Critical current improvement and resistance evaluation of superconducting joint between Bi2223 tapes

We improved the critical current (I c) of the superconducting joint between the Bi2223 tapes by introducing the two-step sintering process. The in-field transport I c of ~ 300 A at 4.2 K and 1 T under a 10−9 Ω criterion was successfully demonstrated. The I c improvement can probably be attributed to the enhancement of the intergrain critical current density for a Bi2223 intermediate layer. Ultra-low in-field joint resistance below 10−14 Ω at 4.2 K and 1 T was also demonstrated using current decay measurement. To our best knowledge, this study is the first to demonstrate a practical level of in-field transport I c and ultra-low in-field joint resistance for the superconducting joint between Bi2223 tapes. We believe that this superconducting joint technology will facilitate development of persistent current mode Bi2223 superconducting magnets.

Canonical Hamiltonian ensemble representation of dephasing dynamics and the impact of thermal fluctuations on quantum-to-classical transition

An important mathematical tool for studying open quantum system theory, which studies the dynamics of a reduced system, is the completely positive and trace-preserving dynamical linear map parameterized by a special parameter-time. Counter-intuitively, akin to the Fourier transform of a signal in time-sequence to its frequency distribution, the time evolution of a reduced system can also be studied in the frequency domain. A recent proposed idea which studies the representation of dynamical processes in the frequency domain, referred to as canonical Hamiltonian ensemble representation (CHER), proved its capability of characterizing the noncalssical traits of the dynamics. Here we elaborate in detail the theoretical foundation within a unified framework and demonstrate several examples for further studies of its properties. In particular, we find that the thermal fluctuations are clearly manifested in the manner of broadening CHER, and consequently rendering the CHER less nonclassical. We also point out the discrepancy between the notions of nonclassicality and non-Markovianity, show multiple CHERs beyond pure dephasing, and, finally, to support the practical viability, propose an experimental realization based upon the free induction decay measurement of nitrogen-vacancy center in diamond.

Electroweak Decays of Highly Charged Ions

In this contribution we review the present status of experimental studies of electroweak decays of highly charged ions. A particular focus will be given on the bound state beta decay measurement of 205Tl.