Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The quantum computer: computer of the future

  1. Oct 17, 2003 #1
    Has any one heard of RSA? Its the cipher used by the NSA, CIA and probably most other government agencies. Its a cipher that uses one way arithimetic(easy to do almost impossible to undo). Anyway a type of computer is being developed to crack this form cipher called the Quantum computer and I was interested if anyone had any idea how a quantum computer works and how for they are in developing them.
  2. jcsd
  3. Oct 17, 2003 #2


    User Avatar
    Science Advisor
    Gold Member

    Last I heard the largest quantum computer only had about 8-bits which means that it has less calculating power than your fingers. Yes I do have a rough idea of te theory that allows quantum computing to work and it's important to note that a quantum computer can only perform some operations, for example the factorisaton of a very large numebr into it's prime factors, in a shorter time than a normal computer.

    There are so many diffficulties associated with maintaining many particle entangled systems that it is not clear yet if quantum computing is practical.
  4. Oct 17, 2003 #3
    A Quantum computer works not on the same basics of a Turing machine, so even those 8 bits are faster than you think. Quantum computers work because they routinely calculate infinite possibilities to arrive at a solution. *That's* why it's so fast. The reason it can handle infinitely large amounts of numbers is because the photon that hits the atom, turning it so that it represents a 1 or 0 in a normal computer, bounces off with an infinite number of possible directions, meaning the atom has an infinite number of possible orienatations. The possible states of an array are about 2 followed by 1,000 zeroes, or larger than the number of atoms in the known universe.
  5. Oct 18, 2003 #4


    User Avatar
    Science Advisor
    Gold Member

    No, 8 qubits is still alsost completely worthless for pratical appliactions.

    Your wrong about how a quantum computer works, a qubit just like a normal bit in a classical computer can only have two states: 1 and 0, the difference is that it may be in a suppostion of the 1 and 0 states.

    An important the thing missed by most people about quantum computers is that due to the fact that you have to collapse the entangled state in order to take a measurement, they perform most operations at the same speed as a classical computer and it's only a few operations (like the factorisations of a large number into it's primes) that it can erform faster than a normal computer.
  6. Oct 18, 2003 #5
    Interestingly, (or not interestingly, depending on your point of view), it was quantum computers that led me here today. I was doing my physics homework and I remembered an article in The New Scientist that I read about quantum computers. So I decided to learn more about them, what I found was easy to understand but then all kinds of complications like decoherence and entanglement came in, so I thought I'd leave it alone and come back to it when I have a Masters.

    Anyway, these are the pages I had a look at, see if the're any good for what you want:

    http://www.cs.caltech.edu/~westside/quantum-intro.html [Broken]
    Last edited by a moderator: May 1, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook