Systematic-Error Signals in the AC Josephson Voltage Standard: Measurement and Reduction

Voltage lead corrections for a pulse-driven ac Josephson voltage standard

“…To first order in phase angle, the vectorial sum of the Josephson voltage and the inductive voltage changes linearly with phase, with the proportionality constant equal to the inductive voltage. This way, we calculate an array inductance of about 7 nH, which agrees well with results from a more direct method for determining the array self-inductance for a similar array [5]. Note that for a compensation current of 7 mA, the corresponding inductive voltage at 1 MHz is 0.3 mV; the square sum of the 100 mV Josephson voltage and the 90 • out-of-phase 0.3 mV inductive voltage gives a deviation of less than 5 μV V -1 , whereas a phase change (while staying on margins) introduces an error of tens or even hundreds of μV V -1 .…”

“…In our setup, the ac coupling is realized by means of a broadband amplifier having a pass-band between 10 MHz and 50 GHz, which is used because the output power of the pulse generator is too low for the Josephson arrays to operate on their first Shapiro step. Extra dc blocks ensure that the common mode signal is fully suppressed [5]. When summing the ac coupled pulse pattern and the LF compensation signal, care must be taken to align the two signals in both phase and amplitude.…”

“…The resonance caused by the inductance and capacitance of the voltage leads can be suppressed by a simple low-pass RCfilter [6], or even simply by a series resistor [5]. Figure 4 shows that the resistance value can be optimized to find the expected ac-ac difference at HF, in this case 700 kHz.…”

“…For frequencies up to 10 kHz such low uncertainties have already been obtained [4]. For frequencies up to 100 kHz, several error sources have been significantly reduced by comparing the ac-dc differences of two arrays on the same chip [5]. However, at these frequencies, the major problem is that the calculable voltage is generated at low temperatures (in our case 4.2 K), whereas the measurements are usually carried out with equipment at room temperature.…”

Two-Volt Josephson Arbitrary Waveform Synthesizer Using Wilkinson Dividers

“…Compared to the previous copper wires, the superconducting interconnects reduce the inductance and resistance of the connection. This reduces sources of error associated with undesirable currents in the voltage leads, which is important because parasitic capacitances, leakage resistances, and other non-ideal circuit components typically produce small ac currents that can flow through the voltage leads [18]–[20]. …”