Achieving sub-electron readout noise in Skipper CCDs

The readout noise for Charge-Coupled Devices (CCDs) has been the main limitation when using these detectors for measuring small amplitude signals. A readout system for a new scientific, low noise CCD is presented in this paper. The Skipper CCD architecture, and its advantages for low noise applications are discussed. A technique for obtaining sub-electron readout noise levels is presented, and its noise and signal characteristics are derived. We demonstrate a very low readout noise of $0.2e^{-}$ RMS. Also, we show the results using the detector in a low-energy X-ray detection experiment.