Coherent Radiation From Voltage-Biased Weakly Connected Superconductors

This Letter reports the generation of coherent radiation with voltage-biased superconducting point contacts at both 30 MHz and 10 KMHz. The method of voltage biasing stabilizes the frequency of the emitted radiation against external noise sources and is tunable over a wide frequency range. We have optimized the electromagnetic coupling of the superconducting generator to the receiver and detected at least 5% of the generated power at 30 MHz. The relation1 V = Φ0ν, where Φ0 is the flux quantum, is satisfied. Furthermore, we have observed harmonics, V = nΦ0ν, and subharmonics, nV = Φ0ν, of this relation. The frequency stability of the emitted radiation was limited by the stability of the bias supply and was measured to be 10−5 at 30 MHz.