Tanay Roy - Bloch Sphere Animation using QuTiP

Bloch Sphere Animation using QuTiP

The following python 3.7 code allows to create animation files (as gif files) on a Bloch sphere using QuTip which is an open-source software based on Python for simulating the dynamics of open quantum systems.

import matplotlib as mpl

from pylab import *

from qutip import *

from matplotlib import cm

import imageio

def animate_bloch(states, duration=0.1, save_all=False):

    b = Bloch()

    b.vector_color = ['r']

    b.view = [-40,30]

    images=[]

    try:

        length = len(states)

    except:

        length = 1

        states = [states]

    ## normalize colors to the length of data ##

    nrm = mpl.colors.Normalize(0,length)

    colors = cm.cool(nrm(range(length))) # options: cool, summer, winter, autumn etc.

    ## customize sphere properties ##

    b.point_color = list(colors) # options: 'r', 'g', 'b' etc.

    b.point_marker = ['o']

    b.point_size = [30]

    for i in range(length):

        b.clear()

        b.add_states(states[i])

        b.add_states(states[:(i+1)],'point')

        if save_all:

            b.save(dirc='tmp') #saving images to tmp directory

            filename="tmp/bloch_%01d.png" % i

        else:

            filename='temp_file.png'

            b.save(filename)

        images.append(imageio.imread(filename))

    imageio.mimsave('bloch_anim.gif', images, duration=duration)

Useful features

The frame rate can be changed by using the "duration" argument. Default is 0.1 seconds.
The "save_all" option can be used to save all intermediate frames as png files.
The code can handle both state vectors or density matrices.
The code can be used to plot a single point as well.

Example 1

Create an animated file using state vectors

states = []

thetas = linspace(0,pi,21)

for theta in thetas:

    states.append((cos(theta/2)*basis(2,0) + sin(theta/2)*basis(2,1)).unit())

animate_bloch(states, duration=0.1, save_all=False)

Below is the output file "bloch_anim.gif".

Example 2

Plotting a single point using density matrix

states = ket2dm((basis(2,0) + 1j*basis(2,1)).unit())

animate_bloch(states, duration=0.1, save_all=False)

Below is the output png or gif file.

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