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

Very basic question

  1. Nov 4, 2011 #1
    I'm reading about decoherence, and I've found I don't understand the most basic thing. Interference between terms in a superposition is only possible, I thought, if the two terms are not orthogonal. But then how can up and down spin states (with respect to some direction) interfere with one another?!

    thanks!
     
  2. jcsd
  3. Nov 4, 2011 #2

    Bill_K

    User Avatar
    Science Advisor

    It would help to hear more about the context, but I think you have to make a distinction between interference and coherence. If two states |ψ1> and |ψ2> are orthogonal they can't directly interfere with each other. Nevertheless they may be in a coherent superposition α|ψ1> + β|ψ2>, meaning there remains the possibility of interference between them following a transition to another state |φ>.
     
  4. Nov 4, 2011 #3
    Thank you... I am fundamentally confused! Could you maybe give an example of such a transition that could lead to inference between orthogonal states?
     
  5. Nov 4, 2011 #4

    Bill_K

    User Avatar
    Science Advisor

    What I'm suggesting is that when you ask for the transition probability to a state |φ>, if the phases of |ψ1> and |ψ2> have been randomized you'll just get two terms, αα*<φ|ψ1><ψ1|φ> + ββ*<φ|ψ2><ψ2|φ>. But if the states are coherent you'll get as well the cross terms αβ*<φ|ψ2><ψ1|φ> + α*β<φ|ψ1><ψ2|φ>. I may be off base, but I think this relates to what you're asking.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Very basic question
Loading...