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PROJECTS/PROGRAMS

Quantum Voltage Project

Summary

Developing Josephson Voltage Standard systems in order to improve the accuracy of both ac and dc voltage measurements. Both liquid-helium based systems and cryocooler-based systems are now in regular use. The PJVS system realizes quantum-defined voltages up to ±10V and step-wise waveforms up to 1 kHz. The JAWS system realizes waveforms with voltages up to 2 V rms from 10 Hz to 1 MHz

Description

Quantum Voltage Project researchers have successfully implemented operation of the superconducting integrated circuits at the heart of the PJVS on a cryogenic refrigerator that cools the device to 4 K. This was accomplished by improving the fabrication of the circuits that contain nearly 300,000 Josephson junctions, developing new packaging that allowed the devices to be easily operated in either liquid helium or on a cryocooler, and optimizing the system performance with improved software algorithms that control the quantum states as a function of the cryostat's cold-head temperature. Quantized voltages can now be programmed over a voltage range of -10 V to +10V with a stable current range of 1.32 mA and at an operating temperature of 4.3 K. The quantum accuracy of the voltage output has been demonstrated for temperature setpoints up to 4.8 K. Since Jan. 2014 the Project has delivered three new PJVS systems, upgraded 3 more systems, and provided seven 10 V and ten 2 V PJVS chips to metrology laboratories around the world.

Undergraduate student Logan Howe, and NIST researchers AnnaFox (holding the new cryopackage) and Alain Rufenacht demonstrate the performance of the cryocooled Programmable Josephson Voltage Standard. The compact cryocooler and cryostat with the PJVS are all contained in the single equipment rack.

Cryocooled NIST Programmable Josephson Voltage Standard system for realizing intrinsically accurate dc voltages from - 10V to +10V. Available as a NIST Standard Reference Instrument.

The quantum standard for ac voltage is the NIST Josephson Arbitrary Waveform Synthesizer (JAWS). The Synthesizer produces sine waves, multi-tone signals, and arbitrary waveforms with quantum accurate and calculable voltages at frequencies up to 1 MHz by digitally programming the quantum states of 25,600 Josephson junctions connected in series. Over the past 3 years improvements in circuit design and fabrication, packaging, and pulse-bias techniques have quadrupled the output voltage to 1 V root-mean-square (RMS) (1.4 V peak amplitude) over an operating current range greater than 2 mA. Quantum Voltage Project researchers recently demonstrated the capabilities of the system by synthesizing a 1 Hz sine wave useful for ac voltage calibrations and a two-tone waveform at kilohertz frequencies that can be used for inter-modulation measurements of analog-to-digital converters. Based on these advances, researchers are completing development of the new 1 V JAWS system, which contains a single cryopackaged 1V chip with 51,200 Josephson junctions, operated by customized pulse-bias electronics. This first in the world system is slated for delivery to the ac voltage calibration laboratory at the U.S. Army Primary Standard Laboratory in September, 2015.