  We report a 2 GHz operation of InGaAs avalanche photodiodes for efficient
single photon detection at telecom wavelengths. Employing a self-differencing
circuit that incorporates tuneability in both frequency and arm balancing,
extremely weak avalanches can now be sensed so as to suppress afterpulsing. The
afterpulse probability is characterized as 4.84% and 1.42% for a photon
detection efficiency of 23.5% and 11.8%, respectively. The device will further
increase the secure bit rate for fiber wavelength quantum key distribution.

Quantum Physics;Instrumentation and Detectors