Low-Noise Amplification, Detection and Spectroscopy of Ultra-Cold Systems in RF Cavities

Masroor H S Bukhari,Zahoor H Shah

doi:10.4236/mi.2016.52002

Abstract

The design and development of a cryogenic Ultra-Low-Noise Signal Amplification (ULNA) and detection system for spectroscopy of ultra-cold systems are reported here for the operation in the 0.5 - 4 GHz spectrum of frequencies (the “L” and “S” microwave bands). The design is suitable for weak RF signal detection and spectroscopy from ultra-cold systems confined in cryogenic RF cavities, as entailed in a number of physics, physical chemistry and analytical chemistry applications, such as NMR/NQR/EPR and microwave spectroscopy, Paul traps, Bose-Einstein Condensates (BEC’s) and cavity Quantum Electrodynamics (cQED). Using a generic Low-Noise Amplifier (LNA) architecture for a GaAs enhancement mode High-Electron Mobility FET device, our design has especially been devised for scientific applications where ultra-low-noise amplification systems are sought to amplify and detect weak RF signals under various conditions and environments, including cryogenic temperatures, with the least possible noise susceptibility. The amplifier offers a 16 dB gain and a 0.8 dB noise figure at 2.5 GHz, while operating at room temperature, which can improve significantly at low temperatures. Both dc and RF outputs are provided by the amplifier to integrate it in a closed-loop or continuous-wave spectroscopy system or connect it to a variety of instruments, a factor which is lacking in commercial LNA devices. Following the amplification stage, the RF signal detection is carried out with the help of a post-amplifier and detection system based upon a set of Zero-Bias Schottky Barrier Diodes (ZBD’s) and a high-precision ultra-low noise jFET operational amplifier. The scheme offers unique benefits of sensitive detection and very-low noise amplification for measuring extremely weak on-resonance signals with substantial low- noise response and excellent stability while eliminating complicated and expensive heterodyne schemes. The LNA stage is fully capable to be a part of low-temperature experiments while being operated in cryogenic conditions down to about 500 mK.

Highlights

Weak signal detection is a substantial part of communications and network engineering, and an important part of experimental physical sciences, where weak Radio Frequency (RF) measurements need to be performed on various physical systems, especially under stringent conditions of extreme temperatures
The first and foremost area is spectroscopy in physics and physical/analytical chemistry, where a weak signal from a sample or atomic/molecular system confined in an RF cavity is measured and its spectra are obtained
Other than the wide area of spectroscopy, some of the important contemporary fields of physical sciences, such as particle physics and condensed-matter physics, entail weak signal detection and spectral analysis from atoms or electrons in cavities. These experiments at times involve ultra-cold systems, such as atoms, molecules or Bose-Einstein Condensates (BEC’s) [4] [5], kept at extremely low temperatures. Some of such applications include cavity Quantum Electrodynamics, resonance studies with resonators working at microwave frequencies [6], cavity-based experiments in particle physics, for instance, photon mass [7] and Dark Matter (DM) axion [8] [9] particles detection, which relies on detection of weak signals arising from resonance in cold RF resonant cavities, most often at cryogenic temperatures

Summary

Introduction

Weak signal detection is a substantial part of communications and network engineering, and an important part of experimental physical sciences, where weak Radio Frequency (RF) measurements need to be performed on various physical systems, especially under stringent conditions of extreme temperatures. Low-Noise Amplifiers (LNA’s) [12], especially narrow-band LNA’s [13] [14], are well-known RF devices which are essential components of every RF communication or wireless system, and find scope in spectroscopy techniques at microwave frequencies as well as in general-purpose RF weak signal detection, spectral analysis and general RF metrology Out of these devices, there are certain designs which offer a very low noise amplification, satisfying the benchmark of noise figures around 0.5 to 1.0 dB at a few GHz with room temperature operation. For cryogenic operation, such as on the fingers of a dilution refrigerator, special low thermal conductivity cables would replace the coaxials, and feed-through low-pass filters would need to be added to all incoming and outgoing leads (except the power) from the LNA cold box

The Detector and Post-Amplifier

Construction

Testing and Results

Conclusions