Non-Technical Abstract Superconducting nanowires can have a kinetic inductance that is several orders of magnitude larger than their magnetic inductance. As a result, high frequency signals on the nanowire experience significant spatial compression as well as a significant reduction in their velocity. The kinetic inductance also varies nonlinearly as a function of the current, creating an opportunity for realizing nonlinear phenomena with extremely minimal dissipation. Through a combination of theory, modeling, and experiment, this project will study these effects in different superconducting nanowire materials and geometries. The understanding gained from these studies will be applied to design new types of ultra-compact microwave devices, which will then be fabricated and characterized. Such devices can serve as important building blocks for the development of more complex systems based on superconducting circuits such as single-photon imagers and quantum computers. This collaborative project brings together groups at Massachusetts Institute of Technology and the University of North Florida, an undergraduate-education focused university, to conduct the proposed research and educational activities, combining the best aspects of both institutions. In particular, the involvement of the University of North Florida creates additional opportunities for undergraduates from diverse backgrounds to participate in the research.
The goal of this project is to create a new superconducting nanowire device platform that can serve as the basis of a monolithic superconducting nanowire microwave integrated circuit technology. This goal will be pursued through four approaches. The first approach is based on exploring materials and geometries that maximize the nanowire's kinetic inductivity, which will result in extremely large characteristic impedances (> 10 kohm) along with slow signal velocities and large spatial compression of the signal wavelengths. Such high impedances create strong decoupling from the environment and have potential applications ranging from the readout of superconducting nanowire single-photon detectors to the design of quantum bits. The second approach will be to fabricate nanowires on extremely high permittivity substrates such as strontium titanate, which has been shown to have a relative permittivity as high as 10,000 at low temperature. This extremely large permittivity will significantly boost the capacitance, bringing the characteristic impedance of high-inductance nanowires close to 50 kohm while simultaneously achieving ultra-slow signal velocities and ultra-compressed signal wavelengths. A 50 kohm impedance is critical to coupling with conventional microwave circuitry. The third approach will focus on understanding and exploiting the nonlinear current-dependence of kinetic inductance in order to create new types of nanowire-based nonlinear microwave devices. Examples of such devices include mixers, tunable couplers, switches, and parametric amplifiers. In order to understand these devices, the project will seek to address fundamental questions such as how quickly the nanowire's kinetic inductance can be modulated, how much loss is associated with this modulation, and how the nonlinearity and the loss depend on the signal power. The fourth approach will leverage the results generated in the first three approaches to develop more complex nanowire-based devices and circuits.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
