skill-033

QuTiP: Quantum Toolbox in Python

Overview

QuTiP provides comprehensive tools for simulating and analyzing quantum mechanical systems. It handles both closed (unitary) and open (dissipative) quantum systems with multiple solvers optimized for different scenarios.

Installation

uv pip install qutip

Optional packages for additional functionality:

# Quantum information processing (circuits, gates)
uv pip install qutip-qip

# Quantum trajectory viewer
uv pip install qutip-qtrl

Quick Start

from qutip import *
import numpy as np
import matplotlib.pyplot as plt

# Create quantum state
psi = basis(2, 0)  # |0⟩ state

# Create operator
H = sigmaz()  # Hamiltonian

# Time evolution
tlist = np.linspace(0, 10, 100)
result = sesolve(H, psi, tlist, e_ops=[sigmaz()])

# Plot results
plt.plot(tlist, result.expect[0])
plt.xlabel('Time')
plt.ylabel('⟨σz⟩')
plt.show()

Core Capabilities

1. Quantum Objects and States

Create and manipulate quantum states and operators:

# States
psi = basis(N, n)  # Fock state |n⟩
psi = coherent(N, alpha)  # Coherent state |α⟩
rho = thermal_dm(N, n_avg)  # Thermal density matrix

# Operators
a = destroy(N)  # Annihilation operator
H = num(N)  # Number operator
sx, sy, sz = sigmax(), sigmay(), sigmaz()  # Pauli matrices

# Composite systems
psi_AB = tensor(psi_A, psi_B)  # Tensor product

See references/core_concepts.md for comprehensive coverage of quantum objects, states, operators, and tensor products.

2. Time Evolution and Dynamics

Multiple solvers for different scenarios:

# Closed systems (unitary evolution)
result = sesolve(H, psi0, tlist, e_ops=[num(N)])

# Open systems (dissipation)
c_ops = [np.sqrt(0.1) * destroy(N)]  # Collapse operators
result = mesolve(H, psi0, tlist, c_ops, e_ops=[num(N)])

# Quantum trajectories (Monte Carlo)
result = mcsolve(H, psi0, tlist, c_ops, ntraj=500, e_ops=[num(N)])

Solver selection guide:

• sesolve: Pure states, unitary evolution
• mesolve: Mixed states, dissipation, general open systems
• mcsolve: Quantum jumps, photon counting, individual trajectories
• brmesolve: Weak system-bath coupling
• fmmesolve: Time-periodic Hamiltonians (Floquet)