QuTiP
QuTiP (Quantum Toolbox in Python) is an open-source Python library for simulating the dynamics of open quantum systems. Model decoherence, dissipation, and environmental effects via the master equation; evolve quantum states in time; compute entanglement and correlations. Used in cavity QED, superconducting qubits, trapped ions, and quantum optics.
A quantum object (Qobj) represents operators and states; the master equation describes how open systems evolve under dissipation. Use collapse operators (Lindblad operators) to model energy loss, dephasing, and spontaneous emission. Evolve systems forward in time, then measure expectation values of observables.
from qutip import * import numpy as np # Damped two-level system H = 2 * np.pi * 0.5 * sigmaz() gamma = 0.1 c_ops = [np.sqrt(gamma) * sigmam()] # Time evolution under master equation times = np.linspace(0, 10, 100) psi0 = basis(2, 0) result = mesolve(H, psi0, times, c_ops, [sigmaz()]) print(result.expect[0])
QuTiP doesn't execute quantum circuits—it solves differential equations. Useful for modeling hardware noise, designing robust pulses, and studying open system dynamics that quantum circuit simulators don't capture.