Implementation of superconductive passive phase shifters in high-speed integrated RSFQ digital circuits

Abstract

The reduction of the critical current density in rapid single-flux quantum (RSFQ) circuits enables new application fields, like quantum computing and photonic detector readout. The low current density fabrication process creates new design challenges, such as lower stability against thermal fluctuations, violation of the lumped elements condition for microstrip inductances and increased sensitivity to the technological spread. To overcome these issues, we suggest a passive phase shifter as a promising alternative technique for superconductive phase dropping in the RSFQ electronics. Here, we study experimentally their applicability in high-speed RSFQ digital circuits. Conclusions are drawn about the impact of the passive phase shifters on the complexity, the speed and the bit error rate of the investigated RSFQ circuits. We demonstrate the successful operation of different circuits with implemented passive phase shifters at low and high speeds.

Two mechanisms of Josephson phase shift generation by an Abrikosov vortex

“…It is anticipated that unconventional junctions either with a fixed phase shift ϕ 0 (ϕ-junctions), or with an in-built spatial phase variation along the junction ∆ϕ (0 − ϕ junctions) may provide additional functionality in Josephson electronics [1][2][3][4]. For example, they can operate as autonomous and persistent phase batteries -one of key elements of quantum [1,[5][6][7][8][9][10][11][12][13][14] and digital Josephson electronics [2,3,15,16]. Such junctions can be also used for development of novel types of cryogenic memory [17][18][19][20][21][22].…”

“…Such junctions can be also used for development of novel types of cryogenic memory [17][18][19][20][21][22]. The π-phase shift is most commonly needed, e.g., for bringing the flux-qubit to the degeneracy point [1,[5][6][7], for realization of complementary digital Josephson electronics [2,3,15,16] and for maximum distinction between 0 and 1 state in a memory cell [17].…”

Implementation of energy efficient single flux quantum digital circuits with sub-aJ/bit operation

“…Josephson junctions [45][46][47][48][49]. Even for conventional RSFQ circuits, the improved operational margins, bit-error rates, and gate memory non-volatility were reported [50][51][52][53].…”

Reconfigurable Josephson Phase Shifter

“…Similar phase shifters have been used for digital RSFQ electronics. 14 , 15 Recently it was shown that an Abrikosov vortex can induce a JPS in nearby JJs in the full [−2π, + 2π] range. 23 , 43 , 44 Since vortices can be easily manipulated (displaced, introduced, or removed) by magnetic field, H , 23 , 45 − 47 current, I , 20 , 48 , 49 and light, 50 , 51 they can be used for creation of memory cells 20 and tunable phase shifters.…”