Identifying diamagnetic interactions in scattering and nonlinear optics

In the generic formulation of optical interactions there is, beyond the familiar electric and magnetic multipolar forms of coupling, an additional diamagnetization term that rarely receives attention. In fact it can give rise to effects that should be observable in the general context of nonlinear optical spectroscopy, as well as scattering. A quantum electrodynamical analysis reveals features of special interest in two specific cases: two-photon absorption and Rayleigh scattering. Diamagnetic contributions are seen to be dispersion free with regards to the frequency of input radiation, and can represent unique interactions within optical absorption and emission processes. There is also a configuration in which diamagnetic couplings, which are quadratic in the magnetic field, can supersede those that are dependent linearly on the electric field strength, such as the electric dipole. In this connection the influence of retroreflected circularly polarized light, which leads to a local distance dependence in magnitude of the electromagnetic fields, produces conditions in which the diamagnetization response can become a prominent feature in two-photon absorption

Nonlocalized Generation of Correlated Photon Pairs in Degenerate Down-Conversion

The achievement of optimum conversion efficiency in conventional spontaneous parametric down- conversion requires consideration of quantum processes that entail multisite electrodynamic coupling, actively taking place within the conversion material. The physical mechanism, which operates through virtual photon propagation, provides for photon pairs to be emitted from spatially separated sites of photon interaction; occasionally pairs are produced in which each photon emerges from a different point in space. The extent of such nonlocalized generation is influenced by individual variations in both distance and phase correlation. Mathematical analysis of the global contributions from this mechanism provides a quantitative measure for a degree of positional uncertainty in the origin of down-converted emission

Raman Optical Activity Using Twisted Photons

Raman optical activity underpins a powerful vibrational spectroscopic technique for obtaining detailed structural information about chiral molecular species. The effect centers on the discriminatory interplay between the handedness of material chirality with that of circularly polarized light. Twisted light possessing an optical orbital angular momentum carries helical phase fronts that screw either clockwise or anticlockwise and, thus, possess a handedness that is completely distinct from the polarization. Here a novel form of Raman optical activity that is sensitive to the handedness of the incident twisted photons through a spin-orbit interaction of light is identified, representing a new chiroptical spectroscopic technique

Quantum delocalization in photon-pair generation

The generation of correlated photon pairs is a key to the production of entangled quantum states, which have a variety of applications within the area of quantum information. In spontaneous parametric down-conversion—the primary method of generating correlated photon pairs—the associated photon annihilation and creation events are generally thought of as being colocated: The correlated pair of photons is localized with regards to the pump photon and its positional origin. A detailed quantum electrodynamical analysis highlights a mechanism exhibiting the possibility of a delocalized origin for paired output photons: The spatial extent of the region from which the pair is generated can be much larger than previously thought. The theory of both localized and nonlocalized degenerate down-conversion is presented, followed by a quantitative analysis using discrete-volume computational methods. The results may have significant implications for quantum information and imaging applications, and the design of nonlinear optical metamaterials