Microwave Kinetic Inductance Detectors – MKIDs
Low-temperature detectors are a proven and indispensable sensor technology. Increasingly, they are being deployed in sensitive, high-speed detection applications in both the scientific and industrial sectors. Throughout the last decades, development of low-temperature detectors focused narrowly on the design of high-sensitivity single-pixel devices. This includes such devices as semiconductor-based photodetectors and bolometers, Magnetic Metallic Calorimeters (MMC), Superconducting Tunnel Junctions (STJ), and Transition Edge Sensors (TES). However, these devices have had limited success in achieving the simultaneous large-scale array sizes and large-bandwidth operation necessary for high-speed, high-resolution detection. The classical design of detector arrays is currently at its limit with respect to both pixel count and complexity of fabrication. With this proposal, we aim at the demonstration of novel low-temperature detectors based on superconducting resonant circuits. One recent demonstration is an implementation known as Microwave Kinetic Inductance Detectors (MKIDs), in which a strip of superconducting material is embedded in a high-frequency resonant circuit. Small variations in the kinetic inductance (surface impedance) of the strip influence the resonating frequency and provide a measurable signal. These sensors are simple to fabricate and are amenable to frequency multiplexing, which will allow massively-parallel readout of giant arrays. Multiplexing is the technique by which a shared channel is used to transmit multiple signals. In the context of low-temperature detectors, this refers to the measurement of multiple pixels utilizing a single shared wire. Time-domain multiplexing achieves channel sharing by switching between pixels coupled to a single wire. This requires at minimum one transistor per pixel to act as a switch, greatly increasing the complexity of the measurement electronics. The switching must also be faster than events occurring in a pixel and therefore slow switching speeds severely limit the pixel count per wire. In contrast, frequency-domain multiplexing achieves channel sharing by designing each pixel to broadcast at a different frequency, in a manner analogous to radio stations. Since each pixel operates at an independent frequency, it is no longer necessary to include switching electronics and monitoring is continuous. This simplification will allow for arrays sizes in the thousand to millions of pixels rather than the tens of pixels currently achievable with time-domain multiplexing. Therefore an important part of the proposed work is the development of digital and analog electronics for large-pixel count readout utilizing frequency-domain multiplexing. We plan to utilize these arrays in a multitude of applications. This includes development of a mm/sub-mm detector for astronomical applications, an improved helium sensor for superfluid hydrodynamic experiments, a novel detector for beta decay in radioactive materials, and an integrated radiofrequency spectrometer (SWIFTS) for atmospheric monitoring. From the fact that we have already begun construction of critical equipment, and our strong collaborations in the low-temperature detector community, we believe we possess an excellent incubating environment. The superconducting resonator based helium detector which we recently demonstrated in Grenoble [Grabovskij, G. J.; Swenson, L. J.; Buisson, O.; Hoffmann, C.; Monfardini, A.; Villégier, J.-C., Applied Physics Letters, 93, 134102 (2008)] provides solid evidence for the viability of our research effort. With the ANR funding, we will assemble a team of an equivalent of 4-5 full time researchers and be at the forefront of this exciting field. The team is composed essentially of young researchers and technical staff. Five out of nine participants (78 out of 105 person-months) with a permanent position are born later than 1970 and received their position within the last few years. It is completed by four expert researchers, adding an inestimable amount of technical and scientific expertise.
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