Aspects of the present disclosure relate to receiving and emitting Terahertz (THz) electromagnetic radiation via one or more Josephson Junction(s) electronically coupled to an antenna structure. Aspects of the present disclosure further relate to a mechanism and methods to analyze a gas and/or identifying a gas (and/or suspension) based its electromagnetic absorption. Together, THz electromagnetic radiation may be emitted from one or more Josephson Junction emitters (transmitters), passed through a gas/suspension of interest, and non-absorbed THz electromagnetic radiation may be detected from one or more Josephson Junction detectors (receivers).

A system includes a substrate, a high-temperature superconductor compound film disposed on the substrate, an array of superconducting regions formed within the film, a plurality of Josephson junctions formed within the film, where each Josephson junction of the plurality of Josephson junctions is formed between adjacent superconducting regions within the array of superconducting regions, and a voltage source connected to the array of superconducting regions. The plurality of Josephson junctions are separated by a distance such that they emit coherent radiation in the terahertz frequency range responsive to a voltage applied to the array of superconducting regions.

A feedback oscillator, with an amplifier whose output is partially fed back to its input, provides a stable reference for standardization and synchronization. The laser is a feedback oscillator whose performance can be limited by quantum fluctuations. The resulting frequency instability, quantified by the Schawlow-Townes formula, sets a limit to laser linewidth. Here, we show that the Schawlow-Townes formula applies to feedback oscillators beyond lasers. This is because it arises from quantum noise added by the amplifier and an out-coupler in the feedback loop. Tracing the origin of quantum noise in an oscillator informs techniques to systematically evade it: squeezing and entanglement can enable sub-Schawlow-Townes linewidth feedback oscillators. We clarify the quantum limits to the stability of feedback oscillators, derive a standard quantum limit (SQL) for feedback oscillators, and disclose quantum strategies for realizing sub-SQL feedback oscillators.