A detector-coupled resonant cavity and instrumentation design for studies in cavity quantum electrodynamics and GHz/THz RF systems

The design of a hi-Q resonant RF cavity with coupled detection scheme and associated instrumentation is reported for studying quantum vacuum within the framework of Quantum Electrodynamics (QED), the quantum theory of interaction of matter with radiation. Although this system could possibly serve in any general QED, cavity QED and RF applications in the range of a few GHz, the design was specifically devised for an experiment in studying intrinsic noise in quantum vacuum owing to vacuum fluctuations, which we call “Eavesdropping on Vacuum”. The center frequency of the cavity is 2.75GHz (which may be modified slightly to around 2.5GHz band for use in contemporary WiLAN and WiFi RF applications), with a high Q value. Initial design is made using copper but in the next stage it will be replaced with Niobium for use in low-temperature (around 0.1-0.3K) studies, making it an SRF (Superconducting Radio Frequency) cavity. A carefully devised scheme of sensitive RF detectors and ultra-low-noise cryogenic Low-Noise Amplifiers (cLNA) is an integral part of the cavity system. Detection element is an array of cavity-backed Au or Au-NbN spiral antennas in association with GaAs Schottky Barrier Diodes (SBD's), in conjunction with GaAs/InP HEMT's working in the GHz to THz regime. External fields are achieved with the help of time-dependent RF fields delivered to the cavity with the help of an antenna coupled with a GaAs Resonant Tunneling Diode (RTD). In addition to the cavity design, this report presents an overview of the detection scheme as well as necessary instrumentation, including RF detection, amplification, and the DAQ (Data Acquisition) required for digital read-out.