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Adiabatic quantum-flux-parametron (AQFP) logic can achieve high energy-efficiency. The bit energy and bit-error-rate (BER) of AQFP gates with under-damped Josephson junctions were simulated. The results indicate that the bit energy reaches 12 yJ, which is only 20% of the thermal energy at 4.2 K, using unshunted 50-μA junctions and excitation currents with a rise/fall time of 2000 ps. Although the bit energy is extremely small, the bias margin, where the BER is less than 10-23, is approximately ±22%. These results indicate there is no minimum energy limitation for the operation of AQFP gates unless the entropy of the system decreases. [ABSTRACT FROM AUTHOR]

Novel reconfigurable superconductive single flux quantum (SFQ) logic devices, the functions of which can be dynamically reconfigured by inputting control signals, have been investigated. The characteristics of single flux quantum circuits can be easily modulated by applying currents or magnetic fields because of the high sensitivity of superconductive circuits. We investigated several design approaches for the realization of dynamically reconfigurable SFQ logic devices. We employed direct current injection to the logic gate using a non-destructive read-out flip-flop. By changing the internal state of the non-destructive read-out flip-flop, the logic function can be dynamically reconfigured. We have designed and tested a dynamically reconfigurable Josephson transmission line (JTL)/delay flip-flop (DFF) circuit. The measured dc bias margin was 72.5–107.2%. Furthermore, we have demonstrated the operation of a variable bit-length shift register, composed of the dynamically reconfigurable JTL/DFF circuits. The investigated design approach can be applied to more sophisticated dynamically reconfigurable single flux quantum logic gates. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated high-speed logic operations of adiabatic quantum-flux-parametron (AQFP) gates through the use of quantum-flux-latches (QFLs). In QFL-based high-speed test circuits (QHTCs), the output data of the circuits under test (CUTs), which are driven by high-speed excitation currents, are stored in QFLs and are slowly read out using low-speed excitation currents. We designed and fabricated three types of QHTCs using QFLs with different circuit parameters, where the CUTs were buffer gates and and gates. We confirmed the correct operation of buffer gates and and gates at 1 GHz. The obtained bias margins of the 1 GHz excitation currents were more than \pm 30% for each QHTC, which is wide enough for high-speed logic operations of AQFP gates. [ABSTRACT FROM PUBLISHER]

Abstract: We have been studying a superconducting quantum-computing system where superconducting Josephson-junction quantum bits (qubits) are controlled and read out by rapid single-flux-quantum (RSFQ) circuits. In this study, we designed and fabricated an on-chip RSFQ microwave pulse generator (MPG), which generates microwave pulses with the time resolution of sub-ns for precise control of qubit states. The output microwave amplitude of the MPG can be amplified to more than 350μV using a multi-flux-quantum (MFQ) driver, which increases the number of the propagating single-flux-quantum (SFQ) pulses. Fundamental properties of the MFQ driver and the RSFQ MPG were measured at 4.2K. It was confirmed that the MFQ driver can amplify an SFQ pulse up to six MFQ pulses and the irradiation time and the amplitude of the output microwave of the RSFQ MPG can be controlled adequately. [ABSTRACT FROM AUTHOR]

We performed yield analysis of large-scale adiabatic-quantum-flux-parametron (AQFP) circuits using circuit simulations based on the Monte Carlo method assuming the distribution of the critical current of Josephson junctions. Based on the simulation results, we also made an analytical model for the circuit yield of large-scale AQFP circuits. The yield analysis indicates that AQFP integrated circuits containing 1 million gates can be realized when the interconnect inductance is about 40 pH and the normalized standard deviation of the critical current is less than 1%. [ABSTRACT FROM AUTHOR]