Snowmass 2021 White Paper: The Windchime Project
  The absence of clear signals from particle dark matter in direct detection
experiments motivates new approaches in disparate regions of viable parameter
space. In this Snowmass white paper, we outline the Windchime project, a
program to build a large array of quantum-enhanced mechanical sensors. The
ultimate aim is to build a detector capable of searching for Planck mass-scale
dark matter purely through its gravitational coupling to ordinary matter. In
the shorter term, we aim to search for a number of other physics targets,
especially some ultralight dark matter candidates. Here, we discuss the basic
design, open R&D challenges and opportunities, current experimental efforts,
and both short- and long-term physics targets of the Windchime project.
