arXiv subjects

Garth A. Jones

Publications and source records attributed to Garth A. Jones.

7 recordsLinked to original sources

arXiv2025

Indirect Communication Between Non-Markovian Baths

In this work we develop a model for an undamped vibration in the presence of an overdamped bath. This two-bath model involves a new derivation of the hierarchical equations of motion (HEOM) for an overdamped Lorentz-Drude (LD) environment that is summed together with an undamped oscillator (UO) bath, termed LDUO-HEOM. We show that information transfer occurs between the two baths, even in the absence of a direct coupling between the baths. This bath-system-bath, mediated information transfer leads to intricate non-Markovian dynamics. The model is analysed using expectation values of the bath coordinates and generates 2D electronic spectra that are in qualitative agreement with single-bath models. Furthermore, the model eliminates the additional superfluous damping introduced by the finite spectral width of the underdamped bath in our previous two-bath underdamped-overdamped, `bath vibration model' [J. Chem. Phys. 156, 084103 (2022)].

quant-ph↗

arXiv2024

Vibrational coherences in half-broadband 2D electronic spectroscopy: spectral filtering to identify excited state displacements

Vibrational coherences in ultrafast pump-probe (PP) and 2D electronic spectroscopy (2DES) provide insight into the excited state dynamics of molecules. Femtosecond coherence spectra (FCS) and 2D beat maps yield information about displacements of excited state surfaces for key vibrational modes. Half-broadband 2DES (HB2DES) uses a PP configuration with a white light continuum probe to extend the detection range and resolve vibrational coherences in the excited state absorption (ESA). However, interpretation of these spectra is difficult as they are strongly dependent on the spectrum of the pump laser and the relative displacement of the excited states along the vibrational coordinates. We demonstrate the impact of these convoluting factors for a model based upon cresyl violet. Careful consideration of the position of the pump spectrum can be a powerful tool in resolving the ESA coherences to gain insights into excited state displacements. The paper also highlights the need for caution in considering the spectral window of the pulse when interpreting these spectra.

physics.chem-ph↗

arXiv2023

Phonon Signatures in Photon Correlations

We show that the second-order, two-time correlation functions for phonons and photons emitted from a vibronic molecule in a thermal bath result in bunching and anti-bunching (a purely quantum effect), respectively. Signatures relating to phonon exchange with the environment are revealed in photon-photon correlations. We demonstrate that cross-correlation functions have a strong dependence on the order of detection giving insight into how phonon dynamics influences the emission of light. This work offers new opportunities to investigate quantum effects in condensed-phase molecular systems.

quant-ph↗

arXiv2021

Measures of Helicity and Chirality of Optical Vortex Beams

Analytical forms of the optical helicity and optical chirality of monochromatic Laguerre-Gaussian optical vortex beams are derived up to second order in the paraxial parameter $kw_0$. We show that input linearly polarised optical vortices which possess no optical chirality, helicity or spin densities can acquire them at the focal plane for values of a beam waist $w_0 \approx λ$ via an OAM-SAM conversion which is manifest through longitudinal (with respect to the direction of propagation) fields. We place the results into context with respect to the intrinsic and extrinsic nature of SAM and OAM, respectively; the continuity equation which relates the densities of helicity and spin; and the newly coined term Kelvins chirality which describes the extrinsic, geometrical chirality of structured laser beams. Finally we compare our work (which agrees with previous studies) to the recent article Köksal, et al. Optics Communications 490, 126907 (2021) which shows conflicting results, highlighting the importance of including all relevant terms to a given order in the paraxial parameter.

physics.optics↗

arXiv2021

Optical vortex dichroism in chiral particles

Circular dichroism is the differential rate of absorption of right- and left-handed circularly polarized light by chiral particles. Optical vortices which convey orbital angular momentum (OAM) possess a chirality associated with the clockwise or anti-clockwise twisting of their wavefront. Here it is highlighted that both oriented and randomly oriented chiral particles absorb photons from twisted beams at different rates depending on whether the vortex twists to the right or the left through a dipole coupling scheme. This is in contrast to previous studies that investigated dipole couplings with vortex modes in the paraxial approximation and showed no such chiral sensitivity to the vortex handedness: only in oriented media where electric quadrupole coupling contributes to optical activity effects due to absorption does such a mechanism exist for paraxial vortices. The distinct difference in the scheme highlighted in this work is that longitudinal fields are taken account of and these allow for OAM transfer even during dipole interactions. Due to the vortex dichroism persisting in randomly oriented collections of chiral particles, the mechanism has a distinct advantage in its potential applicability in chemical and biochemical applications where the systems under study are invariably in the liquid phase. Additionally, the result is put into context in terms of the quantifiable optical chirality, highlighting that optical OAM can in fact increase the optical chirality density of an electromagnetic field.

physics.optics↗

arXiv2020

Relevance of Longitudinal Fields of Paraxial Optical Vortices

Longitudinal electromagnetic fields generally become comparable with the usually dominant transverse components in strongly-focussed, non-paraxial beams. For optical vortex modes it is highlighted here how their angular momentum properties produce longitudinal fields that in general must be accounted for, even within the paraxial regime. First-order longitudinal components of quantized Laguerre-Gaussian modes are derived and numerically studied with respect to the paraxial parameter, highlighting light-matter and spin-orbit interactions that stem from longitudinal fields of weakly-focussed, paraxial beams in free space. New restrictions are cast on the validity of the paraxial approximation for optical vortices interacting with atoms, molecules and other nanostructures.

physics.optics↗

arXiv2018

Perspective: Quantum Hamiltonians for Optical Interactions

The multipolar Hamiltonian of quantum electrodynamics (QED) is extensively employed in chemical and optical physics to treat rigorously the interaction of electromagnetic fields with matter. It is also widely used to evaluate intermolecular interactions. The multipolar version of the Hamiltonian is commonly obtained by carrying out a unitary transformation of the Coulomb gauge Hamiltonian that goes by the name of Power-Zienau-Woolley (PZW). Not only does the formulation provide excellent agreement with experiment, and versatility in its predictive ability, but also superior physical insight. Recently, the foundations and validity of the PZW Hamiltonian have been questioned, raising a concern over issues of gauge transformation and invariance, and whether observable quantities obtained from unitarily equivalent Hamiltonians are identical. Here, an in-depth analysis of theoretical foundations clarifies the issues and enables misconceptions to be identified. Claims of non-physicality are refuted: the PZW transformation and ensuing Hamiltonian are shown to rest on solid physical principles and secure theoretical ground.

quant-ph↗