Superconducting transition-edge sensors (TESs) are highly sensitive detectors and can detect electromagnetic wave radiations from millimeter/submillimeter, optical to 𝑥/γrays, suitable for cosmology, astrophysics, quantum information, and biosensing. In principle, thousands of TESs even more are required to enhance the detection efficiency for large-scale survey. Among other multiplexing schemes, microwave SQUID multiplexer (μMUX), consisting of resonators and RF SQUIDs, has a bandwidth of several GHz, thus multiplexing factor on the order of thousands, more suitable for readout of large TES arrays. We designed and fabricated superconducting coplanar waveguide (CPW) resonators with a high qualityfactor and second-order gradient RF SQUID with two inductive coupling structures respectively. Then, we optimized the critical current density of the Josephson junction and measured the mutual inductance parameters of the second-order gradient structure SQUID, which are consistent with the simulation results. Finally, we fabricated a cryogenic μMUX chip based on RF SQUID and resonator. We discussed the results of the development of μMUX in more detail.
Optical transition-edge sensor (TES) with high quantum efficiency, low dark count rate, and high energy resolution has been used in quantum information and communications. The gap distance between the fiber tip and TES has an influence on the TES performance. Here we measured the interference pattern of our optical TES devices with and without anti-reflection coating and obtain the gap distance. We also obtain the absolute reflectivity of the Ti-TESs by correcting the effect of power splitter and circulator. Our copper block shrinks ~10 μm when cooled from room temperature down to 100 mK. The measured reflectivity is consistent with the simulation taking the dielectric mirror, Ti film and anti-reflection coating into account. In addition, we study the gap distance dependence of the system efficiency, and find that it is in good agreement with the measured reflectivity at 100 mK. These analyses are useful for further improvement of TES packaging.
Transition edge sensors (TES) are highly sensitive detectors and have been widely used at different wavelengths from millimeter to X-ray astronomy. Especially at optical/near infrared wavelengths TES exhibits photon-number resolving capability because of its high energy resolution, which also makes it attractive in quantum information. In order to verify the possibility of space applications, we study the effect of ion irradiation on the performance of titanium-based optical TESs including normal-state resistance (RN), critical temperature (TC), thermal conductance (G), effective response time, detection efficiency, and energy resolution by measuring the DC and optical characteristics. The optical TESs survive in the ion irradiation and their parameters keep almost the same as before ion irradiation, which makes it possible for future space applications.
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