Microsoft Word Kurzweil, Ray The Singularity Is Near doc

Computing with Spin. 
In addition to their negative electrical charge, electrons have another property that can be 
exploited for memory and computation: spin. According to quantum mechanics, electrons spin on an axis, similar to 
the way the Earth rotates on its axis. This concept is theoretical, because an electron is considered to occupy a point in 
space, so it is difficult to imagine a point with no size that nonetheless spins. However, when an electrical charge 
moves, it causes a magnetic field, which is real and measurable. An electron can spin in one of two directions, 
described as "up" and "down,” so this property can be exploited for logic switching or to encode a bit of memory. 
The exciting property of spintronics is that no energy is required to change an electron's spin state. Stanford 
University physics professor Shoucheng Zhang and University of Tokyo professor Naoto Nagaosa put it this way: "We 
have discovered the equivalent of a new 'Ohm's Law' [the electronics law that states that current in a wire equals 
voltage divided by resistance]....[It] says that the spin of the electron can be transported without any loss of energy, or 
dissipation. Furthermore, this effect occurs at room temperature in materials already widely used in the semiconductor 
industry, such as gallium arsenide. That's important because it could enable a new generation of computing devices."
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The potential, then, is to achieve the efficiencies of superconducting (that is, moving information at or close to the 
speed of light without any loss of information) at room temperature. It also allows multiple properties of each electron 
to be used for computing, thereby increasing the potential for memory and computational density. 
One form of spintronics is already familiar to computer users: magnetoresistance (a change in electrical resistance 
caused by a magnetic field) is used to store data on magnetic hard drives. An exciting new form of nonvolatile 
memory based on spintronics called MRAM (magnetic random-access memory) is expected to enter the market within 
a few years. Like hard drives, MRAM memory retains its data without power but uses no moving parts and will have 
speeds and rewritability comparable to conventional RAM. 

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MRAM stores information in ferromagnetic metallic alloys, which are suitable for data storage but not for the 
logical operations of a microprocessor. The holy grail of spintronics would be to achieve practical spintronics effects 
in a semiconductor, which would enable us to use the technology both for memory and for logic. Today's chip 
manufacturing is based on silicon, which does not have the requisite magnetic properties. In March 2004 an 
international group of scientists reported that by doping a blend of silicon and iron with cobalt, the new material was 
able to display the magnetic properties needed for spintronics while still maintaining the crystalline structure silicon 
requires as a serniconductor.
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An important role for spintronics in the future of computer memory is clear, and it is likely to contribute to logic 
systems as well. The spin of an electron is a quantum property (subject to the laws of quantum mechanics), so perhaps 
the most important application of spintronics will be in quantum computing systems, using the spin of quantum-
entangled electrons to represent qubits, which I discuss below. 
Spin has also been used to store information in the nucleus of atoms, using the complex interaction of their 
protons' magnetic moments. Scientists at the University of Oklahoma also demonstrated a "molecular photography" 
technique for storing 1,024 bits of information in a single liquid-crystal molecule comprising nineteen hydrogen 
atoms.
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