ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 23 Oct 2019 23:49:04 GMT2019-10-23T23:49:04Z50271- Power spectrum of electronic heat current fluctuationshttps://scholarbank.nus.edu.sg/handle/10635/97578Title: Power spectrum of electronic heat current fluctuations
Authors: Zhan, F.; Denisov, S.; Hänggi, P.
Abstract: We analyze the fluctuations of an electronic thermal current across an idealized molecular junction. The focus here will be on the spectral features of the resulting heat fluctuations. By use of the Green function method we derive an explicit expression for the frequency-dependent power spectral density of the emerging energy fluctuations. The complex expression simplifies considerably in the limit of zero frequency, yielding the noise intensity of the heat current. The spectral density for the electronic heat fluctuations still depends on the frequency in the zero-temperature limit, assuming different asymptotic behaviors in the low- and high-frequency regions. We further address subtleties and open problems from an experimental view point for measurements of frequency-dependent power spectral densities. Sketch of a molecular junction setup used in the text. The average heat flow is generated by electrons moving from a hot electrode TL across the molecular junction towards a neighboring cold electrode TR. The inter-electrode electronic level ε{lunate}0 can be tuned continuously. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Fri, 01 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/975782013-11-01T00:00:00Z
- Steering bose-einstein condensates despite time symmetryhttps://scholarbank.nus.edu.sg/handle/10635/98022Title: Steering bose-einstein condensates despite time symmetry
Authors: Poletti, D.; Benenti, G.; Casati, G.; Hänggi, P.; Li, B.
Abstract: A Bose-Einstein condensate in an oscillating spatially asymmetric potential is shown to exhibit a directed current for unbiased initial conditions despite time symmetry. This phenomenon occurs only if the interaction between atoms, treated in mean-field approximation, exceeds a critical value. Our findings can be described with a three-mode model. These three-mode model results corroborate well with a many-body study over a time scale which increases with increasing atom number. The duration of this time scale probes the validity of the used mean-field approximation. © 2009 The American Physical Society.
Mon, 30 Mar 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/980222009-03-30T00:00:00Z
- Two-mode Bose-Einstein condensate in a high-frequency driving field that directly couples the two modeshttps://scholarbank.nus.edu.sg/handle/10635/116013Title: Two-mode Bose-Einstein condensate in a high-frequency driving field that directly couples the two modes
Authors: Zhang, Q.; Hänggi, P.; Gong, J.
Abstract: A two-mode Bose-Einstein condensate coupled by a high-frequency modulation field is found to display rich features. An effective stationary Hamiltonian approach reveals the emergence of additional degenerate eigenstates as well as additional topological structures of the spectrum. Possible applications, such as the suppression of nonlinear Landau-Zener tunneling, are discussed. An interesting phenomenon, which we call "deterministic symmetry-breaking trapping" associated with separatrix crossing, is also found in an adiabatic process. © 2008 The American Physical Society.
Tue, 13 May 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1160132008-05-13T00:00:00Z
- Escape driven by α -stable white noiseshttps://scholarbank.nus.edu.sg/handle/10635/96520Title: Escape driven by α -stable white noises
Authors: Dybiec, B.; Gudowska-Nowak, E.; Hänggi, P.
Abstract: We explore the archetype problem of an escape dynamics occurring in a symmetric double well potential when the Brownian particle is driven by white Lévy noise in a dynamical regime where inertial effects can safely be neglected. The behavior of escaping trajectories from one well to another is investigated by pointing to the special character that underpins the noise-induced discontinuity which is caused by the generalized Brownian paths that jump beyond the barrier location without actually hitting it. This fact implies that the boundary conditions for the mean first passage time (MFPT) are no longer determined by the well-known local boundary conditions that characterize the case with normal diffusion. By numerically implementing properly the set up boundary conditions, we investigate the survival probability and the average escape time as a function of the corresponding Lévy white noise parameters. Depending on the value of the skewness β of the Lévy noise, the escape can either become enhanced or suppressed: a negative asymmetry parameter β typically yields a decrease for the escape rate while the rate itself depicts a non-monotonic behavior as a function of the stability index α that characterizes the jump length distribution of Lévy noise, exhibiting a marked discontinuity at α=1. We find that the typical factor of 2 that characterizes for normal diffusion the ratio between the MFPT for well-bottom-to-well-bottom and well-bottom-to-barrier-top no longer holds true. For sufficiently high barriers the survival probabilities assume an exponential behavior versus time. Distinct non-exponential deviations occur, however, for low barrier heights. © 2007 The American Physical Society.
Mon, 12 Feb 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/965202007-02-12T00:00:00Z
- Comment on "coherent ratchets in driven Bose-Einstein condensates"https://scholarbank.nus.edu.sg/handle/10635/115526Title: Comment on "coherent ratchets in driven Bose-Einstein condensates"
Authors: Benenti, G.; Casati, G.; Denisov, S.; Flach, S.; Hänggi, P.; Li, B.; Poletti, D.
Thu, 03 Jun 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1155262010-06-03T00:00:00Z
- Intermediate dynamics between Newton and Langevinhttps://scholarbank.nus.edu.sg/handle/10635/96968Title: Intermediate dynamics between Newton and Langevin
Authors: Bao, J.-D.; Zhuo, Y.-Z.; Oliveira, F.A.; Hänggi, P.
Abstract: A dynamics between Newton and Langevin formalisms is elucidated within the framework of the generalized Langevin equation. For thermal noise yielding a vanishing zero-frequency friction the corresponding non-Markovian Brownian dynamics exhibits anomalous behavior which is characterized by ballistic diffusion and accelerated transport. We also investigate the role of a possible initial correlation between the system degrees of freedom and the heat-bath degrees of freedom for the asymptotic long-time behavior of the system dynamics. As two test beds we investigate (i) the anomalous energy relaxation of free non-Markovian Brownian motion that is driven by a harmonic velocity noise and (ii) the phenomenon of a net directed acceleration in noise-induced transport of an inertial rocking Brownian motor. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/969682006-01-01T00:00:00Z
- Nonlinear Landau-Zener processes in a periodic driving fieldhttps://scholarbank.nus.edu.sg/handle/10635/115835Title: Nonlinear Landau-Zener processes in a periodic driving field
Authors: Zhang, Q.; Hänggi, P.; Gong, J.
Abstract: Effects of a periodic driving field on Landau-Zener (LZ) processes are studied using a nonlinear two-mode model that describes the mean-field dynamics of a many-body system. A variety of different dynamical phenomena in different parameter regimes of the driving field are discussed and analyzed. These include shifted, weakened, or enhanced phase dependence of nonlinear LZ (NLZ) processes, nonlinearity-enhanced population transfer in the adiabatic limit and Hamiltonian chaos on the mean-field level. The emphasis of this work is based on how the impact of a periodic driving field on LZ processes with self-interaction differs from those without self-interaction. Apart from gaining knowledge of driven NLZ processes, our findings can be used to gauge the strength of nonlinearity and for efficient manipulation of the mean-field dynamics of many-body systems. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Thu, 03 Jul 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1158352008-07-03T00:00:00Z
- Slowly rocking symmetric, spatially periodic Hamiltonians: The role of escape and the emergence of giant transient directed transporthttps://scholarbank.nus.edu.sg/handle/10635/97956Title: Slowly rocking symmetric, spatially periodic Hamiltonians: The role of escape and the emergence of giant transient directed transport
Authors: Hennig, D.; Schimansky-Geier, L.; Hänggi, P.
Abstract: The nonintegrable Hamiltonian dynamics of particles placed in a symmetric, spatially periodic potential and subjected to a periodically varying field is explored. Such systems can exhibit a rich diversity of unusual transport features. In particular, depending on the setting of the initial phase of the drive, the possibility of a giant transient directed transport in a symmetric, space-periodic potential when driven with an adiabatically varying field arises. Here, we study the escape scenario and corresponding mean escape times of particles from a trapping region with the subsequent generation of a transient directed flow of an ensemble of particles. It is shown that for adiabatically slow inclination modulations the unidirectional flow proceeds over giant distances. The direction of escape and, hence, of the flow is entirely governed whether the periodic force, modulating the inclination of the potential, starts out initially positive or negative. In the phase space, this transient directed flow is associated with a long-lasting motion taking place within ballistic channels contained in the non-uniform chaotic layer. We demonstrate that for adiabatic modulations all escaping particles move ballistically into the same direction, leading to a giant directed current. © 2008 EDP Sciences/Società Italiana di Fisica/Springer-Verlag.
Tue, 01 Apr 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979562008-04-01T00:00:00Z
- Artificial Brownian motors: Controlling transport on the nanoscalehttps://scholarbank.nus.edu.sg/handle/10635/95821Title: Artificial Brownian motors: Controlling transport on the nanoscale
Authors: Hänggi, P.; Marchesoni, F.
Abstract: In systems possessing spatial or dynamical symmetry breaking, Brownian motion combined with unbiased external input signals, deterministic and random alike, can assist directed motion of particles at submicron scales. In such cases, one speaks of "Brownian motors." In this review the constructive role of Brownian motion is exemplified for various physical and technological setups, which are inspired by the cellular molecular machinery: the working principles and characteristics of stylized devices are discussed to show how fluctuations, either thermal or extrinsic, can be used to control diffusive particle transport. Recent experimental demonstrations of this concept are surveyed with particular attention to transport in artificial, i.e., nonbiological, nanopores, lithographic tracks, and optical traps, where single-particle currents were first measured. Much emphasis is given to two- and three-dimensional devices containing many interacting particles of one or more species; for this class of artificial motors, noise rectification results also from the interplay of particle Brownian motion and geometric constraints. Recently, selective control and optimization of the transport of interacting colloidal particles and magnetic vortices have been successfully achieved, thus leading to the new generation of microfluidic and superconducting devices presented here. The field has recently been enriched with impressive experimental achievements in building artificial Brownian motor devices that even operate within the quantum domain by harvesting quantum Brownian motion. Sundry akin topics include activities aimed at noise-assisted shuttling other degrees of freedom such as charge, spin, or even heat and the assembly of chemical synthetic molecular motors. This review ends with a perspective for future pathways and potential new applications. © 2009 The American Physical Society.
Tue, 06 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958212009-01-06T00:00:00Z
- Directed transport in periodically rocked random sawtooth potentialshttps://scholarbank.nus.edu.sg/handle/10635/96242Title: Directed transport in periodically rocked random sawtooth potentials
Authors: Denisov, S.I.; Lyutyy, T.V.; Denisova, E.S.; Hänggi, P.; Kantz, H.
Abstract: We study directed transport of overdamped particles in a periodically rocked random sawtooth potential. Two transport regimes can be identified which are characterized by a nonzero value of the average velocity of particles and a zero value, respectively. The properties of directed transport in these regimes are investigated both analytically and numerically in terms of a random sawtooth potential and a periodically varying driving force. Precise conditions for the occurrence of transition between these two transport regimes are derived and analyzed in detail. © 2009 The American Physical Society.
Mon, 04 May 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962422009-05-04T00:00:00Z
- Anomalous heat diffusionhttps://scholarbank.nus.edu.sg/handle/10635/95800Title: Anomalous heat diffusion
Authors: Liu, S.; Hänggi, P.; Li, N.; Ren, J.; Li, B.
Abstract: Consider anomalous energy spread in solid phases, i.e., Δx2(t)≡∫(x-x)2ρE(x,t)dx tβ, as induced by a small initial excess energy perturbation distribution ρE(x,t=0) away from equilibrium. The second derivative of this variance of the nonequilibrium excess energy distribution is shown to rigorously obey the intriguing relation d2Δx2(t)/dt2=2CJJ(t)/(kBT2c), where CJJ(t) equals the thermal equilibrium total heat flux autocorrelation function and c is the specific volumetric heat capacity. Its integral assumes a time-local Helfand-like relation. Given that the averaged nonequilibrium heat flux is governed by an anomalous heat conductivity, the energy diffusion scaling determines a corresponding anomalous thermal conductivity scaling behavior. © 2014 American Physical Society.
Tue, 28 Jan 2014 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958002014-01-28T00:00:00Z
- Shuttling heat across one-dimensional homogenous nonlinear lattices with a Brownian heat motorhttps://scholarbank.nus.edu.sg/handle/10635/97915Title: Shuttling heat across one-dimensional homogenous nonlinear lattices with a Brownian heat motor
Authors: Li, N.; Zhan, F.; Hänggi, P.; Li, B.
Abstract: We investigate directed thermal heat flux across one-dimensional homogenous nonlinear lattices when no net thermal bias is present on average. A nonlinear lattice of Fermi-Pasta-Ulam-type or Lennard-Jones-type system is connected at both ends to thermal baths which are held at the same temperature on temporal average. We study two different modulations of the heat bath temperatures, namely: (i) a symmetric, harmonic ac driving of temperature of one heat bath only and (ii) a harmonic mixing drive of temperature acting on both heat baths. While for case (i) an adiabatic result for the net heat transport can be derived in terms of the temperature-dependent heat conductivity of the nonlinear lattice a similar such transport approach fails for the harmonic mixing case (ii). Then, for case (ii), not even the sign of the resulting Brownian motion induced heat flux can be predicted a priori. A nonvanishing heat flux (including a nonadiabatic reversal of flux) is detected which is the result of an induced dynamical symmetry breaking mechanism in conjunction with the nonlinearity of the lattice dynamics. Computer simulations demonstrate that the heat flux is robust against an increase of lattice sizes. The observed ratchet effect for such directed heat currents is quite sizable for our studied class of homogenous nonlinear lattice structures, thereby making this setup accessible for experimental implementation and verification. © 2009 The American Physical Society.
Thu, 06 Aug 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/979152009-08-06T00:00:00Z
- Many-Body Coherent Destruction of Tunnelinghttps://scholarbank.nus.edu.sg/handle/10635/97147Title: Many-Body Coherent Destruction of Tunneling
Authors: Gong, J.; Morales-Molina, L.; Hänggi, P.
Abstract: A new route to coherent destruction of tunneling is established by considering a monochromatic fast modulation of the self-interaction strength of a many-boson system. The modulation can be tuned such that only an arbitrarily, apriori prescribed number of particles are allowed to tunnel. The associated tunneling dynamics is sensitive to the odd or even nature of the number of bosons. © 2009 The American Physical Society.
Wed, 23 Sep 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/971472009-09-23T00:00:00Z
- Dissipationless directed transport in rocked single-band quantum dynamicshttps://scholarbank.nus.edu.sg/handle/10635/96249Title: Dissipationless directed transport in rocked single-band quantum dynamics
Authors: Gong, J.; Poletti, D.; Hanggi, P.
Abstract: Using matter waves that are trapped in a deep optical lattice, dissipationless directed transport is demonstrated to occur if the single-band quantum dynamics is periodically tilted on one half of the lattice by a monochromatic field. Most importantly, the directed transport can exist for almost all system parameters, even after averaged over a broad range of single-band initial states. The directed transport is theoretically explained within ac-scattering theory. Total reflection phenomena associated with the matter waves traveling from a tilting-free region to a tilted region are emphasized. The results are of relevance to ultracold physics and solid-state physics, and may lead to powerful means of selective, coherent, and directed transport of cold particles in optical lattices. © 2007 The American Physical Society.
Wed, 07 Mar 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/962492007-03-07T00:00:00Z
- Rectification in synthetic conical nanopores: A one-dimensional Poisson-Nernst-Planck modelhttps://scholarbank.nus.edu.sg/handle/10635/97778Title: Rectification in synthetic conical nanopores: A one-dimensional Poisson-Nernst-Planck model
Authors: Kosińska, I.D.; Goychuk, I.; Kostur, M.; Schmid, G.; Hänggi, P.
Abstract: Ion transport in biological and synthetic nanochannels is characterized by phenomena such as ion current fluctuations and rectification. Recently, it has been demonstrated that nanofabricated synthetic pores can mimic transport properties of biological ion channels. Here, the ion current rectification is studied within a reduced one-dimensional (1D) Poisson-Nernst-Planck (PNP) model of synthetic nanopores. A conical channel of a few nm to a few hundred nm in diameter, and of a few μm long is considered in the limit where the channel length considerably exceeds the Debye screening length. The rigid channel wall is assumed to be weakly charged. A one-dimensional reduction of the three-dimensional problem in terms of corresponding entropic effects is put forward. The ion transport is described by the nonequilibrium steady-state solution of the 1D Poisson-Nernst-Planck system within a singular perturbation treatment. An analytic formula for the approximate rectification current in the lowest order perturbation theory is derived. A detailed comparison between numerical results and the singular perturbation theory is presented. The crucial importance of the asymmetry in the potential jumps at the pore ends on the rectification effect is demonstrated. This so constructed 1D theory is shown to describe well the experimental data in the regime of small-to-moderate electric currents. © 2008 The American Physical Society.
Wed, 26 Mar 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977782008-03-26T00:00:00Z
- Nonequilibrium density-matrix description of steady-state quantum transporthttps://scholarbank.nus.edu.sg/handle/10635/97334Title: Nonequilibrium density-matrix description of steady-state quantum transport
Authors: Dhar, A.; Saito, K.; Hänggi, P.
Abstract: With this work we investigate the stationary nonequilibrium density matrix of current carrying nonequilibrium steady states of in-between quantum systems that are connected to reservoirs. We describe the analytical procedure to obtain the explicit result for the reduced density matrix of quantum transport when the system, the connecting reservoirs, and the system-reservoir interactions are described by quadratic Hamiltonians. Our procedure is detailed for both electronic transport described by the tight-binding Hamiltonian and for phonon transport described by harmonic Hamiltonians. For the special case of weak system-reservoir couplings, a more detailed description of the steady-state density matrix is obtained. Several paradigm transport setups for interelectrode electron transport and low-dimensional phonon heat flux are elucidated. © 2012 American Physical Society.
Wed, 18 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973342012-01-18T00:00:00Z
- Ratcheting heat flux against a thermal biashttps://scholarbank.nus.edu.sg/handle/10635/97759Title: Ratcheting heat flux against a thermal bias
Authors: Li, N.; Hänggi, P.; Li, B.
Abstract: Merely rocking the temperature in one heat bath can direct a steady heat flux from cold to hot against a (time-averaged) non-zero thermal bias in stylized nonlinear lattice junctions that are sandwiched between two heat baths. Likewise, for an average zero-temperature difference between the two contacts a net, ratchet-like heat flux emerges. Computer simulations show that this very heat flux can be manipulated and even reversed by suitably tailoring the frequency (≲100 MHz) of the alternating-temperature field. © Europhysics Letters Association. 2008.
Tue, 01 Jan 2008 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977592008-01-01T00:00:00Z
- Thermostated Hamiltonian dynamics with log oscillatorshttps://scholarbank.nus.edu.sg/handle/10635/98389Title: Thermostated Hamiltonian dynamics with log oscillators
Authors: Campisi, M.; Hänggi, P.
Abstract: With this work, we present two new methods for the generation of thermostatted, manifestly Hamiltonian dynamics and provide corresponding illustrations. The basis for this new class of thermostats is the peculiar thermodynamics as exhibited by logarithmic oscillators. These two schemes are best suited when applied to systems with a small number of degrees of freedom. © 2013 American Chemical Society.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/983892013-01-01T00:00:00Z
- Generalized Gibbs state with modified Redfield solution: Exact agreement up to second orderhttps://scholarbank.nus.edu.sg/handle/10635/96705Title: Generalized Gibbs state with modified Redfield solution: Exact agreement up to second order
Authors: Thingna, J.; Wang, J.-S.; Hänggi, P.
Abstract: A novel scheme for the steady state solution of the standard Redfield quantum master equation is developed which yields agreement with the exact result for the corresponding reduced density matrix up to second order in the system-bath coupling strength. We achieve this objective by use of an analytic continuation of the off-diagonal matrix elements of the Redfield solution towards its diagonal limit. Notably, our scheme does not require the provision of yet higher order relaxation tensors. Testing this modified method for a heat bath consisting of a collection of harmonic oscillators we assess that the system relaxes towards its correct coupling-dependent, generalized quantum Gibbs state in second order. We numerically compare our formulation for a damped quantum harmonic system with the nonequilibrium Greens function formalism: we find good agreement at low temperatures for coupling strengths that are even larger than expected from the very regime of validity of the second-order Redfield quantum master equation. Yet another advantage of our method is that it markedly reduces the numerical complexity of the problem; thus, allowing to study efficiently large-sized system Hilbert spaces. © 2012 American Institute of Physics.
Mon, 21 May 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/967052012-05-21T00:00:00Z
- Analytically solvable model of a driven system with quenched dichotomous disorderhttps://scholarbank.nus.edu.sg/handle/10635/95784Title: Analytically solvable model of a driven system with quenched dichotomous disorder
Authors: Denisov, S.I.; Kostur, M.; Denisova, E.S.; Hänggi, P.
Abstract: We perform a time-dependent study of the driven dynamics of overdamped particles that are placed in a one-dimensional, piecewise linear random potential. This setup of spatially quenched disorder then exerts a dichotomous varying random force on the particles. We derive the path integral representation of the resulting probability density function for the position of the particles and transform this quantity of interest into the form of a Fourier integral. In doing so, the evolution of the probability density can be investigated analytically for finite times. It is demonstrated that the probability density contains both a δ -singular contribution and a regular part. While the former part plays a dominant role at short times, the latter rules the behavior at large evolution times. The slow approach of the probability density to a limiting Gaussian form as time tends to infinity is elucidated in detail. © 2007 The American Physical Society.
Wed, 27 Jun 2007 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/957842007-06-27T00:00:00Z
- Berry-phase-induced heat pumping and its impact on the fluctuation theoremhttps://scholarbank.nus.edu.sg/handle/10635/95864Title: Berry-phase-induced heat pumping and its impact on the fluctuation theorem
Authors: Ren, J.; Hänggi, P.; Li, B.
Abstract: Applying adiabatic, cyclic two-parameter modulations we investigate quantum heat transfer across an anharmonic molecular junction contacted with two heat baths. We demonstrate that the pumped heat typically exhibits a Berry-phase effect in providing an additional geometric contribution to heat flux. Remarkably, a robust fractional quantized geometric phonon response is identified as well. The presence of this geometric phase contribution in turn causes a breakdown of the fluctuation theorem of the Gallavotti-Cohen type for quantum heat transfer. This can be restored only if (i) the geometric phase contribution vanishes and if (ii) the cyclic protocol preserves the detailed balance symmetry. © 2010 The American Physical Society.
Tue, 27 Apr 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958642010-04-27T00:00:00Z
- Molecular wires acting as quantum heat ratchetshttps://scholarbank.nus.edu.sg/handle/10635/97253Title: Molecular wires acting as quantum heat ratchets
Authors: Zhan, F.; Li, N.; Kohler, S.; Hänggi, P.
Abstract: We explore heat transfer in molecular junctions between two leads in the absence of a finite net thermal bias. The application of an unbiased time-periodic temperature modulation of the leads entails a dynamical breaking of reflection symmetry, such that a directed heat current may emerge (ratchet effect). In particular, we consider two cases of adiabatically slow driving, namely, (i) periodic temperature modulation of only one lead and (ii) temperature modulation of both leads with an ac driving that contains a second harmonic, thus, generating harmonic mixing. Both scenarios yield sizable directed heat currents, which should be detectable with present techniques. Adding a static thermal bias allows one to compute the heat current-thermal load characteristics, which includes the ratchet effect of negative thermal bias with positive-valued heat flow against the thermal bias, up to the thermal stop load. The ratchet heat flow in turn generates also an electric current. An applied electric stop voltage, yielding effective zero electric current flow, then mimics a solely heat-ratchet-induced thermopower ("ratchet Seebeck effect"), although no net thermal bias is acting. Moreover, we find that the relative phase between the two harmonics in scenario (ii) enables steering the net heat current into a direction of choice. © 2009 The American Physical Society.
Mon, 14 Dec 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/972532009-12-14T00:00:00Z
- Negative mobility induced by colored thermal fluctuationshttps://scholarbank.nus.edu.sg/handle/10635/97307Title: Negative mobility induced by colored thermal fluctuations
Authors: Kostur, M.; Luczka, J.; Hänggi, P.
Abstract: Anomalous transport of non-Markovian thermal Brownian particle dynamics in spatially periodic symmetric systems that is driven by time-periodic symmetric driving and constant bias is investigated numerically. The Brownian dynamics is modeled by a generalized Langevin equation with exponentially correlated Gaussian thermal noise, obeying the fluctuation-dissipation theorem. We study the role of nonzero correlation time of thermal fluctuations for the occurrence of absolute negative (linear) mobility (ANM) near zero bias, negative-valued, nonlinear mobility (NNM), and negative differential mobility (NDM) at finite bias away from equilibrium. We detect that a nonzero thermal correlation time can either enhance or also diminish the value of ANM. Moreover, finite thermal noise correlation can induce NDM and NNM in regions of parameter space for which such ANM and NNM behaviors are distinctly absent for limiting white thermal noise. In parts of the parameter space, we find a complex structure of regions of linear and nonlinear negative mobility: islands and tongues which emerge and vanish under parameters manipulation. While certain such anomalous transport regimes fade away with increasing temperature some specific regions interestingly remain rather robust. Outside those regimes with anomalous mobility, the ac/dc driven transport is either normal or the driven Brownian particles are not transported at all. © 2009 The American Physical Society.
Fri, 20 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/973072009-11-20T00:00:00Z
- Quantum machine using cold atomshttps://scholarbank.nus.edu.sg/handle/10635/97691Title: Quantum machine using cold atoms
Authors: Ponomarev, A.V.; Denisov, S.; Hänggi, P.
Abstract: For a machine to be useful in practice, it preferably has to meet two requirements: namely, (i) to be able to perform work under a load and (ii) its operational regime should ideally not depend on the time at which the machine is switched-on. We devise a minimal setup, consisting of two atoms only, for an ac-driven quantum motor which fulfills both these conditions. Explicitly, the motor consists of two different interacting atoms placed into a ring-shaped periodic optical potential - an optical "bracelet," - resulting from the interference of two counter-propagating Laguerre-Gauss laser beams. This bracelet is additionally threaded by a pulsating magnetic flux. While the first atom plays a role of a quantum "carrier," the second serves as a quantum "starter," which sets off the "carrier" into a steady rotational motion. For fixed zero-momentum initial conditions the asymptotic carrier velocity saturates to a unique, nonzero value which becomes increasingly independent on the starting time with increasing "bracelet"-size. We identify the quantum mechanisms of rectification and demonstrate that our quantum motor is able to perform useful work. Copyright © 2010 American Scientific Publishers.
Mon, 01 Nov 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/976912010-11-01T00:00:00Z
- Boosting work characteristics and overall heat-engine performance via shortcuts to adiabaticity: Quantum and classical systemshttps://scholarbank.nus.edu.sg/handle/10635/95880Title: Boosting work characteristics and overall heat-engine performance via shortcuts to adiabaticity: Quantum and classical systems
Authors: Deng, J.; Wang, Q.-H.; Liu, Z.; Hänggi, P.; Gong, J.
Abstract: Under a general framework, shortcuts to adiabatic processes are shown to be possible in classical systems. We study the distribution function of the work done on a small system initially prepared at thermal equilibrium. We find that the work fluctuations can be significantly reduced via shortcuts to adiabatic processes. For example, in the classical case, probabilities of having very large or almost zero work values are suppressed. In the quantum case, negative work may be totally removed from the otherwise non-positive-definite work values. We also apply our findings to a micro Otto-cycle-based heat engine. It is shown that the use of shortcuts, which directly enhances the engine output power, can also increase the heat-engine efficiency substantially, in both quantum and classical regimes. © 2013 American Physical Society.
Thu, 12 Dec 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/958802013-12-12T00:00:00Z
- Reduced density matrix for nonequilibrium steady states: A modified Redfield solution approachhttps://scholarbank.nus.edu.sg/handle/10635/97780Title: Reduced density matrix for nonequilibrium steady states: A modified Redfield solution approach
Authors: Thingna, J.; Wang, J.-S.; Hänggi, P.
Abstract: We describe a method to obtain the reduced density matrix (RDM) correct up to second order in system-bath coupling in nonequilibrium steady-state situations. The RDM is obtained via a scheme based on analytic continuation, using the time-local Redfield-like quantum master equation, which was earlier used by the same authors to obtain the correct thermal equilibrium description. This nonequilibrium modified Redfield solution is then corroborated with the exact RDM obtained via the nonequilibrium Green's function technique for the quantum harmonic oscillator. Lastly, the scheme is compared to different quantum master equations (QMEs), namely the time-local Redfield-like and the Lindblad-like QMEs, in order to illustrate the differences between each of these approaches. © 2013 American Physical Society.
Wed, 20 Nov 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/977802013-11-20T00:00:00Z
- The ring of brownian motion: The good, the bad and the simply sillyhttps://scholarbank.nus.edu.sg/handle/10635/98928Title: The ring of brownian motion: The good, the bad and the simply silly
Authors: Hanggi, P.
Abstract: In this plenary talk I give an account on the blossoming role that Brownian motion Theory and Experiment played - and still keeps doing so - in germinating and advancing several, partially diverse physical disciplines. Although the use of Brownian motion concepts generally most favorably impacted those scientific areas there are also some abuses where the application of such concepts may not describe satisfactorily physical reality. © 2009 American Institute of Physics.
Thu, 01 Jan 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/989282009-01-01T00:00:00Z