Josephson ratio

The intrinsic sampler resolution is essentially determined by the ratio of current density to specific capacitance of a Josephson junction pulser contained in the sampling circuit. For picosecond resolution with existing helium temperature superconducting technologies, junction current densities are approaching 104 to 105 A/cm2. The upper end of this is at the limit that has presently been demonstrated for the YBaCuO superconductor itself at 77 K, so achieving such density in a junction will be a major challenge. 

The earliest work in this area is now more than 45 years old [63]. Patton and Josephson [63] proposed estimating the importance of an aroma compound to the sensory character of a food by calculating the ratio of the concentration of a compound in a food to its sensory threshold in that food. This ratio is known now as... 

The first of the macroscopic quantum effects to be demonstrated was the ac Josephson effect, whereby 2e/h is established via the invariant ratio nV/V for irradiation at frequency V and noting the n th step voltage, V. This has been a powerful tool in the service of electrical measurements. The history, which has been well reviewed by Petley, shows a rapid evolution from laboratory curiosity through a significant determination of a to the role of maintenance of the operational unit of voltage [16]. Incidentally, the early history of this area of work is an instance in which electrical metrology made a distinct impact on atomic physics. It will be recalled that a key issue of the early 1960 s was the discrepancy between values of a obtained from fine-structure measurement and those deduced from hyperfine structure. This story is well told in the widely known summary, due to Taylor,... 

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