Quantum-Based Modulated Microwave Waveforms

This article presents a superconducting voltage source that generates modulated microwave waveforms with quantum-based stability. The voltage source-an RF Josephson Arbitrary Waveform Synthesizer (RF-JAWS)-uses a superconducting IC with an array of 4500 series-connected Josephson junctions (JJs) that are embedded in a coplanar waveguide (CPW) transmission line. The JJs are driven with 100-ps wide current pulses that force each JJ to generate voltage pulses with a quantized integrated area. A pulse sequence is created using a delta-sigma (Delta-Sigma) algorithm to generate a 101-tone waveform with a 40-MHz instantaneous bandwidth around 1005 MHz with a flat power distribution of -53 dBm and a Schroeder phase distribution. The JJ's quantum-based nonlinearity produces an amplitude stability with respect to various drive and bias parameters of +/- 0.005 dB and a detrended phase stability of +/- 0.05 degrees. The stability of the source is verified without the need for calibrated measurements. Another Delta-Sigma pulse sequence generates a 10-MHz quadrature-phase shift-keying (QPSK) waveform on a 1005-MHz carrier that has the same stability and the mean error vector magnitude (EVM) of -48 dB. This work is a step toward creating a quantum-based reference source for power and cross-frequency phase calibrations, as well as a reference-modulated signal source for calibrating telecommunication links.