There has been renewed interest in utilizing quantum limited amplifiers for detection of weak microwave signals. Such amplifiers have allowed for ultra-sensitive detection in radio astronomy (such as dark matter searches or cosmic microwave background studies), detectors with photon number resolution, ultra-secure quantum communications, and real time monitoring of superconducting quantum bits. Detection of low level signals, particularly at the single photon level is challenging, where amplifiers which have noise levels which are limited by quantum mechanical fluctuations are required for a satisfactory signal-to-noise ratio measurement. In this project a novel traveling-wave parametric amplifier (TWPA) composed of a tunable metamaterial transmission line which will allow for efficient parametric amplification of a weak signal over a broad bandwidth in the microwave regime utilizing low-loss superconducting circuits is developed. The metamaterial transmission line which makes up the proposed amplifier can be tuned to have a negative refractive index which allows for efficient amplification over very short lengths, which aides in the reduction of noise and promotes scalability.
Students participating in this research will be exposed to state-of-the-art experimental techniques in modern solid-state science and engineering, and will also be able to share their enthusiasm for science and engineering by participating in outreach activities to K-12 students and teachers. Outreach activities include mobile atomic force microscope demonstrative laboratory which are brought to K-12 institutions.to demonstrate nanoscience concepts.
Present state-of-the-art TWPA designs have been primarily based on series arrays of Josephson junctions as originally introduced in the early 1980s. Limitations in these designs have prevented their wide-spread use and adoption. These limitations have to do with: phase matching, weak nonlinearities, and excessive noise several times the quantum limit. In this research program we propose to take an entirely different approach to phase matching in a TWPA. The proposed TWPA is composed of a metamaterial transmission line which will allow for efficient parametric amplification over a broad bandwidth in the microwave regime utilizing low-loss superconducting circuits. The metamaterial transmission line is composed of a unique network of coupled magnetically frustrated asymmetric superconducting quantum interference devices. The tunability of the refractive index (impedance) of the proposed metamaterial transmission line in situ allows for the nonlinear component of the refractive index to be tuned from positive to negative which can phase match a weak signal to a strong pump and result in efficient parametric amplification of the weak signal. The proposed TWPA is expected to deliver high gain (> 20 dB) over a broad bandwidth (> 5 GHz) while maintaining quantum limited in noise performance. The objectives of the proposed research are: (1) to fabricate prototype TWPAs (2) Characterize the gain, bandwidth, dynamic range, and added noise (3) Validate the quantum limited in noise nature of the TWPA (4) Investigate the performance of the TWPA in the presence of parameter variations (4) Study loss mechanisms in the TWPA which contribute to excessive noise.
