Josephson junction computer

An important potential use is in logic components in high-speed computers. Josephson Junctions can switch states very quickly (as low as 6 picoseconds). Moreover they have very low power consumption and can be packed closely without generating too much heat. It is possible that computers based on such devices could operate 50 times faster than the best existing machines. The effects are named after Brian Josephson (1940- ), who predicted them theoretically in 1962. 

Other early designs of classical reversible computers included Landauer s Bag and Pipes Model [land82a] (in which pipes are used as classical mechanical conduits of information carried by balls). Brownian motion reversible computers ([benn88], [keyesTO]) and Likharev s model based on the Josephson junction [lik82]. One crucial drawback to these models (aside from their impracticality), however, is that they are all decidedly macroscopic. If we are to probe the microscopic limits of computation, we must inevitably deal with quantum phenomena and look for a quantum mechanical reversible computer. 

Josephson junctions for passive microwave devices, satellite-communication systems, and computer logic gates. 

Josephson junctions may be arranged in a variety of ways for other purposes. Perhaps, the best-known application is to computers combinations of Josephson junctions can be designed to act as a very fast switch with low power dissipation or as a memory element. The theoretical switching time is about lOpsec and the power dissipation about InW, giving a product of switching time per power consumption several orders of magnitude better than that of transistors. 

Fig. 1. Special equipment required to fabricate low-temperature superconducting junctions. Josephson junctions are comprised of aluminum oxide sandwiched between layers of niobium. These trilayer devices are considered vital to the very-high-speed signal processing demands of next-generation computers, radar, and communication systems. Shown in illustration is scientist Dr. Joonhee Kang. (Westinghouse Electric Corporation)...

In 1962, B. Josephson recognized the implications of the complex order parameter for the dynamics of the superconductor, and in particular when one considers a system consisting of two bulk conductors connected by a weak link." This research led to tile development of a series of weak link devices commonly called Josephson junctions. See also Josephson Tunnel-Junction. These devices hold much promise for achieving ultra high-speed computers where switching time is of the order of 1CT11 second. 

If and when a Josephson junction computer is built, the junction s size and low power dissipation would allow manufacturers to put more guts and gas into their machines. Their cycle times—the time required for a chip to perform one task—would be substantially shortened. Such a computer might, in fact, fill a cube only 2 inches on a side and operate more than fifty times faster than the best that are available today. No mean feat, considering that the world s first all-electronic computer, ENIAC (for Electronic Numerical Integrator and Calculator), covered some 1,500 square feet of floor space at the University of Pennsylvania, where it had its maiden run in 1946, was jam-packed with some twenty thousand vacuum tubes, and weighed in at more than 30 tons. Moreover, its computations were measured in seconds—not a nanosecond, a picosecond (a trillionth of a second), or a femtosecond (a quadrillionth of a second), the measurements computer designers are accustomed to shooting for today. 

But let s return to Josephson junctions for a moment. Even though a computer made of these incredible instruments has not yet been built, the junctions themselves, as we have said, are in use, fabricated of conventional superconducting materials. They are also beginning to appear in devices run by the new superconducting ceramics. 

The last two papers are also related to quantum computing issues, in particular the characterization of various kinds of qubits based on Josephson junctions. 

In spite of well-developed classical theory, the interest to investigation of synchronization phenomena essentially increased within last two decades and this discipline still remains a field of active research, due to several reasons. First, a discovery and analysis of chaotic dynamics in low-dimensional deterministic systems posed a problem of extension of the theory to cover the case of chaotic oscillators as well. Second, a rapid development of computer technologies made a numerical analysis of complex systems, which still cannot be treated analytically, possible. Finally, a further development of synchronization theory is stimulated by new fields of application in physics (e.g., systems of coupled lasers and Josephson junctions), chemistry (oscillatory reactions), and in biology, where synchronization phenomena play an important role on all levels of organization, from cells to physiological subsystems and even organisms. 

Thin-fiim technology has also played an important role in developing Josephson superconducting devices, which offer outstanding advantages in constructing ultrahigh-speed computers, These are tunnel-junction type devices. 

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