27 Sep 2007
Researchers from Germany and the UK have used commercial avalanche photo-diodes in quantum information processing for moderate to high bit-rate applications.
The experimental setup minimizes the complexity of the detection scheme by using picosecond (ps) pulsed light at appropriate repetition rates, which also lessens dead-time limitations (J. Phys. B: At. Mol. Opt. Phys. 40 3909-3921).
The researchers determined the regime of linear avalanche photo-diode (APD) operation by using a ps-pulsed diode laser with variable repetition rates between 0.5 MHz and 80 MHz. The linearity at high repetition rates is limited by the APD dead time, and a nonlinear response arises at higher photon numbers due to multiphoton events.
By using the APDs in time multiplexed detectors (TMD), the researchers achieved photon-number resolution by 'photon chopping'. This detection setup extends the linear response function to higher photon numbers and statistical methods can be used to compensate for nonlinearity.
The data acquisition speed limit of the TMD is determined by the APD dead time. With dead times of 50 ns for commercially available APD modules, operation at data rates of up to 20 MHz is possible, making this a powerful tool to quickly characterize quantum states in the photon-number bases and allowing the collection of large number of statistical data in short measurement time.