Switching Terahertz Waves using Exceptional Points

In quantum mechanics, $e\phantom{\rule{0}{0ex}}x\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l$ $p\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}s$ are non-Hermitian degeneracies with intriguing properties, and the non-Hermiticity gives an extra degree of freedom that allows for innovative applications. Exploiting the unique topological structure of energy surfaces near the exceptional point, the authors propose a terahertz switch in which the system's transmission can be tuned by changing the chemical potential of monolayer graphene. Their idea can in principle be applied to design a switch for other frequency ranges, and manipulating the energy surfaces of non-Hermitian systems can serve as a useful paradigm to design photonic devices with further functionalities.