Chen Geng-Hua

The copper isotope effect in Ba2Y Cu3O7

Abstract The effect of isotopic substitution on the superconducting Tc in the 90 K superconductors Ba2Y Cu3O7 by replacing ordinary copper Cu with 63Cu and 65Cu has been studied. The transition temperatures are found to be the same within experimental error of ± 0.2K. This indicates that the copper isotope effect is absent in this material, as in the cases of oxygen.

Nb/Al-AlOx/Nb junctions with controllable critical current density for qubit application

Nb/Al-AlOx/Nb tunnel junctions with controllable critical current density JC are fabricated using the standard selective Nb etching process. Tunnel barriers are formed in different oxygen exposure conditions (oxygen pressure P and oxidation time t), giving rise to JC ranging from 100 A/cm2 to above 2000 A/cm2. JC shows a familiar linear dependence on P × t in logarithmic scales. We calculate the energy levels of the phase- and flux-type qubits using the achievable junction parameters and show that the fabricated Nb/Al-AlOx/Nb tunnel junctions can be used conveniently for quantum computation applications in the future.

THE DISTRIBUTION OF THE ORDER PARAMETER IN JOSEPHSON TUNNELLING JUNCTION

The distribution of the order parameter in a Josephson junction has been investigated theoretically. There are upper and lower critical thicknesses dc and dm in a Josephson junction. The tunnelling junction is a normal superconductor when d dc.

Retrieval of original signals for superconducting quantum interference device operating in flux locked mode

We discuss a simple relation between the input and output signals of a superconducting quantum interference device magnetometer operating in flux locked mode in a cosine curve approximation. According to this relation, an original fast input signal can be easily retrieved from its distorted output response. This technique can be used in some areas such as sensitive and fast detection of magnetic or metallic grains in medicine and food security checking.