  We have developed a non-destructive readout system that uses a floating-gate
amplifier on a thick, fully depleted charge coupled device (CCD) to achieve
ultra-low readout noise of 0.068 e- rms/pix. This is the first time that
discrete sub-electron readout noise has been achieved reproducibly over
millions of pixels on a stable, large-area detector. This allows the precise
counting of the number of electrons in each pixel, ranging from pixels with 0
electrons to more than 1500 electrons. The resulting CCD detector is thus an
ultra-sensitive calorimeter. It is also capable of counting single photons in
the optical and near-infrared regime. Implementing this innovative
non-destructive readout system has a negligible impact on CCD design and
fabrication, and there are nearly immediate scientific applications. As a
particle detector, this CCD will have unprecedented sensitivity to low-mass
dark matter particles and coherent neutrino-nucleus scattering, while
astronomical applications include future direct imaging and spectroscopy of
exoplanets.
