Properties of superconducting nanowires set the performance level for superconducting nanowire single photon detectors (SNSPDs). Reset time in commonly employed large area SNSPDs, 1–10 ns, is known to be limited by the nanowire’s kinetic inductance to the load impedance ratio. On the other hand, reduction of the kinetic inductance in small area (waveguide integrated) SNSPDs prevents biasing them close to the critical current due to latching into a permanent resistive state. In order to reduce the reset time in SNSPDs, superconducting nanowires with both low kinetic inductance and fast electron energy relaxation are required. In this paper, we report on a study of kinetic inductance in narrow (15–100 nm) and long (up to 120 μm) superconducting MgB₂ nanowires made from 5 nm thick films, offering such combination of properties. Such films were grown using hybrid physical chemical vapor deposition, resulting in a critical temperature of ∼32 K, and a switch current density of 5 10⁷ A cm⁻² (at 4.8 K). Using microwave reflectometry, we measured a kinetic inductance of L _k0(4.8 K) = 1.3–1.6 pH/□ regardless of the nanowire width, which results in a magnetic field penetration depth of ∼90 nm. These values are very close to those in pristine MgB₂. We showed that after excitations by a 50 fs pulsed laser the reset time in 35 nm 120 μm MgB₂ nanowires is 130 ps, which is more than a factor of 10 shorter than in NbN nanowires of similar length-to-width ratios. Depending on the bias current, such MgB₂ nanowires function as single-, double, or triple-photon detectors for both visible (λ = 630 nm) and infrared (λ = 1550 nm) photons, with a dark count rate of <10 cps. Although the apparent photon detection efficiency seems so far to be low, further technological advances (uniform nanowire width, smaller thickness, increasing the switching current closer to the pair-breaking current) may improve this figure of merit.

超导纳米线的属性设置了超导纳米线单光子探测器（SNSPD）的性能水平。众所周知，通常使用的大面积SNSPDs的复位时间为1-10 ns，这受纳米线的动电感与负载阻抗比的限制。另一方面，减小小面积（集成波导的）SNSPD的动感可防止由于锁存到永久电阻状态而将其偏置到接近临界电流的位置。为了减少SNSPD中的复位时间，需要具有低动感和快速电子能量弛豫的超导纳米线。在本文中，我们对动态电感的在窄（15-100 nm）的研究报告和长（长达120 μ M）超导的MgB ₂由5 nm厚的薄膜制成的纳米线，提供了这些特性的组合。使用混合物理化学气相沉积法生长此类薄膜，其临界温度约为32 K，开关电流密度为5 10 ⁷ A cm ^-2（在4.8 K下）。使用微波反射法，我们测量的动电感为L _k0（4.8 K）= 1.3–1.6 pH /□，而与纳米线的宽度无关，这导致磁场穿透深度约为90 nm。这些值非常接近原始MgB _2中的值。我们发现，通过后50个飞秒激励脉冲激光复位时间在35纳米120 μ米的MgB ₂纳米线为130 ps，比类似的长宽比的NbN纳米线短10倍。根据偏置电流的不同，此类MgB ₂纳米线可充当可见光（λ = 630 nm）和红外光（λ = 1550 nm）的单光，双光或三光子探测器，暗计数率小于10 cps 。尽管到目前为止，表观光子检测效率似乎很低，但是进一步的技术进步（均匀的纳米线宽度，更小的厚度，将开关电流增加到更接近成对断开电流的水平）可以改善这一品质因数。