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/* qft.c: Quantum Fourier Transform
Copyright 2003 Bjoern Butscher, Hendrik Weimer
This file is part of libquantum
libquantum is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published
by the Free Software Foundation; either version 3 of the License,
or (at your option) any later version.
libquantum is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with libquantum; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA
*/
#include "gates.h"
#include "qureg.h"
/* Perform a QFT on a quantum register. This is done by application of
conditional phase shifts and hadamard gates. At the end, the
position of the bits is reversed. */
void quantum_qft(int width, quantum_reg *reg)
{
int i, j;
for(i=width-1; i>=0; i--)
{
for(j=width-1; j>i; j--)
quantum_cond_phase(j, i, reg);
quantum_hadamard(i, reg);
}
}
void quantum_qft_inv(int width, quantum_reg *reg)
{
int i, j;
for(i=0; i<width; i++)
{
quantum_hadamard(i, reg);
for(j=i+1; j<width; j++)
quantum_cond_phase_inv(j, i, reg);
}
}
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