  A number of applications in basic science and technology would benefit from
high fidelity photon number resolving photodetectors. While some recent
experimental progress has been made in this direction, the requirements for
true photon number resolution are stringent, and no design currently exists
that achieves this goal. Here we employ techniques from fundamental quantum
optics to demonstrate that detectors composed of subwavelength elements
interacting collectively with the photon field can achieve high-performance
photon number resolution. We propose a new design that simultaneously achieves
photon number resolution, high efficiency, low jitter, low dark counts, and
high count rate. We discuss specific systems that satisfy the design
requirements, pointing to the important role of nanoscale device elements.
