Synchronous single-photon detection with self-resetting, GHz-gated superconducting NbN nanowires

Abstract

We demonstrate a GHz-gated operation of resonator-coupled superconducting nanowire single-photon detectors suitable for synchronous applications. In comparison with conventional dc-biased nanowire detectors, this method prevents the detector from latching and can suppress dark counts and background noise. Using a gating frequency of 3.8 GHz and a fast, synchronized laser diode, we show that the detector's operation point follows the oscillating current and its detection efficiency depends on the relative frequency and phase of the bias and modulated optical signal. The obtained experimental results are in good agreement with simulations, showing that the duty cycle of a gated detector can be adjusted in a wide range in the case of a pronounced saturation of the current-dependent detection efficiency. This operation mode could be suitable for applications such as quantum key distribution and time-of-flight laser ranging.

High comprehensive performance superconducting nanowire single photon detector

“…超导纳米线单光子探测器 (Superconducting Nanowire Single Photon Detectors， SNSPD)作为一种极限光信号探测器，凭借高探测效率 [1] 、低噪声 [2] 、高响应速 度 [3] 和低时间抖动 [4] 的优势，在一众单光子探测器中崭露头角，广泛应用于深空 通信 [5] 、光量子计算 [6] 、单光子激光雷达 [7] 等前沿技术中，并逐步向实用化、产 品化迈进。 SNSPD 的时间特性， 即响应速度和时间抖动， 是其最具吸引力的优势之一。 但在实际应用中，往往需要探测器具有优异的综合性能，即同时满足两个或两个 以上的参数要求 [8] 。 如在高速量子密钥分发的实验中， 为实现更高的实时成码率， 在系统的接收端需要探测器兼顾高探测效率、低暗计数、高响应速度和低时间抖 动。又如在量子计算的玻色采样环节，多光子玻色采样符合计数与探测器的探测 效率和响应速度直接相关，进而影响了采样时间。然而，以往的结果往往只面向 单一指标进行了优化。目前，兼顾 SNSPD 时间特性和探测效率的方式大体上分 为两种。一种方式围绕读出电路等外部因素展开，如通过改善电脉冲的读出来提 高器件最大计数率，降低时间抖动 [9] 。如美国麻省理工大学的 Calandri 小组就曾 利用差分双端读出电路减小探测器时间抖动 [10] 。另一种方式则是从探测器内部 入手，通过改变超导薄膜内禀属性、调整纳米线几何参数等手段完成。然而各内 部参数之间存在相互制约的关系 [11,12] ，所以这一方式一直存在技术挑战。 SNSPD 依靠超导纳米线吸收输入的单光子能量拆散库珀对，并在宽度方向 上形成局域有阻热点实现对微弱光的探测 [13,14] 。在有阻区形成再驰豫掉的过程 中，其能够快速地在电路中输出一个电压脉冲，使得光子转变为电信号并实现持 续可测 [15,16] 。因此为提高纳米线接收光子的概率，主流的 SNSPD 均采用蜿蜒回 形结构。线长较短的小光敏面 SNSPD 在时间特性上具有显著优势，这是因为纳 米线的动态电感与线长成正比， 而动态电感会对探测器的输出光响应脉冲带来直 接影响。根据 SNSPD 响应电路模型 [17] ，脉冲上升沿时间𝜏 rise ~𝐿K /𝑅 N ，下降沿时 间𝜏 fall ~𝐿K /𝑅 𝐿 ，这里 L K 是纳米线的动态电感，R N 是纳米线正常态的电阻，R L 表 示读出端负载电阻，通常为 50 Ω。当动态电感减小时，探测事件的时间分布会 因更短的𝜏 rise 而缩窄，从而使器件的时间精度提高，时间抖动降低。同样的，探 测器的电驰豫时间会因更短的𝜏 fall 而缩短，从而更快地恢复其探测光子的能力， 提升响应速度。除此之外，缩小光敏面更容易获得加工缺陷少的探测器，降低由 纳米线均匀性引发的时间抖动 [18] 。但光敏面缩小会导致器件光耦合及光吸收难 度增大，影响器件的探测效率，因此需要对现有 SNSPD 的器件结构和对准方式 进行改进。美国 NIST 的 Reddy 等人通过优化分布式布拉格反射器(Distributed Bragg Reflector，DBR)光学腔、增加抗反射层和光纤间隔层实现了 20 μm 光敏 面器件较高的探测效率 [19] 。荷兰代尔夫特大学的常进等人采用了能够使光束多 次反射后发散更小的 Au/SiO 2 膜腔，并调整了光纤端面与探测器芯片之间的空气 气隙，从而在 16 μm 尺寸光敏面上实现了极高的探测效率 [20] 。天津大学的胡小 龙等人使用了模场适配器将光纤出射光的模场直径由原先的 10 μm 缩小为 6.3 μm，从而在 10.2 μm 的小尺寸光敏面上实现了高效率光耦合 [21] 。 在 SNSPD 走向实用化、产品化的过程中，除探测器芯片表现出的技术特性 外，探测器的封装方式也是其在实际应用时值得被关注的问题。目前，光纤与探 测器芯片的封装大多采用两种方式，一种是基于激光器、显微镜、电荷耦合元件 图形传感器、微机械位移平台实现的手动对光封装方式 [22] 。在这一方式中，芯 片和光纤首先需要依靠高精度机械加工的分体式铜制封装盒分别固定， 然后利用 微米级加工精度的垫片调节 Z 方向使光纤出射光的焦平面与芯片平面重叠，接 着通过微机械位移平台调节 X-Y 方向使光斑对准芯片光敏面，从而完成对单一 SNSPD 探测器的光耦合。 这一封装方案具有精度高、 芯片加工容错度大的优势， 但也有耗时长、体积大、重复性差的劣势。另一种方式则是基于光纤套管自准直 耦合(以下简称"自对准")对探测器进行封装。该方案是 2011 年首次由美国国 家标准与技术研究所 Miller 小组开发用于超导转变沿探测器的封装 [23] ，之后 Marsili 等人又将自对准结构应用在了 SNSPD 上 [24] Zhang W, You L, Li H, Huang J, Lv C, Zhang L, Liu X, Wu J, Wang Z, Xie X…”

Coupled Multiphysics Modelling of Sensors for Chemical, Biomedical, and Environmental Applications with Focus on Smart Materials and Low-Dimensional Nanostructures

“…We should also mention that hybrid systems, metamaterials, and various hierarchical materials (e.g., with additions made to CNTs or nanowires to increase sensitivity) represent another important avenue of recent endeavors. Superconducting nanowire-based sensors have also been a subject of intensive investigations [ 52 , 53 , 54 , 55 , 56 ]. While new nanomaterials continue to be developed and analyzed, the issues of their synthesis and fabrication (along with the processes for preparing such nanomaterials for sensor applications) are outside the scope of this paper, and the interested reader may consult the relevant literature on these issues, such as an excellent recent review [ 57 ].…”

Chip-Scale Quantum Emitters

“…Consequently, novel design architectures and fabrication techniques with the ability to integrate the quantum elements into chip-scale electronics are essential [24]. To exploit the quantum circuit technology, the implementation of a scalable architecture must be established beyond the realm of 'mere' engineering and, therefore, a transformative approach is required [25]. For example, superconducting qubits and superconducting nanowire single-photon detectors operate in an RF regime [25].…”

“…To exploit the quantum circuit technology, the implementation of a scalable architecture must be established beyond the realm of 'mere' engineering and, therefore, a transformative approach is required [25]. For example, superconducting qubits and superconducting nanowire single-photon detectors operate in an RF regime [25]. Due to the power dissipation, footprint, limited frequency, and accuracy of the CMOS standard devices used for control and readout, the scale-up in the size of this kind of single-photon detector is limited when we attempt to achieve the required performances in real-world applications [25,26].…”

“…For example, superconducting qubits and superconducting nanowire single-photon detectors operate in an RF regime [25]. Due to the power dissipation, footprint, limited frequency, and accuracy of the CMOS standard devices used for control and readout, the scale-up in the size of this kind of single-photon detector is limited when we attempt to achieve the required performances in real-world applications [25,26]. Tasker et al believed that the classical interface hardware for integrated quantum photonics is still being implemented with large-footprint discrete electronics that limit device scalability and performance.…”