Enhanced Bidirectional Transduction between Microwave and Optical Fields through anti-PT symmetry*

We set forth a two-mode anti-PT symmetric converter, consisting of a microwave cavity coupled dissipatively to a ferrite (YIG) sphere, which enables an efficient bidirectional conversion between microwave and optical signals. This arrangement supports significant improvements in the conversion efficiency when compared to dispersively coupled setups. Specifically, when the YIG is irradiated by a microwave beam and extraneous losses are assumed sufficiently low, the strong coherence introduced by the mediating waveguide leads to an efficiency enhancement by a few orders of magnitude. Such a spectacular improvement is an upshot of the emergence of a long-lived, dark mode associated with a quasi-real singularity of the hybrid system. Additionally, in spite of the symmetrical nature of the Faraday coupling driving the conversion, a fundamental asymmetry ensues in the efficiencies of microwave-to-optical and optical-to-microwave transduction. Given the topicality of dissipatively coupled hybrid systems, particularly in the context of cavity magnonics, our conversion schemes would allow simple laboratory implementation.