Quantum Voltage Project

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.

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.