##// END OF EJS Templates
upstream » ipython
RSS

Clone from https://github.com/ipython/ipython.git

Wrap os.path functions in method calls...
Wrap os.path functions in method calls Some functions from os.path are now references to C functions (e.g. isdir on Windows). This breaks the path module, because compiled functions do not get bound to an object instance. All os.path functions have been wrapped in method calls, out of general caution. Closes gh-737
Brian E. Granger - - Load All Authors

File last commit:

r4637:d919e2ec
r4833:fc05f375
Show More
qft.ipynb
163 lines | 35.6 KiB | text/plain | TextLexer
/ docs / examples / notebooks / qft.ipynb
History | Annotation | Raw |Copy content |Copy permalink

Quantum Fourier Transform

In [1]:
%load_ext sympyprinting
In [2]:
from sympy import sqrt, symbols, Rational
from sympy import expand, Eq, Symbol, simplify, exp, sin
from sympy.physics.quantum import *
from sympy.physics.quantum.qubit import *
from sympy.physics.quantum.gate import *
from sympy.physics.quantum.grover import *
from sympy.physics.quantum.qft import QFT, IQFT, Fourier
from sympy.physics.quantum.circuitplot import circuit_plot

QFT is useful for a quantum algorithm for factoring numbers which is exponentially faster than what is thought to be possible on a classical machine.
The transform does a DFT on the state of a quantum system
There is a simple decomposition of the QFT in terms of a few elementary gates.

QFT Gate and Circuit

Build a 3 qubit QFT and decompose it into primitive gates.

In [3]:
fourier = QFT(0,3).decompose(); fourier
Out[3]:
$$SWAP_{0,2} H_{0} C_{0}{\left(S_{1}\right)} H_{1} C_{0}{\left(T_{2}\right)} C_{1}{\left(S_{2}\right)} H_{2}$$
In [4]:
circuit_plot(fourier, nqubits=3)
Out[4]:
<sympy.physics.quantum.circuitplot.CircuitPlot object at 0x4992910>
No description has been provided for this image

The QFT circuit can be represented in various symbolic forms.

In [5]:
m = represent(fourier, nqubits=3)
In [6]:
m
Out[6]:
$$\left(\begin{smallmatrix}\frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2}\\\frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi}\\\frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath}\\\frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi}\\\frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2}\\\frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi}\\\frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath}\\\frac{1}{4} \sqrt{2} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} \mathbf{\imath} & - \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi} & - \frac{1}{4} \sqrt{2} & \frac{1}{4} \sqrt{2} \mathbf{\imath} e^{\frac{1}{4} \mathbf{\imath} \pi} & \frac{1}{4} \sqrt{2} \mathbf{\imath} & \frac{1}{4} \sqrt{2} e^{\frac{1}{4} \mathbf{\imath} \pi}\end{smallmatrix}\right)$$
In [7]:
represent(Fourier(0,3), nqubits=3)*4/sqrt(2)
Out[7]:
$$\left(\begin{smallmatrix}1 & 1 & 1 & 1 & 1 & 1 & 1 & 1\\1 & \omega & \omega^{2} & \omega^{3} & \omega^{4} & \omega^{5} & \omega^{6} & \omega^{7}\\1 & \omega^{2} & \omega^{4} & \omega^{6} & 1 & \omega^{2} & \omega^{4} & \omega^{6}\\1 & \omega^{3} & \omega^{6} & \omega & \omega^{4} & \omega^{7} & \omega^{2} & \omega^{5}\\1 & \omega^{4} & 1 & \omega^{4} & 1 & \omega^{4} & 1 & \omega^{4}\\1 & \omega^{5} & \omega^{2} & \omega^{7} & \omega^{4} & \omega & \omega^{6} & \omega^{3}\\1 & \omega^{6} & \omega^{4} & \omega^{2} & 1 & \omega^{6} & \omega^{4} & \omega^{2}\\1 & \omega^{7} & \omega^{6} & \omega^{5} & \omega^{4} & \omega^{3} & \omega^{2} & \omega\end{smallmatrix}\right)$$

QFT in Action

Build a 3 qubit state to take the QFT of.

In [8]:
state = (Qubit('000') + Qubit('010') + Qubit('100') + Qubit('110'))/sqrt(4); state
Out[8]:
$$\frac{1}{2} \left({\left|000\right\rangle } + {\left|010\right\rangle } + {\left|100\right\rangle } + {\left|110\right\rangle }\right)$$

Perform the QFT.

In [9]:
qapply(fourier*state)
Out[9]:
$$\frac{1}{2} \sqrt{2} {\left|000\right\rangle } + \frac{1}{2} \sqrt{2} {\left|100\right\rangle }$$