Quantum nanophotonics is an active research field with emerging applications that range from quantum computing to imaging and telecommunications. This has motivated scientists and engineers to develop sources for entangled photons that can be integrated into nano-scale photonic circuits. Practical application of nanoscale devices requires a high photon-pair generation rate, room-temperature operation, and entangled photons emitted at telecommunications wavelengths in a directional manner.

Optical superoscillation refers to a wave packet that can oscillate locally in a frequency exceeding its highest Fourier component. This intriguing phenomenon enables production of extremely localized waves that can break the optical diffraction barrier. Indeed, superoscillation has proven to be an effective technique for overcoming the diffraction barrier in optical superresolution imaging. The trouble is that strong side lobes accompany the main lobes of superoscillatory waves, which limits the field of view and hinders application.

Interaction of a laser pulse and a relativistic electron beam in a dipole magnet. Credit: Shanghai Advanced Research Institute.

Electromagnetic (EM) waves in the terahertz (THz) regime contribute to important applications in communications, security imaging, and bio- and chemical sensing. Such wide applicability has resulted in significant technological progress. However, due to weak interactions between natural materials and THz waves, conventional THz devices are typically bulky and inefficient. Although ultracompact active THz devices do exist, current electronic and photonic approaches to dynamic control have lacked efficiency.