TY - JOUR A1 - Palm, Timo A1 - Nalbach, Peter T1 - Suppressing relaxation through dephasing JF - Physical Review A. Atomic, molecular, and optical physics N2 - We study the nonequilibrium dynamics of a quantum system under the influence of two noncommuting fluctuation sources, i.e., purely dephasing fluctuations and relaxational fluctuations. We find that increasing purely dephasing fluctuations suppress increasing relaxation in the quantum system. This effect is further enhanced when both fluctuation sources are fully correlated. These effects arise for medium to strong primary fluctuations already when the secondary fluctuations are weak due to their noncommuting coupling to the quantum system. Dephasing, in contrast, is increased by increasing any of the two fluctuations. Fully correlated fluctuations result in overdamping at much lower system-bath coupling than uncorrelated noncommuting fluctuations. In total, we observe that treating subdominant secondary environmental fluctuations perturbatively leads, as neglecting them, to erroneous conclusions. KW - quantum dissipation KW - noncommuting fluctuations Y1 - 2021 U6 - https://doi.org/10.1103/PhysRevA.103.022206 SN - 2469-9926 VL - 103 IS - 2 SP - Artikelnr. 022206 ER - TY - JOUR A1 - Nalbach, Peter T1 - Single-molecule junctions sensitive to binary solvent mixtures JF - Physical Review B N2 - We propose a quantum-mechanical model to calculate the nonlinear differential conductance of a single molecular junction immersed in a solvent, either in pure form or as a binary mixture with varying volume fraction. The solvent mixture is captured by a dielectric continuum model for which the resulting spectral density is determined within the Gladstone-Dale approach. The conductance of the molecular junction is calculated by a real-time diagrammatic technique. We find a strong variation of the conductance maximum for varying volume fraction of the solvent mixture. Importantly, the calculated molecular nonlinear conductance shows a very good agreement with experimentally measured data for common molecular junctions in various polar solvent mixtures. Y1 - 2022 U6 - https://doi.org/https://doi.org/10.1103/PhysRevB.106.075413 VL - 2022 IS - 106 SP - Article Number: 075413 ER - TY - JOUR A1 - Nalbach, Peter A1 - Javanbakht, Samaneh A1 - Stahl, Christopher A1 - Thorwart, Michael T1 - Stueckelberg Oscillations in a Two-State Two-Path Model of a Conical Intersection JF - Annalen der Physik N2 - The two-state two-path model is introduced as a minimized model to describe the quantum dynamics of an electronic wave packet in the vicinity of a conical intersection. It involves two electronic potential energy surfaces each of which hosts a pair of quasi-classical trajectories over which the wave packet is assumed to be delocalized. When both trajectories evolve dynamically either diabatically or adiabatically, the full wave packet dynamics shows only features of the dynamics around avoided level crossings in the vicinity of the conical intersection. When one trajectory evolves adiabatically whereas the other trajectory follows a diabatic evolution, quantum mechanical interference of the wave packet components on each path generates Stueckelberg oscillations in the transition probability. These are surprisingly robust against a dissipative environment and, thus, should be a marker for conical intersections. Y1 - 2017 U6 - https://doi.org/10.1002/andp.201600147 SN - 1521-3889 VL - 529 IS - 9 SP - 1600147 ER - TY - JOUR A1 - Duan, Hong-Guang A1 - Dijkstra, Arend G. A1 - Nalbach, Peter T1 - Efficient tool to calculate two-dimensional optical spectra for photoactive molecular complexes JF - Physical Review E Y1 - 2015 VL - 92 SP - 042708 ER - TY - JOUR A1 - Nacke, Phillipp A1 - Otterpohl, Florian A1 - Thorwart, Michael A1 - Nalbach, Peter T1 - Dephasing and pseudocoherent quantum dynamics in super-Ohmic environments JF - Physical Review A N2 - Dephasing in quantum systems is typically the result of their interaction with environmental degrees of freedom. We investigate within a spin-boson model the influence of a super-Ohmic environment on the dynamics of a quantum two-state system. A super-Ohmic environment thereby models typical bulk phonons which are a common disturbance for solid state quantum systems as, for example, nitrogen-vacancy centers. By applying the numerically exact quasiadiabatic path-integral approach we show that for strong system-bath coupling, pseudocoherent dynamics emerges, i.e., oscillatory dynamics at short times due to slaving of the quantum system to the bath dynamics. We extend the phase diagram known for sub-Ohmic and Ohmic environments into the super-Ohmic regime and observe a pronounced nonmonotonous behavior. Super-Ohmic purely dephasing fluctuations strongly suppress the amplitude of coherent dynamics at very short times with no subsequent further decay at later times. Nevertheless, they render the dynamics overdamped. The corresponding phase separation line shows also a nonmonotonous behavior, very similar to the pseudocoherent dynamics. Y1 - 2023 U6 - https://doi.org/https://doi.org/10.1103/PhysRevA.107.062218 VL - 2023 IS - 107 SP - Article Number: 062218 ER - TY - JOUR A1 - Gurski, Gregor A1 - Kirchberg, Henning A1 - Nalbach, Peter A1 - Thorwart, Michael T1 - Hydration shell effects in ac-driven single-molecule junctions JF - Physical Review B N2 - We propose a quantum-mechanical model to calculate the current through a single molecular junction immersed in a solvent and surrounded by a thin shell of bound water under an applied ac voltage. The solvent plus hydration shell are captured by a dielectric continuum model for which the resulting spectral density is determined. Here the dielectric properties, e.g., the Debye relaxation time and the dielectric constant, of the bulk solvent and the hydration shell as well as the shell thickness directly enter. We determine the charge current through the molecular junction under an ac voltage in the sequential tunneling regime where we solve a quantum master equation by a real-time diagrammatic technique. Interestingly, the Fourier components of the charge current show an exponential-like decline when the hydration shell thickness increases. Finally, we apply our findings to binary solvent mixtures with varying volume fractions and find that the current is highly sensitive to both the hydration shell thickness as well as the volume fraction of the solvent mixture, giving rise to possible applications as shell and concentration sensors on the molecular scale. Y1 - 2023 U6 - https://doi.org/https://doi.org/10.1103/PhysRevB.107.165413 VL - 2023 IS - 107 SP - Article Number: 165413 ER - TY - JOUR A1 - Nalbach, Peter T1 - Crossing time in the dissipative Landau-Zener quantum dynamics JF - The European Physical Journal B N2 - We study the dynamics of a quantum two-state system driven through an avoided crossing under the influence of a super-Ohmic environment. We determine the Landau–Zener probability employing the numerical exact quasi-adiabatic path integral and a Markovian weak coupling approach. Increasing the driving time in the numerical protocol, we find converged results which shows that super-Ohmic environments only influence the Landau Zener probability within a finite crossing time window. This crossing time is qualitatively determined by the environmental cut-off energy. At weak coupling, we show that the Markovian weak coupling approach provides an accurate description. Since pure dephasing of a super-Ohmic bath is non-Markovian, this highlights that pure dephasing hardly influences the Landau–Zener probability. The finite crossing time window, thus, results from the suppression of relaxation once the energy splitting exceeds the environmental cut-off energy. Y1 - 2022 U6 - https://doi.org/https://doi.org/10.1140/epjb/s10051-022-00306-z VL - 2022 IS - 41 SP - Article number: 41 ER - TY - JOUR A1 - Kirchberg, Henning A1 - Nalbach, Peter A1 - Thorwart, Michael T1 - Nonequilibrium quantum solvation with a time-dependent Onsager cavity JF - The journal of chemical physics Y1 - 2018 SN - 0021-9606 VL - 148 IS - 16 SP - 164301 ER - TY - JOUR A1 - Nalbach, Peter A1 - Javanbakht, Samaneh A1 - Stahl, Christopher A1 - Thorwart, Michael T1 - Stueckelberg oscillations in a two-state two-path model of a conical intersection JF - Annalen der Physik N2 - The two-state two-path model is introduced as a minimized model to describe the quantum dynamics of an electronic wave packet in the vicinity of a conical intersection. It involves two electronic potential energy surfaces each of which hosts a pair of quasi-classical trajectories over which the wave packet is assumed to be delocalized. When both trajectories evolve dynamically either diabatically or adiabatically, the full wave packet dynamics shows only features of the dynamics around avoided level crossings in the vicinity of the conical intersection. When one trajectory evolves adiabatically whereas the other trajectory follows a diabatic evolution, quantum mechanical interference of the wave packet components on each path generates Stueckelberg oscillations in the transition probability. These are surprisingly robust against a dissipative environment and, thus, should be a marker for conical intersections. KW - open quantum systems KW - conical intersection KW - nonadiabatic dynamics Y1 - 2016 U6 - https://doi.org/10.1002/andp.201600147 ER - TY - JOUR A1 - Reichert, Josha A1 - Nalbach, Peter A1 - Thorwart, Michael T1 - Dynamics of a quantum two-state system in a linearly driven quantum bath JF - Physical Review A N2 - When an open quantum system is driven by an external time-dependent force, the coupling of the driving to the central system is usually included, whereas the impact of the driving field on the bath is neglected. We investigate the effect of a quantum bath of linearly driven harmonic oscillators on the relaxation dynamics of a quantum two-level system which is not directly driven. In particular, we calculate the frequency-dependent response of the system when the bath is subject to Dirac and Gaussian driving pulses. We show that a time-retarded effective force on the system is induced by the driven bath which depends on the full history of the perturbation and the spectral characteristics of the underlying bath. In particular, when a structured Ohmic bath with a pronounced Lorentzian peak is considered, the dynamical response of the system to a driven bath is qualitatively different than that of the undriven bath. Specifically, additional resonances appear which can be directly associated with a Jaynes-Cummings-like effective energy spectrum. Y1 - 2016 VL - 94 IS - 3 SP - 032127 ER - TY - JOUR A1 - Schechter, Moshe A1 - Nalbach, Peter A1 - Burin, A. L. T1 - Nonuniversality and strongly interacting two-level systems in glasses at low temperatures JF - New journal of physics. The open-access journal for physics N2 - Recent experimental results showing atypical nonlinear absorption and marked deviations from well known universality in the low temperature acoustic and dielectric losses in amorphous solids prove the need for improving the understanding of the nature of two-level systems (TLSs) in these materials. Here we suggest the study of TLSs focused on their properties which are nonuniversal. Our theoretical analysis shows that the standard tunneling model and the recently suggested two-TLS model provide markedly different predictions for the experimental outcome of these studies. Our results may be directly tested in disordered lattices, e.g KBr:CN, where there is ample theoretical support for the validity of the two-TLS model, as well as in amorphous solids. Verification of our results in the latter will significantly enhance understanding of the nature of TLSs in amorphous solids, and the ability to manipulate them and reduce their destructive effect in various cutting edge applications including superconducting qubits. Y1 - 2018 U6 - https://doi.org/10.1088/1367-2630/aac930 SN - 1367-2630 VL - 20 IS - June SP - 063048 ER - TY - JOUR A1 - Otterpohl, Florian A1 - Nalbach, Peter A1 - Thorwart, Michael T1 - Hidden Phase of the Spin-Boson Model JF - Physical Review Letters N2 - A quantum two-level system immersed in a sub-Ohmic bath experiences enhanced low-frequency quantum statistical fluctuations which render the nonequilibrium quantum dynamics highly non-Markovian. Upon using the numerically exact time-evolving matrix product operator approach, we investigate the phase diagram of the polarization dynamics. In addition to the known phases of damped coherent oscillatory dynamics and overdamped decay, we identify a new third region in the phase diagram for strong coupling showing an aperiodic behavior. We determine the corresponding phase boundaries. The dynamics of the quantum two-state system herein is not coherent by itself but slaved to the oscillatory bath dynamics. Y1 - 2022 U6 - https://doi.org/https://doi.org/10.1103/PhysRevLett.129.120406 VL - 2022 IS - 129 SP - Article Number: 120406 ER - TY - JOUR A1 - Nalbach, Peter A1 - Leyton, Vicente T1 - Magnus expansion for a chirped quantum two-level system JF - Physical Review A N2 - We derive a Magnus expansion for a frequency chirped quantum two-level system. We obtain a time-independent effective Hamiltonian which generates a stroboscopic time evolution. At lowest order the according dynamics is identical to results from using a rotating wave approximation. We determine, furthermore, also the next higher-order corrections within our expansion scheme in correspondence to the Bloch-Siegert shifts for harmonically driven systems. Importantly, our scheme can be extended to more complicated systems, i.e., even many-body systems. Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevA.98.023855 VL - 98 IS - 2 SP - 023855 ER -