  The fast Fourier transform (FFT) is one of the most successful numerical
algorithms of the 20th century and has found numerous applications in many
branches of computational science and engineering. The FFT algorithm can be
derived from a particular matrix decomposition of the discrete Fourier
transform (DFT) matrix. In this paper, we show that the quantum Fourier
transform (QFT) can be derived by further decomposing the diagonal factors of
the FFT matrix decomposition into products of matrices with Kronecker product
structure. We analyze the implication of this Kronecker product structure on
the discrete Fourier transform of rank-1 tensors on a classical computer. We
also explain why such a structure can take advantage of an important quantum
computer feature that enables the QFT algorithm to attain an exponential
speedup on a quantum computer over the FFT algorithm on a classical computer.
Further, the connection between the matrix decomposition of the DFT matrix and
a quantum circuit is made. We also discuss a natural extension of a radix-2 QFT
decomposition to a radix-d QFT decomposition. No prior knowledge of quantum
computing is required to understand what is presented in this paper. Yet, we
believe this paper may help readers to gain some rudimentary understanding of
the nature of quantum computing from a matrix computation point of view.
