Question: 1 0 points ) ( Can a function be evaluated at two places with a single quantumquery? ) Here we consider the problem where we
pointsCan a function be evaluated at two places with a single quantumquery?Here we consider the problem where we have a query oracle for a function f : and the goal is to obtain information about both f and f with a single query.We assume that the query oracle is in the usual form of a unitary operator Uf that, forall a b maps a b to a b f a For simplicity, we consider methods thatemploy only two qubits in all and are expressible by a circuit of the form V Uf W where V and W are twoqubit unitaries and the gates labelled are measurements in thestandard basis. Therefore, it can be assumed that the input state to the query ie rightafter V is applied is a twoqubit state of the form where We will talk about what normal matrix means later in the course, but you dont need to worry aboutits definition now. The matrices in parts a and b are normal.For each of the four functions of the form f : give thequantum state right after the query has been performed ie right before W isappliedb points If there is a measurement procedure that perfectly distinguishes betweenthe four states in part a then they must be mutually orthogonal. Show that, fora measurement to be able to perfectly determine the value of f it must be thecase that Hint: think of the orthogonality relationships that need tohold.c points Show that, if the states are such that f can be determined perfectlyfrom them, then f cannot be determined with probability better than whichis no better than random guessingHint: You may use the result in part b forthis.d points Optional for bonus credit for all students: The above analysis isrestricted to methods that use two qubits. Show that, for all m any strategythat uses m qubits V and W are mqubit unitaries and the query gate Uf actson the last two qubits and determines f perfectly cannot determine f withprobability better than
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