1. NIST Charlie Burroughs Paul Dresselhaus Mike Elsbury Sam Benz Yi-Hua Tang June Sims METAS Alain Rüfenacht

2. Our Main Objective: “Apply Josephson technology to develop Intrinsic Voltage Standards from DC to 100 kHz.” DC uncertainties of 0.1 nV/V ( ultimately ) AC uncertainties of 0.1 µV/V ( ultimately ) Present dc/ac Systems: Pulse Driven ACJVS, V out = 275 mV rms (unprecedented low distortion) PJVS Stepwise Synthesis, V out = 10 V rms (ultimately) technique #1: Sampled Comparison technique #2: Direct RMS Measurements

3. “Conventional” and “Programmable” JVS systems (overview, pros & cons) Pursuit of “Turnkey” Operation _________________________________________________________ AC Waveform Synthesis (stepwise approximation) AC Systematic Errors Summary

4. Zero Crossing Steps ( allowing use of non-uniform junctions ) Steps always overlap ( all 20 000 junctions in series) No control of actual step number (on each junction) Levinson et al. 1977 & Sulivan (NIST) 150  A 15  m x 30  m Nb-NbO-PbInAu Kautz, Hamilton and Lloyd, 1987 96 GHz

5. 101 109 Josephson Junctions ±3.9 V @ 18.5 GHz Triple-Stacked MoSi 2 13 bias segments “Flex” cryo-package Probe: 50 Ohm coaxes (13 Inputs, 1 Output) Ternary configuration (instead of binary)

6. 268 800 Josephson Junctions ±10 V @ 18.5 GHz 32 sub-arrays, 12 x 17 mm Double-Stacked NbSi

7. Measured V-I Curves of a Typical sub-array (13 200 junctions): Microwave Frequency = 18.3 GHz V dc = N f / K J-90 = 0.499 505 89 V IbIb IaIa

8. We specify the PJVS “State” using 13 characters with one symbol for each cell in the array. For example: “000PPPNPNPPPN” has a total number of junctions N = 29958, which produces V out = 1.115 066 877 V.

9. Josephson Equation: V out = N f / K J-90 N = number Junctions f = frequency ( 18.0 GHz ) Parameters below have a finite range over which the Josephson relation holds: bias current microwave power chip temperature This independence is the reason Josephson systems are “Intrinsic” Standards.

10. Wide range of microwave Frequency (many GHz) Wide range of microwave Power (many dB) Large bias current margins (even for Ic = 4.5 mA) Optimized for cryocooler operation (250 mW cooling power) Chip characterization = fully automated ***

11. Josephson Technology Transparent ( same as zener reference ) Cryogenics should be Transparent ( cryocooler option)

12. 10V PJVS Chip “Step Flatness” Test: Entire Chip Active (32 sub-arrays) Frequency = 19.3 GHz Measured Slope = -9nV ± 41nV (k=2)

13. “Conventional” and “Programmable” JVS systems (overview, pros & cons) Pursuit of “Turnkey” Operation _________________________________________________________ AC Waveform Synthesis (stepwise approximation) AC Systematic Errors Summary

14. AC Waveform Synthesis (stepwise approximation) Calculation of V out for AC waveforms Transition Timing Error (systematic error)

15. What is not precisely known: Transitions (Shape & Timing) (1) We can Measure the transitions (2) We can Model the transitions (attempt to accurately predict) What is precisely known: V array at each of settled state (This is sufficient for sampled comparisons) We want to know V out exactly (rms value, spectral content, etc…)

16. 20 nSec rise time Consider this example: 1024 sample sine wave 60 Hz fundamental 16.3 µSec per sample limiting cases ±2 ns Change in Total RMS Value: ±4.8 parts in 10 7

17. RMS voltage simulation dt = 500 ps

18. Interestingly, these results are independent of: (n ≥ 32) Transition Time (5 ns, 20 ns, 50 ns, …) Number of Samples, (n = 32, 64, 256, 1000, …) Time Placement Accuracy, Δt (of every transition) Upper & Lower Bound (µV/V) at 60 Hzat 1kHzat 10 kHz ±2 ns±0.48±8.0±80 ±1 ns±0.24±4.0±40 ±500 ps±0.12±2.0±20 ±200 ps±0.05±0.8±8

19. The PJVS Output Voltage changes with all of the parameters below for AC stepwise synthesis: microwave power bias current chip temperature overshoot & ringing in transitions interaction between drive channels deviations in current setpoints Why? Because these parameters change either I-V curve shape or I bias set-point, which determine V out during the transitions.

20. The PJVS Output Voltage changes with all of the parameters below for AC stepwise synthesis: microwave power bias current chip temperature transients between levels Interaction between drive channels deviations in current setpoints PJVS is “adjustable” for stepwise AC: It produces a very stable, reproducible voltage, until some bias parameter changes, and then it produces a slightly different stable, reproducible voltage.

21. “Conventional” and “Programmable” JVS systems (New 10V PJVS chips enable next generation systems for DC & AC) Pursuit of “Turnkey” Operation (PJVS stability and large operating margins = higher level of automation) (New 10V PJVS chips optimized for cryocooler operation) _________________________________________________________ AC Waveform Synthesis (stepwise approximation) AC Systematic Errors (special techniques necessary to overcome fundamental limitations) (i.e., sampled comparisons, fast reversed DC, etc…)