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

职务名称：理解和工程的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的操作速度和定时精度是例外。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中可以实现的目标。特别是一种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少量的光，即单个光子的到达。由于其出色的速度和精度特性，它已在广泛的领域得到应用。例如，量子密钥分发，未来的安全通信方法，关键依赖于光子检测的定时精度，以保证安全性。在相关领域，新兴的量子计算推动力，如发生在光子集成电路上的那些，依赖于对单个光子的精确检测。不幸的是，虽然超导纳米线单光电探测器的速度限制是很好理解的，我们还不知道是什么限制了定时精度（通常称为“抖动”），因此还不能工程改进。许多理论已经发展出来，可以解释这些超导纳米线的功能。然而，这些理论都不能证明在这些探测器中看到的抖动。在这项工作中，我们将研究超导纳米线单光子探测器中抖动的基本限制，从而在广泛的应用领域中实现改进。 例如，通信数据速率直接取决于抖动，因为标准低功率数字通信协议脉冲位置调制使用定时精度来增强数据速率。通过研究和表征这些探测器中可能的定时抖动来源，这项工作将直接增加相关应用在工业、空间和国防领域的影响。尽管超导纳米线从20世纪70年代就开始研究，并已被用作辐射传感器超过13年，但其皮秒时间尺度的动力学仍然没有完全理解。早期试图解释超导纳米线单光子探测器中的时序动力学的尝试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时间尺度效应与环境原因联系起来，而另一些理论则与超导纳米线物理学固有的过程联系起来。例如，提出了检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，作为在两个不同偏置电流下入射光子数量的函数，但是与间隙抑制时间的理论模型的拟合很差，并且没有提到抖动。后来，相位滑移中心被认为是初始热点产生的机制，但这些分析再次表明，相位滑移中心与抖动没有实质性的联系。在这个项目中，我们将探讨普遍接受的理论在该领域以及未开发的抖动来源使用数值和实验方法。我们已经确定了纳米线操作的几个关键组成部分，我们认为这些组成部分可能是抖动的来源：（1）纳米线自谐振;（2）涡旋捕获;（3）热点微观物理中的随机元素。我们打算表征这些可能的来源的抖动贡献，并设计修改后的设备，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.