Collaborative research: Understanding and Engineering the Timing Precision of Superconducting Nanowire Single Photon Detectors

题目：理解和设计超导纳米线单光子探测器的定时精度超导电子和辐射传感器以其运行速度和定时精度而著称。因此，它们在空间通信、计量、传感和计算等关键领域得到了应用。因此，这些设备的性能限制了在这些领域可以实现的目标。有一种类型的超导探测器已经证明了高速度和定时精度：超导纳米线单光子探测器。这种类型的探测器能够探测到尽可能小的光的到达，即单个光子。由于其优异的速度和精度特性，它已经在各种各样的领域得到了应用。例如，量子密钥分发，未来的安全通信方式，关键依赖于光子探测的定时精度，以保证安全性。在一个相关的领域，新兴的量子计算的发展，比如发生在光子集成电路上的量子计算，依赖于对单个光子的精确探测。不幸的是，虽然我们很清楚超导纳米线单光电探测器的速度限制，但我们还不知道是什么限制了定时精度（通常被称为“抖动”），因此还不能设计改进。许多理论都可以解释这些超导纳米线是如何工作的。然而，这些理论都不能证明在这些探测器中看到的抖动是合理的。在这项工作中，我们将研究超导纳米线单光子探测器抖动的基本限制，从而使其在广泛的应用领域得到改进。例如，通信数据速率直接取决于抖动，因为标准的低功耗数字通信协议，脉冲位置调制，使用定时精度来提高数据速率。通过研究和表征这些探测器中时间抖动的可能来源，这项工作将直接增加在工业，空间和国防中的相关应用的影响。尽管超导纳米线自20世纪70年代以来就被研究，并被用作辐射传感器超过13年，但它们的皮秒时间尺度动力学仍然没有被完全理解。早期试图解释超导纳米线单光子探测器的时间动力学集中在可能的微观起源上。在基于超导纳米线的辐射传感器领域，一些理论将这些皮秒级时间尺度效应与环境原因联系起来，而另一些理论则将其与超导纳米线的内在物理过程联系起来。例如，提出了探测机制的热点模型来解释光子到达和电压响应之间的时间延迟是两种不同偏置电流下入射光子数的函数，但与间隙抑制时间的理论模型拟合较差，没有提到抖动。后来，相滑移中心被认为是最初热点产生的机制，但同样，从这些分析中没有得到与抖动的实质性联系。在这个项目中，我们将探索在该领域普遍接受的理论以及使用数值和实验方法的未探索的抖动源。我们已经确定了纳米线操作的几个关键组成部分，我们认为它们可能是抖动的来源：(1)纳米线自共振；(2)涡陷；(3)热点微观物理中的随机元素。我们打算描述这些可能的来源的抖动贡献，并设计修改的设备，可以减少这些贡献的抖动。

Title: Understanding and Engineering the Timing Precision of Superconducting Nanowire Single Photon DetectorsSuperconducting electronics and radiation sensors are exceptional for their speed of operation and precision of timing. As a result, they find application in critical niches such as space communications, metrology, sensing, and computation. The performance of these devices thus sets the limit of what can be achieved in these domains. One type of superconducting detector in particular has demonstrated high speed and timing precision: the superconducting nanowire single photon detector. This type of detector is able to detect the arrival of the smallest amounts of light possible, a single photon. As a result of its excellent speed and precision characteristics, it has found application in a wide variety of areas. For example, quantum key distribution, the secure communications method of the future, crucially relies on timing precision of photon detection in order to guarantee security. In a related field, emerging quantum computing thrusts such as those taking place on photonic integrated circuits rely on the precise detection of single photons. Unfortunately, although the speed limitations of the superconducting nanowire single photodetector are well understood, we do not yet understand what limits timing precision (typically referred to as "jitter"), and thus cannot yet engineer improvement. Many theories have been developed that can explain how these superconducting nanowires function. However, none of these theories can justify the jitter seen in these detectors. In this work, we will investigate the fundamental limits of jitter in superconducting nanowire single-photon detectors, and thus enable improvements in a wide array of application areas. For example, communication data rates depend directly on the jitter because the standard low- power digital communication protocol, pulse-position-modulation, uses timing precision to enhance the data rate. By investigating and characterizing possible sources of timing jitter in these detectors, this work will directly increase the impact of the relevant applications in industry, space, and defense.Although superconducting nanowires have been studied since the 1970s and have been used as radiation sensors for over 13 years, their picosecond-time-scale dynamics are still not fully understood. Early attempts to explain the timing dynamics in superconducting nanowire single photon detectors focused on possible microscopic origins. In the field of radiation sensors based on superconducting nanowires, some theories related these picosecond-time-scale effects to environmental causes and others to processes intrinsic to the physics of the superconducting nanowires. For example, the hotspot model of the detection mechanism was suggested to explain the time delay between the photon arrival and voltage response as a function of number of incident photons at two different bias currents, but fitting to a theoretical model of gap suppression time was poor and no mention of jitter was made. Later, phase slip centers were purported as the mechanism for the initial hotspot creation but again, no substantive connection to jitter came about from those analyses. In this project, we will probe commonly accepted theories in the field as well as unexplored sources of jitter using both numerical and experimental approaches. We have identified several key components of the nanowire operation that we consider likely sources of jitter: (1) nanowire self-resonance; (2) trapping of vortices; and (3) stochastic elements in the microscopic physics of the hotspot. We intend to characterize the jitter contributions of each of these possible sources, and design modified devices that can reduce these contributions to jitter.