  We demonstrate high-efficiency, shot-noise-limited differential
photodetection with real-time signal conditioning, suitable for feedback-based
quantum control of atomic systems. The detector system has quantum efficiency
of 0.92, is shot-noise limited from 7.4 x 10^5 to 3.7 x 10^8 photons per pulse,
and provides real-time voltage-encoded output at up to 2.3 Mpulses per second.
