gel processing), the second is mechanical attrition, and the third is gas-phase synthesis (aerosol). The properties of the final product may differ significantly depending on the fabrication route. Currently, there are no economical large-scale production processes for nanoparticles. This hinders the widespread applications of nanomaterials in products. The Idaho National Laboratory (INL) is engaging in research and development of advanced modular hybrid plasma reactors for low cost production of nanoparticles that is predicted to accelerate application research and enable the formation of technology innovation alliances that will result in the commercial production of nanocomposites for alternative energy production devices such as fuel cells, photovoltaics and electrochemical double layer capacitors.

This Chapter deals with theoretical developments in the subject of quantum information and quantum computation, and includes an overview of classical information and some relevant quantum mechanics. The discussion covers topics in quantum communication, quantum cryptography, and quantum computation, and concludes by considering whether a perspective in terms of quantum information sheds new light on the conceptual problems of quantum mechanics.

Richard Feynman's observation that quantum mechanical effects could not be simulated efficiently on a computer led to speculation that computation in general could be done more efficiently if it used quantum effects. This speculation appeared justified when Peter Shor described a polynomial time quantum algorithm for factoring integers. In quantum systems, the computational space increases exponentially with the size of

An overview of the random network model invented by Chalker and Coddington, and its generalizations, is provided. After a short introduction into the physics of the Integer Quantum Hall Effect, which historically has been the motivation for introducing the network model, the percolation model for electrons in spatial dimension 2 in a strong perpendicular magnetic field and a spatially correlated random potential is described. Based on this, the network model is established, using the concepts of percolating probability amplitude and tunneling. Its localization properties and its behavior at the critical point are discussed including a short survey on the statistics of energy levels and wave function amplitudes. Magneto-transport is reviewed with emphasis on some new results on conductance distributions. Generalizations are performed by establishing equivalent Hamiltonians. In particular, the significance of mappings to the Dirac model and the two dimensional Ising model are discussed. A description of renormalization group treatments is given. The classification of two dimensional random systems according to their symmetries is outlined. This provides access to the complete set of quantum phase transitions like the thermal Hall transition and the spin quantum Hall transition in two dimension. The supersymmetric effective field theory for the critical properties of network models is formulated. The network model is extended to higher dimensions including remarks on the chiral metal phase at the surface of a multi-layer quantum Hall system.

Stochastic semiclassical gravity of the 90's is a theory naturally evolved from semiclassical gravity of the 80's and quantum field theory in curved spacetimes of the 70's. Whereas semiclassical gravity is based on the semiclassical Einstein equation with sources given by the expectation value of the stress-energy tensor of quantum fields, stochastic semiclassical gravity is based on the Einstein-Langevin equation, which has in addition sources due to the noise kernel. The noise kernel is the vacuum expectation value of the (operator-valued) stress-energy bi-tensor which describes the fluctuations of quantum matter fields in curved spacetimes. A new criterion for the validity of semiclassical gravity may also be formulated from the viewpoint of this theory. In the first part, we describe the fundamentals of this new theory via two approaches: the axiomatic and the functional. The axiomatic approach is useful to see the structure of the theory from the framework of semiclassical gravity, showing the link from the mean value of the stress-energy tensor to their correlation functions. The functional approach uses the Feynman-Vernon influence functional and the Schwinger-Keldysh closed-time-path effective action methods which are convenient for computations. It also brings out the open systems concepts and the statistical and stochastic contents of the theory such as dissipation, fluctuations, noise and decoherence. We then focus on the properties of the stress energy bi-tensor. We obtain a general expression for the noise kernel of a quantum field defined at two distinct points in an arbitrary curved spacetime as products of covariant derivatives of the quantum field's Green function, and show from this that the trace anomaly of the noise kernel is zero for massless conformal scalar fields. In the second part, we describe three applications of stochastic gravity theory. First, we consider metric perturbations in a Minkowski spacetime. We offer an analytical solution of the Einstein-Langevin equation and compute the two-point correlation functions for the linearized Einstein tensor and for the metric perturbations. We also prove that Minkowski spacetime is a stable solution of semiclassical gravity. Second, we discuss structure formation from the

This review summarizes and amplifies on recent investigations of coupled quantum dynamical systems with few degrees of freedom in the short wavelength, semiclassical limit. Focusing on the correspondence between quantum and classical physics, we mathematically formulate and attempt to answer three fundamental questions: (i) How can one drive a small dynamical quantum system to behave classically ? (ii) What determines the rate at which two single-particle quantummechanical subsystems become entangled when they interact ? (iii) How does irreversibility occur in quantum systems with few degrees of freedom ? These three questions are posed in the context of the quantum-classical correspondence for dynamical systems with few degrees of freedom, and we accordingly rely on two short-wavelength approximations to quantum mechanics to answer them -the trajectory-based semiclassical approach on one hand, and random matrix theory on the other hand. We construct novel investigative procedures towards decoherence and the emergence of classicality out of quantumness in dynamical systems coupled to external degrees of freedom. In particular we show how dynamical properties of chaotic classical systems, such as local exponential instability in phase-space, also affects their quantum counterpart. For instance, it is often the case that the fidelity with which a quantum state is reconstructed after an imperfect time-reversal operation decays with the Lyapunov exponent of the corresponding classical dynamics. For not unrelated reasons, but perhaps more surprisingly, the rate at which two interacting quantum subsystems become entangled can also be governed by the subsystem's Lyapunov exponents. Our method allows at each stage in our investigations to differentiate quantum coherent effects -those related to phase interferences -from classical ones -those related to the necessarily extended envelope of quantal wavefunctions. This makes it clear that all occurences of Lyapunov exponents we witness have a classical origin, though they require rather strong decoherence effects to be observed. We extensively rely on numerical experiments to illustrate our findings and briefly comment on possible extensions to more complex problems involving environments with many interacting dynamical systems, going beyond the uncoupled harmonic oscillators model of Caldeira and Leggett.

In this paper, we present a FinFET compact model and its associated parameter extraction methodology. This explicit model accounts for all major small geometry effects and allows accurate simulations of both n- and p-type FinFETs. The model core is physics-based (long-channel model) and some semiempirical corrections are introduced in order to accurately simulate the behavior of ultrashort (L = 25 nm) and ultrathin (WSi = 3 nm) FinFETs. The parameter extraction relies on a software suite allowing an automatic parameter extraction. In this work, the development of our parameter extraction procedure is based on 3-D simulation results. The optimization of parameters related to quantum effects, short-channel effects and channel length modulation illustrates the methodology of parameter extraction. Finally, we compare the FinFET characteristics (drain current and small signal parameters) obtained by our explicit compact model with 3-D numerical simulations for different Fin widths and ch...

Technological computation is entering the quantum realm, focusing attention on biomolecular information processing systems such as proteins, as presaged by the work of Michael Conrad. Protein conformational dynamics and pharmacological evidence suggest that protein conformational states-fundamental information units ('bits') in biological systems-are governed by quantum events, and are thus perhaps akin to quantum bits ('qubits') as utilized in quantum computation. 'Real time' dynamic activities within cells are regulated by the cell cytoskeleton, particularly microtubules (MTs) which are cylindrical lattice polymers of the protein tubulin. Recent evidence shows signaling, communication and conductivity in MTs, and theoretical models have predicted both classical and quantum information processing in MTs. In this paper we show conduction pathways for electron mobility and possible quantum tunneling and superconductivity among aromatic amino acids in tubulins. The pathways within tubulin match helical patterns in the microtubule lattice structure, which lend themselves to topological quantum effects resistant to decoherence. The Penrose-Hameroff 'Orch OR' model of consciousness is reviewed as an example of the possible utility of quantum computation in MTs.

a b s t r a c t MOS devices go 3D, new quantum effect devices appear in the research labs. This paper discusses the impact of various innovative device architectures on circuit design. Examples of circuits with FinFETs or Multi-Gate-FETs are shown and their performance is compared with classically scaled CMOS circuits both for digital and analog applications. As an example for novel quantum effect devices beyond CMOS we discuss circuits with Tunneling Field Effect Transistors and their combination with classical MOSFETs and MuGFETs. Finally the potential of more substantial paradigm changes in circuit design will be exploited for the example of magnetic quantum cellular automata using a novel integrated magnetic field clocking scheme.

We describe quantum Monte Carlo methods for simulating quantum systems. These techniques are particularly well-suited for nanomaterials where quantum effects often fall outside conventional approaches. We review recent applications to quantum dots, buckyballs, and superfluid helium nanoclusters. (For Handbook of Computational Nanotechnology Encyclopedia of Nanoscience and Nanotechnology)

We give an overview of the Integer Quantum Hall Effect. We propose a mathematical framework using Non-Commutative Geometry as defined by A. Connes. Within this framework, it is proved that the Hall conductivity is quantized and that plateaux occur when the Fermi energy varies in a region of localized states. PACS numbers: 73.40.Hm, 02.30.Wd, 72.15.Rn This article will appear in the October 94 special issue of the Journal of Mathematical Physics.

The pressure of fundamental limits on classical computation and the promise of exponential speedups from quantum effects have recently brought quantum circuits [10] to the attention of the Electronic Design Automation community . We discuss efficient quantum logic circuits which perform two tasks: (i) implementing generic quantum computations and (ii) initializing quantum registers. In contrast to conventional computing, the latter task is nontrivial because the state-space of an n-qubit register is not finite and contains exponential superpositions of classical bit strings. Our proposed circuits are asymptotically optimal for respective tasks and improve earlier published results by at least a factor of two.

The search for experimental demonstrations of the quantum behavior of macroscopic mechanical resonators is a fastly growing field of investigation and recent results suggest that the generation of quantum states of resonators with a mass at the microgram scale is within reach. In this chapter we give an overview of two important topics within this research field: cooling to the motional ground state, and the generation of entanglement involving mechanical, optical and atomic degrees of freedom. We focus on optomechanical systems where the resonator is coupled to one or more driven cavity modes by the radiation pressure interaction. We show that robust stationary entanglement between the mechanical resonator and the output fields of the cavity can be generated, and that this entanglement can be transferred to atomic ensembles placed within the cavity. These results show that optomechanical devices are interesting candidates for the realization of quantum memories and interfaces for continuous variable quantum communication networks.

We utilized a fully self-consistent quantum mechanical simulator based on the Contact Block Reduction (CBR) method to optimize a 10 nm FinFET device and meet the International Technology Roadmap for Semiconductors (ITRS) projections for double-gate high-performance logic technology devices. We found that the device ON-current approaching the value projected by the ITRS can be obtained using a conventional unstrained Si channel and a SiO 2 gate insulator. We also performed a detailed analysis of the gate leakage under different bias conditions. Our simulation results show that the quantum mechanical effects significantly enhance the intrinsic switching speed of the device. In our simulations, quantum confinement in both the gates and the channel has been taken into account self-consistently. The obtained theoretical value of the intrinsic switching speed for the considered FinFET device exceeds the ITRS-projected value.

The simple preparation of Co 3 O 4 nanoparticles from a solid organometallic molecular precursor N-N 0bis(salicylaldehyde)-1,2-phenylenediimino cobalt(II); Co(salophen) has been achieved via two simple steps: firstly, the Co(salophen) precursor was precipitated from the reaction of cobalt(II) acetate and N-N 0 -bis(salicylaldehyde)-1,2-phenylenediimino; H 2 salophen; in propanol under nitrogen condition; then, cubic phase Co 3 O 4 nanoparticles with the size of mostly 30-50 nm could be produced by thermal treatment of the Co(salophen) in air at 773 K for 5 h. The as-synthesized products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electronic microscopy (SEM). These results confirm that the resulting oxide was pure single-crystalline Co 3 O 4 nanoparticles. The optical property test indicates that the absorption peak of the nanoparticles shifts towards short wavelength, and the blue shift phenomenon might be ascribed to the quantum effect. The hysteresis loops of the obtained samples reveal the ferromagnetic behaviors the enhanced coercivity (H c ) and decreased saturation magnetization (M s ) in contrast to their respective bulk materials.

Quantum walks on the line with a single particle possess a classical analog. Involving more walkers opens up the possibility to study collective quantum effects, such as many particle correlations. In this context, entangled initial states and indistinguishability of the particles play a role. We consider directional correlations between two particles performing a quantum walk on a line. For non-interacting particles we find analytic asymptotic expressions and give the limits of directional correlations. We show that introducing δ-interaction between the particles, one can exceed the limits for non-interacting particles.

Standard lore asserts that quantum effects generically forbid the occurrence of light (non-pseudo-Goldstone) scalars having masses smaller than the Kaluza Klein scale, M KK , in extra-dimensional models, or the gravitino mass, M 3/2, in supersymmetric situations. We argue that a hidden assumption underlies this lore: that the scale of gravitational physics, M g , (e.g the string scale, M s , in string theory) is of order the Planck mass, \( {M_p} = \sqrt {{8\pi G}} \simeq {10^{18}} \) GeV. We explore sensitivity to this assumption using the spectrum of masses arising within the specific framework of large-volume string compactifications, for which the ultraviolet completion at the gravity scale is explicitly known to be a Type IIB string theory. In such models the separation between M g and M p is parameterized by the (large) size of the extra dimensional volume, \( \mathcal{V} \) (in string units), according to M p : M g : M KK : M 3/2 ∝ 1: \( {\mathcal{V}^{ - {{1} \left/ {2} \right.}}}:{\mathcal{V}^{ - {{2} \left/ {3} \right.}}}:{\mathcal{V}^{ - 1}} \) . We find that the generic size of quantum corrections to masses is of the order of M KK M 3/2/M p ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{5} \left/ {3} \right.}}}}} \right.} \) . The mass of the lighest modulus (corresponding to the extra-dimensional volume) which at the classical level is M V ≃ \( {{{{M_p}}} \left/ {{{\mathcal{V}^{{{3} \left/ {2} \right.}}}}} \right.} \) ≪M 3/2 ≪M KK is thus stable against quantum corrections. This is possible because the couplings of this modulus to other forms of matter in the low-energy theory are generically weaker than gravitational strength (something that is also usually thought not to occur according to standard lore). We discuss some phenomenological and cosmological implications of this observation.

. In this paper, we explore the theory of the equation of state from the view point of Ihm-Song-Mason ISM equation of state, which has been derived on the basis of statistical mechanical perturbation theory, and is characterized by three temperature dependent parameters, a , b, B , and a free parameter G . This equation is 2 applied well to non-polar fluids in subcritical and supercritical regions and to molten alkali metals. We present results that show G varies slightly with temperature. Among the nobles group, G values are quite the same and are correlated except He, which deviates so much even no moderate correlation is seen. In the alkali metals group, G values are roughly the same for K, Rb, and Cs but are different for Li and Na. We have previously shown that G conforms to B , the second virial coefficient, and thus to the nature of the particular fluid system. 2 These observations plus the discussion on quantum mechanical law of corresponding states suggest that the ISM equation of state stands as an analytical equation of state which explicitly incorporates quantum effects by the U U Ž U U . parameter G . Then, we suggest a law of corresponding states as p s p Õ , T , G where, asterisks stand for reduced pressure, volume, and temperature, respectively. q

We report periodic spin-polarized density functional theory (DFT) predictions of hydrogen adsorption, absorption, dissolution, and diffusion energetics on and in ferromagnetic (FM) body-centered cubic (bcc) iron. We find that H prefers to stay on the Fe surface instead of subsurfaces or in bulk. Hydrogen dissolution in bulk Fe is predicted to be endothermic, with hydrogen occupying tetrahedral (t) sites over a wide range of concentrations. This is consistent with the known low solubility of H in pure Fe. In the initial absorption step, we predict that H occupies the deep subsurface t-site for Fe(110) and the shallow subsurface t-site for Fe(100). Diffusion of H into Fe subsurfaces is predicted to have a much lower barrier for Fe(100) than Fe(110). For H diffusion in bulk Fe, we find that H diffuses through bcc Fe not via a straight line trajectory, but rather hops from one t-site to a neighboring t-site by a curved path. Moreover, we exclude a previously suggested path via the octahedral site, due to its higher barrier and the rank of the saddle point. Quantum effects on H diffusion through bulk Fe are discussed.

We study the Einstein relation for the diffusivity to mobility ratio ͑DMR͒ in quantum wires ͑QWs͒ of III-V, ternary, and quaternary materials in the presence of light waves, whose unperturbed energy band structures are defined by the three band model of Kane. It has been found, taking n-InAs, n-InSb, n-Hg 1−x Cd x Te, n-In 1−x Ga x As y P 1−y lattice matched to InP as examples, that the respective DMRs exhibit decreasing quantum step dependence with the increasing film thickness, decreasing electron statistics, increasing light intensity and wavelength, with different numerical values. The nature of the variations is totally band structure dependent and is influenced by the presence of the different energy band constants. The strong dependence of the DMR on both the light intensity and the wavelength reflects the direct signature of the light waves which is in contrast as compared to the corresponding QWs of the said materials in the absence of photoexcitation. The classical equation of the DMR in the absence of any field has been obtained as a special case of the present analysis under certain limiting conditions and this is the indirect test of the generalized formalism. We have suggested an experimental method of determining the DMR in QWs of degenerate materials having arbitrary dispersion laws and our results find six applications in the field of quantum effect devices. Downloaded 15 Sep 2010 to 131.180.130.114. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 094314-2 Ghatak et al. J. Appl. Phys. 103, 094314 ͑2008͒ Downloaded 15 Sep 2010 to 131.180.130.114. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions

In this chapter, we present the capabilities of the VHDL-AMS hardware description language for developing compact models. After a brief description of the VHDL-AMS language, we present two meaningful case studies on design oriented models of MOSFET.

There have been lots of interest in pyrochlore Iridates A2Ir2O7 where both strong spin-orbital coupling and strong correlation are present. A recent LDA calculation 1 suggests that the system is likely in a novel three dimensional topological semi-metallic phase: a Weyl semi-metal. Such a system has zero carrier density and arrives at the quantum limit even in a weak magnetic field. In this paper we discuss two novel quantum effects of this system in a magnetic field: a pressure-induced anomalous Hall effect and a magnetic field induced charge density wave at the pinned wavevector connecting Weyl nodes with opposite chiralities. A general formula of the anomalous hall coefficients in a Weyl semi-metal is also given. Both proposed effects can be probed by experiments in the near future, and can be used to detect the Weyl semi-metal phase.

The idea that quantum-mechanical phenomena can play nontrivial roles in biology has fascinated researchers for a century. Here we review some examples of such effects, including light-harvesting in photosynthesis, vision, electron-and proton-tunneling, olfactory sensing, and magnetoreception. We examine how experimental tests have aided this field in recent years and discuss the importance of developing new experimental probes for future work. We examine areas that should be the focus of future studies and touch on questions such as biological relevance of quantum-mechanical processes. To exemplify current research directions, we provide some detailed discussions of quantum-coherence in photosynthetic light-harvesting and highlight the crucial interplay between experiment and theory that has provided leaps in our understanding. We address questions about why coherence matters, what it is, how it can be identified, and how we should think about optimization of light-harvesting and the role coherence plays.

Graphene has a multitude of striking properties that make it an exceedingly attractive material for various applications, many of which will emerge over the next decade. However, one of the most promising applications lie in exploiting its peculiar electronic properties which are governed by its electrons obeying a Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff))

Based on a true phase space probability distribution function and an ensemble averaging procedure we have recently developed [Phys. Rev. E 65, 021109 (2002)] a non-Markovian quantum Kramers' equation to derive the quantum rate coefficient for barrier crossing due to thermal activation and tunneling in the intermediate to strong friction regime. We complement and extend this approach to weak friction regime to derive quantum Kramers' equation in energy space and the rate of decay from a metastable well. The theory is valid for arbitrary temperature and noise correlation. We show that depending on the nature of the potential there may be a net reduction of the total quantum rate below its corresponding classical value which is in conformity with earlier observation. The method is independent of path integral approaches and takes care of quantum effects to all orders.

A threshold condition different from the classical one is proposed for MOSFET with quantum effects, and is based on self-consistent numerical solution of the Schrödinger’s and Poisson’s equations. Furthermore, an accurate 1D threshold-voltage model including polysilicon-depletion effects is built by experimental fitting. Simulated results exhibit good agreement with measurement data. Based on this 1D model, a 2D quantum-modified threshold-voltage model for small MOSFET is developed by solving the quasi-2D Poisson’s equation and taking short-channel effects and quantum-mechanical effects into consideration. The model can also be used for deep-submicron MOSFET with high-k gate-dielectric and reasonable design of device parameters.

By amplifying photonic qubits it is possible to produce states that contain enough photons to be seen with the human eye, potentially bringing quantum effects to macroscopic scales []. In this paper we theoretically study quantum states obtained by amplifying one side of an entangled photon pair with different types of optical cloning machines for photonic qubits. We propose a detection scheme that involves lossy threshold detectors (such as the human eye) on the amplified side and conventional photon detectors on the other side. We show that correlations obtained with such coarse-grained measurements prove the entanglement of the initial photon pair and do not prove the entanglement of the amplified state. We emphasize the importance of the detection loophole in Bell violation experiments by giving a simple preparation technique for separable states that violate a Bell inequality without closing this loophole. Finally, we analyze the genuine entanglement of the amplified states and...

When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron-hole degeneracy and vanishing carrier mass near the point of charge neutrality 1,2 . Indeed, a distinctive half-integer quantum Hall effect has been predicted 3-5 theoretically, as has the existence of a non-zero Berry's phase (a geometric quantum phase) of the electron wavefunction-a consequence of the exceptional topology of the graphene band structure 6,7 . Recent advances in micromechanical extraction and fabrication techniques for graphite structures 8-12 now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of magneto-transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual halfinteger quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.

The Cornwall-Jackiw-Tomboulis (CJT) effective action for composite operators at finite temperature is used to investigate the chiral phase transition within the framework of the linear sigma model as the low-energy effective model of quantum chromodynamics (QCD). A new renormalization prescription for the CJT effective action in the Hartree-Fock (HF) approximation is proposed. A numerical study, which incorporates both thermal and quantum effect, shows that in this approximation the phase transition is of first order. However, taking into account the higher-loop diagrams contribution the order of phase transition is unchanged.

Evidence for signaling, communication, and conductivity in microtubules (MTs) has been shown through both direct and indirect means, and theoretical models predict their potential use in both classical and quantum information processing in neurons. The notion of quantum information processing within neurons has been implicated in the phenomena of consciousness, although controversies have arisen in regards to adverse physiological temperature effects on these capabilities. To investigate the possibility of quantum processes in relation to information processing in MTs, a biophysical MT model is used based on the electrostatic interior of the tubulin protein. The interior is taken to constitute a double-well potential structure within which a mobile electron is considered capable of occupying at least two distinct quantum states. These excitonic states together with MT lattice vibrations determine the state space of individual tubulin dimers within the MT lattice. Tubulin dimers are taken as quantum well structures containing an electron that can exist in either its ground state or first excited state. Following previous models involving the mechanisms of exciton energy propagation, we estimate the strength of exciton and phonon interactions and their effect on the formation and dynamics of coherent exciton domains within MTs. Also, estimates of energy and timescales for excitons, phonons, their interactions, and thermal effects are presented. Our conclusions cast doubt on the possibility of sufficiently long-lived coherent exciton/phonon structures existing at physiological temperatures in the absence of thermal isolation mechanisms. These results are discussed in comparison with previous models based on quantum effects in non-polar hydrophobic regions, which have yet to be disproved.

A new analytical model is presented for the inversion charge of surrounding-gate transistors (SGTs). Quantum effects are taken into account by means of a modified capacitance model that includes the inversion charge centroid and a correction to the threshold voltage. A drain current model for the SGT that includes velocity saturation, short channel, and velocity overshoot effects is also developed. The model accurately reproduces both simulated and experimental results for different silicon core radii and gate voltages.

Spintronics is a new branch of electronics based on purely quantum effects. Instead of carrier charge transfer, as in usual electronics, it evokes carrier's spin transfer. The search of new materials suitable for injecting and transferring carriers with a preferential spin orientation is of paramount importance for the development of spintronics. Here we report a ®rst experimental evidence of room temperature direct spin polarized injection in sexithienyl (T 6 ), a prototypical organic semiconductor, from colossal magnetoresistance manganite La 0.7 Sr 0.3 MnO 3 (LSMO). A strong magnetoresistance (up to 30%) was measured on nanostructured planar hybrid junctions LSMO/T 6 /LSMO. The spin diffusion length in T 6 is about 200 nm at room temperature. The results are discussed taking into account possible spin-¯ip mechanisms in organic material and interface effects. q

A direct comparison of quantum and classical dynamical systems can be accomplished through the use of distribution functions. This is useful for both fundamental investigations such as the nature of the quantum-classical transition as well as for applications such as quantum feedback control. By affording a clear separation between kinematical and dynamical quantum effects, the Wigner distribution is particularly valuable in this regard. Here we discuss some consequences of the fact that when closed-system classical and quantum dynamics are treated in Gaussian approximation, they are in fact identical. Thus, it follows that several results in the so-called `semiquantum' chaos actually arise from approximating the classical, and not the quantum dynamics. (Similarly, opposing claims of quantum suppression of chaos are also suspect.) As a simple byproduct of the analysis we are able to show how the Lyapunov exponent appears in the language of phase space distributions in a way that clearly underlines the difference between quantum and classical dynamical situations. We also informally discuss some aspects of approximations that go beyond the Gaussian approximation, such as the issue of when quantum nonlinear dynamical corrections become important compared to nonlinear classical corrections.