Abstract: Detection of ultrahigh energy (UHE) neutrinos is key to identifying the most energetic objects and processes in the universe. These are the sources of UHE cosmic rays that have been detected at earth with energies exceeding 1 Joule per nucleon (roughly the kinetic energy of a bird in flight). As UHE cosmic messengers, neutrinos are unparalleled for their ability to travel from their sources to the Earth, interacting only weakly with matter, and therefore able to traverse great distances unimpeded. UHE neutrinos can also provide a powerful handle on physics beyond the standard model. However, their flux decreases significantly with increasing energy. This, coupled with their weak interaction, makes them very challenging to detect at energies above those successfully probed by IceCube.
In this talk, I will discuss the extensive experimental work that has been performed to meet these challenges. I will start with a general overview of the experimental landscape, and then focus on our new experimental effort, the Radar Echo Telescope (RET), which uses well-known radar technology to attempt detection of the cascade produced by these UHE neutrinos as they interact in polar ice. I will discuss the theory and storied history of the radar echo method, and recent experimental work including our summer 2023 deployment of a prototype detector. I will conclude with a discussion of the UHE neutrino landscape in the near future, and the exciting possibilities of complementary measurements of the UHE neutrino sky.