Fast quantum search algorithm and Bounds on it

Abstract

We recast Grover's generalised search algorithm in a geometric language even when the states are not approximately orthogonal. We provide a possible search algorithm based on an arbitrary unitary transformation which can speed up the steps still further. We discuss the lower and upper bounds on the transition matrix elements when the unitary operator changes with time, thereby implying that quantum search process can not be too fast or too slow. This is a remarkable feature of quantum computation unlike classical one. Quantum mechanical uncertainty relation puts bounds on search process. Also we mention the problems of perturbation and other issues in time-dependent search operation.