Single-Flux-Quantum Multiplier Circuits for Synthesizing Gigahertz Waveforms With Quantum-Based Accuracy

Area of Science:

• Superconducting electronics
• Quantum metrology
• Microwave engineering

Background:

• Accurate synthesis of high-frequency waveforms is crucial for communications metrology.
• Existing methods face limitations in precision and calibration.
• Quantum phenomena offer a path towards enhanced accuracy and reproducibility.

Purpose of the Study:

• To design, simulate, and experimentally demonstrate key components for a self-calibrated programmable waveform reference.
• To develop a microwave-frequency digital-to-analog converter (DAC) using single flux quantum (SFQ) circuits.
• To create a superconducting-quantum-interference-device (SQUID) based amplifier for quantum-accurate signal synthesis.

Main Methods:

• Fabrication of SFQ and SQUID circuits using a Nb/NbxSi(1-x)/Nb Josephson-junction (JJ) process with self-shunted JJs.
• Design and simulation of SFQ voltage multiplier circuits incorporating SFQ-splitters and SQUID transformers.
• Experimental synthesis and characterization of single-tone and multitone gigahertz waveforms at 4 K.

Main Results:

• Successful demonstration of SFQ-based DAC and SQUID-based amplifier components.
• Quantized pulse output signals from the SFQ voltage multiplier.
• Stable and reproducible synthesis of gigahertz waveforms at 4 K across various operational parameters.

Conclusions:

• The developed SFQ and SQUID components are viable for a quantum-based programmable waveform reference.
• The fabrication process yields high-performance superconducting devices.
• Proposed circuit designs offer pathways for higher synthesis frequencies and improved output characteristics.