Quantum Interference in Two-Photon Scattering by Lossy Spheres Reveals Spectral Symmetry Effects

The scattering of light provides fundamental insights into how matter interacts with electromagnetic radiation, and recent work explores this phenomenon with a focus on the complex interplay of quantum and classical effects. A. Ciattoni, along with colleagues, investigates how two photons scatter from a macroscopic sphere that absorbs some light, revealing surprising interference patterns. This research demonstrates that the way photons interact with the sphere depends critically on their initial properties and the sphere’s characteristics, leading to constructive or destructive interference in the detected light. Importantly, the team shows that these interference effects are highly sensitive to the shape of the incoming light pulses, suggesting a novel method for identifying entangled photons using the properties of lossy materials and offering a new avenue for quantum technologies.

Quantum interference effects in two-photon scattering by a macroscopic lossy sphere Researchers investigate the quantum optical scattering of two-photon wavepackets by a macroscopic lossy sphere using a refined quantum electrodynamic model incorporating modified noise. When two photons impinge upon the sphere, the resulting scattered field exhibits quantum interference phenomena, revealing how quantum effects manifest in light-matter interactions at scales where classical descriptions typically suffice. This study provides insights into photon behaviour in lossy environments and deepens our understanding of light-matter interactions at the quantum level.

The sphere undergoes investigation from two directions, resulting in three independent scattering processes where two, one, or zero photons survive. Non-collinearity of the incoming photons creates two quantum paths, leading to interference effects in the detection of these processes, governed by the wavepacket’s spectral symmetry. By exploiting rotational invariance, the research demonstrates that different scattering geometries exist, allowing for coincidence detection of scattered photons exhibiting perfect constructive or destructive, Hong-Ou-Mandel, interference, regardless of whether the scattering is symmetric or asymmetric.

Quantum Field Theory in Lossy Materials

This compilation assembles concepts related to quantum electrodynamics, scattering theory, and light-matter interactions, particularly within lossy and dispersive materials. It covers the theoretical foundations and key techniques used to describe light interacting with complex materials, extending standard quantum electrodynamics to account for light interacting with lossy and dispersive materials.

References detail how to correctly quantize the electromagnetic field within a dielectric medium, accounting for absorption and frequency-dependent properties. A significant portion focuses on the scattering of electromagnetic waves by particles, especially in the Mie regime, and how to treat scattering in the presence of loss and dispersion. The challenges of modeling materials that absorb light and have frequency-dependent refractive indices are repeatedly emphasized, requiring careful treatment of the material’s response to the electromagnetic field.

Many references relate to the interaction of light with nanoscale objects, where quantum effects become important, including localized surface plasmons, strong coupling, and the modification of light-matter interactions at the nanoscale. The references also explore how to extend quantum electrodynamics to describe the collective behaviour of many atoms or molecules in a material, crucial for understanding macroscopic optical properties. A recurring theme is the use of a modified noise approach to account for the effects of loss and dispersion on the fluctuating electromagnetic field, incorporating dissipation into the quantum description.

Key concepts highlighted include the quantization of the electromagnetic field in dielectrics, Kramers-Kronig relations ensuring causality, local field corrections accounting for the field experienced by atoms within a material, and the powerful Green’s function approach for solving electromagnetic problems. The tensor scattering matrix describes the scattering of electromagnetic waves by anisotropic objects, while Bell states and spectral symmetry are relevant to generating and characterizing non-classical light sources. Mie theory provides a cornerstone for scattering theory, and Fano resonance describes a sharp resonance when a discrete state interacts with a continuum.

Strong coupling, where light-matter interaction exceeds dissipation, leads to hybrid light-matter states. The Langevin noise approach provides a method for incorporating dissipation into quantum electrodynamics. The inclusion of recent publications indicates that this is an active area of research with ongoing developments.

Lossy Sphere Scattering Enhances Interference Effects

This research demonstrates a significant advance in understanding how light interacts with matter, specifically through the scattering of two-photon wavepackets by lossy spheres. Scientists have shown that these interactions result in multiple scattering processes, where two, one, or zero photons survive, and that the resulting interference effects are highly sensitive to the geometry of the incoming light and the spectral characteristics of the wavepackets. This work extends beyond traditional beam splitters by offering greater flexibility in scattering geometry and enabling interference effects not possible with transparent objects.

The team discovered that classical Mie resonances within the lossy sphere dramatically enhance these interference effects, creating spectral bandwidths where constructive and destructive interference are particularly strong. Importantly, the probability of detecting scattered photons is demonstrably affected by the symmetry of the incoming wavepacket’s spectrum, particularly when the wavepacket’s frequency aligns with a Mie resonance. This sensitivity, with discrepancies of several orders of magnitude between symmetric and antisymmetric wavepackets, suggests a novel technique for identifying polariton entanglement.

The authors acknowledge that the analysis focuses on specific scattering geometries and wavepacket characteristics, and that further investigation is needed to explore the full range of possibilities. Future work could focus on experimentally verifying these findings and exploring the potential for developing new devices based on these principles. The research provides a foundation for exploring light-matter interactions in complex systems and opens avenues for innovative approaches to quantum information processing.