%pylab inline

from qutip import *

def visualize(result):
    fig, ax = subplots(figsize=(12,6))
    for idx, e in enumerate(result.expect):
        ax.plot(result.times, e, label="%d" % idx)
    ax.legend()

H0 = -2*pi*(tensor(sigmaz(), identity(2)) + tensor(identity(2), sigmaz()))
Hint = 2*pi*0.1 * tensor(sigmax(), sigmax())

H = H0 + Hint

H

energy_level_diagram([H], figsize=(6,6), show_ylabels=True);

psi_gg = tensor(basis(2, 0), basis(2, 0))
psi_eg = tensor(basis(2, 1), basis(2, 0))
psi_ge = tensor(basis(2, 0), basis(2, 1))
psi_ee = tensor(basis(2, 1), basis(2, 1))

c_op1 = tensor(destroy(2), identity(2))
c_op2 = tensor(identity(2), destroy(2))

psi0 = psi_eg

tlist = linspace(0, 15, 100)
result = mesolve(H, psi0, tlist,
                 [sqrt(0.1) * c_op1, sqrt(0.25) * c_op2],
                 [ket2dm(psi_gg), ket2dm(psi_ge), ket2dm(psi_eg), ket2dm(psi_ee)])

visualize(result)

# We are only interested in these states
keep_states = [0, 1, 2]

# or equivalently, not interested in these states
remove_states = [3]

H_sub = H.eliminate_states(remove_states)

H_sub

H_sub = H.extract_states(keep_states)

H_sub

energy_level_diagram([H_sub], figsize=(6,6), show_ylabels=True);

psi0_sub = psi0.extract_states(keep_states, normalize=True)

psi0_sub

c_op1_sub = c_op1.extract_states(keep_states)
c_op2_sub = c_op2.extract_states(keep_states)

psi_gg_sub = psi_gg.extract_states(keep_states)
psi_eg_sub = psi_eg.extract_states(keep_states)
psi_ge_sub = psi_ge.extract_states(keep_states)

tlist = linspace(0, 15, 100)
result = mesolve(H_sub, psi0_sub, tlist,
                 [sqrt(0.1) * c_op1_sub, sqrt(0.25) * c_op2_sub],
                 [ket2dm(psi_gg_sub), ket2dm(psi_ge_sub), ket2dm(psi_eg_sub)])

visualize(result)

from qutip.ipynbtools import version_table
version_table()