  The 2021 Snowmass Energy Frontier panel wrote in its final report "The
realization of a Higgs factory will require an immediate, vigorous and targeted
detector R&D program". Both linear and circular $e^+e^-$ collider efforts have
developed a conceptual design for their detectors and are aggressively pursuing
a path to formalize these detector concepts. The U.S. has world-class expertise
in particle detectors, and is eager to play a leading role in the next
generation $e^+e^-$ collider, currently slated to become operational in the
2040s. It is urgent that the U.S. organize its efforts to provide leadership
and make significant contributions in detector R&D. These investments are
necessary to build and retain the U.S. expertise in detector R&D and future
projects, enable significant contributions during the construction phase and
maintain its leadership in the Energy Frontier regardless of the choice of the
collider project. In this document, we discuss areas where the U.S. can and
must play a leading role in the conceptual design and R&D for detectors for
$e^+e^-$ colliders.
