arXiv subjects

Roger Andrews

Publications and source records attributed to Roger Andrews.

6 recordsLinked to original sources

arXiv2025

Photon-Mediated Hybridization and Dissipative Transport in a Cavity-QED Ring-Acceptor Architecture

We investigate excitation transfer in an engineered cavity QED transport architecture consisting of an N-site donor ring coupled coherently to a central acceptor and driven by a single quantized photon mode. The system evolves under a Lindblad master equation including spontaneous loss and pure dephasing. In the ordered symmetric limit, the dynamics reduce exactly to a photon-bright mode-acceptor trimer, allowing closed-form analytic expressions for transfer efficiencies and mode-resolved losses. We demonstrate that near-unity efficiency arises from photon-mediated hybridization that generates a dark transport channel in which ring population is strongly suppressed. This cavity-induced mechanism bypasses dissipative dark modes of the ring and is distinct from conventional excitonic transport or environmentally assisted quantum transport (ENAQT). Static disorder in photon-ring coupling activates lossy ring modes through hybridization, while intra-ring coupling primarily shifts spectral crossings and can restore efficiency by separating dissipative channels. The model is interpreted as a tunable quantum-optical transport device. Our analytic reduction provides clear design principles for engineered quantum transport networks operating in cavity-QED platforms.

physics.optics↗

arXiv2025

Quantum Excitation Transfer in an Artificial Photosynthetic Light-Harvesting System

We analytically derive transfer probabilities and efficiencies for an artificial light-harvesting photosynthetic system, which consists of a ring coupled to a central acceptor. For an incident photon pair, we find near-perfect single excitation transfer efficiency with negligible double excitation transfer in the weak coupling regime. In the strong coupling regime, single excitation transfer efficiency was greater than 90%, while the double excitation efficiency was approximately 50%. We have found that the three main factors which determine high transfer efficiencies are large acceptor probabilities, long acceptor decay times, and strong photon-ring coupling. A possible implementation of the theoretical framework to bio-inspired solar energy devices is also discussed.

physics.chem-ph↗

arXiv2020

The effect of disorder on polaritons in a coupled array of cavities

The effect of disorder in the intensity of the driving laser on a coupled array of cavities described by a Bose-Hubbard Hamiltonian for dark-state polaritons is investigated. A canonically-transformed Gutzwiller wave function is used to investigate the phase diagram and dynamics of a one-dimensional system with uniformly distributed disorder in the Rabi frequency. In the phase diagram, we find the emergence of a Bose glass phase that increases in extent as the strength of the disorder increases. We study the dynamics of the system when subject to a ramp in the Rabi frequency which, starting from the superfluid phase, is decreased linearly and then increased to its initial value. We investigate the dependence of the density of excitations, the relaxation of the superfluid order parameter and the excess energy pumped into the system on the inverse ramp rate, $τ$. We find that, in the absence of disorder, the defect density oscillates with a constant envelope, while the relaxation of the order parameter and excess energy oscillate with $τ^{-1.5}$ and $τ^{-2}$ envelopes respectively. In the presence of disorder in the Rabi frequency, the defect density oscillates with a decaying envelope, the relaxation of the order parameter no longer decreases as $τ$ increases while the residual energy decreases as $τ$ increases. The rate at which the envelope of the defect density decays increases with increasing disorder strength, while the excess energy falls off more slowly with increasing disorder strength.

cond-mat.other↗

arXiv2020

Polariton dynamics of a disordered three-cavity system of four-level atom

The effect of disorder in the intensity of the driving laser on the dynamics of a disordered three-cavity system of four-level atoms is investigated. This system can be described by a Bose-Hubbard Hamiltonian for dark-state polaritons. We examine the evolution of the first- and second-order correlation functions, the photon and atomic excitation numbers and the basis state occupation probabilities. We use the full Hamiltonian and the approximate Bose-Hubbard Hamiltonian with uniform and speckle disorder, as well as with different dipole couplings. We find that the results for the two Hamiltonians are in good agreement. We also find that it is possible to obtain bunching and antibunching of the polaritons by varying the dipole couplings and that polaritons can be driven into a purely photonic state by varying the laser intensity.

cond-mat.other↗

arXiv2020

The dynamics of a polariton dimer in a disordered coupled array of cavities

We investigate the effect of disorder in the laser intensity on the dynamics of dark-state polaritons in an array of 20 cavities, each containing an ensemble of four-level atoms that is described by a Bose-Hubbard Hamiltonian. We examine the evolution of the polariton number in the cavities starting from a state with either one or two polaritons in one of the cavities. For the case of a single polariton without disorder in the laser intensity, we calculate the wavefunction of the polariton and find that it disperses away from the initial cavity with time. The addition of disorder results in minimal suppression of the dispersal of the wavefunction. In the case of two polaritons with an on-site repulsion to hopping strength ratio of 20, we find that the polaritons form a repulsively bound state or dimer. Without disorder the dimer wavefunction disperses similarly to the single polariton wavefunction but over a longer time period. The addition of sufficiently strong disorder results in localization of the polariton dimer. The localization length is found to be described by a power law with exponent -1.31. We also find that we can localise the dimer at any given time by switching on the disorder.

cond-mat.mes-hall↗

arXiv2004

Spontaneous and stimulated emission tuning characteristics of a Josephson junction in a microcavity

We have investigated theoretically the tuning characteristics of a Josephson junction within a microcavity for one-photon spontaneous emission and for one-photon and two-photon stimulated emission. For spontaneous emission, we have established the linear relationship between the magnetic induction and the voltage needed to tune the system to emit at resonant frequencies. For stimulated emission, we have found an oscillatory dependence of the emission rate on the initial Cooper pair phase difference and the phase of the applied field. Under specific conditions, we have also calculated the values of the applied radiation amplitude for the first few emission maxima of the system and for the first five junction-cavity resonances for each process. Since the emission of photons can be controlled, it may be possible to use such a system to produce photons on demand. Such sources will have applications in the fields of quantum cryptography, communications and computation.

cond-mat.supr-con↗