Devices made from high-temperature superconductors could replace semiconductors in carrying out digital logic operations and may provide components for quantum computers.
High-speed digital data links from 4-K superconductor electronics to room temperature are challenging due to the fact that energy/bit for single flux quantum logic is many (six) orders of magnitude lower than that of standard room-temperature logic. Our approach of building an energy-efficient high-speed data link involves a joint electrical-thermal design of a temperature-distributed architecture using different electronic technologies. This differential digital data link design involves superconductor, multiple cryogenic semiconductor and additional room-temperature semiconductor circuitry. The current design involves three cryogenic semiconductor ICs for integration with a multistage cryocooled digital system. The first cryogenic semiconductor IC is designed to operate at 4 K with a power consumption of 0.3 mW and interface directly with the superconductor differential single flux quantum/dc drivers. For testing it, a superconductor carrier chip containing an analog-to-digital converter has been designed for the HYPRES dual-Jc(4.5 and 20kA/cm2) fabrication process.
We have developed a new superconducting digital technology, Reciprocal Quantum Logic, that uses ac power carried on a transmission line, which also serves as a clock. Using simple experiments, we have demonstrated zero static power dissipation, thermally limited dynamic power dissipation, high clock stability, high operating margins, and a low bit-error rate. These features indicate that the technology is scalable to far more complex circuits at a significant level of integration. On the system level, Reciprocal Quantum Logic combines the high speed and low-power signal levels of single-flux-quantum signals with the design methodology of semiconductor digital logic, including low static power dissipation, low latency combinational logic, and efficient device count.
Using of traditional logic elements in digital electronics has ensured the development of a wide range of electronic devices for many years. In parallel, research and development of logical elements are carried out on the basis of other non-traditional physical phenomena or effects, in particular logic elements based on the phenomenon of superconductivity, the prospect of which is the use of very small energy consumption and ultrahigh performance. For superconducting logic elements, using various Josephson cryoelectronic structures, known as Josephson cryotrons, based on the stationary and non-stationary effects of Josephson. On the basis of the Josephson cryotrons, one can create Josephson elements of computer memory, and Josephson elements of digital logic. The main requirements for the Josephson cryotrons are a stable operating mode and high speed or short switching time. Information about the mode of operation and the speed give us the transition characteristics of the cryotrons - the time dependence of the voltage on the cryotron while changing its logical state, which can be obtained either experimentally, or theoretically. This work aims at a search for new ways of increasing the switching rate of digital logical operators by employing physical structures other than the traditional semiconductor-based schemes. We propose the principles of designing digital logical operators based on Josephson cryotrons, whose operation utilizes the stationary and dynamical Josephson effects, and describe the operational principles of the logical elements “AND” and “OR” bases on tunneling Josephson junctions “superconductor-insulator-superconductor”. Our proposed mathematical models for the commutation processes in such logical elements allowed us to calculate their transition characteristics during the switching and to determine the main parameters in such models. It was shown that the logical elements “AND” and “OR” can be implemented on individual cryotrons and that their logical state can be controlled by input signals in a form of current pulses. Such logical elements meet all the requirements for digital logical elements and have switching time of about 2-3 ps, which indicates their significantly increased switching rate.