Quasiparticle generation efficiency in superconducting thin films
Quasiparticle generation efficiency in superconducting thin films
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DOI：
10.1088/0953-2048/27/5/055012
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发表时间：
2014-01
影响因子：
3.6
通讯作者：
T. Guruswamy;D. Goldie;S. Withington
中科院分区：
文献类型：
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作者：
T. Guruswamy;D. Goldie;S. Withington
厚度约30-500纳米的薄膜超导体被用作光子、声子或更多外来粒子的非平衡量子探测器。在确定它们的极限灵敏度时，最基本的问题之一是感兴趣的量子与被探测到的准粒子耦合的效率。作为低温超导谐振器，薄膜是生产量子敏感可阵列传感器的有吸引力的候选者，读出使用额外的微波探针。在Chang和Scalapino （1978 J. low Temp. Phys. 31 - 32）描述的耦合动力学方程框架内，我们计算了具有代表性的清洁薄膜超导体（Al）中低能光子的准粒子产生效率ηs，其工作温度远低于其超导转变温度，并作为薄膜厚度的函数。我们还包括了低频探头的影响。我们表明，与考虑相对厚的薄膜或无限体积的早期模型相比，薄膜上的声子损失减少了高达40%的ηs。我们还表明，探针和信号的存在略微提高了生成效率。我们得出结论，这类探测器的最终极限噪声等效功率是由薄膜的几何形状决定的。
Thin-film superconductors with thickness ∼30–500 nm are used as non-equilibrium quantum detectors for photons, phonons or more exotic particles. One of the most basic questions in determining their limiting sensitivity is the efficiency with which the quanta of interest couple to the detected quasiparticles. As low temperature superconducting resonators, thin films are attractive candidates for producing quantum-sensitive arrayable sensors and the readout uses an additional microwave probe. We have calculated the quasiparticle generation efficiency ηs for low energy photons in a representative, clean thin-film superconductor (Al) operating well below its superconducting transition temperature as a function of film thickness, within the framework of the coupled kinetic equations described by Chang and Scalapino (1978 J. Low Temp. Phys. 31 1–32). We have also included the effect of a lower frequency probe. We show that phonon loss from the thin film reduces ηs by as much as 40% compared to earlier models that considered relatively thick films or infinite volumes. We also show that the presence of the probe and signal enhances the generation efficiency slightly. We conclude that the ultimate limiting noise equivalent power of this class of detector is determined by the thin-film geometry.