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Showing papers in "EPL in 2003"


Journal ArticleDOI
01 Feb 2003-EPL
TL;DR: In this paper, the authors show that the rate at which nodes acquire links depends on the node's degree, offering direct quantitative support for the presence of preferential attachment, which is a key ingredient of many current models proposed to capture the topological evolution of complex networks.
Abstract: A key ingredient of many current models proposed to capture the topological evolution of complex networks is the hypothesis that highly connected nodes increase their connectivity faster than their less connected peers, a phenomenon called preferential attachment Measurements on four networks, namely the science citation network, Internet, actor collaboration and science coauthorship network indicate that the rate at which nodes acquire links depends on the node's degree, offering direct quantitative support for the presence of preferential attachment We find that for the first two systems the attachment rate depends linearly on the node degree, while for the last two the dependence follows a sublinear power law

572 citations


Journal ArticleDOI
01 Feb 2003-EPL
TL;DR: In this article, the authors analyzed daily prices of 29 commodities and 2449 stocks over a period of ≈ 15 years and found that the price fluctuations for commodities have a significantly broader multifractal spectrum than for stocks.
Abstract: We analyze daily prices of 29 commodities and 2449 stocks, each over a period of ≈ 15 years. We find that the price fluctuations for commodities have a significantly broader multifractal spectrum than for stocks. We also propose that multifractal properties of both stocks and commodities can be attributed mainly to the broad probability distribution of price fluctuations and secondarily to their temporal organization. Furthermore, we propose that, for commodities, stronger higher-order correlations in price fluctuations result in broader multifractal spectra.

322 citations


Journal ArticleDOI
01 Jan 2003-EPL
TL;DR: In this paper, the 3.5 eV nuclear transition in isolated atoms was detected using a double-resonance method by probing the hyperfine structure of a transition in the electron shell, and it was shown that the frequency of the nuclear transition is independent of external magnetic fields to first order and of electric fields to second order.
Abstract: We propose high-resolution laser spectroscopy of the 3.5 eV nuclear transition in Th-229 in isolated atoms. Laser excitation of the nucleus can be detected efficiently in a double-resonance method by probing the hyperfine structure of a transition in the electron shell. It is shown that for a suitably chosen electronic level, the frequency of the nuclear transition is independent of external magnetic fields to first order and of electric fields to second order. This makes Th-229 a possible reference for an optical clock of very high accuracy. The nuclear-electronic double-resonance method can be conveniently applied to a laser-cooled ion of 229Th3+ in a radiofrequency trap. Further applications of nuclear laser spectroscopy are discussed.

291 citations


Journal ArticleDOI
01 Feb 2003-EPL
TL;DR: In this article, the Curie temperatures of the diluted magnetic semiconductors (Ga, Mn)As, Ga, Cr)As and Cr)N are evaluated from first principles.
Abstract: Curie temperatures of the diluted magnetic semiconductors (Ga, Mn)As, (Ga, Mn)N, (Ga, Cr)As and (Ga, Cr)N are evaluated from first principles. The electronic structure is calculated in the local spin density approximation by using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation to describe the substitutional and spin disorder. From the total energy differences between the ferromagnetic state and the spin-glass state, realistic estimations of Curie temperatures are achieved by using a mapping on the Heisenberg model in the mean-field approximation. Effects of additional carrier doping treatments are also investigated. Very large Curie temperatures are obtained, lying above room temperature for (Ga, Mn)N, (Ga, Cr)As and (Ga, Cr)N. Upon hole doping the Curie temperature of (Ga, Mn)N further increases, while (Ga, Mn)As shows a plateau behavior.

287 citations


Journal ArticleDOI
01 Apr 2003-EPL
TL;DR: In this paper, the equations of motion for the coupled dynamics of order parameter and concentration for the nematic phase of driven particles on a solid surface were constructed, and they imply giant number fluctuations with a standard deviation proportional to the mean in dimension d = 2 of primary relevance to experiment, and long time tails in the autocorrelation of the particle velocities despite the absence of a hydrodynamic velocity field.
Abstract: We construct the equations of motion for the coupled dynamics of order parameter and concentration for the nematic phase of driven particles on a solid surface, and show that they imply i) giant number fluctuations, with a standard deviation proportional to the mean in dimension d = 2 of primary relevance to experiment, and ii) long-time tails $\sim t^{-d/2}$in the autocorrelation of the particle velocities despite the absence of a hydrodynamic velocity field. Our predictions can be tested in experiments on aggregates of amoeboid cells as well as on layers of agitated granular matter.

281 citations


Journal ArticleDOI
01 Apr 2003-EPL
TL;DR: In this paper, scaling arguments are used to predict the maximal deformation and contact time of a water drop when it is thrown on a super-hydrophobic substrate, and this approach is completed by a model describing the flow inside the drop.
Abstract: It has been shown that a water drop can bounce persistently, when thrown on a super-hydrophobic substrate. We present here scaling arguments which allow us to predict the maximal deformation and the contact time of the drop. This approach is completed by a model describing the flow inside the drop, and by original experimental data.

262 citations


Journal ArticleDOI
01 Sep 2003-EPL
TL;DR: In this article, minimal discrete models of the Boltzmann equation consistent with equilibrium thermodynamics are derived, which recover correct hydrodynamics in arbitrary dimensions, and a new discrete velocity model is proposed for the simulation of the Navier-Stokes-Fourier equation and is tested in the setup of Taylor vortex flow.
Abstract: We derive minimal discrete models of the Boltzmann equation consistent with equilibrium thermodynamics, and which recover correct hydrodynamics in arbitrary dimensions. A new discrete velocity model is proposed for the simulation of the Navier-Stokes-Fourier equation and is tested in the setup of Taylor vortex flow. A simple analytical procedure for constructing the equilibrium for thermal hydrodynamics is established. For the lattice Boltzmann method of isothermal hydrodynamics, the explicit analytical form of the equilibrium distribution is presented. This results in an entropic version of the isothermal lattice Boltzmann method with the simplicity and computational efficiency of the standard lattice Boltzmann model.

247 citations


Journal ArticleDOI
01 Jul 2003-EPL
TL;DR: It is shown that the voter model on small-world networks does not display the emergence of complete order in the thermodynamic limit, and the nontrivial connectivity pattern leads to the counterintuitive conclusion that long-range connections inhibit the ordering process.
Abstract: We investigate how the topology of small-world networks affects the dynamics of the voter model for opinion formation. We show that, contrary to what occurs on regular topologies with local interactions, the voter model on small-world networks does not display the emergence of complete order in the thermodynamic limit. The system settles in a stationary state with coexisting opinions whose lifetime diverges with the system size. Hence the nontrivial connectivity pattern leads to the counterintuitive conclusion that long-range connections inhibit the ordering process. However, for networks of finite size, for which full uniformity is reached, the ordering process takes a time shorter than on a regular lattice of the same size.

234 citations


Journal ArticleDOI
01 Sep 2003-EPL
TL;DR: The existence of stable solitons in two-dimensional and three-dimensional media governed by the self-focusing cubic nonlinear Schrodinger equation with a periodic potential is demonstrated by means of the variational approximation (VA) and in direct simulations as discussed by the authors.
Abstract: The existence of stable solitons in two- and three-dimensional (2D and 3D) media governed by the self-focusing cubic nonlinear Schrodinger equation with a periodic potential is demonstrated by means of the variational approximation (VA) and in direct simulations. The potential stabilizes the solitons against collapse. Direct physical realizations are a Bose-Einstein condensate (BEC) trapped in an optical lattice, and a light beam in a bulk Kerr medium of a photonic-crystal type. In the 2D case, the creation of the soliton in a weak lattice potential is possible if the norm of the field (number of atoms in BEC, or optical power in the Kerr medium) exceeds a threshold value (which is smaller than the critical norm leading to collapse). Both single-cell and multi-cell solitons are found, which occupy, respectively, one or several cells of the periodic potential, depending on the soliton's norm. Solitons of the former type and their stability are well predicted by VA. Stable 2D vortex solitons are found too.

223 citations


Journal ArticleDOI
01 Dec 2003-EPL
TL;DR: In this paper, the authors demonstrate the large electromechanical response in nematic liquid-crystalline elastomers filled with a very low ( ~ 0.01%) concentration of carbon nanotubes, aligned along the nematic director at preparation.
Abstract: We demonstrate, for the first time, the large electromechanical response in nematic liquid-crystalline elastomers filled with a very low ( ~ 0.01%) concentration of carbon nanotubes, aligned along the nematic director at preparation. The nanotubes create a very large effective dielectric anisotropy of the composite. Their local field-induced torque is transmitted to the rubber elastic network and is registered as the exerted uniaxial stress of order ~ 1 kPa in response to a constant field of order ~ 1 MV/m. We investigate the dependence of the effect on field strength, nanotube concentration and reproducibility under multiple field-on and -off cycles. The results indicate the potential of the nanotube-nematic elastomer composites as electrically driven actuators.

181 citations


Journal ArticleDOI
01 Apr 2003-EPL
TL;DR: A critical traffic load is found above which the probability of massive traffic congestions destroying the network communication capabilities is finite.
Abstract: We study the tolerance to congestion failures in communication networks with scale-free topology. The traffic load carried by each damaged element in the network must be partly or totally redistributed among the remaining elements. Overloaded elements might fail on their turn, triggering the occurrence of failure cascades able to isolate large parts of the network. We find a critical traffic load above which the probability of massive traffic congestions destroying the network communication capabilities is finite.

Journal ArticleDOI
01 Oct 2003-EPL
TL;DR: In this article, the authors showed that the temperature dependence of the modulus of filled elastomers can be explained by a long-ranged gradient of the polymer matrix glass transition temperature in the vicinity of the particles.
Abstract: By studying model systems consisting of poly(ethyl acrylate) polymer chains covalently bound to silica particles, we show here how the temperature dependence of the modulus of filled elastomers can be explained by a long-ranged gradient of the polymer matrix glass transition temperature in the vicinity of the particles. We are led to this conclusion by comparing NMR and mechanical data. We show thereby that the mechanisms of reinforcement are the same as those which lead to an increase of the glass transition temperature of strongly adsorbed thin polymer films. It allows us in particular to propose a new time-temperature superposition law for the filled elastomers viscoelasticity.

Journal ArticleDOI
01 Sep 2003-EPL
TL;DR: A simple model which combines both preferential attachment and distance selection characterized by a typical finite "interaction range" shows that if the total length is fixed, the optimal network which minimizes both thetotal length and the diameter lies in between the scale-free and spatial networks.
Abstract: In many networks such as transportation or communication networks, distance is certainly a relevant parameter. In addition, real-world examples suggest that when long-range links are existing, they usually connect to hubs—the well-connected nodes. We analyze a simple model which combines both these ingredients—preferential attachment and distance selection characterized by a typical finite "interaction range". We study the crossover from the scale-free to the "spatial" network as the interaction range decreases and we propose scaling forms for different quantities describing the network. In particular, when the distance effect is important i) the connectivity distribution has a cut-off depending on the node density, ii) the clustering coefficient is very high, and iii) we observe a positive maximum in the degree correlation (assortativity) whose numerical value is in agreement with empirical measurements. Finally, we show that if the total length is fixed, the optimal network which minimizes both the total length and the diameter lies in between the scale-free and spatial networks. This phenomenon could play an important role in the formation of networks and could be an explanation for the high clustering and the positive assortativity which are non-trivial features observed in many real-world examples.

Journal ArticleDOI
01 Jul 2003-EPL
TL;DR: In this article, it was shown that thermophoresis in lysozyme solutions has a very distinctive behavior: particle motion can indeed be tuned from "thermophobic" (towards the cold) to ''thermophilic'' (along ∇T) by decreasing T. The observed temperature behavior weakly depends on electrostatic effects, and rather suggests a primary role of hydrophobic interactions, further supported by comparison with the temperature dependence of the equilibrium solubility.
Abstract: Thermophoresis, unlike thermal diffusion in simple mixtures, consists in particle drift induced by a temperature gradient ∇T. We show that thermophoresis in lysozyme solutions has a very distinctive behavior: particle motion can indeed be tuned from "thermophobic" (towards the cold) to "thermophilic" (along ∇T) by decreasing T. The observed temperature behaviour weakly depends on electrostatic effects, and rather suggests a primary role of hydrophobic interactions, further supported by comparison with the temperature dependence of lysozyme equilibrium solubility. Most of the observed features can be qualitatively understood by envisaging thermophoresis as a "microscopic Marangoni effect", due to thermally induced gradients of the interfacial free energy.

Journal ArticleDOI
01 Jun 2003-EPL
TL;DR: In this paper, the shape distortions that occur during the drying of sessile drops of polymer solution are shown to be related to buckling instability, and a comparison of the times that characterize drying kinetics and glassy skin formation enables to predict instability occurrence.
Abstract: The large shape distortions that occur during the drying of sessile drops of polymer solution are shown to be related to a buckling instability. As solvent evaporates, polymers accumulate near the vapor/drop interface and, depending on the experimental conditions, can form a glassy skin which bends as the volume it encloses decreases. A comparison of the times that characterize drying kinetics and glassy skin formation enables us to predict instability occurrence. Good agreement is found with measurements performed at different polymer concentrations, drop volumes and drying rates.

Journal ArticleDOI
01 Aug 2003-EPL
TL;DR: In this article, a distributed-order fractional Fokker-Planck equations with a power law weighting function was proposed to describe the acceleration of a particle's position at long times.
Abstract: Several classes of physical systems exhibit ultraslow diffusion for which the mean-squared displacement at long times grows as a power of the logarithm of time (strong anomaly) and share the interesting property that the probability distribution of particle's position at long times is a double-sided exponential. We show that such behaviors can be adequately described by a distributed-order fractional Fokker-Planck equations with a power law weighting function. We discuss the equations and the properties of their solutions, and connect this description with a scheme based on continuous-time random walks.

Journal ArticleDOI
01 Jun 2003-EPL
TL;DR: In this paper, the elastic deformation of a fluid membrane induced by an adhering spherical colloidal particle within the framework of a Helfrich energy was theoretically studied, and a full optimization of the membrane shape was found to find a continuous binding and a discontinuous envelopment transition.
Abstract: We theoretically study the elastic deformation of a fluid membrane induced by an adhering spherical colloidal particle within the framework of a Helfrich energy. Based on a full optimization of the membrane shape we find a continuous binding and a discontinuous envelopment transition, the latter displaying a potentially substantial energy barrier. A small-gradient approximation permits membrane shape and complex energy to be calculated analytically. While this only leads to a good representation of the complex geometry for very small degrees of wrapping, it still gives the correct phase boundaries in the regime of low tension.

Journal ArticleDOI
01 Apr 2003-EPL
TL;DR: In this paper, a self-consistent theory of Anderson localization is presented, which yields a simple algorithm to obtain the typical local density of states as an order parameter, thereby reproducing the essential features of a phase diagram of localization-delocalization quantum phase transition in the standard lattice models of the disordered electron problem.
Abstract: We present a self-consistent theory of Anderson localization that yields a simple algorithm to obtain the typical local density of states as an order parameter, thereby reproducing the essential features of a phase diagram of localization-delocalization quantum phase transition in the standard lattice models of the disordered electron problem. Due to the local character of our theory, it can easily be combined with dynamical mean-field approaches to strongly correlated electrons, thus opening an attractive avenue for a genuine non-perturbative treatment of the interplay of strong interactions and strong disorder.

Journal ArticleDOI
01 Oct 2003-EPL
TL;DR: In this article, a single photon entangled with the vacuum is used to teleport single-mode quantum states of light by means of the Bennett protocol, which results in the truncation of their Fock expansion to the first two terms.
Abstract: We employ the quantum state of a single photon entangled with the vacuum (|GROUPA|GROUPB − |GROUPA|GROUPB), generated by a photon incident upon a symmetric beam splitter, to teleport single-mode quantum states of light by means of the Bennett protocol. The teleportation of coherent states results in the truncation of their Fock expansion to the first two terms. We analyze the teleported ensembles by means of homodyne tomography and obtain fidelities of up to 99 per cent for low-source state amplitudes. This work is an experimental realization of the quantum scissors device proposed by Pegg, Phillips and Barnett (Phys. Rev. Lett., 81 (1998) 1604).

Journal ArticleDOI
01 Aug 2003-EPL
TL;DR: In this paper, it was shown that under a suitable assumption on the pressure tensor, the mass and momentum balance equations of hydrodynamical theory, introduced in the early 1980s by many authors to describe matrix separation, yield the equations of the Madelung fluid that are equivalent to the Schrodingerlike equation with logarithmic nonlinearity.
Abstract: We show that, under a suitable assumption on the pressure tensor, the mass and momentum balance equations of hydrodynamical theory, introduced in the early 1980s by many authors to describe matrix separation, yield the equations of the Madelung fluid that are equivalent to the Schrodinger-like equation with logarithmic nonlinearity. This equation has solitary-waves solutions as required by many experimental volcanic models.

Journal ArticleDOI
01 Jan 2003-EPL
TL;DR: In this article, it was shown that the average length of trajectories through the system is independent of the characteristics of the diffusion process and therefore depends only on the geometry of the system.
Abstract: Starting from a simple animal-biology example, a general, somewhat counter-intuitive property of diffusion random walks is presented. It is shown that for any (non-homogeneous) purely diffusing system, under any isotropic uniform incidence, the average length of trajectories through the system (the average length of the random walk trajectories from entry point to first exit point) is independent of the characteristics of the diffusion process and therefore depends only on the geometry of the system. This exact invariance property may be seen as a generalization to diffusion of the well-known mean-chord-length property (Case K. M. and Zweifel P. F., Linear Transport Theory (Addison-Wesley) 1967), leading to broad physics and biology applications.

Journal ArticleDOI
01 Jan 2003-EPL
TL;DR: In this paper, the existence of a system size coherence resonance effect for coupled excitable systems was shown numerically, showing that the regularity in the signal emitted by an ensemble of globally coupled FitzHugh-Nagumo systems, under excitation by independent noise sources, is optimal for a particular value of the number of coupled systems.
Abstract: We show the existence of a system size coherence resonance effect for coupled excitable systems. Namely, we demonstrate numerically that the regularity in the signal emitted by an ensemble of globally coupled FitzHugh-Nagumo systems, under excitation by independent noise sources, is optimal for a particular value of the number of coupled systems. This resonance is shown through several different dynamical measures: the time correlation function, correlation time and jitter.

Journal ArticleDOI
01 Jul 2003-EPL
TL;DR: In this article, it was shown that the dipole response in a thin cell of dilute vapour exhibits sub-Doppler features due to the relative enhancement of the slow atom contribution, with respect to the transient nature of the interaction with moving atoms.
Abstract: In a thin cell of dilute vapour, the absorption spectrum exhibits sub-Doppler features due to the relative enhancement of the slow atom contribution, with respect to the transient nature of the interaction with moving atoms. For a two-level system in the linear regime, the narrowest response is predicted to be found for a λ/2 thickness, as an effect of the coherent character of the dipole response as early described by Romer and Dicke (Phys. Rev., 99 (1955) 532) in the microwave regime. We report here on the direct observation of this effect in the optical regime in an ultra-thin vapour cell. This effect is shown to vanish for a thickness equal to λ, and a revival is observed at 3λ/2, as expected from the predicted λ-periodicity. The experiment is performed on the D1 resonance line of Cs vapour (λ = 894 nm), in a specially designed cell, whose thickness varies locally.

Journal ArticleDOI
01 May 2003-EPL
TL;DR: In this article, the in-plane optical conductivity of Bi2Sr2CaCu2O 8 + δ films with small carrier density up to large carrier density (overdoped) was derived from accurate reflectivity data.
Abstract: The in-plane optical conductivity of Bi2Sr2CaCu2O 8 + δ films with small carrier density (underdoped) up to large carrier density (overdoped) is derived from accurate reflectivity data. Integrating the conductivity up to increasingly higher frequencies yields the energy scale involved in the formation of the condensate. At least in the underdoped sample, states extending up to 2 eV contribute to the superfluid. This anomalously large energy scale may be assigned to a change of in-plane kinetic energy at the superconducting transition, and is compatible with an electronic pairing mechanism.

Journal ArticleDOI
Keiji Saito1
01 Jan 2003-EPL
TL;DR: In this article, the authors investigated how the normal energy transport is realized in one-dimensional quantum systems using a quantum spin system and found that the autocorrelation function in the Green-Kubo formula decays as t−1.5 to a finite value which vanishes rapidly with the increase of the system size.
Abstract: We investigate how the normal energy transport is realized in one-dimensional quantum systems using a quantum spin system. The direct investigation of local energy distribution under thermal gradient is made using the quantum master equation, and the mixing properties and the convergence of the Green-Kubo formula are investigated when the number of spin increases. We find that the autocorrelation function in the Green-Kubo formula decays as ~ t−1.5 to a finite value which vanishes rapidly with the increase of the system size. As a result, the Green-Kubo formula converges to a finite value in the thermodynamic limit. These facts strongly support the realization of Fourier heat law in a quantum system.

Journal ArticleDOI
01 Mar 2003-EPL
TL;DR: In this article, the authors examined how a crude polydisperse emulsion can be transformed into a monodisperse one by applying a shear step on a crude emulsion.
Abstract: How can a crude polydisperse emulsion be transformed into a monodisperse one? Mason and Bibette (Phys. Rev. Lett., 77 (1996) 3481) have experimentally discovered this phenomenon by applying a shear step on a crude emulsion. In this paper, we examine how this transformation occurs. Our strategy is to prepare calibrated emulsions and to examine the fragmentation kinetics as a function of the initial droplet size. We show that the fragmentation process involves two distinct regimes. At short time (shorter than one second), the droplet diameter decreases abruptly. The droplets deform into long threads that undergo a Rayleigh instability. The obtained diameter is mainly determined by the applied stress and weakly depends on the viscosity ratio between the dispersed and continuous phases. After this first step, the resulting droplets can, once again, break up into daughter droplets. This second mechanism is much slower with a characteristic time of several hundred seconds. Depending on the initial size, the first step can vanish and only the second slow step subsists.

Journal ArticleDOI
01 Jun 2003-EPL
TL;DR: In this paper, generalized Husimi functions at the interfaces of dielectric systems were introduced to identify mechanisms of wave confinement and escape directions in optical micro-resonators, and give insight into the structure of resonance wave functions.
Abstract: We introduce generalized Husimi functions at the interfaces of dielectric systems. Four different functions can be defined, corresponding to the incident and departing wave on both sides of the interface. These functions allow to identify mechanisms of wave confinement and escape directions in optical microresonators, and give insight into the structure of resonance wave functions. Off resonance, where systematic interference can be neglected, the Husimi functions are related by Snell's law and Fresnel's coefficients.

Journal ArticleDOI
01 Oct 2003-EPL
TL;DR: In this paper, a first-principles investigation of the lattice dynamics and electron-phonon coupling of the high-Tc superconductor YBa2Cu3O7 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method is presented.
Abstract: We present a first-principles investigation of the lattice dynamics and electron-phonon coupling of the high-Tc superconductor YBa2Cu3O7 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. The calculated phonon dispersion curves are in excellent agreement with Raman, infrared and neutron data. Calculation of the Eliashberg function α2F leads to a small electron-phonon coupling λ = 0.27 in disagreement with earlier approximate treatments. Our calculations strongly support the view that conventional electron-phonon coupling is not an important contribution to superconductivity in high-Tc materials.

Journal ArticleDOI
01 Feb 2003-EPL
TL;DR: It is shown that it is possible to differentiate between dynamical and measurement noise, and a new criterion is presented to verify the correct embedding for chaotic dynamics with dynamical noise.
Abstract: This letter reports on a new method of analysing experimentally gained time series with respect to different types of noise involved, namely, we show that it is possible to differentiate between dynamical and measurement noise. This method does not depend on previous knowledge of model equations. For the complicated case of a chaotic dynamics spoiled at the same time by dynamical and measurement noise, we even show how to extract from data the magnitude of both types of noise. As a further result, we present a new criterion to verify the correct embedding for chaotic dynamics with dynamical noise.

Journal ArticleDOI
01 Apr 2003-EPL
TL;DR: In this article, a solid-state implementation of an all-optical spin-based quantum computer is presented, which is based on spin degrees of freedom of electrons confined in semiconductor quantum dots, thus benefiting from relatively long coherence times.
Abstract: We present a solid-state implementation of an all-optical spin-based quantum computer. Our proposal for a quantum-computing device is based on the spin degrees of freedom of electrons confined in semiconductor quantum dots, thus benefitting from relatively long coherence times. Combining Pauli blocking effects with properly tailored ultrafast laser pulses, we obtain sub-picosecond spin-dependent switching of the Coulomb interaction, which is the essence of our gating operations. This allows us to realize fast quantum gates which do not translate into fast decoherence times and pave the way for an all-optical spin-based quantum computer.