Other Condensed Matter

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New submissions for Fri, 17 May 24

[1]  arXiv:2405.09812 [pdf, ps, other]

Title: Mean-field and cumulant approaches to modelling organic polariton physics

Authors: Piper Fowler-Wright

Comments: PhD Thesis

Subjects: Other Condensed Matter (cond-mat.other); Quantum Physics (quant-ph)

In this thesis we develop methods for many-body open quantum systems and apply them to systems of organic polaritons. The methods employ a mean-field approach to reduce the dimensionality of large-scale problems. Initially assuming the absence of correlations in the many-body state, this approach is built upon in two ways.
First, we show how the mean-field approximation can be combined with matrix product operator methods to efficiently simulate the non-Markovian dynamics of a many-body system with strong coupling to multiple environments. We apply this method to calculate the threshold and photoluminescence for a realistic model of an organic laser.
Second, we extend the mean-field description by systematically including higher-order correlations via cumulant expansions of the Heisenberg equations of motion. We investigate the validity and convergence properties of these expansions, both with respect to expansion order and system size, for many-body systems with many-to-one network structures. We then show how the cumulant expansions may be used to calculate spatially resolved dynamics of organic polaritons. This enables a study of organic polariton transport in which we observe reversible conversion to dark exciton states and sub-group-velocity propagation.
The methods established in this work offer versatile tools for analysing large, many-body open quantum systems and investigating finite-size effects. Their application reveals the intricate dynamics of organic polaritons resulting from the interplay of strong light-matter coupling and vibrational effects.

Cross-lists for Fri, 17 May 24

[2]  arXiv:2405.09700 (cross-list from physics.optics) [pdf, ps, other]

Title: Unidirectional Amplification in the Frozen Mode Regime Enabled by a Nonlinear Defect

Authors: Serena Landers, William Tuxbury, Ilya Vitebskiy, Tsampikos Kottos

Comments: 4 pages, 3 figures

Subjects: Optics (physics.optics); Other Condensed Matter (cond-mat.other); Applied Physics (physics.app-ph)

A stationary inflection point (SIP) is a spectral singularity of the Bloch dispersion relation $\omega(k)$ of a periodic structure where the first and the second derivatives of $\omega$ with respect to $k$ vanish. An SIP is associated with a third order exceptional point degeneracy in the spectrum of the unit-cell transfer matrix, where there is a collapse of one propagating and two evanescent Bloch modes. At the SIP frequency, the incident wave can be efficiently converted into the frozen mode with greatly enhanced amplitude and vanishing group velocity. This can be very attractive for applications, including light amplification. Due to its non-resonant nature, the frozen mode regime (FMR) has fundamental advantages over common cavity resonances. Here, we propose a novel scheme for FMR-based unidirectional amplifiers by leveraging a tailored amplification/attenuation mechanism and a single nonlinear defect. The defect breaks the directional symmetry of the periodic structure and enables nonlinearity-related unidirectional amplification/ attenuation in the vicinity of the SIP frequency. We demonstrate the robustness of the amplification mechanism to local impurities and parasitic nonlinearity.

Replacements for Fri, 17 May 24

[3]  arXiv:2405.07832 (replaced) [pdf, ps, other]

Title: Electric-field gradients at the nuclei from all-electron, four-component relativistic density-functional theory using Gaussian-type orbitals

Authors: Marc Joosten, Michal Repisky, Marius Kadek, Pekka Pyykkö, Kenneth Ruud

Comments: 10 pages, 3 tables

Subjects: Other Condensed Matter (cond-mat.other)

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