The gain of sub-terahertz radiation by the mutual synchronization of niobium Josephson junction arrays

We performed experimental investigations of the interaction between separate discrete niobium Josephson junction (JJ) arrays. It was found out that after tuning the arrays to the equal Josephson frequency the amplification of power is registered. The arrays are straight strip lines with 332 JJs oriented in parallel and located on common silicon substrate as well as on different substrates configured in a stack. The effect of amplification is observed at frequencies of up to 204 GHz while the gain relatively to the sum of power from alone radiated arrays can be as large as 3. These results indicate the mutual synchronization of niobium JJ arrays that would forces the submillimeter generation technique based on large JJ arrays with superwavelength dimensions.