Magnetic flux quantum periodicity of the frequency of the on-chip detectable electromagnetic radiation from superconducting flux-flow-oscillators

Superconducting flux-flow-oscillators (FFOs) based on unidirectional flow of magnetic vortices in a single-long Josephson junction (JJ) and operating at 4.2 K are key elements of sub-terahertz integrated-receivers used in radio-astronomy and atmospheric science. Here, we report on the development of sub-terahertz FFOs based on parallel JJ-arrays made of YBa₂Cu₃O_7−δ thin films. Sharp multiple flux-flow resonances were observed in the temperature range 77–89 K in asymmetric JJ-arrays, suggesting that they can operate as a narrow-band FFO in sub-terahertz integrated-receivers at more practical temperatures than 4.2 K. We detected electromagnetic radiation (EM) emitted by symmetric JJ-arrays in the range of 30–45 K using on-chip build superconducting detectors based on single JJs. For both asymmetric and symmetric JJ-arrays, the frequency f of the emitted radiation could be tuned continuously by an applied magnetic flux Φ with a one-flux-quantum Φ₀ periodicity. Remarkably, since f can be tuned continuously, there are no gaps in the frequency range of the emitted EM. The fundamental Φ₀-periodicity of f(Φ) is similar in nature to a SQUID's voltage response V(Φ) and, consequently, using high-performance magnetic flux-to-field conversion and readout techniques, a sensitive field-to-frequency magnetometer can be developed. Incorporated into non-accessible micro/nanostructures as a magnetic sensor, it would allow precise measurements of magnetic-fields from a distance, without the need to measure it locally as the radiation is detected remotely.