Superconduction At Nanowire Levels
Passing electricity through any conductor generates heat. Even the best conductor such as a copper wire offers some resistance to electrons passing through it. As electrons move through the ordinary conductor, they occasionally collide with its atoms and this releases energy as heat.
Cooling ordinary materials to very low temperatures changes the scenario drastically. Cold temperature dampens the Brownian motion of their atoms, allowing electrons to zip past with very few collisions. Therefore, very low voltage difference is required to pump electrons through ordinary materials when they are at cryogenic temperatures.
For example, Niobium Nitride, which is the base for several superconducting circuits, has a relatively high operating temperature of 16 degree Kelvin. This is equivalent to -257 degree Celsius and is achieved with liquid Helium. Within a superconducting chip, the liquid Helium circulates through a system of pipes in an insulating housing, much like Freon circulating inside a household refrigerator.
Although superconducting materials offer huge benefits, cooling to extremely low temperatures is very expensive and many researchers are working across the globe to make the process commercially viable. Researchers at MIT claim to have developed a circuit design that can help to make simple superconducting devices with extremely low electrical resistance much cheaper.
According to the researchers at MIT, chips made using the technology would make them 50-100 times more energy efficient compared to today’s chips. Although their working would not top the speed of current chips, recovering results of calculations that Josephson junctions perform would be made much simpler.
The current research at MIT has the cryotron as its basis. Cryotron or the Cryotron Computer, an experimental computing circuit, was developed by the MIT professor Dudely Buck in the 1950s. Although, the cryotron attracted a great deal of interest at the time as the possible future for a new generation of computers, the Integrated Circuit eclipsed it.
Current research at MIT in this field has resulted in the development of the nanocryotron. Researchers have tested superconducting circuits made with nanocryotron in light detectors and have been successful in registering the arrival of a single photon or light particle. They also wired several of these circuits together to produce the half-adder, a fundamental component of digital arithmetic. This square-centimeter chip has the nTron adder and performs computations using the new superconducting circuit.
A system using liquid-Helium for cooling is sure to increase the power consumption of a superconducting chip. However, given that this increase starts at about one percent of the energy required for a conventional chip, the overall savings can potentially be enormous. For example, making single-photon detectors would become very cost-effective – this being an essential component in any information system exploiting the computational speedup promised by quantum computing.
The nanocryotron or, as the researchers prefer to call it, the nTron, is an individual layer of Niobium Nitrate on an insulator. The device gets its name from its pattern that looks much like a capital ‘T’. The junction of the base and the crossbar tapers to a narrow region, forming a switch to control the current flow through the crossbar by injecting a current in the base.
