Environmental modification of dipole interactions has long been explored in energy transport. Here we consider the effects of a tunable graphene monolayer upon nearly H-type or J-type molecular aggregates, concentrating on the inversion of one type of coupling to the other. Modelling the graphene as being deposited on a metallic substrate, we find that as the surface conductivity of the graphene is varied, there is a corresponding change in the parameter region over which coupling inversion is predicted. This provides a route towards observing the predicted coupling inversion in a real system by dynamically changing the surface conductivity during a single run of an experiment.

The search for photonic devices with a desired functionality is undergoing a revolution due to the emergence of inverse design, where structures are algorithmically grown in such a way that they extremize one or more desired observables. The field of inverse design is large and rapidly-expanding—here we review recent progress towards one particular goal for which it can be used, namely design of cavities that are aiming to influence the interaction of cavity fields with microscopic systems (atoms, molecules, quantum dots, etc). We begin with a pedagogical explanation of the mathematical background of inverse design via topology optimization, detailing gradient-based optimization, metaheuristics and manufacturing constraints. We then review recent developments in enhanced light-matter interactions via optical cavity optimization, including planar resonators, photonic crystals and whispering gallery mode resonators, among others. We end with an outlook towards the frontiers of cavity design, including multi-objective design, plasmonics and nuclear quantum optics.

Cooperative optical effects are enabled and controlled by interactions between molecular dipoles, meaning that their mutual orientation is of paramount importance to, for example, superabsorbing light-harvesting antennas. Here we show how to move beyond the possibilities of simple geometric tailoring, demonstrating how a metallic sphere placed within a ring of parallel dipoles engineers an effective Hamiltonian that generates "guide-sliding" states within the ring system. This allows steady-state superabsorption in noisy room temperature environments, outperforming previous designs while being significantly simpler to implement. As exemplified by this showcase, our approach represents a powerful design paradigm for tailoring cooperative light-matter effects in molecular structures that extends beyond superabsorbing systems, to a huge array of quantum energy transport systems.

We present a general-purpose algorithm for automatic production of a structure inducing a desired Casimir-Polder force and develop a geometry that exerts a repulsion on a ground-state atom. The results are reminiscent of the ring-like geometries previously used to induce repulsion, but with some new features and-importantly-discovered completely independently of any input from the user. This represents a powerful new, to the best of our knowledge, paradigm in the study of atom-surface forces: instead of the user testing various geometries against a desired figure of merit, the goal can be specified, and then an appropriate geometry can be created automatically.

In this work we generalise the adjoint method of inverse design to nonreciprocal media. As a test case, we use three-dimensional topology optimization via the level-set method to optimise one-way energy transfer for point-like source and observation points. To achieve this we introduce a suite of tools, chiefly what we term the `Faraday-adjoint' method which allows for efficient shape optimization in the presence of magneto-optical media. We carry out an optimization based on a very general equation that we derive for energy transfer in a nonreciprocal medium, and link finite-different time-domain numerics to analytics via a modified Born series generalised to a tensor permittivity. This work represents a stepping stone towards practical nanophotonic optical isolation, often regarded as the `holy grail' of integrated photonics.

The behavior of an atomic system is influenced by introducing a metallic surface. This work explores how the decay landscape can be altered by the presence of sharp corners. We utilize analytical expressions for Hertz and vector potentials in the presence of a perfectly conducting wedge with arbitrary opening angle to obtain the relevant electrostatic Green's functions. We use these to examine two scenarios: the modified spontaneous decay of a single atom, which leads us to speculate about potential applications in microscopy, and the case of a more fundamental, theoretical interest, the behavior of an entangled pair of atoms near a corner. The latter, when two atoms are positioned "out of the line of sight," opens up a possible line of investigation into devices that are able to "see around corners."

We examine the low-energy spectrum and polarisation of the dipole moments of two static polar molecules under the influence of an external dc electric field and their anisotropic dipole-dipole interaction. We model the molecules as quantum rigid rotors to take their rotational degrees of freedom into account, and consider a selection of linear, symmetric and asymmetric top molecules. We provide a comprehensive examination of the energy spectra and polarisation of the dipoles for varying inter-molecular separation and direction of the electric field, and find that the properties of the molecules depend strongly on the field's direction at short separations, showing the importance of accounting for molecular rotation. Our results provide important insight into applications of cold molecules for quantum computation and molecular dipolar gases.

We expand the theoretical toolbox for controllable quantum reflection by departing from a simple planar reflector. We introduce a circular hole (a micropore) of variable size, for which the electrostatic image potential can be exactly calculated. We combine this with two-dimensional simulations of wavepacket propagation at arbitrary angle of incidence to show that the quantum reflection probability can be tuned over a wide range of values.

Our experience of the world around us is governed almost entirely by light–matter interactions. At the most fundamental level, such interactions are described by quantum electrodynamics (QED), a well-established theory that has stood up to decades of experimental testing to remarkable degrees of precision. However, the complexity of real systems almost always means that the quantum electrodynamical equations describing a given scenario are often infeasible or impractical to solve. Thus, a sequence of approximations and idealisations are made, in order to build up from the simple case of an isolated electron interacting with a gauge field leading to the deceptively simple laws governing reflection and refraction at mirrors and lenses. This review provides a pedagogical overview of this journey, concentrating on cases where external boundary conditions can be used as a control method. Beginning from the fundamental Lagrangian, topics include gauge freedom, perturbative macroscopic QED descriptions of spontaneous decay, Casimir–Polder forces, resonant energy transfer, interatomic Coulombic decay, all of which are described in terms of the dyadic Green's tensor that solves the Helmholtz equation. We discuss in detail how to calculate this tensor in practical situations before outlining new techniques in the design and optimisation of perturbative light–matter interactions, highlighting some recent advances in free-form, unconstrained inverse design of optical devices. Finally, an outlook towards the frontiers in the interaction of quantum light with matter is given, including its interface with chemical reactivity via polaritonic chemistry and quantum chemistry via quantum electrodynamical density functional theory (QEDFT).

Superposing multiple plane waves can generate helicity lattices in which the optical helicity varies regularly in space. Here we propose an inverse design method for constructing arbitrary helicity structures based on placing a digital object of dielectric inclusions in three-dimensional space. We apply the method to design structures that reproduce two-dimensional lattices embedded within a three-dimensional region using only a single plane wave as an input. In order to demonstrate the power and flexibility of our method, we go beyond the paradigm of a regular lattice and propose structures that can create arbitrary images consisting of regions of varying helicity, again using only a single plane wave as an input.

We reveal the existence of polarizing quantum phases for the enantiomers of cold, interacting chiral molecules in an optical helicity lattice by means of an extended Bose-Hubbard model. These recently proposed lattices have sites with alternating helicity which exert a discriminatory force on chiral molecules with different handedness. In our study of the phase diagram we find that a strong dipolar repulsion between molecules results in the separation of left and right enantiomers.

Casimir–Polder interactions cause energy and momentum exchange between microscopic and macroscopic bodies, a process mediated by quantum fluctuations in the coupled matter-electromagnetic field system. The dynamics of such effects are yet to be experimentally investigated due to the dominance of static effects at currently attainable atomic velocities. However, Y. Guo and Z. Jacob [ Opt. Express , 22:26193-26202, 2014] have proposed a non-static two-plate set-up where quantum fluctuation mediated effects have a strong velocity-dependent resonance, leading to a giant friction force on the plates. Here a more easily realisable set-up, a moving atom between two stationary plates, is analysed within a QED framework to establish the spectroscopic Casimir-Polder effects on the atom, and their velocity dependence. While no large velocity-dependent enhancement is found, expressions for the plate-induced spectroscopic effects on the atom were found, and further shown to be equivalent to the Doppler-shifted static result within certain velocity constraints. A numerical analysis investigates the behaviour of this system for the well studied case of the 6 D 3 / 2 → 7 P 1 / 2 transition in 133 Cs interacting with sapphire plates.

The PHENIX collaboration presents a systematic study of $\pi^0$ production from $p$$+$$p$, $p$$+$Al, $p$$+$Au, $d$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. Measurements were performed with different centrality selections as well as the total inelastic, 0%--100%, selection for all collision systems. For 0%--100% collisions, the nuclear modification factors, $R_{xA}$, are consistent with unity for $p_T$ above 8 GeV/$c$, but exhibit an enhancement in peripheral collisions and a suppression in central collisions. The enhancement and suppression characteristics are similar for all systems for the same centrality class. It is shown that for high-$p_T$-$\pi^0$ production, the nucleons in the $d$ and $^3$He interact mostly independently with the Au nucleus and that the counter intuitive centrality dependence is likely due to a physical correlation between multiplicity and the presence of a hard scattering process. These observations disfavor models where parton energy loss has a significant contribution to nuclear modifications in small systems. Nuclear modifications at lower $p_T$ resemble the Cronin effect -- an increase followed by a peak in central or inelastic collisions and a plateau in peripheral collisions. The peak height has a characteristic ordering by system size as $p$$+$Au $>$ $d$$+$Au $>$ $^{3}$He$+$Au $>$ $p$$+$Al. For collisions with Au ions, current calculations based on initial state cold nuclear matter effects result in the opposite order, suggesting the presence of other contributions to nuclear modifications, in particular at lower $p_T$.

Resonant energy transfer from a donor to an acceptor is one of the most basic interactions between atomic and molecular systems. In real-life situations, the donor and acceptor are not isolated but in fact coupled to their environment and to other atoms and molecules. The presence of a third body can modify the rate of energy transfer between donor and acceptor in distinctive and intricate ways, especially when the three-site system is itself interacting with a larger macroscopic background such as a solvent. The rate can be calculated perturbatively, which ordinarily requires the summation of very large numbers of Feynman-like diagrams. Here we demonstrate a method based on canonical perturbation theory that allows us to reduce the computational effort required, and use this technique to derive a formula for the rate of three-body resonance energy transfer in a background environment. As a proof of principle, we apply this to the situation of a dimer positioned near a dielectric interface, with a distant third molecule controlling the rate, finding both enhancement or suppression of the rate depending on system parameters.

The effect of cavities or plates upon the electromagnetic quantum vacuum are considered in the context of electro-optic sampling (EOS), revealing how they can be directly studied. These modifications are at the heart of e.g. the Casimir force or the Purcell effect such that a link between EOS of the quantum vacuum and environment-induced vacuum effects is forged. Furthermore, we discuss the microscopic processes underlying EOS of quantum-vacuum fluctuations, leading to an interpretation of these experiments in terms of exchange of virtual photons. With this in mind it is shown how one can reveal the dynamics of vacuum fluctuations by resolving them in the frequency and time domains using EOS experiments.

We implement a shape optimization algorithm for body-assisted light-matter interactions described by the formalism of macroscopic quantum electrodynamics. The approach uses the level-set method to represent and incrementally evolve dielectric environments. Utilizing finite-difference time-domain techniques we demonstrate the ability of the algorithm by optimizing the rate of resonance energy transfer in two dimensions. The resulting geometries enhance the transfer rate by several orders of magnitude.

We provide an in-depth discussion of a theoretical framework recently introduced [Lindel et al., Phys. Rev. A 102, 041701(R) (2020)] which is capable of predicting the electromagnetic field emerging from a nonlinear crystal through which a coherent laser pulse is shone. This framework is based on macroscopic quantum electrodynamics and includes dispersion and absorption effects inside the crystal and allows for arbitrary optical environments through the classical Green's tensor. We introduce a diagrammatic approach with which the nonlinear processes contributing to the electric field operator up to certain orders in the perturbation series can be represented in a convenient way. Applying this framework to the setup of electro-optic sampling experiments of the polaritonic quantum vacuum, we derive analytical results for the electro-optic sampling between distinct spatiotemporal regions. Also, we discuss different approximations and the parameter ranges in which they apply including angled or diverging beams, thermal fluctuations, as well as (linear) absorption effects upon the polaritonic quantum vacuum. Finally, we compare these theoretical results to experimental data.