Pabellon, Argentina
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Quinteiro G.F.,IFIBA | Dmitruk P.,IFIBA | Aligia A.A.,Bariloche Atomic Center
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A semiconductor microcavity embedding donor impurities and excited by a laser field is modeled. By including general decay and dephasing processes, in particular, cavity photon leakage, detailed simulations show that control over the spin dynamics is significantly enhanced in high-quality-factor cavities, in which case picosecond laser pulses may produce spin flip with high-fidelity final states. © 2012 American Physical Society.

Lopez Nacir D.L.,IFIBA | Mazzitelli F.D.,IFIBA | Mazzitelli F.D.,Bariloche Atomic Center | Trombetta L.G.,IFIBA
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We consider an interacting Lifshitz field with z=3 in a curved spacetime. We analyze the renormalizability of the theory for interactions of the form λn, with arbitrary even n. We compute the running of the coupling constants both in the ultraviolet and infrared regimes. We show that the Lorentz-violating terms generate couplings to the spacetime metric that are not invariant under general coordinate transformations. These couplings are not suppressed by the scale of Lorentz violation and therefore survive at low energies. We point out that in these theories, unless the effective mass of the field is many orders of magnitude below the scale of Lorentz violation, the coupling to the four-dimensional Ricci scalar ξ( 4)R 2 does not receive large quantum corrections ξ1. We argue that quantum corrections involving spatial derivatives of the lapse function (which appear naturally in the so-called healthy extension of the Hořava-Lifshitz theory of gravity) are not generated unless they are already present in the bare Lagrangian. © 2012 American Physical Society.

Schmiegelow C.T.,IFIBA | Bendersky A.,IFIBA | Larotonda M.A.,CEILAP | Paz J.P.,IFIBA
Physical Review Letters | Year: 2011

Several methods, known as quantum process tomography, are available to characterize the evolution of quantum systems, a task of crucial importance. However, their complexity dramatically increases with the size of the system. Here we present a new method for quantum process tomography. We describe a new algorithm that can be used to selectively estimate any parameter characterizing a quantum process. Unlike any of its predecessors this new quantum tomographer combines two virtues: it requires investing a number of physical resources scaling polynomially with the number of qubits and at the same time it does not require any ancillary resources. We present the results of the first implementation of this quantum device, characterizing quantum processes affecting two qubits encoded in heralded single photons. Even for this small system our method displays clear advantages over the other existing ones. © 2011 American Physical Society.

Schmiegelow C.T.,IFIBA | Larotonda M.A.,CEILAP | Paz J.P.,IFIBA
Physical Review Letters | Year: 2010

We present the results of the first photonic implementation of a new method for quantum process tomography. The method {originally presented by A. Bendersky et al.} enables the estimation of any element of the χ-matrix that characterizes a quantum process using resources that scale polynomially with the number of qubits. It is based on the idea of mapping the estimation of any χ-matrix element onto the average fidelity of a quantum channel and estimating the latter by sampling randomly over a special set of states called a 2-design. With a heralded single photon source we fully implement such algorithm and perform process tomography on a number of channels affecting the polarization qubit. The method is compared with other existing ones, and its advantages are discussed. © 2010 The American Physical Society.

Intronati G.A.,IFIBA | Intronati G.A.,CNRS Institute of Genetics and of Molecular and Cellular Biology | Intronati G.A.,CEA Saclay Nuclear Research Center | Tamborenea P.I.,IFIBA | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We study the effect of the Dresselhaus spin-orbit interaction on the electronic states and spin relaxation rates of cylindrical quantum dots defined on quantum wires having wurtzite lattice structure. The linear and cubic contributions of the bulk Dresselhaus spin-orbit coupling (SOC) are taken into account, along with the influence of a weak external magnetic field. The previously found analytic solution for the electronic states of cylindrical quantum dots with zinc blende lattice structures with Rashba interaction is extended to the case of quantum dots with wurtzite lattices. For the electronic states in InAs dots, we determine the spin texture and the effective g factor, which shows a scaling collapse when plotted as a function of an effective renormalized dot-size-dependent spin-orbit coupling strength. The acoustic-phonon-induced spin relaxation rate is calculated and the transverse piezoelectric potential is shown to be the dominant one. © 2013 American Physical Society.

Alani I.,IFIBA | Santillan O.P.,Institute Matematicas Luis Santalo IMAS
Journal of Cosmology and Astroparticle Physics | Year: 2016

In the present work some generalizations of the Hawking singularity theorems in the context of f(R) theories are presented. The main assumptions are: the matter fields stress energy tensor satisfies the condition (Tij-(gij/2)T)kikj ≥ 0 for any generic unit time like field ki; the scalaron takes bounded positive values during its evolution and the resulting space time is globally hyperbolic. Then, if there exist a Cauchy hyper-surface Σ for which the expansion parameter θ of the geodesic congruence emanating orthogonally from Σ satisfies some specific bounds, then the resulting space time is geodesically incomplete. Some mathematical results of reference [92] are very important for proving this. The generalized theorems presented here apply directly for some specific models such as the Hu-Sawicki or Starobinsky ones [27,38]. For other scenarios, some extra assumptions should be implemented in order to have a geodesically incomplete space time. The hypothesis considered in this text are sufficient, but not necessary. In other words, their negation does not imply that a singularity is absent. © 2016 IOP Publishing Ltd and Sissa Medialab srl.

Quinteiro G.F.,IFIBA | Tamborenea P.I.,IFIBA
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We theoretically investigate the interband transitions and quantum kinetics induced by light carrying orbital angular momentum, or twisted light, in bulk semiconductors. We pose the problem in terms of the Heisenberg equations of motion of the electron populations, and interband and intraband coherences. Our theory extends the free-carrier semiconductor Bloch equations to the case of photoexcitation by twisted light. The theory is formulated using cylindrical coordinates, which are better suited to describe the interaction with twisted light than the usual Cartesian coordinates used to study regular optical excitation. We solve the equations of motion in the low excitation regime, and obtain analytical expressions for the coherences and populations; with these, we calculate the orbital angular momentum transferred from the light to the electrons and the paramagnetic and diamagnetic electric current densities. © 2010 The American Physical Society.

Wisniacki D.A.,IFIBA | Schlagheck P.,University of Liège
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

When an integrable classical system is perturbed, nonlinear resonances are born, grow, and eventually disappear due to chaos. In this paper the quantum manifestations of such a transition are studied in the standard map. We show that nonlinear resonances act as a perturbation that break eigenphase degeneracies for unperturbed states with quantum numbers that differ in a multiple of the order of the resonance. We show that the eigenphase splittings are well described by a semiclassical expression based on an integrable approximation of the Hamiltonian in the vicinity of the resonance. The morphology in phase space of these states is also studied. We show that the nonlinear resonance imprints a systematic influence in their localization properties. © 2015 American Physical Society.

Calzetta E.,IFIBA | Kandus A.,State University of Santa Cruz
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We study the possibility that primordial magnetic fields generated in the transition between inflation and reheating posses magnetic helicity, HM. The fields are induced by stochastic currents of scalar charged particles created during the mentioned transition. We estimate the rms value of the induced magnetic helicity by computing different four-point scalar quantum electrodynamics Feynman diagrams. For any considered volume, the magnetic flux across its boundaries is in principle not null, which means that the magnetic helicity in those regions is gauge dependent. We use the prescription given by Berger and Field and interpret our result as the difference between two magnetic configurations that coincide in the exterior volume. In this case, the magnetic helicity gives only the number of magnetic links inside the considered volume. We calculate a concrete value of HM for large scales and analyze the distribution of magnetic defects as a function of the scale. Those defects correspond to regular as well as random fields in the considered volume. We find that the fractal dimension of the distribution of topological defects is D=1/2. We also study if the regular fields induced on large scales are helical, finding that they are and that the associated number of magnetic defects is independent of the scale. In this case, the fractal dimension is D=0. We finally estimate the intensity of fields induced at the horizon scale of reheating and evolve them until the decoupling of matter and radiation under the hypothesis of the inverse cascade of magnetic helicity. The resulting intensity is high enough and the coherence length long enough to have an impact on the subsequent process of structure formation. © 2014 American Physical Society.

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