ESUH

Collaboration

- Italy: INFN: Genova, CNR

National Responsible: M.Marinelli (Ge)

1.Goal of the experiment

The voltage-current characteristic of a Josephson junction, coupled with a radio wave, has constant-voltage steps (Shapiro steps), their amplitude is an integer multilpe of the quantum flux times the radio wave frequency. The goal of the experiment is to find how nearly equal are the steps, produced by two junctions coupled to the same RF source.

More on the Experiment....

2.

Activities during 2001

The present comparison sensitivity is better than 10-17V. This limit comes from the magnetic coupling between the junction DC polarization currents and the superconducting loop, made by the two junctions and their connections with the SQUID input coil. The comparisons have been made using two chips having one working junction per chip; no one of the available chips had both the junctions working. The use of both junctions on the same chip strongly reduces both the loop inductance and the hmutual inductances with the polarization currents. It has been proved that the limit to the sensitivity coming from the rest of the apparatus is about 10-20V

The superconducting loop inductance L has been measured causing the entrance of a well-known number of quantum fluxes inside the loop and measuring, by the SQUID, the relative change of the circulating current I. This prove also that the contacts, between the pads on the chip and the rest of the loop, are superconducting. We also measured that the circulating current does not change for long time (hours), having both the junctions on the step zero (no RF power applied).

Prof. Matteo Cirillo, Physics Department University of Rome 2, Tor Vergata and Dott. Gabriella Castellano, IESS CNR, Rome joined the experiment to help with the design and construction of new chips. They are under construction in the Prof. Cirillo laboratory.

Consequentely, the following milestones have been achieved:

To finish the measurements with all the present chips (30-06-2001) - 100% fulfilled.

To finish the measurements with the new chips (31-12-2001) - 0% fulfilled since the new chips are under construction.

Milestones 2002

Make the comparison between two junctions on the new chips, under costruction in the Physics Department, University of Rome 2, Tor Vergata. | 31-12-2002

3. INFN contribution to the experiment in terms of manpower and financial support

-Manpower: 2 researchers (1 FTE), 0.33 technician and the support of the mechanics workshops, the mechanical design and liquid helium services of the Genoa section.

-Budget for the Year 2002: 2 kEuro (in Dotazioni GrII Sez.Genova)

4. Number of publication in refereed journals:

5. Conference talks:

6. Number of undergraduate and doctoral thesis on the experiment:

-N.8 Laurea diplomas (One has a university permanent position and all the others are working in the electronic and communication industry)

7. Leadership roles in the experiment

The experiment has been designed and built in Genoa.

8. Innovative instruments

See point 2 in More on the Experiment....

9. Competing experiments

This experiment has been done the first time by Clarke [1] and after by Tsai, Jain, Lukens [2], [3], an interesting review of the physical problem has been written by Mc Donald on the Science magazine [4].

- [1] J.Clarke, Phys. Rev. Lett 21, 1566 (1968)
- [2] Tsai, Jain, Lukens, Phys. Rev. Lett. 51, 316(1983)
- [3] Jain, Lukens, Tsai, Phys. Rev. Lett. 58, 1168 (1987)
- [4] D.G. Mc Donald, Science 247, 177(1990)

10. No international committee has reviewed this experiment