Verification of stable operation of rapid single flux quantum devices with frequency-dependent dissipation

Abstract

Abstract. It has been suggested that rapid single flux quantum (RSFQ) devices could be used as the classical interface of superconducting qubit systems. One problem is that the interface acts as a dissipative environment for a qubit. Recently, ways to modify the RSFQ damping to reduce the dissipation have been introduced. One of the solutions is to damp the Josephson junctions by a frequency-dependent linear circuit instead of the plain resistor. The approach has previously been experimentally tested with a simple SFQ comparator. In this paper we perform experiments with a full RSFQ circuit, and thus conclude that in terms of stable operation the approach is applicable to scalable RSFQ circuits. Realization and optimization issues are also discussed. Contents

Single flux quantum circuits with damping based on dissipative transmission lines

“…[17] and verified in Ref. [18]. This linear circuit consisting of thin-film resistor and plate on-chip capacitor is relatively simple for fabrication.…”

“…Moreover, the large size of the RC line shunts makes it, in principle, possible to attach cooling fins of larger volume. These cooling fins may have a more efficient thermal contact to the large "hot" area of the RC line shunt than in the case of relatively small resistive shunts or the RC shunts [18].…”

“…These resonances may present a problem in Nb-based on-chip capacitors having very low losses. (The RC shunts with such capacitors were realized in VTT technology with a critical current density j c = 30 A/cm 2 [18].) Therefore, the lateral dimensions of the capacitors (100 µm by 160 µm with 140 nm thick Nb 2 O 5 dielectric yielding C = 35 pF [18]) should not exceed λ p /8 (≈ 170 µm), where λ p is the electromagnetic wavelength in the dielectric at the plasma frequency.…”

“…Recently, a simpler realization of RSFQ networks with a frequency-dependent damping based on shunting the junctions by serial RC circuits (see figure 1(c)) has been proposed in [17] and verified in [18]. This linear circuit, consisting of a thin-film resistor and a plate on-chip capacitor, is relatively simple for fabrication.…”