Publications (27)83.12 Total impact
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ABSTRACT: Enhanced rates in multichromophoric resonance energy transfer are shown to be well described by a classical theory based on classical electrodynamics. In a coupling configuration between $N_A$ acceptors and $N_D$ donors, the theory correctly predicts an enhancement of the energy transfer rate dependent on the total number of donoracceptor pairs, $N_A N_D$. As an example, the theory, applied to the transfer rate in LH II, gives results in excellent agreement with experiment.12/2014;  [Show abstract] [Hide abstract]
ABSTRACT: Synchronization is a ubiquitous phenomenon occurring in social, biological, and technological systems when the internal rythms of their constituents are adapted to be in unison as a result of their coupling. This natural tendency towards dynamical consensus has spurred a large body of theoretical and experimental research in recent decades. The Kuramoto model constitutes the most studied and paradigmatic framework in which to study synchronization. In particular, it shows how synchronization appears as a phase transition from a dynamically disordered state at some critical value for the coupling strength between the interacting units. The critical properties of the synchronization transition of this model have been widely studied and many variants of its formulations have been considered to address different physical realizations. However, the Kuramoto model has been studied only within the domain of classical dynamics, thus neglecting its applications for the study of quantum synchronization phenomena. Based on a systembath approach and within the Feynman pathintegral formalism, we derive equations for the Kuramoto model by taking into account the first quantum fluctuations. We also analyze its critical properties, the main result being the derivation of the value for the synchronization onset. This critical coupling increases its value as quantumness increases, as a consequence of the possibility of tunneling that quantum fluctuations provide.Physical Review E 11/2014; 90(51):052904. · 2.33 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Determining the spectral density of a molecular system immersed in a proteomic scaffold and in contact to a solvent is a fundamental challenge in the coarsegrained description of, e.g., electron and energy transfer dynamics. Once the spectral density is characterized, all the time scales are captured and no artificial separation between fast and slow processes need be invoked. Based on the fluorescence Stokes shift function, we utilize a simple and robust strategy to extract the spectral density of a number of molecular complexes from available experimental data. Specifically, we show that experimental data for dye molecules in several solvents, amino acid proteins in water, and some photochemical systems (e.g., rhodopsin and green fluorescence proteins), are well described by a threeparameter family of subOhmic spectral densities that are characterized by a fast initial Gaussianlike decay followed by a slow algebraiclike decay rate at long times.The Journal of Chemical Physics 10/2014; 141(17). · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Contrary to the conventional wisdom that deviations from standard thermodynamics originate from the strong coupling to the bath, it is shown that these deviations are intimately linked to the power spectrum of the thermal bath. Specifically, it is shown that the lower bound of the dispersion of the total energy of the system, imposed by the uncertainty principle, is dominated by the bath power spectrum and therefore, quantum mechanics inhibits the system thermalequilibriumstate from being described by the canonical Boltzmann's distribution. This is in sharp contrast to the classical case, for which the thermal equilibrium distribution of a system interacting via central forces with pairwiseselfinteracting environment, irrespective of the interaction strength, is shown to be \emph{exactly} characterized by the canonical Boltzmann distribution. As a consequence of this analysis, we define an \emph{effective coupling} to the environment that depends on all energy scales in the system and reservoir interaction. Sample computations in regimes predicted by this effective coupling are demonstrated. For example, for the case of strong effective coupling, deviations from standard thermodynamics are present and, for the case of weak effective coupling, quantum features such as stationary entanglement are possible at high temperatures.01/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The ability of an environment to assist in onephoton phase control relies upon entanglement between the system and bath and on the breaking of the time reversal symmetry. Here, onephoton phase control is examined analytically and numerically in a model system, allowing an analysis of the relative strength of these contributions. Further, the significant role of nonMarkovian dynamics and of moderate systembath coupling in enhancing onephoton phase control is demonstrated, and an explicit role for quantum mechanics is noted in the existence of initial nonzero stationary coherences. Finally, desirable conditions are shown to be required to observe such environmentally assisted control, since the system will naturally equilibrate with its environment at longer times, ultimately resulting in the loss of phase control.The Journal of Chemical Physics 10/2013; 139(16):164123. · 3.12 Impact Factor 
Article: Innermost Stable Circular Orbits and Epicyclic Frequencies Around a Magnetized Neutron Star
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ABSTRACT: A fullrelativistic approach is used to compute the radius of the innermost stable circular orbit (ISCO), the Keplerian, framedragging, precession and oscillation frequencies of the radial and vertical motions of neutral test particles orbiting the equatorial plane of a magnetized neutron star. The spacetime around the star is modelled by the six parametric solution derived by Pachon et al. It is shown that the inclusion of an intense magnetic field, such as the one of a neutron star, have nonnegligible effects on the above physical quantities, and therefore, its inclusion is necessary in order to obtain a more accurate and realistic description of the physical processes occurring in the neighbourhood of this kind of objects such as the dynamics of accretion disk. The results discussed here also suggest that the consideration of strong magnetic fields may introduce nonnegligible corrections in, e.g., the relativistic precession model and therefore on the predictions made on the mass of neutron stars.Universitas Scientiarum. 09/2013; 19(1).  [Show abstract] [Hide abstract]
ABSTRACT: The underlying mechanisms for one photon phase control are revealed through a master equation approach. Specifically, two mechanisms are identified, one operating on the laser time scale and the other on the time scale of the systembath interaction. The effects of the secular and nonsecular Markovian approximations are carefully examined.Faraday Discussions 01/2013; 163:48595. · 4.19 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Under natural conditions, excitation of biological molecules, which display nonunitary open system dynamics, occurs via incoherent processes such as temperature changes or irradiation by sunlight/moonlight. The dynamics of such processes is explored analytically in a nonMarkovian generic model. Specifically, a system S in equilibrium with a thermal bath TB is subjected to an external incoherent perturbation BB (such as sunlight) or another thermal bath TB', which induces time evolution in (S+TB). Particular focus is on (i) the extent to which the resultant dynamics is coherent, and (ii) the role of "stationary coherences", established in the (S+TB) equilibration, in the response to the second incoherent perturbation. Results for systems with parameters analogous to those in light harvesting molecules in photosynthesis show that the resultant dynamical behaviour is incoherent beyond a very short response to the turnon of the perturbation.Physical Review A 10/2012; 87(2). · 2.99 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We consider the general open system problem of a charged quantum oscillator confined in a harmonic trap, whose frequency can be arbitrarily modulated in time, that interacts with both an incoherent quantized (blackbody) radiation field and with an arbitrary coherent laser field. We assume that the oscillator is initially in thermodynamic equilibrium with its environment, a nonfactorized initial density matrix of the system and the environment, and that at $t=0$ the modulation of the frequency, the coupling to the incoherent and the coherent radiation are switched on. The subsequent dynamics, induced by the presence of the blackbody radiation and the laser field, is studied in the framework of the influence functional approach. This approach allows incorporating, in \emph{analytic closed formulae}, the nonMarkovian character of the oscillatorenvironment interaction at any temperature as well the nonMarkovian character of the blackbody radiation and its zeropoint fluctuations. Expressions for the time evolution of the covariance matrix elements of the quantum fluctuations and the reduced densityoperator are obtained.Journal of Mathematical Physics 07/2012; · 1.18 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We examine computational techniques and methodologies currently in use to explore electronic excitation energy transfer in the context of lightharvesting complexes in photosynthetic antenna systems, and comment on some new insights into the underlying physics. Advantages and pitfalls of these methodologies are discussed, as are some physical insights into the photosynthetic dynamics. By combining results from molecular modelling of the complexes (structural description) with an effective nonequilibrium statistical description (time evolution), we identify some general features, regardless of the particular distribution in the protein scaffold, that are central to lightharvesting dynamics and, that could ultimately be related to the high efficiency of the overall process. Based on these general common features, some possible new directions in the field are discussed.Physical Chemistry Chemical Physics 06/2012; 14(29):10094108. · 4.20 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Whether analytic exact vacuum(electrovacuum) solutions of the Einstein(EinsteinMaxwell) field equations can accurately describe or not the exterior spacetime of compact stars remains still an interesting open question in Relativistic Astrophysics. As an attempt to establish their level of accuracy, the radii of the Innermost Stable Circular Orbits (ISCOs) of test particles given by analytic exterior spacetime geometries have been compared with the ones given by numerical solutions for neutron stars (NSs) obeying a realistic equation of state (EoS). It has been so shown that the sixparametric solution of Pach\'on, Rueda, and Sanabria (2006) (hereafter PRS) is more accurate to describe the NS ISCO radii than other analytic models. We propose here an additional test of accuracy for analytic exterior geometries based on the comparison of orbital frequencies of neutral test particles. We compute the Keplerian, framedragging, as well as the precession and oscillation frequencies of the radial and vertical motions of neutral test particles for the Kerr and PRS geometries; then we compare them with the numerical values obtained by Morsink and Stella (1999) for realistic NSs. We identify the role of highorder multipole moments such as the mass quadrupole and current octupole in the determination of the orbital frequencies especially in the rapid rotation regime. The results of this work are relevant to cast a separatrix between black hole (BH) and NS signatures as well as probe the nuclear matter EoS and NS parameters from the QuasiPeriodic Oscillations (QPOs) observed in Low Mass XRay Binaries.The Astrophysical Journal 12/2011; 756(1). · 6.28 Impact Factor 
Article: The Physical Basis for Longlived Electronic Coherence in Photosynthetic Light Harvesting Systems
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ABSTRACT: The physical basis for observed longlived electronic coherence in photosynthetic lightharvesting systems is identified using an analytically soluble model. Three physical features are found to be responsible for their long coherence lifetimes: i) the small energy gap between excitonic states, ii) the small ratio of the energy gap to the coupling between excitonic states, and iii) the fact that the molecular characteristics place the system in an effective low temperature regime, even at ambient conditions. Using this approach, we obtain decoherence times for a dimer model with FMO parameters of $\approx$ 160 fs at 77 K and $\approx$ 80 fs at 277 K. As such, significant oscillations are found to persist for 600 fs and 300 fs, respectively, in accord with the experiment and with previous computations. Similar good agreement is found for PC645 at room temperature, with oscillations persisting for 400 fs. The analytic expressions obtained provide direct insight into the parameter dependence of the decoherence time scales.Journal of Physical Chemistry Letters 07/2011; · 6.69 Impact Factor  Journal of Physical Chemistry Letters 01/2011; · 6.69 Impact Factor
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ABSTRACT: Decoherence due to contact with a hot environment typically restricts quantum phenomena to the low temperature limit, k_{B}T/ℏω≪1 (ℏω is the typical energy of the system). Here we report the existence of a nonequilibrium state for two coupled, parametrically driven, dissipative harmonic oscillators which, contrary to generalized intuition, has stationary entanglement at high temperatures. This clarifies the role of temperature and could lighten the burden on quantum experiments requiring delicate precooling setups.Physical Review Letters 10/2010; 105(18):180501. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the electromagnetic and gravitational fields of the proton and electron in terms of the Einstenian gravity via the introduction of an arbitrary Lande $g$factor in the KerrNewman solution. We show that at length scales of the order of the reduced Compton wavelength, corrections from different values of the $g$factor are not negligible and discuss the presence of general relativistic effects in highly ionized heavy atoms. On the other hand, since at the Comptonwavelength scale the gravitational field becomes spin dominated rather than mass dominated, we also point out the necessity of including angular momentum as a source of corrections to Newtonian gravity in the quantum description of gravity at this scale.Classical and Quantum Gravity 09/2010; 28. · 3.10 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a comprehensive study of semiclassical phasespace propagation in the Wigner representation, emphasizing numerical applications, in particular as an initialvalue representation. Two semiclassical approximation schemes are discussed. The propagator of the Wigner function based on van Vleck's approximation replaces the Liouville propagator by a quantum spot with an oscillatory pattern reflecting the interference between pairs of classical trajectories. Employing phasespace path integration instead, caustics in the quantum spot are resolved in terms of Airy functions. We apply both to two benchmark models of nonlinear molecular potentials, the Morse oscillator and the quartic double well, to test them in standard tasks such as computing autocorrelation functions and propagating coherent states. The performance of semiclassical Wigner propagation is very good even in the presence of marked quantum effects, e.g., in coherent tunneling and in propagating Schrodinger cat states, and of classical chaos in fourdimensional phase space. We suggest options for an effective numerical implementation of our method and for integrating it in MonteCarloMetropolis algorithms suitable for highdimensional systems.The Journal of Chemical Physics 06/2010; 132(21):214102. · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The phasespace pathintegral approach to the damped harmonic oscillator is analyzed beyond the Markovian approximation. It is found that pairs of nonclassical trajectories contribute to the pathintegral representation of the Wigner propagating function. Due to the linearity of the problem, the sum coordinate of a pair still satisfies the classical equation of motion. Furthermore, it is shown that the broadening of the Wigner propagating function of the damped oscillator arises due to the timenonlocal interaction mediated by the heat bath. Comment: 8 pages, 3 figures, accepted for publication in Chemical PhysicsChemical Physics 05/2010; · 2.03 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We show the existence of an entangled nonequilibrium state at very high temperatures when two linearly coupled harmonic oscillators are parametrically driven and dissipate into two independent heat baths. This result has a twofold meaning: first, it fundamentally shifts the classicalquantum border to temperatures as high as our experimental ability allows us, and second, it can help increase by at least one order of magnitude the temperature at which current experimental setups are operated. Comment: accepted in Phys. Rev. LettPhysical Review Letters 02/2010; · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the relationship of the spectral form factor with quantum as well as classical probabilities to return. Defining a quantum return probability in phase space as a trace over the propagator of the Wigner function allows us to identify and resolve manifolds in phase space that contribute to the form factor. They can be associated with classical invariant manifolds such as periodic orbits, but also to nonclassical structures such as sets of midpoints between periodic points. In contrast to scars in wave functions, these features are not subject to the uncertainty relation and therefore need not show any smearing. They constitute important exceptions from a continuous convergence in the classical limit of the Wigner towards the Liouville propagator. We support our theory with numerical results for the quantum cat map and the harmonically driven quartic oscillator.Physical Review Letters 05/2009; 102(15):150401. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The existence of chaotic behavior for the geodesics of the test particles orbiting compact objects is a subject of much current research. Some years ago, Gu\'eron and Letelier [Phys. Rev. E \textbf{66}, 046611 (2002)] reported the existence of chaotic behavior for the geodesics of the test particles orbiting compact objects like black holes induced by specific values of the quadrupolar deformation of the source using as models the ErezRosen solution and the Kerr black hole deformed by an internal multipole term. In this work, we are interesting in the study of the dynamic behavior of geodesics around astrophysical objects with intrinsic quadrupolar deformation or nonisotropic stresses, which induces nonvanishing quadrupolar deformation for the nonrotating limit. For our purpose, we use the TomimatsuSato spacetime [Phys. Rev. Lett. \textbf{29} 1344 (1972)] and its arbitrary deformed generalization obtained as the particular vacuum case of the five parametric solution of Manko et al [Phys. Rev. D 62, 044048 (2000)], characterizing the geodesic dynamics throughout the Poincar\'e sections method. In contrast to the results by Gu\'eron and Letelier we find chaotic motion for oblate deformations instead of prolate deformations. It opens the possibility that the particles forming the accretion disk around a large variety of different astrophysical bodies (nonprolate, e.g., neutron stars) could exhibit chaotic dynamics. We also conjecture that the existence of an arbitrary deformation parameter is necessary for the existence of chaotic dynamics. Comment: 7 pages, 5 figuresPhysical Review D 01/2007; 75(023008):1. · 4.69 Impact Factor
Publication Stats
156  Citations  
83.12  Total Impact Points  
Top Journals
Institutions

2011–2014

University of Toronto
 Department of Chemistry
Toronto, Ontario, Canada


2011–2013

University of Antioquia
 Instituto de Física
Antioquia, Departamento de Antioquia, Colombia


2010

University of the Balearic Islands
 Institute for CrossDisciplinary Physics and Complex Systems (IFISC)
Palma, Balearic Islands, Spain


2006–2010

National University of Colombia
 Departamento de Física (Bogotá)
Medellín, Departamento de Antioquia, Colombia 
University of Zulia
Maracaibo, Estado Zulia, Venezuela


2006–2007

Industrial University of Santander
 School of Physics
Bucaramanga, Departamento de Santander, Colombia
