  We describe a superconducting transition edge sensor based on a nanoscale
niobium detector element. This device is predicted to be capable of
energy-resolved near-IR single-photon detection with a GHz count rate. The
increased speed and sensitivity of this device compared to traditional
transition edge sensors result from the very small electronic heat capacity of
the nanoscale detector element. In the present work, we calculate the predicted
thermal response time and energy resolution. We also discuss approaches for
achieving efficient optical coupling to the sub-wavelength detector element
using a resonant near-IR antenna.
