Currents and Phases in Quantum Rings.

Edris Faizabadi

By applying electric harmonic signals on two point of a quantum ring with phase difference , the induced current is calculated theoretically. The method is based on defining all the operators in the Hilbert space of side band states defined in terms of Floquet theorem. Using this method, we have calculated the electronic pumped current as a function of phase difference of applied electric signals. By controlling on phase difference, it is shown that a polar pumped current can be induced in quantum ring. Φ

Sigríður Sif Gylfadóttir

Thomas Ihn, Andreas Fuhrer, K. Ensslin +2 more

Guang-Yu Yi, Zhichao Li, Xiaohui Chen +2 more

The Josephson effect in a superconductor/triple-quantum-dot ring/superconductor structure is theoretically investigated. We find that in this structure, interdot spin correlation can be driven, which contributes to the occurrence of new 0 and $\ensuremath{\pi}$ phases of the Josephson current. Moreover, in the 0-$\ensuremath{\pi}$ phase-transition process, an intermediate bistable phase appears in which the Josephson current is completely suppressed. By analyzing the interdot spin correlation, the electron motion mechanism is clarified. We then attribute the disappearance of the Josephson current to the occurrence of the Josephson-Fano effect. What is interesting is that the disappearing Josephson current is accompanied by the apparent persistent current in the ring whose direction is determined by the superconducting phase difference. With the calculated results, we consider such a structure to be a candidate for the realization of the persistent current bit.

L. D. Jackel, Terrence D. Clark, Robert A. Buhrman

An investigation has been made of the effect of the weak link current-phase relation on noise in rf biased SQUIDs. Non-sinusoidal current-phase relations have been observed in various weak links and these non-sinusoidal relations have been correlated with significantly increased intrinsic noise in the SQUID ring. The current-phase relation is also found to affect the amplitude of the rf SQUID ring dissipation. The result of a rf SQUID system noise analysis shows that, due to increased intrinsic noise and reduced ring dissipation, the minimum attainable noise for a SQUID ring having a very non-sinusoidal current-phase relation is considably greater than for a ring with a sinusoidal relation.

陳光胤, Guang-Yin Chen, 褚德三 +1 more