New reversible superconducting circuits using pi-shift loops

Aleksandar Andreski, Ariando Ariando, Thomas Ortlepp +2 more

Tomohiro Kamiya, Shozo TANIGUCHI, Kyosuke Sano +2 more

Hans Hilgenkamp, Ariando Ariando, Henk-Jan H. Smilde +5 more

Thomas Ortlepp, Kok-Leei Foo, C.J.M. Verwijs +2 more

Olaf Mielke, Thomas Ortlepp, J. Kunert +2 more

The rapid single-flux quantum electronics (RSFQ) is a superconducting, naturally digital circuit family which is currently close to being commercially applied. RSFQ is outstanding because of its very low switching energy resulting in very low power consumption. This advantage causes, however, a significant influence of thermal noise. For industrial applications, a certain noise immunity is required which is still a challenge, especially for circuits of higher complexity. Integrating phase-shifting elements is a new concept for further improvements concerning stability against the influence of thermal noise. We have already shown that the implementation of phase-shifting elements significantly reduces the influence of thermal noise on circuit behavior by experimentally analyzing the bit-error rate (Mielke et al 2009 IEEE Trans. Appl. Supercond. 19 621–5). Concepts which are easily implementable in standard niobium technology are especially promising. The π-phaseshifter consists of a superconducting loop which is able to store a single flux quantum. The loop current related to the stored flux creates a well-defined phase shift. To achieve the correct functionality of complex circuits it is essential to store exactly one flux quantum in each π-phaseshifter during the cooling down of the chip. Thus, for studying the feasibility of this new approach, the initialization reliability of the π-phaseshifter needs to be verified. We present an experimental investigation of this reliability to obtain a general assessment for the application of the π-phaseshifter in niobium technology. Furthermore, we compare the configuration shielded by a solid ground plane with a configuration with a ground-plane hole below the π-phaseshifter. Justified by the experimental results we suggest programmable RSFQ circuits based on π-phaseshifters. The characteristics of these devices can be influenced by a controlled initialization of the π-phaseshifter. The fabrication was performed by FLUXONICS Foundry.

D Balashov, Boyko Dimov, M. Khabipov +6 more

Quantized values of magnetic flux trapped in a superconducting loop enable a new type of passive phase shifting elements. These elements can be incorporated into digital Josephson circuits making their design compact. We have proven the functionality of such phase shifters fabricated in conventional Nb/Al trilayer technology. We report on the successful low speed operation of a rapid single flux quantum toggle flip-flop circuit with the integrated passive pi-phase shifting element.