Twisted molecular excitons as mediators for changing the angular momentum of light

Abstract

Molecules with C N or C N h symmetry can absorb quanta of optical angular momentum to generate twisted excitons with well-defined quasi-angular momenta of their own. Angular momentum is conserved in such interactions at the level of a paraxial approximation for the light beam. A sequence of absorption events can thus be used to create a range of excitonic angular momenta.Subsequent decay can produce radiation with a single angular momentum equal to that accumulated. Such molecules can thus be viewed as mediators for changing the angular momentum of light. This sidesteps the need to exploit nonlinear light-matter interactions based on higher-order susceptibilities. A tight-binding paradigm is used to verify angular momentum conservation and demonstrate how it can be exploited to change the angular momentum of light. The approach is then extended to a time-dependent density functional theory setting where the key results are shown to hold in a many-body, multi-level setting.

Quantum electrodynamics in modern optics and photonics: tutorial

“…In eliciting the physics for the majority of applications discussed above, it has generally proved sufficient to use plane-wave representations of the quantum radiation modes, together with their polarization properties. Nonetheless, the same QED methods are highly amenable to application in the sphere of structured light [207], leading, for example, to the discovery that it is possible to deliver vortex photons by direct emission from suitably excited arrays [208][209][210] and so paving the way for a range of technical developments and implementations [211][212][213][214][215][216]. Whether the optical orbital angular momentum (OAM) of structured light could be transferred to the internal electronic degrees of freedom of an atom or molecule has been a well-debated topic, with highly significant implications in spectroscopy [217].…”

First-principles methodology for determining the angular momentum of excitons

“…In addition, quantum entanglement of states with AM > 10000 has been observed in Ref. 34. Only recently there are attempts to manipulate the AM of twisted light by excitons 35,36 .…”

“…This technical progress makes it possible to employ excitons to efficiently process and manipulate information encoded in light by bridging the gap between photonics and electronics 56 . An exciton that is generated by illuminating a molecule with C N (N ≥ 3) symmetry by twisted light, for example, obtains the AM of the absorbed photon, and it turns out that a chain of such molecules can be used to create excitonic wave packets with well defined linear and angular momenta 35,36,57 . A succession of absorption events generates excitonic wave packets carrying a range of AM.…”

Quantum formulation for nanoscale optical and material chirality: symmetry issues, space and time parity, and observables

“…Whilst beams of light with this vortex structure can routinely be produced by passing conventional Gaussian light through a variety of optical elements-notably spatial light modulators [76], it has been shown that rotationally symmetric chiral arrays can deliver vortex photons by direct emission [5,[77][78][79], as illustrated in figure 8. There is in fact a wide variety of other beams conveying orbital angular momentum, some including several kinds of modified-Gaussian vortex [80] described as having a perfect optical vortex structure [81], and others with the propagation-invariant character of Bessel beams [82].…”