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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

The study of single photon detector for quantum key distribution

Zhengjun Wei, Jindong Wang, Kaizhen Li, Peng Zhou, Changjun Liao, Jianping Guo, Songhao Liu

Published Oct 26, 2007• 1 citation
Publisher

Abstract

This paper introduces the design of a single photon detector based on the AT89C51 single chip microcontroller for quantum key distribution at telecommunication wavelengths. An avalanche photodiode (APD) is operated in Geiger mode and stabilized at temperature of 228K for translating the single photon signals into electrical pulses. The photon induced avalanche pulses are amplified and converted to digital data. The microcontroller discriminates the data, counting the number of photons, and then displays the photon number and the detection efficiency on a LCD display. The instrument can effectively support the study of quantum key distribution.

DOI
10.1117/12.756615

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Applied Physics Letters•Oct 25, 2006•0 citations
This paper introduces the design of a single photon detector based on the AT89C51 single chip microcontroller for quantum key distribution at telecommunication wavelengths. An avalanche photodiode (APD) is operated in Geiger mode and stabilized at temperature of 228K for translating the single photon signals into electrical pulses. The photon induced avalanche pulses are amplified and converted to digital data. The microcontroller discriminates the data, counting the number of photons, and then displays the photon number and the detection efficiency on a LCD display. The instrument can effectively support the study of quantum key distribution.
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.
The technology of quantum cryptography, based on the quantum properties of light, allows a random sequence of bits to be transmitted over an unprotected communication channel in such a way that an attacker's interference in the transmission process creates additional noise in the channel and is detected by legitimate users. One of the important elements of a quantum system is a single-photon detector. The closest to solving this problem is a device for recording single photons using avalanche photodiodes (APD) [1 - 6]. In this work, a scheme for amplifying current pulses flowing through a single-photon detector is proposed, using a charge-sensitive amplifier Amptek A250. The noise characteristics of the Amptek A250 amplifier are such that its contribution to detector noise is negligible. After amplification, the pulses are fed to the inputs of the comparators. The amplitude discrimination threshold of the first is selected above the level of the amplifier's own noise. The amplitude discrimination threshold of the second comparator is chosen so that the speed of pulse counting at the output of the first comparator is n times greater than at the output of the second comparator. From the outputs of the comparators, pulses are fed to the input of the microcontroller. When the microcontroller calculates a given number of N pulses, a corresponding signal for the DAC is formed at its output, which converts the digital signal into a control voltage for the power source of the avalanche photodiode. The developed device allows to increase the quantum efficiency of registration up to 48%.
Single-photon detection concept is the most crucial factor that determines the performance of quantum key distribution (QKD) systems. In this paper, a simulator with time domain visualizers and configurable parameters using continuous time simulation approach is presented for modeling and investigating the performance of single-photon detectors operating in Gieger mode at the wavelength of 830 nm. The widely used C30921S silicon avalanche photodiode was modeled in terms of avalanche pulse, the effect of experiment conditions such as excess voltage, temperature and average photon number on the photon detection efficiency, dark count rate and afterpulse probability. This work shows a general repeatable modeling process for significant performance evaluation. The most remarkable result emerged from the simulated data generated and detected by commercial devices is that the modeling process provides guidance for single-photon detectors design and characterization. The validation and testing results of the single-photon avalanche detectors (SPAD) simulator showed acceptable results with the theoretical and experimental results reported in related references and the device's data sheets.
Modeling and design of a single photon detector and its various characteristics are presented. It is a type of avalanche photo diode (APD) designed to suit the requirements of a Quantum Key Distribution (QKD) detection system. The device is modeled to operate in a gated mode at liquid nitrogen temperature for minimum noise and maximum gain. Different types of APDs are compared for best performance. The APD is part of an optical communication link, which is a private channel to transmit the key signal. The encrypted message is sent via a public channel. The optical link operates at a wavelength of 1.55μm. The design is based on InGaAs with a quantum efficiency of more than 75% and a multiplication factor of 1000. The calculated dark current is below 10-12A with an overall signal to noise ratio better than 18 dB. The device sensitivity is better than -40 dBm, which is more than an order of magnitude higher than the dark current, corresponding to a detection sensitivity of two photons in pico-second pulses.
A commercial avalanche photodiode (APD) and the circuitry needed to operate it as a single-photon detector (SPD) have been integrated onto a single PC board (PCB). At temperatures accessible with Peltier coolers (∼200–240 K), the PCB-SPD achieves high detection efficiency (DE) at 1308 and 1545 nm with low dark-count probability (e.g. ∼10−6/bias pulse at DE = 20%, 220 K), making it useful for quantum key distribution (QKD). The board generates fast bias pulses, cancels noise transients, amplifies the signals, and sends them to an on-board discriminator. A digital blanking circuit suppresses afterpulsing.
We provide a direct comparison between the InGaAs avalanche photodiode (APD) and the NbN superconducting single photon detector (SSPD) for applications in fiber-based quantum cryptography. The quantum efficiency and dark count rate were measured for each detector, and used to calculate the quantum bit error rate (QBER) and shared key rate for a QKD link. The results indicate that, despite low quantum efficiency, the speed of the SSPD makes it a superior detector for quantum information applications. Finally, we present results of an initial integration of an SSPD into a receiver node of the DARPA quantum network to perform quantum key distribution. Encoding quantum information on single photons has enabled the realization of a number of unique communication schemes such as the implementation of the BB84 protocol for quantum key distribution 1 and quantum dense coding. 2 Furthermore, the implementation of these schemes using photons at telecommunication wavelengths has permitted their extension to fiber optic networks, 3,4 drastically increasing the practicality of quantum information processing. To date, the state of the art in commercially available single photon detection at telecommunication wavelengths (1550 nm) has been the thermo-electrically cooled InGaAs avalanche photodiode (APD). The cooled InGaAs APD is generally operated at T = -60°C in the reverse-biased Geiger mode. Though these detectors have been successfully implemented in operating QKD links in optical fiber, the InGaAs APD suffers from afterpulsing effects that limit the key exchange rates. New SPD (single photon detector) technologies based on superconducting materials are emerging that hold tremendous promise for drastically increasing the photon counting rate and eliminating dark noise.57 The SSPD consists of a NbN thin film (t ∼ 5 nm) patterned into a narrow (w ∼ 100 nm) microstrip meander that is ∼ 500μm in length. The detector is cooled to T < 4K in a closed cycle refrigeration unit and a bias current I b is supplied to the device just below the superconducting critical current (I c ). When a photon is incident upon the microstrip superconductivity is broken in the region local to photon absorption and a normal state region is formed in the device. The current passing through the device causes a measurable voltage pulse in the detector that can be amplified and shaped to act as an input for traditional logic circuitry. Due to the unique electronic bandstructure in a superconducting material the intrinsic response time of the device is on the order of picoseconds, so that the repetition rate may be increased above 1 GHz 8 without being susceptible to afterpulsing effects that plague the InGaAs APD. 9 To make a direct comparison between the InGaAs APD and the SSPD both were placed in a SPD characterization testbed to measure quantum efficiency and dark count rate at a variety of bias conditions. The QBER for a QKD link is calculated from the measured parameters and then compared to requirements for a provably secure QKD link. Following detector characterization, one of the nodes of the DARPA Quantum Network operated by BBN Technologies 3 utilized an SSPD in the receiver to transmit key material. The demonstration provides an in situ comparison between the InGaAs APD, normally operated in the BBN link, and the SSPD.