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I Quantum computers

  1. May 24, 2016 #1
    I was reading about quantum computers and the article was saying about how cold everything has to be for qubits to exist in a superposition state. Why do things like the double slit experiment with single photons work at room temperature? Because when you get the interference pattern with single photons, that's a superposition of states as well, isn't it? Or that's how it was explained to me.
  2. jcsd
  3. May 24, 2016 #2
    I think the key is that with a quantum computer, you "store" the superposition long enough to perform several quantum operations on it. While it is being stored, it needs to be isolated from anything that could measure of affect it.
    Also, in the interference experiment, you are only dealing with a single particle at a time. With a quantum processor, you are guiding the interaction of many qubits.

    There are a handful of quantum computer "gates". Perhaps someone with more knowledge about this than myself can explain why these "gates" cannot be applied dynamically to photons. I suspect the problem is that even though a photon can interact with superpositions of itself, it will not interact very well with other photons.
  4. May 24, 2016 #3


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    Photonic qubits are not sensitive to the temperature of the environment since they do not really interact with anything.
    Qubits made of matter: be it atom, ions or superconductors do need to be cooled to very low temperatures.
  5. May 24, 2016 #4


    Staff: Mentor

    Congratulations on a very intelligent question.

    In addition to what the others said, there is a huge difference in the perfection needed to succeed. A quantum bit can be disturbed by any interaction with the environment during a long period of time..

    The double slit experiment needs many photons or many electrons to form an interference pattern on the screen. If some of them get scattered before the slits, they don't get through the slits and thus aren't counted. Photons scattered after the slit and before the screen, as well as photons from the apparatus walls or elsewhere, prevent the pattern on the screen from being perfect. That's especially true where theory says that zero photons should hit that spot on the screen. Zero is very hard to achieve in real life. But even if the interference pattern is imperfect, the mere existence of any pattern at all makes the double slit experiment succeed.

    I remember when I first heard of the double slit experiment. The explanation started with only one slit being open and looking at the pattern on the screen. The fact that opening a second slit could cause fewer photons to hit any spot completely amazed me. That simple observation leads one to the inescapable conclusion that we must look beyond classical physics for an explanation. IMO, that is all that's needed to declare the double slit experiment successful.
  6. May 29, 2016 #5
    Thanks for the answers, it's very interesting topic!
  7. Jun 13, 2016 #6
    Here's a recent article you may be interested in:
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