Photonics: Forbidden light

Nicholas Rivera

Anedio Ranfagni, Ilaria Cacciari

Measurements of delay time in the transfer of modulation between a modulated to an unmodulated one, both of them derived by the same microwave source, are reported and interpreted. In the light of these results, the transfer of modulation can be hypothesized as due to a stochastic, classically-forbidden process, assisted by a photon–photon scattering mechanism.

Rachel Pei Chin Won

Anonymous, Gopal Dixit

High-harmonic generation in solids provides a powerful window into light-driven electron dynamics on attosecond timescales, yet the role of quantum fluctuations of the driving field remains largely unexplored. Here, we show that the quantum state of light offers a nonclassical degree of freedom for controlling strong-field dynamics in quantum materials. Using graphene driven by bicircular quantum light composed of counterrotating ω and 2 ω components, we theoretically predict that squeezing-induced fluctuations break the dynamical symmetry of the classical bicircular field and activate otherwise forbidden harmonics. By analyzing the helicity-resolved harmonic spectra, we uncover robust polarization signatures uniquely dictated by the squeezed mode's profile, including a relative-phase-controlled helicity switching in the lowest orders. Crucially, second-order intensity correlations reveal that these forbidden harmonics exhibit strongly enhanced, super-Poissonian photon-number fluctuations, confirming that they inherit and directly transduce the nonclassical statistics of the squeezed driving vacuum. Our findings establish forbidden harmonics as high-fidelity optical probes of the quantum state of light and provide additional opportunities at the intersection of quantum optics, strong-field physics, and lightwave engineering in quantum materials.

Axel André, Mikhail D. Lukin

When a resonance associated with electromagnetically induced transparency in an atomic ensemble is modulated by an off-resonant standing light wave, a band of frequencies can appear for which light propagation is forbidden. We show that dynamic control of such a band gap can be used to coherently convert a propagating light pulse into a stationary excitation with nonvanishing photonic component. This can be accomplished with high efficiency and negligible noise even at the level of few-photon quantum fields thereby facilitating possible applications in quantum nonlinear optics and quantum information.