arXiv subjects

Marian Florescu

Publications and source records attributed to Marian Florescu.

At least 19 recordsLinked to original sources

arXiv2026

Strong suppression of the photonic density of states in three-dimensional disordered silicon networks

Photonic bandgaps can open not only in crystalline dielectric materials but also in amorphous structures. Self-uniform amorphous gyroid networks have been proposed as promising disordered photonic architectures. Motivated by numerical studies, we combine direct laser-writing lithography with advanced materials processing to fabricate these structures from high-refractive-index silicon. Spectroscopic measurements at mid-infrared wavelengths reveal pronounced transmission minima. To investigate the formation of photonic band gaps in amorphous structures, we develop polarization-resolved transmission spectroscopy that separates ballistic and multiply scattered contributions, enabling direct identification of the underlying transport regimes. We observe a strong suppression of diffuse transmission, providing direct experimental evidence for a breakdown of conventional diffuse transport associated with a strongly reduced photonic density of states. Together with large-scale numerical simulations, our results establish the presence of a deep photonic pseudogap in an amorphous three-dimensional dielectric material and open new opportunities for observing disorder-induced localization phenomena, including Anderson localization of light.

physics.optics↗

arXiv2025

The Effect of Permanent Dipoles on Dark States in Molecular Dimers

Many organic molecules possess large permanent dipole moments that differ depending on the electronic state. These permanent dipoles influence both intermolecular coupling and interactions with the optical fields, yet they are often neglected in typical theoretical quantum optics treatments. Here, we investigate the optical properties and their effect on dark states of dimers possessing such permanent dipoles. We show that when monomers have excitation-dependent permanent dipoles, optical transitions between the bright and dark states of the dimer are enabled. We investigate how permanent dipoles allow for the existence of static driving terms between the ground and excited states of each monomer. In turn, these can cause the excited states of the monomers to couple indirectly to the zero excitation state of the dimer. This leads to interference between permanent and transition dipoles and can result in the formation of dark states that are entirely localised. Furthermore, dark states formed through indirect coupling exhibit enhanced robustness against energy level fluctuations, which may improve the efficiency of the design of photovoltaic devices.

quant-ph↗

arXiv2024

Dynamical Decoherence and Memory Effects in Green Fluorescent Proteins by Dielectric Relaxation

In this article, we explore the dynamical decoherence of the chromophores within a green fluorescent protein when coupled to a finite-temperature dielectric environment. Such systems are of significant interest due to their anomalously long coherence lifetimes compared to other biomolecules. We work within the spin-boson model and employ the Hierarchical Equations of Motion formalism which allows for the accounting of the full non-perturbative and non-Markovian characteristics of the system dynamics. We analyse the level coherence of independent green fluorescent protein chromophores and the energy transfer dynamics in homo-dimer green fluorescent proteins, focusing on the effect of dielectric relaxation on the timescales of these systems. Using the Fluctuation-Dissipation theorem, we generate spectral densities from local electric susceptibility generated from Poisson's equation and employ a Debye dielectric model for the solvent environment. For different system architectures, we identify a number of very striking features in the dynamics of the chromophore induced by the dielectric relaxation of the environment, resulting in strong memory effects that extend the coherence lifetime of the system. Remarkably, the complex architecture of the green fluorescent protein, which includes a cavity-like structure around the atomic system, is well suited to preserving the coherences in the homo-dimer system. The system dynamics generate a dynamical correlation between the coherent energy transfer between its sub-systems and the entropy production, which can lead to transient reductions in entropy, a unique feature of the non-Markovian nature of the system-environment interaction.

physics.chem-ph↗

arXiv2024

Stealthy and hyperuniform isotropic photonic bandgap structure in 3D

In photonic crystals the propagation of light is governed by their photonic band structure, an ensemble of propagating states grouped into bands, separated by photonic band gaps. Due to discrete symmetries in spatially strictly periodic dielectric structures their photonic band structure is intrinsically anisotropic. However, for many applications, such as manufacturing artificial structural color materials or developing photonic computing devices, but also for the fundamental understanding of light-matter interactions, it is of major interest to seek materials with long range non-periodic dielectric structures which allow the formation of {\it isotropic} photonic band gaps. Here, we report the first ever 3D isotropic photonic band gap for an optimized disordered stealthy hyperuniform structure for microwaves. The transmission spectra are directly compared to a diamond pattern and an amorphous structure with similar node density. The band structure is measured experimentally for all three microwave structures, manufactured by 3D-Laser-printing for meta-materials with refractive index up to $n=2.1$. Results agree well with finite-difference-time-domain numerical investigations and a priori calculations of the band-gap for the hyperuniform structure: the diamond structure shows gaps but being anisotropic as expected, the stealthy hyperuniform pattern shows an isotropic gap of very similar magnitude, while the amorphous structure does not show a gap at all. The centimeter scaled microwave structures may serve as prototypes for micrometer scaled structures with bandgaps in the technologically very interesting region of infrared (IR).

physics.app-ph↗

arXiv2023

Optical polaron formation in quantum systems with permanent dipoles

Many optically active systems possess spatially asymmetric electron orbitals. These generate permanent dipole moments, which can be stronger than the corresponding transition dipole moments, significantly affecting the system dynamics and creating polarised Fock states of light. We derive a master equation for these systems by employing an optical polaron transformation that captures the photon mode polarisation induced by the permanent dipoles. This provides an intuitive framework to explore their influence on the system dynamics and emission spectrum. We find that permanent dipoles introduce multiple-photon processes and a photon sideband which causes substantial modifications to single-photon transition dipole processes. In the presence of an external drive, permanent dipoles lead to an additional process that we show can be exploited to optimise the decoherence and transition rates. We derive the emission spectrum of the system, highlighting experimentally detectable signatures of optical polarons, and measurements that can identify the parameters in the system Hamiltonian, the magnitude of the differences in the permanent dipoles, and the steady-state populations of the system.

quant-ph↗

arXiv2022

Quantum memory effects in atomic ensembles coupled to photonic cavities

In this article we explore the dynamics of many-body atomic systems symmetrically coupled to a single Lorentzian photonic cavity. Our study reveals interesting dynamical characteristics including non-zero steady states, superradiant decay, enhanced energy transfer and the ability to modulate oscillations in the atomic system by tuning environmental degrees of freedom. We also analyse a configuration consisting of a three-atom chain embedded in a photonic cavity. Similarly, we find a strong enhancement of the energy transfer rate between the two ends of the chain and identified specific initial conditions that lead to significantly reduced dissipation between the two atoms at the end of the chain. Another configuration of interest consists of two symmetrical detuned reservoirs with respect to the atomic system. In the single-atom case, we show that it is possible to enhance the decay rate of the system by modulating its reservoir detuning, while in the many-atom case, this results in dynamics akin to the on-resonant cavity. Finally, we examine the validity of rotating wave approximation through a direct comparison against the numerically exact hierarchical equations of motion approach. We find good agreement in the weak coupling regime while in the intermediate coupling regime, we identify qualitative similarities, but the rotating wave approximation becomes less reliable. In the moderate coupling regime, we find deviation of the steady states due to the formation of mixed photon atom states.

quant-ph↗

arXiv2022

Quantum Reservoir Computing Implementations for Classical and Quantum Problems

Quantum reservoir computing has emerged as a promising paradigm within the field of quantum machine learning, harnessing the inherent properties of quantum systems to optimise and enhance information processing capabilities. Here, we explore the potential of quantum-inspired machine learning methodologies by leveraging the complex dynamics of quantum reservoirs to address computationally challenging tasks with enhanced efficiency and accuracy. To this end, we employ an open quantum system model comprising two-level atomic ensembles coupled to Lorentzian photonic cavities to construct a quantum physical reservoir computer layer for a recurrent neural network. We evaluate the effectiveness of this approach by applying it to a standard machine learning image-recognition problem and benchmarking its performance against a conventional neural network of similar architecture, but lacking the quantum physical reservoir computer layer. Remarkably, as the dataset size increases, the quantum physical reservoir computer outperforms the conventional neural network, requiring fewer training epochs and a smaller dataset to achieve comparable accuracy. Furthermore, we employ the quantum physical reservoir computing approach to model the dynamics of open quantum systems, focusing on atomic system ensembles interacting with a structured photonic reservoir associated with a photonic band-gap material. Our results reveal that the quantum reservoir computer provides equally powerful representations for quantum dynamical problems, maintaining effectiveness even under constraints of limited training data.

quant-ph↗

arXiv2021

Non-Markovian Dynamics of a Single Excitation within Many-Body Dissipative Systems

We explore the dynamics of $N$ coupled atoms to a generic bosonic reservoir under specific system symmetries. In the regime of multiple atoms coupled to a single reservoir with identical couplings, we identify remarkable effects, notably that the initial configuration of the atomic excited state amplitudes strongly impacts the dynamics of the system and can even fully sever the system from its environment. Additionally, we find that steady state amplitudes of the excited states become independent of the choice of the reservoir. The framework introduced is applied to a structured photonic reservoir associated with a photonic crystal, where we show it reproduces previous theoretical and experimental results and it predicts superradiant behaviour within the single-excitation regime.

quant-ph↗

arXiv2019

Complete photonic band gaps in 3D foams

To-date, despite remarkable applications in optoelectronics and tremendous amount of theoretical, computational and experimental efforts, there is no technological pathway enabling the fabrication of 3D photonic band gaps in the visible range. The resolution of advanced 3D printing technology does not allow to fabricate such materials and the current silica-based nanofabrication approaches do not permit the structuring of the desired optical material. Materials based on colloidal self-assembly of polymer spheres open 3D complete band gaps in the infrared range, but, owing to their critical index, not in the visible range. More complex systems, based on oriented tetrahedrons, are still prospected. Here we show, numerically, that FCC foams (Kepler structure) open a 3D complete band gap with a critical index of 2.80, thus compatible with the use of rutile TiO2. We produce monodisperse solid Kepler foams including thousands of pores, down to 10 um, and present a technological pathway, based on standard technologies, enabling the downsizing of such foams down to 400 nm, a size enabling the opening of a complete band gap centered at 500 nm.

physics.app-ph↗

arXiv2017

High-Q photonic crystal cavities in all-semiconductor photonic-crystal heterostructures

Photonic crystal cavities enable the realization of high Q-factor and low mode-volume resonators, with typical architectures consisting of a thin suspended periodically-patterned layer to maximize confinement of light by strong index guiding. We investigate a heterostructure-based approach comprising a high refractive index core and lower refractive index cladding layers. Whilst confinement typically decreases with decreasing index contrast between the core and cladding layers, we show that, counter-intuitively, due to the confinement provided by the photonic band structure in the cladding layers, it becomes possible to achieve Q-factors $>10^4$ with only a small refractive index contrast. This opens up new opportunities for implementing high Q-factor cavities in conventional semiconductor heterostructures, with direct applications to the design of electrically-pumped nano-cavity lasers using conventional fabrication approaches.

physics.app-ph↗

arXiv2017

Hyperuniform disordered phononic structures

We demonstrate the existence of large phononic band gaps in designed hyperuniform (isotropic) disordered two-dimensional (2D) phononic structures of Pb cylinders in epoxy matrix. The phononic band gaps in hyperuniform disordered phononic structures are comparable to band gaps of similar periodic structures, for both out-of-plane and in-plane polarizations. A large number of localized modes is identified near the band edges, as well as, diffusive transmission throughout the rest of the frequency spectrum. Very high-Q cavity modes for both out-of-plane and in-plane polarizations are formed by selectively removing a single cylinder out of the structure. Efficient waveguiding with almost 100% transmission trough waveguide structures with arbitrary bends is also presented. We expand our results to thin three-dimensional layers of such structures and demonstrate effective band gaps related to the respective 2D band gaps. Moreover, the drop in the Q factor for the three-dimensional structures is not more than three orders of magnitude compared to the 2D ones.

cond-mat.dis-nn↗

arXiv2017

Reciprocal space engineering with hyperuniform gold metasurfaces

Hyperuniform geometries feature correlated disordered topologies which follow from a tailored k-space design. Here we study gold plasmonic hyperuniform metasurfaces and we report evidence of the effectiveness of k-space engineering on both light scattering and light emission experiments. The metasurfaces possess interesting directional emission properties which are revealed by momentum spectroscopy as diffraction and fluorescence emission rings at size-specific k-vectors. The opening of these rotational-symmetric patterns scales with the hyperuniform correlation length parameter as predicted via the spectral function method.

physics.optics↗

arXiv2015

High-Q Optical Cavities in Hyperuniform Disordered Materials

We introduce the first designs for high-Q photonic cavities in slab architectures in hyperuniform disordered solids displaying isotropic band gaps. Despite their disordered character, hyperuniform disordered structures have the ability to tightly confine the TE-polarised radiation in slab configurations that are readily fabricable. The architectures are based on carefully designed local modifications of otherwise unperturbed hyperuniform dielectric structures. We identify a wide range of confined cavity modes, which can be classified according to their approximate symmetry (monopole, dipole, quadrupole, etc.) of the confined electromagnetic wave pattern. We demonstrate that quality factors ($Q$) $Q>10^{9}$ can be achieved for purely 2D structures, and that for three--dimensional finite-height photonic slabs, quality factors $Q>20,000$ can be maintained.

cond-mat.mes-hall↗

arXiv2013

Photonic band gap in isotropic hyperuniform disordered solids with low dielectric contrast

We report the first experimental demonstration of a TE-polarization photonic band gap (PBG) in a 2D isotropic hyperuniform disordered solid (HUDS) made of dielectric media with a index contrast of 1.6:1, very low for PBG formation. The solid is composed of a connected network of dielectric walls enclosing air-filled cells. Direct comparison with photonic crystals and quasicrystals permitted us to investigate band-gap properties as a function of increasing rotational isotropy. We present results from numerical simulations proving that the PBG observed experimentally for HUDS at low index contrast has zero density of states. The PBG is associated with the energy difference between complementary resonant modes above and below the gap, with the field predominantly concentrated in the air or in the dielectric. The intrinsic isotropy of HUDS may offer unprecedented flexibilities and freedom in applications (i. e. defect architecture design) not limited by crystalline symmetries.

cond-mat.mes-hall↗

arXiv2013

Isotropic Band Gaps and Freeform Waveguides Observed in Hyperuniform Disordered Photonic Solids

Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the first experimental realization of an isotropic complete photonic band gap (PBG) in a two-dimensional (2D) disordered dielectric structure. This structure is designed by a constrained-optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al2O3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this novel class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This first experimental verification of a complete PBG and realization of functional defects in this new class of materials demonstrates their potential as building blocks for precise manipulation of photons in planar optical micro-circuits and has implications for disordered acoustic and electronic bandgap materials.

cond-mat.mes-hall↗

arXiv2013

Optical cavities and waveguides in hyperuniform disordered photonic solids

Using finite difference time domain and band structure computer simulations, we show that it is possible to construct optical cavities and waveguide architectures in hyperuniform disordered photonic solids that are unattainable in photonic crystals. The cavity modes can be classified according to the symmetry (monopole, dipole, quadrupole,etc.) of the confined electromagnetic wave pattern. Owing to the isotropy of the band gaps characteristic of hyperuniform disordered solids, high-quality waveguides with freeform geometries (e.g., arbitrary bending angles) can be constructed that have no analogue in periodic or quasiperiodic solids. These capabilities have implications for many photonic applications.

cond-mat.mes-hall↗

arXiv2010

Effects of Random Link Removal on the Photonic Band Gaps of Honeycomb Networks

We explore the effects of random link removal on the photonic band gaps of honeycomb networks. Missing or incomplete links are expected to be common in practical realizations of this class of connected network structures due to unavoidable flaws in the fabrication process. We focus on the collapse of the photonic band gap due to the defects induced by the link removal. We show that the photonic band gap is quite robust against this type of random decimation and survives even when almost 58% of the network links are removed.

physics.optics↗

arXiv2010

Designer disordered materials with large complete photonic band gaps

We present designs of 2D isotropic, disordered photonic materials of arbitrary size with complete band gaps blocking all directions and polarizations. The designs with the largest gaps are obtained by a constrained optimization method that starts from a hyperuniform disordered point pattern, an array of points whose number variance within a spherical sampling window grows more slowly than the volume. We argue that hyperuniformity, combined with uniform local topology and short-range geometric order, can explain how complete photonic band gaps are possible without long-range translational order. We note the ramifications for electronic and phononic band gaps in disordered materials.

physics.optics↗