Terahertz quantum plasmonics at nanoscales and angstrom scales

Abstract

Through the manipulation of metallic structures, light–matter interaction can enter into the realm of quantum mechanics. For example, intense terahertz pulses illuminating a metallic nanotip can promote terahertz field–driven electron tunneling to generate enormous electron emission currents in a subpicosecond time scale. By decreasing the dimension of the metallic structures down to the nanoscale and angstrom scale, one can obtain a strong field enhancement of the incoming terahertz field to achieve atomic field strength of the order of V/nm, driving electrons in the metal into tunneling regime by overcoming the potential barrier. Therefore, designing and optimizing the metal structure for high field enhancement are an essential step for studying the quantum phenomena with terahertz light. In this review, we present several types of metallic structures that can enhance the coupling of incoming terahertz pulses with the metals, leading to a strong modification of the potential barriers by the terahertz electric fields. Extreme nonlinear responses are expected, providing opportunities for the terahertz light for the strong light–matter interaction. Starting from a brief review about the terahertz field enhancement on the metallic structures, a few examples including metallic tips, dipole antenna, and metal nanogaps are introduced for boosting the quantum phenomena. The emerging techniques to control the electron tunneling driven by the terahertz pulse have a direct impact on the ultrafast science and on the realization of next-generation quantum devices.

Roadmap of Terahertz Imaging 2021

“…This is possible if one accepts electric field confinement in only one direction using micro-and nano-slits in thin metal films, single ones or arrays thereof, with a length which corresponds to a half-wavelength resonance at the targeted THz frequency [281,282]. With special fabrication techniques, the slits can be brought to a width deep in the nanometer and even sub-nanometer regime [283][284][285]. The extreme wave confinement brings forth intriguing phenomena, such as a strongly enhanced absorption cross-section of molecules, conducive to single-molecule detection [286].…”

Terahertz Nano-Imaging with s-SNOM

“…The spatial resolution in one dimension is determined by the width of the slit. With special processes, nanometer-scale widths have been achieved [11]. In order to obtain a sufficiently strong transmittance through the narrow slit to allow for measurements with a good dynamic range, the length of the slit is usually chosen such that a standing-wave resonance occurs at the THz frequency band of interest [12].…”

More Than 30 000-fold Field Enhancement of Terahertz Nanoresonators Enabled by Rapid Inverse Design

“…Furthermore, this methodology opens up new possibilities for exploring terahertz nonlinear and quantum phenomena with narrower gaps. 48,49 ■ METHODS Inverse Design Method. Our inverse design method is constructed using the "reinforcement learning designer" toolbox in MATLAB.…”