arXiv subjects

Philip Bleicker

Publications and source records attributed to Philip Bleicker.

5 recordsLinked to original sources

arXiv2021

Dynamic mean-field theory for dense spin systems at infinite temperature

A dynamic mean-field theory for spin ensembles (spinDMFT) at infinite temperatures on arbitrary lattices is established. The approach is introduced for an isotropic Heisenberg model with $S = \tfrac12$ and external field. For large coordination numbers, it is shown that the effect of the environment of each spin is captured by a classical time-dependent random mean-field which is normally distributed. Expectation values are calculated by averaging over these mean-fields, i.e., by a path integral over the normal distributions. A self-consistency condition is derived by linking the moments defining the normal distributions to spin autocorrelations. In this framework, we explicitly show how the rotating wave approximation becomes a valid description for increasing magnetic field. We also demonstrate that the approach can easily be extended. Exemplarily, we employ it to reach a quantitative understanding of a dense ensemble of spins with dipolar interaction which are distributed randomly on a plane including static Gaussian noise as well.

cond-mat.stat-mech↗

arXiv2021

Charge dynamics in magnetically disordered Mott insulators

With the aid of both a semi-analytical and a numerically exact method we investigate the charge dynamics in the vicinity of half-filling in the one- and two-dimensional $t$-$J$ model derived from a Fermi-Hubbard model in the limit of large interaction $U$ and hence small exchange coupling $J$. The spin degrees of freedom are taken to be disordered. So we consider the limit $0 < J \ll T \ll W$ where $W$ is the band width. We focus on evaluating the spectral density of a single hole excitation and the charge gap which separates the upper and the lower Hubbard band. One of the key findings is the evidence for the absence of sharp edges of the Hubbard band, instead Gaussian tails appear.

cond-mat.str-el↗

arXiv2020

Probing thermalization in quenched (non-)integrable Fermi-Hubbard models

Using numerically exact methods we examine the Fermi-Hubbard model on arbitrary cluster topology. We focus on the question which systems eventually equilibrate or even thermalize after an interaction quench when initially prepared in a state highly entangled between system and bath. We find that constants of motion in integrable clusters prevent equilibration to the thermal state. We discuss the size of fluctuations during equilibration and thermalization and the influence of integrability. The influence of real space topology and in particular of infinite-range graphs on equilibration and thermalization is studied.

cond-mat.str-el↗

arXiv2018

Strong quenches in the one-dimensional Fermi-Hubbard model

The one-dimensional Fermi-Hubbard model is used as testbed for strong global parameter quenches. With the aid of iterated equations of motion in combination with a suitable scalar product for operators we describe the dynamics and the long-term behavior in particular of the system after interaction quenches. This becomes possible because the employed approximation allows for oscillatory dynamics avoiding spurious divergences. The infinite-time behavior is captured by an analytical approach based on stationary phases; no numerical averages over long times need to be computed. We study the most relevant frequencies in the dynamics after the quench and find that the local interaction $U$ as well as the band width $W$ dominate. In contrast to former studies a crossover instead of a sharp dynamical transition depending on the strength of the quench is identified. For weak quenches the band width is more important while for strong quenches the local interaction $U$ dominates.

cond-mat.str-el↗

arXiv2016

Persisting correlations of a central spin coupled to large spin baths

The decohering environment of a quantum bit is often described by the coupling to a large bath of spins. The quantum bit itself can be seen as a spin $S=1/2$ which is commonly called the central spin. The resulting central spin model describes an important mechanism of decoherence. We provide mathematically rigorous bounds for a persisting magnetization of the central spin in this model with and without magnetic field. In particular, we show that there is a well defined limit of infinite number of bath spins. Only if the fraction of very weakly coupled bath spins tends to 100\% does no magnetization persist.

quant-ph↗