Abstract
The PTB Josephson Arbitrary Waveform Synthesizer (JAWS) enables the generation of arbitrary waveforms up to voltages of 70 mVRMS (199 mVPP) using two Josephson arrays in series containing 4000 Josephson junctions each. The SNS-like double-stacked junctions are based on NbxSi1-x as barrier material. While the JAWS system is typically operated using a Dewar with liquid helium, the operation in a closed-cycle pulse-tube cryocooler at temperatures around 4.2 K range was here investigated and successfully demonstrated. For this purpose a special designed cryoprobe was used to provide high quality pulses to the Josephson arrays.
Highlights
Pulse-driven Josephson junctions are the basis for one version of an AC Josephson voltage standard which enables the synthesis of arbitrary AC waveforms with extremely pure frequency spectra
By mounting the Josephson Arbitrary Waveform Synthesizer (JAWS) chip in a specially designed cryoprobe we investigated the opportunity to operate this JAWS array with a pulse tube cryocooler
The results clearly demonstrate that a stable operation of the JAWS system in this cryocooler is possible using our purpose-built cryoprobe for temperatures above 4.2 K
Summary
Pulse-driven Josephson junctions are the basis for one version of an AC Josephson voltage standard which enables the synthesis of arbitrary AC waveforms with extremely pure frequency spectra. Our JAWS setup enables the synthesis of spectrally pure bipolar arbitrary waveforms with a signal-to-noise ratio of up to 120 dBc. As already demonstrated, amplitudes of up to 184 mVRMS (521 mVpp) can be generated for DC-voltages and AC-voltages in a frequency range from 60 Hz to 1 MHz by connecting two arrays in series with 12,000 Josephson junctions in total (see Figure 1) [7]. Urano et al operated the Josephson arrays of an optoelectronics JAWS system in a two stage Gifford-MacMahon refrigerator [8] They demonstrated the synthesis of AC waveforms with voltages below 1 mVRMS and higher harmonics suppressed by −80 dBc at most
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