arXiv subjects

Gert-Ludwig Ingold

Publications and source records attributed to Gert-Ludwig Ingold.

At least 55 records · Page 3Linked to original sources

arXiv2008

Finite quantum dissipation: the challenge of obtaining specific heat

We consider a free particle coupled with finite strength to a bath and investigate the evaluation of its specific heat. A harmonic oscillator bath of Drude type with cutoff frequency omega_D is employed to model an ohmic friction force with dissipation strength gamma. Two scenarios for obtaining specific heat are presented. The first one uses the measurement of the kinetic energy of the free particle while the second one is based on the reduced partition function. Both descriptions yield results which are consistent with the Third Law of thermodynamics. Nevertheless, the two methods produce different results that disagree even in their leading quantum corrections at high temperatures. We also consider the regime where the cutoff frequency is smaller than the friction strength, i.e. omega_D 1.

quant-ph↗

arXiv2008

Detection of interaction-induced nonlocal effects using perfectly transmitting nanostructures

We consider one-dimensional transport through an interacting region in series with a point-like one-body scatterer. When the conductance of the interacting region is perfect, independently of the interaction strength, a nonlocal interaction effect yields a total conductance of the composed system that depends on the interaction strength and is lower than the transmission of the one-body scatterer. This qualitative nonlocal effect allows to probe the dressing cloud of an interacting system by ideal noninteracting leads. The conductance correction increases with the strength of the interaction and the reflection of the one-body scatterer (attaining relative changes >50%), and decreases with the distance between the interacting region and the one-body scatterer. Scaling laws are obtained and possible experimental realizations are suggested.

cond-mat.mes-hall↗

arXiv2007

Sidebands in the light absorption of driven metallic nanoparticles

The dynamics of the surface plasmon in laser-driven metallic nanoparticles is described by means of a master-equation formalism. Within the Markov approximation, the dynamics is studied for different regimes ranging from weak excitation in photoabsorption experiments to strong excitation in pump-probe spectroscopy. It is shown that two collective levels are sufficient to describe the dynamics of the surface plasmon. On this basis, we predict the appearance of sidebands in the absorption spectrum of the probe laser field in pump-probe experiments.

cond-mat.mes-hall↗

arXiv2007

Anomaly in the relaxation dynamics close to the surface plasmon resonance

We propose an explanation for the anomalous behaviour observed in the relaxation dynamics of the differential optical transmission of noble-metal nanoparticles. Using the temperature dependences of the position and the width of the surface plasmon resonance, we obtain a strong frequency dependence in the time evolution of the transmission close to the resonance. In particular, our approach accounts for the slowdown found below the plasmon frequency. This interpretation is independent of the presence of a nearby interband transition which has been invoked previously. We therefore argue that the anomaly should also appear for alkaline nanoparticles.

cond-mat.mes-hall↗

arXiv2006

Relation between phase space coverage and entanglement for spin-1/2 systems

For systems of two and three spins 1/2 it is known that the second moment of the Husimi function can be related to entanglement properties of the corresponding states. Here, we generalize this relation to an arbitrary number of spins in a pure state. It is shown that the second moment of the Husimi function can be expressed in terms of the lengths of the concurrence vectors for all possible partitions of the N-spin system in two subsystems. This relation implies that the phase space distribution of an entangled state is less localized than that of a non-entangled state. As an example, the second moment of the Husimi function is analyzed for an Ising chain subject to a magnetic field perpendicular to the chain axis.

quant-ph↗

arXiv2006

Lissajous curves and semiclassical theory: The two-dimensional harmonic oscillator

The semiclassical treatment of the two-dimensional harmonic oscillator provides an instructive example of the relation between classical motion and the quantum mechanical energy spectrum. We extend previous work on the anisotropic oscillator with incommensurate frequencies and the isotropic oscillator to the case with commensurate frequencies for which the Lissajous curves appear as classical periodic orbits. Because of the three different scenarios depending on the ratio of its frequencies, the two-dimensional harmonic oscillator offers a unique way to explicitly analyze the role of symmetries in classical and quantum mechanics.

quant-ph↗

arXiv2006

Surface plasmon in metallic nanoparticles: renormalization effects due to electron-hole excitations

The electronic environment causes decoherence and dissipation of the collective surface plasmon excitation in metallic nanoparticles. We show that the coupling to the electronic environment influences the width and the position of the surface plasmon resonance. A redshift with respect to the classical Mie frequency appears in addition to the one caused by the spill-out of the electronic density outside the nanoparticle. We characterize the spill-out effect by means of a semiclassical expansion and obtain its dependence on temperature and the size of the nanoparticle. We demonstrate that both, the spill-out and the environment-induced shift are necessary to explain the experimentally observed frequencies and confirm our findings by time-dependent local density approximation calculations of the resonance frequency. The size and temperature dependence of the environmental influence results in a qualitative agreement with pump-probe spectroscopic measurements of the differential light transmission.

cond-mat.mes-hall↗

arXiv2006

Quantum Brownian motion and the Third Law of thermodynamics

The quantum thermodynamic behavior of small systems is investigated in presence of finite quantum dissipation. We consider the archetype cases of a damped harmonic oscillator and a free quantum Brownian particle. A main finding is that quantum dissipation helps to ensure the validity of the Third Law. For the quantum oscillator, finite damping replaces the zero-coupling result of an exponential suppression of the specific heat at low temperatures by a power-law behavior. Rather intriguing is the behavior of the free quantum Brownian particle. In this case, quantum dissipation is able to restore the Third Law: Instead of being constant down to zero temperature, the specific heat now vanishes proportional to temperature with an amplitude that is inversely proportional to the ohmic dissipation strength. A distinct subtlety of finite quantum dissipation is the result that the various thermodynamic functions of the sub-system do not only depend on the dissipation strength but depend as well on the prescription employed in their definition.

quant-ph↗

arXiv2005

Charge Tunneling Rates in Ultrasmall Junctions

1. Introduction 2. Description of the environment 3. Electron tunneling rates for single tunnel junctions 4. Examples of electromagnetic environments 5. Tunneling rates in Josephson junctions 6. Double junction and single electron transistor 7. Microscopic foundation

cond-mat.mes-hall↗

arXiv2004

Fundamental Aspects of Quantum Brownian Motion

With this work we elaborate on the physics of quantum noise in thermal equilibrium and in stationary non-equilibrium. Starting out from the celebrated quantum fluctuation-dissipation theorem we discuss some important consequences that must hold for open, dissipative quantum systems in thermal equilibrium. The issue of quantum dissipation is exemplified with the fundamental problem of a damped harmonic quantum oscillator. The role of quantum fluctuations is discussed in the context of both, the nonlinear generalized quantum Langevin equation and the path integral approach. We discuss the consequences of the time-reversal symmetry for an open dissipative quantum dynamics and, furthermore, point to a series of subtleties and possible pitfalls. The path integral methodology is applied to the decay of metastable states assisted by quantum Brownian noise.

quant-ph↗

arXiv2004

Residual conductance of correlated one-dimensional nanosystems: A numerical approach

We study a method to determine the residual conductance of a correlated system by means of the ground-state properties of a large ring composed of the system itself and a long non-interacting lead. The transmission probability through the interacting region and thus its residual conductance is deduced from the persistent current induced by a flux threading the ring. Density Matrix Renormalization Group techniques are employed to obtain numerical results for one-dimensional systems of interacting spinless fermions. As the flux dependence of the persistent current for such a system demonstrates, the interacting system coupled to an infinite non-interacting lead behaves as a non-interacting scatterer, but with an interaction dependent elastic transmission coefficient. The scaling to large lead sizes is discussed in detail as it constitutes a crucial step in determining the conductance. Furthermore, the method, which so far had been used at half filling, is extended to arbitrary filling and also applied to disordered interacting systems, where it is found that repulsive interaction can favor transport.

cond-mat.mes-hall↗

arXiv2003

Charge transport through a molecule driven by a high-frequency field

We study the current and the associated noise for the transport through a two-site molecule driven by an external oscillating field. Within a high-frequency approximation, the time-dependent Hamiltonian is mapped to a static one with effective parameters that depend on the driving amplitude and frequency. This analysis allows an intuitive physical picture explaining the nontrivial structure found in the noise properties as a function of the driving amplitude. The presence of dips in the Fano factor permits a control of the noise level by means of an appropriate external driving.

cond-mat.mes-hall↗

arXiv2003

Phase space signatures of the Anderson transition

We use the inverse participation ratio based on the Husimi function to perform a phase space analysis of the Anderson model in one, two, and three dimensions. Important features of the quantum states remain observable in phase space in the large system size limit, while they would be lost in a real or momentum space description. From perturbative approaches in the limits of weak and strong disorder, we find that the appearance of a delocalization-localization transition is connected to the coupling, by a weak potential, of momentum eigenstates which are far apart in momentum space. This is consistent with recent results obtained for the Aubry-Andre model and provides a novel view on the metal-insulator transition.

cond-mat.dis-nn↗

arXiv2002

The electrostatic potential profile along a biased molecular wire: A model quantum mechanical calculation

We study the electrostatic potential of a molecular wire bridging two metallic electrodes in the limit of weak contacts. With the use of a tight-binding model including a fully three-dimensional treatment of the electrostatics of the molecular junction, the potential is shown to be poorly screened, dropping mostly along the entire molecule. In addition, we observe pronounced Friedel oscillations that can be related to the breaking of electron-hole symmetry. Our results are in semi-quantitative agreement with recent state-of-the-art ab initio calculations and point to the need of a three-dimensional treatment to properly capture the behavior of the electrostatic potential. Based on these results, current-voltage curves are calculated within the Landauer formalism. It is shown that Coulomb interaction partially compensates the localization of the charges induced by the electric field and consequently tends to suppress zones of negative differential resistance.

physics.chem-ph↗

arXiv2002

Conductance through a One-Dimensional Correlated System: Relation to Persistent Currents and Role of the Contacts

Based on a recent proposal [O.P. Sushkov, Phys. Rev. B 64, 155319 (2001)], we relate the quantum conductance through a sample in which electrons are strongly correlated to the persistent current of a large ring, composed of the sample and a non-interacting lead. A scaling law in the lead length allows to extrapolate to a well-defined value of the conductance, depending only on intrinsic properties of the sample and the nature of the contacts between the sample and the lead. For strongly disordered samples, the conductance is found to be enhanced by the interaction.

cond-mat.str-el↗

arXiv2002

Path Integrals and Their Application to Dissipative Quantum Systems

Introduction Path Integrals - Introduction - Propagator - Free Particle - Path Integral Representation of Quantum Mechanics - Particle on a Ring - Particle in a Box - Driven Harmonic Oscillator - Semiclassical Approximation - Imaginary Time Path Integral Dissipative Systems - Introduction - Environment as Collection of Harmonic Oscillators - Effective Action Damped Harmonic Oscillator - Partition Function - Ground State Energy and Density of States - Position Autocorrelation Function

quant-ph↗

arXiv2002

On the electrostatic potential profile in biased molecular wires

The potential profile across a biased molecular junction is calculated within the framework of a simple Thomas-Fermi type screening model. In particular, the relationship between this profile and the lateral molecular cross section is examined. We find that a transition from a linear potential profile to a potential that drops mainly near the molecule-metal contacts occurs with increasing cross section width, in agreement with numerical quantum calculations.

physics.chem-ph↗

arXiv2002

Delocalization and Heisenberg's uncertainty relation

In the one-dimensional Anderson model the eigenstates are localized for arbitrarily small amounts of disorder. In contrast, the Harper model with its quasiperiodic potential shows a transition from extended to localized states. The difference between the two models becomes particularly apparent in phase space where Heisenberg's uncertainty relation imposes a finite resolution. Our analysis points to the relevance of the coupling between momentum eigenstates at weak potential strength for the delocalization of a quantum particle.

cond-mat.dis-nn↗