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What is a quantum computer?
Answered by HowStuffWorks
  • HowStuffWorks


  1. Before we try to describe quantum computing, let's first set the backdrop for why having one might not only be necessary but also a logical (pardon the computer pun) next step in computer evolution. For years now, the computing world has been operating pretty efficiently under the thumb of Moore's Law (named for Intel guru Gordon Moore), which, loosely speaking, says that computing power will double every two years, as transistors get smaller and smaller. But the trouble is, chips are starting to max out -- there is only so much smaller they can get. Even the coiner of Moore's Law himself thinks so [source: McMillan].

    Going forward, then, how else to keep getting small but to drill down to the atom? A classic computer reads binary code -- everything is broken down into a language of ones and zeros. The computer reads these ones and zeros as data and instructions. A quantum computer, however, computes on an atom and not silicone -- in theory, as we're still a long way from seeing an actual quantum computer. The idea is that a quantum computer creates a quantum state in which quantum bits, or qubits, can exist. A qubit is an odd concept -- unlike binary bits, qubits can be a one, a zero or both a one and a zero at the same time (the latter is a state called "superposition" in quantum theory). With enough qubits you could process a complicated problem in a fraction of the time it would take a classical computer to complete. The quantum computer could calculate all possible outcomes at once. The computer would rank results by percentage -- one might have a 95 percent chance of being right while all other results added together comprise the other 5 percent.

    So far, quantum computers have proven difficult to maintain in any practical sense. One problem stems from interference -- basically any vibrations that are strong enough to harm the spin of an electron being used in quantum computing.


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