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Photon drive for quantum flux transfer

Josephson AC voltage standard with optical pulse drive successfully implemented

PTB-News 3.2019
24.09.2019
Especially interesting for

metrology institutes

calibration laboratories

manufacturers of electrical precision measuring instruments

At PTB, a pulse-driven Josephson standard for the generation of AC voltages has been realized where the voltage pulses are synthesized by means of optical components. This has advantages compared to the conventional operating procedure where the driving voltage pulses are conducted onto the superconducting chip via RF conductors.

cture of the JAWS chip with 3000 integrated Josephson junctions and of the photodiode chip carrier (PDCC) connected to the optical waveguide.

Josephson Arbitrary Waveform Synthesizers (JAWS) allow quantized AC voltages to be synthesized with arbitrary and spectrally pure waveforms. They are based on series arrays of superconducting Josephson junctions of the kind manufactured in the Clean Room Center of PTB. Effective output voltages of more than 2 V have already been demonstrated at PTB. For this purpose, 16 JAWS arrays were operated in series with the driving voltage pulses being conducted onto the superconducting Josephson junctions, which were cooled in a liquid helium dewar, via an RF conductor per array.

As an alternative to the use of several RF conductors, a procedure was developed within the scope of the QuADC EMPIR metrology research program in which the driving voltage pulses are generated optically in the immediate vicinity of the JAWS chips. This simplifies the experimental setup, which, in turn, will make it easier to further increase the output voltages and to market the system. The new procedure is based on the use of fast photodiodes which are resistant to low temperatures and are coupled to optical supply fibers. The photodiodes are mounted on a custom-made silicon carrier chip by means of flip chip technology. The optical pulses generated with a pulsed laser outside the helium bath are transmitted to the photodiodes via an optical fiber. At the photodiodes, they are converted into electric pulses and fed to the JAWS arrays over a short distance. In the first test conducted with an array consisting of 3000 Josephson junctions, effective sinusoidal output voltages of 6.6 mV (18.6 mV from peak to peak) and a frequency of 1875 Hz were generated.

Another advantage of this new procedure is the reduced noise background of the output signal generated. This considerably improves the signal-to-noise ratio of the waveforms generated, especially above 1 MHz.

The next step is to enhance the integration density of the photodiodes to enable several JAWS arrays to be operated at the same time and thus the output voltage to be increased.

Contact

Oliver Kieler
Department 2.4
Quantum Electronics
Phone: +49 531 592-2410
Opens window for sending emailoliver.kieler(at)ptb.de

Scientific publication

O. Kieler, B. Karlsen, P. A. Ohlckers, E. Bardalen, M. N. Akram, R. Behr, J. Ireland, J. Williams, H. Malmbekk, L. Palafox, R. Wendisch: Optical pulsedrive for the pulse-driven ac Josephson voltage standard. IEEE Trans. Appl. Supercond. 29, 1200205 (2019)