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The Universality of the Quantum Fourier Transform in Forming the Basis of Quantum Computing Algorithms

Charles M. Bowden, Goong Chen, Zijian Diao, Andreas Klappenecker

quant-pharXiv:quant-ph/0007122

Abstract

The quantum Fourier transform (QFT) is a powerful tool in quantum computing. The main ingredients of QFT are formed by the Walsh-Hadamard transform H and phase shifts P(.), both of which are 2x2 unitary matrices as operators on the two-dimensional 1-qubit space. In this paper, we show that H and P(.) suffice to generate the unitary group U(2) and, consequently, through controlled-U operations and their concatenations, the entire unitary group U(2n) on n-qubits can be generated. Since any quantum computing algorithm in an n-qubit quantum computer is based on operations by matrices in U(2n), in this sense we have the universality of the QFT.

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