  In the last decade, several photon counting technologies have been developed
opening a new window for experiments in the low photon number regime. Several
ongoing and future projects in HEP benefit from these developments, which will
also have a large impact outside HEP. During the next decade there is a clear
technological opportunity to fully develop these sensors and produce a large
impact in HEP. In this white paper we discuss the need for photon counting
technologies in future projects, and present some technological opportunities
to address those needs.
