title: Collapsing a perfect superposition to a chosen quantum state without measurement.
abstract: Given a perfect superposition of [Formula: see text] states on a quantum system of [Formula: see text] qubits. We propose a fast quantum algorithm for collapsing the perfect superposition to a chosen quantum state [Formula: see text] without applying any measurements. The basic idea is to use a phase destruction mechanism. Two operators are used, the first operator applies a phase shift and a temporary entanglement to mark [Formula: see text] in the superposition, and the second operator applies selective phase shifts on the states in the superposition according to their Hamming distance with [Formula: see text]. The generated state can be used as an excellent input state for testing quantum memories and linear optics quantum computers. We make no assumptions about the used operators and applied quantum gates, but our result implies that for this purpose the number of qubits in the quantum register offers no advantage, in principle, over the obvious measurement-based feedback protocol.
authors.affiliation: Department of Mathematics and Computer Science, Faculty of Science, Alexandria University, Alexandria, Egypt.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Younes
authors.affiliation: University of Science and Technology, Zewail City of Science and Technology, Cairo, Egypt; Department of Mathematics, Faculty of Science, Sohag University, Sohag, Egypt.
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Abdel-Aty
mesh_terms: D000465:Algorithms
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