Round 12: Tossup 5

For a controlled operation, the value of this quantity applied to the second input is “kicked back” to the first input. Order-finding in Shor’s algorithm involves a subproblem in which this quantity of an eigenvalue is estimated to solve the task of finding an eigenvalue from the eigenstate of a unitary operator. The azimuthal angle on a Bloch sphere represents this quantity, which is shifted by rotations around its z-axis. The relative value of this quantity of a qubit is physically relevant unlike its global value, since the latter only contributes a factor of “the exponential of i theta” to the wave function that does not affect probability. If this quantity is the same for two waves, they are coherent and constructively interfere. (10[1])For 10 points, name this quantity representing the angular shift at which a wave begins. ■END■

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