Josephson Junction Array Achieves 30 Gb/s Data Rates with Cryogenic BiCMOS Integration

The development of ultra-precise signal generation is crucial for advanced technologies, and researchers are now demonstrating a significant step forward by integrating superconducting circuits with advanced cryogenic electronics. Yerzhan Kudabay, Oliver Kieler, and Michael Starkloff, along with colleagues from Braunschweig University of Technology, Physikalisch-Technische Bundesanstalt (PTB), and Supracon AG, have successfully combined a Josephson junction array with a custom-designed cryogenic BiCMOS pulse pattern generator. This innovative system achieves data rates of 30 Gb/s while operating at extremely low temperatures, and represents the first integration of its kind. The team’s achievement paves the way for a fully integrated Josephson arbitrary waveform synthesizer, promising ultra-low-noise signals with applications in sensitive voltage and information systems.

The research team developed a BiCMOS circuit capable of generating high-speed return-to-zero pulses at data rates of 30 Gb/s while consuming 302mW at 4 K, effectively transferring magnetic flux through each Josephson junction. This innovative circuit acts as a cryogenic pulse pattern generator, delivering precisely timed electrical pulses to the junction array. To the best of their knowledge, this work represents the first successful integration of a Josephson junction array with a cryogenic BiCMOS chip, paving the way for fully integrated Josephson arbitrary waveform synthesizers.

The system operates by harnessing the principles of pulse-density-to-voltage modulation, where a sequence of current pulses with a time-dependent repetition frequency is applied to the Josephson junction array. Each pulse transfers one magnetic flux quantum through each junction, creating well-defined plateaus, known as Shapiro steps, in the array’s current-to-voltage characteristics. The team implemented a compact printed circuit board, measuring 20 × 27 mm², incorporating a 16:1 serializer alongside an array of non-hysteretic Nb/NbSix/Nb Josephson junctions. This configuration allows for the generation of quantum-accurate arbitrary waveforms from DC up to the MHz range, suppressing harmonic distortion and enabling precise waveform synthesis.

The BiCMOS serializer, previously characterized as a standalone component, was successfully integrated with the Josephson junction array to validate its operation as part of a complete cryogenic pulse pattern generator. Scientists utilized superconductor-normal conductor-superconductor Josephson junctions, chosen for their non-hysteretic characteristics, ensuring stable and repeatable switching events. The team demonstrated wide and flat Shapiro steps in the junction array’s current-to-voltage characteristics, confirming the system’s ability to generate quantized voltage waveforms with inherently fine resolution. This innovative approach enables the creation of AC quantum voltage standards with significantly reduced harmonic content compared to conventional methods.

Integrated Circuit Drives High-Fidelity Waveform Synthesis

Scientists have successfully integrated a cryogenic BiCMOS integrated circuit with a superconducting Josephson junction array, achieving a significant breakthrough in the development of Josephson Arbitrary Waveform Synthesizers (JAWS). This work demonstrates, for the first time, a fully integrated system capable of generating ultra-low-noise signals for quantum voltage metrology and quantum information systems. The BiCMOS circuit functions as a high-speed pulse pattern generator, delivering data rates of 30 Gb/s while consuming 302mW at 4 K. Experiments reveal that each electrical pulse from the serializer effectively transfers one magnetic flux quantum through every Josephson junction, resulting in well-defined plateaus, known as Shapiro steps, in the array’s current-to-voltage characteristics.

The system utilizes a compact printed circuit board measuring 20x 27 mm², incorporating a 16:1 serializer alongside an array of non-hysteretic Nb/NbSix/Nb Josephson junctions. This integration reduces system complexity and enhances scalability, crucial for operation at cryogenic temperatures where cooling capacity is limited. The JAWS operates on the principle of pulse-density-to-voltage modulation, achieving inherently quantized resolution. Measurements confirm that the average output voltage is directly determined by the number of junctions, the number of flux quanta per pulse, and the pulse repetition frequency. This approach enables the generation of waveforms with extremely high spectral purity, suppressing harmonic distortion and allowing for clean and precise waveform generation.

This work demonstrates the successful integration of a high-speed BiCMOS serializer with a Josephson junction array, representing a significant advance in cryogenic electronics. The researchers achieved data rates of 30 gigabits per second while maintaining stable operation at temperatures as low as 4 Kelvin, a crucial requirement for many quantum technologies. This integration allows for the generation of precise, low-noise signals, essential for applications in quantum metrology and information systems. The system exhibits wide and flat Shapiro steps, confirming the feasibility of combining conventional high-speed electronics with superconducting quantum standards. The serializer operates effectively across a broad temperature range, from 4 Kelvin up to room temperature, and at high data rates, highlighting the importance of robust clock distribution in cryogenic environments. While acknowledging that this is a proof-of-concept demonstration, the team suggests future work will focus on further optimizing the system and exploring its potential in advanced quantum applications.