A measurement system for determining the gain distributions of avalanche photodiodes (APDs) in a low gain range is presented. The system is based on an ultralow-noise charge--sensitive amplifier and detects the output carriers from an APD. The noise of the charge--sensitive amplifier is as low as 4.2 electrons at a sampling rate of 200 Hz. The gain distribution of a commercial Si APD with low average gains are presented, demonstrating the McIntyre theory in the low gain range.
Implementation of high-speed quantum key distribution~(QKD) has become one of the major focus in the field, which produces high key-generation rate for applications. To achieve high-speed QKD, tailored techniques are developed and employed to quickly generate and detect quantum states. However, these techniques may introduce unique loopholes to compromise the security of QKD systems. In this paper, we investigate the loopholes of self-differencing~(SD) avalanche photodiode~(APD) detector, typically used for high-speed detection in a QKD system, and demonstrate experimental testing of SD APD de…
Afterpulsing noise in InGaAs/InP single photon avalanche photodiodes (APDs) is caused by carrier trapping and can be suppressed successfully through limiting the avalanche charge via sub-nanosecond gating. Detection of faint avalanches requires an electronic circuit that is able to effectively remove the gate-induced capacitive response while keeping photon signals intact. Here we demonstrate a novel ultra-narrowband interference circuit (UNIC) that can reject the capacitive response by up to 80 dB per stage with little distortion to avalanche signals. Cascading two UNIC's in a readout circuit…
A graphical presentation of signal delays in the datasets of Weihs et al
在来自Weihs等人的实验的数据集中雪崩光电二极管事件的时序的图形表示。[Phys. Rev. Lett. 81，5039（1998）]表明了两种类型的信号延迟的存在：（1）对于一对横向电光调制器的输入的快速切换的引入导致对于一部分重合的雪崩光电二极管事件的大约20纳秒的延迟;这种效应先前已经被注意到，但是如这里所考虑的数据提出了不同的原因。(2)存在依赖于事件发生在哪个雪崩光电二极管中的延迟;这种效应之前也已经注意到，即使只有当雪崩光电二极管事件之间的相对时间差接近时间戳的所述0.5纳秒精度时才非常明显（但由于75皮秒分辨率，它是可识别的）。第二个效应的原因是四个雪崩光电二极管的信号延迟之间的差异，可以通过简单的局部调整进行校正（对Bell-CHSH不等式的违反程度几乎没有影响）。
Integrated technologies greatly enhance the prospects for practical quantum information processing and sensing devices based on trapped ions. High-speed and high-fidelity ion state readout is critical for any such application. Integrated detectors offer significant advantages for system portability and can also greatly facilitate parallel operations if a separate detector can be incorporated at each ion-trapping location. Here we demonstrate ion quantum state detection at room temperature utilizing single-photon avalanche diodes (SPADs) integrated directly into the substrate of silicon ion tra…
Multilayer graded-bandgap avalanche photodiodes (APDs) are the future deterministic photomultipliers, owing to their deterministic amplification with twofold stepwise gain via impact ionization when operated in the staircase regime. Yet, the stepwise impact ionization irregularities worsen as the number of steps increases. These irregularities in impact ionization are the major source of noise in these APDs. These solid-state devices could replace conventional silicon photomultiplier tubes if they are carefully studied and designed. A noise model for multistep staircase APDs, considering equal…
InGaAs single-photon avalanche photodiodes (APDs) are key enablers for high-bit rate quantum key distribution. However, the deviation of such detectors from ideal models can open side-channels for an eavesdropper, Eve, to exploit. The phenomenon of backflashes, whereby APDs reemit photons after detecting a photon, gives Eve the opportunity to passively learn the information carried by the detected photon without the need to actively interact with the legitimate receiver, Bob. Whilst this has been observed in slow-gated detectors, it has not been investigated in fast-gated APDs where it has bee…
Avalanche photodiodes (APDs) are well-suited for single-photon detection on quantum communication satellites as they are a mature technology with high detection efficiency without requiring cryogenic cooling. They are, however, prone to significantly increased thermal noise caused by in-orbit radiation damage. Previous work demonstrated that a one-time application of thermal annealing reduces radiation-damage-induced APD thermal noise. Here we examine the effect of cyclical proton irradiation and thermal annealing. We use an accelerated testing environment which emulates a realistic two-year o…
Single photon detectors have dark count rates that depend strongly on the bias level for detector operation. In the case of weak light sources such as novel lasers or single-photon emitters, the rate of counts due to the light source can be comparable to that of the detector dark counts. In such cases, a characterization of the statistical properties of the dark counts is necessary. The dark counts are often assumed to follow a Poisson process that is statistically independent of the incident photon counts. This assumption must be validated for specific types of photodetectors. In this work, w…
We build and test a single-photon detector based on a Si avalanche photodiode Excelitas 30902SH thermoelectrically cooled to -100 deg. C. Our detector has dark count rate below 1 Hz, 500 um diameter photosensitive area, photon detection efficiency around 50%, afterpulsing less than 0.35%, and timing jitter under 1 ns. These characteristics make it suitable for long-distance free-space quantum communication links, which we briefly discuss. We also report an improved method that we call long-time afterpulsing analysis, used to determine and visualise long trap lifetimes at different temperatures…
