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Abstract: Ultra-fast operation with ultra-low power consumption and ballistic transmission of signals are attractive features of single-flux-quantum (SFQ) circuits for building large-scale digital systems. We have been designing SFQ circuits based on the bit-serial architecture, which can reduce the circuit area and timing error induced by clocking skew. In the bit-serial circuits, a serial–parallel converter, which is one of key circuits, is used for I/O interfaces, address decoders, multipliers and so on. In this paper, we propose a novel architecture for the SFQ serial–parallel converter whose latency is very small compared with conventional one. And, we have designed some SFQ circuits suitable for the proposed circuit. As an example, we have implemented and tested SFQ 4-bit multifunctional buffers using the SRL 2.5kA/cm2 niobium standard process. We have successfully confirmed all functions of the multifunctional buffer at low speed. [Copyright &y& Elsevier]

Abstract: A new on-chip microwave generator for manipulating superconductive quantum bits (qubits) have been proposed. To perform practical quantum computation, on-chip microwave generators, which can be controlled by single flux quantum (SFQ) circuits, are desirable because multiple qubits can be driven simultaneously with high accuracy by an SFQ control circuit and the number of wires between qubits and room-temperature electronics can be reduced. The proposed on-chip microwave generator is composed of an SFQ clock generator, which generates a periodic SFQ pulse train, and a band-pass filter. A sinusoidal microwave can be obtained by filtering an output of the SFQ clock generator. Simulation results indicate that the generated microwave has a sharp spectrum, which can be chopped by controlling the SFQ clock generator. Moreover, a phase of the generated microwave can be accurately controlled by adding a phase control circuit, which is composed of cascaded toggle flip-flops, between the SFQ clock generator and the filter. The results indicate that we can perform fast and accurate quantum gate operations using the proposed on-chip microwave generator. [Copyright &y& Elsevier]

Highlights: [•] Balanced Josephson comparator decisions depend on previous decisions at high frequencies. [•] The maximum effective data rate is lower than the clock frequency. [•] Tradeoff between maximum effective data rate and minimum comparator gray-zone. [ABSTRACT FROM AUTHOR]