Physicists are hotly pursuing the construction of quantum computers, which would harness the quirks of quantum mechanics to perform certain computations more efficiently than a conventional computer.
1 The fundamental feature of a quantum computer is that it uses qubits instead of bits. A qubit may be a particle such as an electron, with “spin up” (blue) representing 1, “spin down” (red) representing 0, and quantum states called super positions that involve spin up and spin down simultaneously (yellow).
2 A small number of particles in superposition states can carry an enormous amount of information: a mere 1,000 particles can be in a superposition that represents every number from 1 to 21,000 (about 10300), and a quantum computer would manipulate all those numbers in parallel, for instance, by hitting the particles with laser pulses.
3 when the particles’ states are measured at the end of the computation, however, all but one random version of the 10300 parallel states vanish. Clever manipulation of the particles could nonetheless solve certain problems very rapidly, such as factoring a large number.
“Quantum computing studies theoretical computation systems (quantum computers) that make direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data.”
From the Cambridge University Paper quantum computing discussed the theory in details, student and other physicist can check the computing in details:
A good quantum computer algorithm ensures that computational paths leading to a wrong answer cancel out and that paths leading to a correct answer reinforce.
The Good News
If a large, ideal quantum computer would face most of the same limitations as our present-day classical computers do, should the physicists working on the extraordinarily hard task of building even rudimentary quantum computers pack up and go home? I believe the answer is no, for four reasons.
■ If quantum computers ever become a reality, the “killer app” for them will most likely not be code breaking but rather something so obvious it is rarely even mentioned: simulating quantum physics. This is a fundamental problem for chemistry, nanotechnology and other fields, important enough that Nobel Prizes have been awarded even for partial progress.
■ As transistors in microchips approach the atomic scale, ideas from quantum computing are likely to become relevant for classical computing as well.
■ Quantum computing experiments focus attention directly on the most mystifying features of quantum mechanics—and I hope that the less we can sweep those puzzles under the rug, the more we will be forced to understand them.
■ Quantum computing can be seen as the most stringent test to which quantum mechanics itself has ever been subjected. In my opinion, the most exciting possible outcome of quantum computing research would be to discover a fundamental reason why quantum computers are not possible. Such a failure would overturn our current picture of the physical world, whereas success would merely confirm it.
Uber-Computers from Exotic Physics?
Although quantum computers seem unlikely to solve NP-complete problems quickly, certain other 
extraordinary, speculative physical processes would allow construction of computers with that ability and much more. Time travel, for instance, would make it possible to efficiently solve any PSPACE problem, including those harder than NP-complete ones—such as how to play the perfect game of chess on any size board, including those larger than the standard 8 X 8 version. Employing time travel to solve problems would not be as simple as having a computer finish a long computation in the far future and send the answer back to itself in the present, but that kind of loop in time would be exploited. Just one problem: the speculative processes defy the known laws of physics..
Why the Internet Hasn’t Helped the Economy: It’s Too Green a Technology
Although the creation of the Internet is thought to mark a new era in human history, its effect on society, especially in economic terms, has proven unremarkable. Known as Solow’s Paradox, after the Nobel Prize winning economist and MIT professor Robert Solow, data show that economic productivity has decreased since the creation of the Internet.
In fact, the more we invest in information technology as a nation, the less efficient our economy becomes. This is not a causal relationship, to be sure, but it’s troubling when we consider how past technological innovation has effected the nation.
The economic gains achieved by last century’s technology, from automobiles to indoor appliances, are enormous compared to those of our present digital age. From 1939 to 2000, economic productivity increased nearly three percent each year, but from its peak in 2009, productivity has declined. In other words, longer hours are needed to achieve the same economic output.
History also shows us it takes time for technology to find it’s right place in society. The technology that enabled the telephone, for example, was originally intended to let people listen to live opera from their homes. So what digital technology looks like later in the century is truly anybody’s guess.
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