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 - TY - JOUR A1 - Palm, Timo A1 - Nalbach, Peter T1 - Nonperturbative environmental influence on dephasing JF - Physical Review A N2 - Environmental noise leads to dephasing and relaxation in a quantum system. Often, a rigorous treatment of multiple noise sources within a system-bath approach is not possible. We discuss the influence of environmental fluctuations on a quantum system whose dynamics is dephasing already due to a phenomenologically treated additional noise source. For this situation, we develop a path-integral approach, which allows us to treat the system-environment coupling in a numerically exact way, and additionally we extend standard perturbative approaches. We observe strong deviations between the numerically exact and the perturbative results even for weak system-bath coupling. This shows that standard perturbative approaches fail for additional, even weak, system-bath couplings if the system dynamics is already dissipative. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevA.96.032105 SN - 2469-9926 VL - 96 IS - 3 SP - 032105 ER - TY - JOUR A1 - Mujica-Martinez, Cesar A1 - Nalbach, Peter T1 - On the influence of underdamped vibrations on coherence and energy transfer times in lightharvesting complexes JF - Annalen der Physik Y1 - 2015 VL - 527 SP - 592 EP - 600 ER -