  In the field of superconducting electronics, the on-chip generation of AC
radiation is essential for further advancements. Although a Josephson junction
can emit AC radiation from a purely DC voltage bias, the coherence of this
radiation is significantly limited by Johnson-Nyquist noise. We relate this
limitation to the thermodynamic uncertainty relation (TUR) in the field of
stochastic thermodynamics. Recent findings indicate that the thermodynamic
uncertainty relation can be broken by a classical pendulum clock. We
demonstrate how the violation of the TUR can be used as a design principle for
radiation sources by showing that a superconducting clock circuit emits
coherent AC radiation from a DC bias.
