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Measure in grover's alg and shift phase

  1. Apr 6, 2005 #1
    hi , i am new here so at first i want to say hello to all of You.
    as title says i have two questions about qrover's algorithm, first one is more general i guess:
    1. in the most of articles i have read about this algorithm the measure wasn't well explained,problem is that authors wrote "now we measure first n qubits"
    when we are using n+1 ( one is as control qubit in oracles transformation)
    my question is.. how we can measure only n qubits? what about that control qubit? i know it is not important one but i guess we cant just throw it out...
    2. i am not sure if i well understand the shift phase , i mean the step when our solution qubit |x> changes its state to -|x>
    is all about that in the oracle transformation? when we got gubit register |z> ( made from state |00..0> by H x H ... x H gates) and single qubit in state |1> and then we apply the H gate on it? and on that n+1 qubits we apply simple black box and in result : (-1)^f(z)|z>*[(|0>-|1>)/sqrt(2)] ( where f(x)=1 for solution and 0 for others)
    is is all about changing the phase on solution qubit?
    i hope my text is readable enough ; ) ( maybe little chaotic)
    looking forward for replays.
  2. jcsd
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