Visualizing Quantum Dynamics with Qutip

Mihirsinh Chauhan
3 min readSep 12, 2023


Welcome to Day 11 of our journey into the world of quantum computing and Qutip. Today, we’ll explore how to visualize the dynamics of quantum systems using Qutip. Visualization is a powerful tool for gaining insights into the behavior of quantum states as they evolve over time.

Visualizing Quantum Dynamics:

In quantum mechanics, the state of a quantum system is described by a complex vector called a ket (∣ψ⟩). As time progresses, the quantum state may evolve according to a Hamiltonian operator (H) or undergo measurements.

Qutip provides various visualization tools to help us understand these quantum dynamics. Let’s explore some of them:

Plotting Expectation Values:

We can calculate and plot the expectation values of operators over time to visualize how they evolve. For example, if we have a qubit in a superposition state, we can plot the expectation values of the Pauli operators (σx​, σy​, σz​) over time to see how they change.

import qutip as qt
import numpy as np
import matplotlib.pyplot as plt

# Define parameters
omega = 1.0 # Angular frequency

# Create the Hamiltonian for a qubit in a magnetic field along X-axis
H = 0.5 * omega * qt.sigmax()

# Initial state |0⟩
psi_0 = qt.basis(2, 0)

# Time points for simulation
times = np.linspace(0, 10, 100)

# Perform unitary evolution
result = qt.mesolve(H, psi_0, times, [], [])

# Calculate expectation values of Pauli operators
expect_x = qt.expect(qt.sigmax(), result.states)
expect_y = qt.expect(qt.sigmay(), result.states)
expect_z = qt.expect(qt.sigmaz(), result.states)

# Plot the results
plt.plot(times, expect_x, label='<σx>')
plt.plot(times, expect_y, label='<σy>')
plt.plot(times, expect_z, label='<σz>')
plt.ylabel('Expectation Value')
plt.title('Expectation Values of Pauli Operators')

This code calculates and plots the expectation values of the Pauli operators over time, providing insights into how the quantum state evolves.


Bloch Sphere Visualization:

The Bloch sphere is a 3D representation of the state of a qubit. We can use Qutip’s qt.Bloch() class to visualize the quantum state on the Bloch sphere.

b = qt.Bloch()

This code visualizes the final state of the qubit on the Bloch sphere, allowing us to see how it evolved geometrically.


Density Matrix Visualization:

For multi-qubit systems or mixed states, we can visualize the density matrix, which describes the state of the system. The qt.matrix_histogram() function helps us visualize the density matrix.

# Calculate the density matrix
density_matrix = qt.ket2dm(result.states[-1]) # Final state

# Visualize the density matrix

This code generates a histogram-like visualization of the density matrix, providing insights into the quantum state’s components.



In Day 11, we’ve explored various visualization techniques for understanding quantum dynamics using Qutip. We’ve visualized expectation values, used the Bloch sphere for qubit visualization, and visualized the density matrix. These tools are crucial for gaining insights into the behavior of quantum systems and are invaluable for quantum research and programming. As we move forward, we’ll continue to explore advanced topics in quantum computing and Qutip. Stay tuned for more quantum adventures!

#day11 for #Quantum30 day challenge



Mihirsinh Chauhan

《Quantum computing Enthusiast |Future Innovator》《Under grad at SVNIT | ML| Buisness Amateur》