A Microwave Quantum-Defined Millivolt Source

We demonstrate a tenfold increase in the amplitude of microwave-frequency waveforms generated by a quantum-defined superconducting voltage source, with an open-circuit signal of 17.56 mV rms at 1.005 GHz. The voltage source is an RF Josephson arbitrary waveform synthesizer (RF-JAWS) that utilizes a circuit that is cooled to 4 K and is composed of an array of 4500 Josephson junctions. These junctions are connected in series along the center conductor of a 50-
$\Omega $
superconducting coplanar waveguide transmission line. We introduce a new zero-forcing equalization technique for reducing distortion in drive current pulse patterns. This technique allows an increase in the amplitude of the quantum-based voltage waveforms while suppressing parasitic feedthrough signals to −75 dBc. Synthesizing a two-tone delta–sigma waveform, we monitor an audio-frequency 10-kHz tone of less than 100-
$\mu \text{V}$
rms amplitude while simultaneously measuring the 1.005-GHz tone of −28.12-dBm power in a 50-
$\Omega $
environment. The two-tone synthesis allows simultaneous verification of correct operation of the voltage source using time-efficient low-frequency measurement techniques as well as slower microwave measurements.