Jingwei Yang1,Tzu-Yu Peng2,1,Jia-Wern Chen1,Li-Chung Yang1,2,Yu-Jung Lu1,2
Research Center for Applied Sciences1,National Taiwan University2
Jingwei Yang1,Tzu-Yu Peng2,1,Jia-Wern Chen1,Li-Chung Yang1,2,Yu-Jung Lu1,2
Research Center for Applied Sciences1,National Taiwan University2
Superconducting photon detectors (SPDs) have many advantages like low dark noise, low time jitter, and broad detection range. However, there are some trade-offs that should be taken into account during fabricating the device. For example, a superconducting wire with narrower width performs a higher detection efficiency than a wider wire, but its detection area becomes smaller and its critical temperature is suppressed at the same time. On the other hand, a typical nano-meander shows high polarization sensitivity, which is inconvenient in many applications, e.g., quantum communication using MMF coupled systems. To overcome this predicament, we design a superconducting NbN microwire photon detector with gap plasmon enhancement. The gap plasmon resonance in an Al<sub>2</sub>O<sub>3</sub> layer between Ag nanostructure and NbN microwire confines a strong electrical field, which destroys the Cooper pairs and further promotes the detection efficiency. For instance, we discovered a localized plasmonic resonance, which resonated at 532 nm wavelength, at the edge of Ag nanocube with 40 nm long and 30 nm thick. Hence, we can enhance the photon response of the detector to the visible range which can attribute to the gap plasmon resonance and the minimum detectable power of light is 4.4 nW. We design 9 different sizes of Ag nanocubes with side lengths of 30 nm to 70 nm (thickness of 30 nm) as a unit cell that resonate at different wavelengths to demonstrate a broadband photon detector with high detection efficiency from visible to NIR. In addition, though the choice of nanocube and microwire makes polarization sensitivity of the device lower, we still can make an SPD with polarization-dependent gap plasmon resonance by the different length-wide ratios of Ag nanoantenna. In the end, we discuss the potential for superconducting microwire photon detector applications, such as large active area, tunable polarization sensitivity, and low time jitter, etc.