Single photon generation and low noise detection based on APD for Quantum Key Distribution

Naoto Namekata, Hiroki Takesue, Toshimori Honjo +2 more

We have demonstrated quantum key distribution (QKD) over 100 km using single-photon detectors based on InGaAs/InP avalanche photodiodes (APDs). We implemented the differential phase shift QKD (DPS-QKD) protocol with electrically cooled and 2-GHz sinusoidally gated APDs. The single-photon detector has a dark count probability of 2.8 × 10(-8) (55 counts per second) with a detection efficiency of 6 %, which enabled us to achieve 24 kbit/s secure key rate over 100 km of optical fiber. The DPS-QKD system offers better performances in a practical way than those achieved using superconducting single-photon detectors. Moreover, the distance that secure keys against the general individual attacks can be distributed has been extended to 160 km.

赵峰 Zhao Feng

Xiuliang Chen, Chunyuan Zhou, Guang Wu +2 more

In our experiment, two InGaAs/InP avalanche photodiodes (APD) were used in the quantum key distribution (QKD) system for single-photon detection at telecom communication wavelength (1310/1550 nm). By using properly designed passive-quenching circuit, the photo-detection efficiency of the APD could reach 10% at 1550 nm. In order to decrease the dark count rate efficiently, we designed a coincident counting circuits for single-photon detection. Before the APD signals were sent to the signal processing circuit, the avalanche signals were amplified and shaped into the TTL pulses. In order to obtain an accurate and efficient data acquisition and to transfer synchronically several signals such as the TTL signals and pulses from Random generators, we designed a signal processing circuit with the parallel port whose speed limitation is about 100Kb/s. In our experiments of single-photon interference and quantum cryptography, the electronic designs presented us satisfactory performance and results. To achieve much higher speed for the data acquisition, we also employed the Universal Serial Bus System (USB2.0) to interface our single-photon avalanche detectors and random generators used in our QKD system, which was believed to improve the performance of QKD such as the key distribution speed.

S. Cova, Alberto Tosi, Franco Zappa +1 more

頼俊 足立

陳政儒

In this thesis, we investigate the single photon detection ability of Avalanche Photodiode (APD) at 1550 nm and improve the single photon detection efficiency by using Self-Differencing technique. In order to apply this experimental setup to the Quantum Key Distribution (QKD) system, we have to discuss and analyze characteristic parameters of APD, including Dark Count Rate (DCR), Single Photon Detection Efficiency (SPDE), Noise Equipment Power (NEP) and Quantum Bit Error Rate (QBER). For the purpose of reducing the spike effect caused by the capacitance in the APD, we try to process the output signal from the conventional setup output using the Self-Differencing circuit for spike cancelling. Moreover, it can also significantly decrease discrimination level. At lower discrimination level can let us catch more avalanche signals and raise the detection performance. This setup makes it more efficient under the -50℃. In our experiment, we investigate the influence of single photon detection efficiency from different parameters, such as temperature, excess bias voltage, pulse width and gated frequency. To demonstrate the afterpulsing effect by releasing the trapped carriers in the lower temperature, we cool down the APD to the temperature of -70℃. We also choose the best parameters to calculate the results of Quantum Bit Error Rate (QBER) and the transmission distance in theory. All of that are prepared for the structuring a Quantum Key Distribution (QKD) system in the future studies. Finally, using the self-differencing schematic at a temperature of -50℃, with a repetition rate of 100 KHz, and the excess bias voltage of 3 V, the best single-photon detection efficiency of 17.43% and the equivalent noise power is as low as 1.92×10-15 W/Hz1/2 were obtained. It is found that the minimum dark count rate of 1.2×10-5 appears when the temperature is -60℃ and the excess bias voltage is 1.6 V. Using above condition, the corresponding back to back quantum bit error rate is 3.09%. The maximum available transmission distance is 42 Km in which the quantum bit error rate is expected below 15%.