Study of LR-Loading Technique for Low-Power Single Flux Quantum Circuits

A single-flux-quantum (SFQ) circuit is thought to be very suitable as a peripheral circuit for superconducting quantum bits (qubits), which can manipulate and detect the qubit state at a temperature state similar to qubits. Even though the power consumption of SFQ circuits is extremely small, it is still sufficient to heat the substrate at a temperature below 1 K. We have investigated and demonstrated low-power SFQ circuits for this application, using the LR-loading technique, which can reduce the static power consumption of the SFQ circuits. Simulation results show that the ratio of the switching speed to the time constant of the bias circuit is important for the stable operation of low-power SFQ circuits. The static power consumption of SFQ circuits can be reduced to the same order as the dynamic power consumption through optimization of the circuit parameters. We have designed and tested a low-power SFQ clock generator using the LR-loading technique and confirmed its stable operation at 4.2 K, where the power consumption is reduced by 93% compared with ordinary biased circuits.