Terahertz waves squeeze themselves into extreme aspect ratio slot antennas. In the middle of a nano slot antennas, the electric field intensity can be a billion times stronger than the incident one. Thereby, at large enough incident field, quantum tunneling of electrons through nanometer and Angstrom sized gaps are inevitable [1-3]. These efforts originated from nearly perfect transmission through terahertz slot antennas with tens of microns of feature size, and together with its nanometer sized counterparts [4-5]. We will discuss our recent results on tunneling through macroscopic rings of quantum barriers. Surface current driven tunneling provides a new paradigm compared with the conventional voltage driven tunneling, being ultrasensitive to the global geometry and symmetry of the planar geometry. Macroscopic geometries can be used to govern total tunneling currents.
 Y. M. Bahk et al., “Electromagnetic Saturation of Angstrom-Sized Quantum Barriers at Terahertz Frequencies”, Physical Review Letters 115, 125501(2015) *cover article.
 Joon-Yeon Kim et al., “Terahertz Quantum Plasmonics of Nanoslot Antennas in Nonlinear Regime”, Nano Letters 15 (10), 6683-6688 (2015).
 Xiaoshu Chen, H. R. Park et al., “Atomic layer lithography of wafer-scale nanogap arrays for extreme confinement of electromagnetic waves”, Nat. Comm. 4, 2361 (2013).
 J. W. Lee et al., “Terahertz Electromagnetic Wave Transmission through Random Arrays of Single Rectangular Holes and Slits in Thin Metallic Sheets”, Physical Review Letters 99, 137401 (2007).
 M. A. Seo et al., “Terahertz field enhancement by a metallic nano slit operating beyond the skin-depth limit”, Nat. Photonics 3, 152 (2009).