Josephson Technology

Our working group is focused on the research and development of circuits for voltage standards based on the Josephson effects in close co-operation with the working group 2.41. These highly-integrated superconductive circuits are used for precision electrical voltage measurements. Here, Josephson voltage standards for AC applications have increasingly gained in importance in recent years, after conventional 1 V and 10 V Josephson voltage standards are successfully operated for DC applications in all major national metrology institutes (NMI) and some company laboratories world-wide. In contrast to conventional voltage standards consisting of underdamped Josephson junctions, programmable voltage standards are based on overdamped Josephson junctions, which are realised by SNS or SINIS multilayer structures (S: Superconductor, I: Insulator, N: Normal metal). These overdamped Josephson junctions show a non-hysteretic current-voltage-characteristic, which remains single-valued under microwave irradiation. In order to reach output voltages of 1 V or 10 V, thousands or even tens of thousands Josephson junctions are connected in series arrays. These series arrays are fabricated using the technology of the department in the Clean Room Facility of PTB.

We focus our activities on the research and development of highly-integrated series arrays for AC Josephson voltage standards with a close co-operation with the working group 2.41, which is focused on designs and layouts. Here, we are engaged in investigations of two types of AC voltage standards, which are based on binary-divided and pulse-driven series arrays, respectively. Because of their operation principle being similar to an Digital-to-Analogue Converter (DAC), systems based on binary-divided series arrays are often called programmable Josephson voltage standards. As pulse-driven series arrays enable the synthesis of spectrally pure waveforms, this type is often called Josephson Arbitrary Waveform Synthesizer (JAWS). Using a modified and advanced JAWS set-up, we are able to synthesise waveforms with output voltages of 1 V since mid 2014. Besides binary-divided 1 V series arrays containing 8,192 Josephson junctions, we successfully fabricate 10 V arrays consisting of about 70,000 Josephson junctions for more than 10 years.

In addition to circuits for voltage standards, we also use our technology for fabrication of other circuits containing Josephson junctions as nanoSQUIDs.

Main tasks are:

• development, fabrication, and investigation of binary-divided 1 V and 10 V Josephson series arrays for programmable voltage standards
• development, fabrication, and investigation of series arrays for pulse-driven AC Josephson voltage standards (JAWS)
• fabrication of nanoSQUIDs
• investigation of different materials for optimised Josephson junctions.

The arrays are developed in close co-operation with the working group 2.41 and fabricated using the technology of the department in the Clean Room Facility of PTB. Measurements and applications are performed in close co-operation with the working group 2.63 Josephson Effect, Voltage of department 2.6 Electrical Quantum Metrology. The AC Josephson voltage standards are partly developed within the framework of national and international projects. Within the framework of the European Metrology Research Programme (EMRP), we coordinated the project "Q-WAVE - A quantum standard for sampled electrical measurements" with a runtime from June 2013 to May 2016. The aim of Q-WAVE was to provide direct and efficient traceability for precision devices operating at frequencies up to 10 MHz (further reading: Q-WAVE). We are also contributing to the EMPIR project "QuADC - Waveform metrology based on spectrally pure Josephson waveforms" with a runtime from June 2016 to May 2019 (further reading: QuADC).

Additional information and more details related to our activities are available here.

Some information on terminated projects and events of our working group is available in the archive.