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BoxiLiBoxiLi
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improve the qubit_states function
Support a more general way of definition: - use a list or a string for zero/one/plus/minus state - use a list of integers for defining arbitrary disentangled quantum states (up to a global phase).
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+96
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‎src/qutip_qip/qubits.py‎

Lines changed: 74 additions & 18 deletions
Original file line numberDiff line numberDiff line change
@@ -35,37 +35,93 @@
3535
'qubit_states', 'truncate_to_qubit_state', 'expand_qubit_state']
3636

3737
import qutip
38-
from qutip import (tensor, basis)
3938
import numpy as np
4039
from numpy import sqrt
4140

4241

43-
def qubit_states(N=1, states=[0]):
42+
def qubit_states(states):
4443
"""
45-
Function to define initial state of the qubits.
44+
Shortcut to generate disentangled qubit states.
4645
4746
Parameters
4847
----------
49-
N : Integer
50-
Number of qubits in the register.
51-
states : List
52-
Initial state of each qubit.
48+
states : list or str
49+
- If a list consisting of ``0``, ``1``, ``"0"``, ``"1"``, ``"+"``
50+
and ``"-"``, return the corresponding zero/one/plus/minus state.
51+
- If a string consisting of ``0``, ``1``, ``+``, ``-``,
52+
same as above.
53+
- If a list of float or complex numbers,
54+
each number is mapped to a state of the form
55+
:math:`\\sqrt{1 - |a|^2} \\left|0\\right\\rangle + a |1\\rangle`,
56+
where :math:`a` is the given number.
5357
5458
Returns
55-
----------
56-
qstates : Qobj
57-
List of qubits.
59+
-------
60+
quantum_states : :obj:`qutip.Qobj`
61+
The generated qubit states.
5862
63+
Examples
64+
--------
65+
>>> from qutip_qip.qubits import qubit_states
66+
>>> qubit_states([0, 0]) # doctest: +NORMALIZE_WHITESPACE
67+
Quantum object: dims = [[2, 2], [1, 1]], shape = (4, 1), type = ket
68+
Qobj data =
69+
[[1.]
70+
[0.]
71+
[0.]
72+
[0.]]
73+
>>> qubit_states([1, "+"]) # doctest: +NORMALIZE_WHITESPACE
74+
Quantum object: dims = [[2, 2], [1, 1]], shape =
75+
(4, 1), type = ket
76+
Qobj data =
77+
[[0. ]
78+
[0. ]
79+
[0.70710678]
80+
[0.70710678]]
81+
>>> qubit_states("-") # doctest: +NORMALIZE_WHITESPACE
82+
Quantum object: dims = [[2], [1]], shape = (2, 1), type = ket
83+
Qobj data =
84+
[[ 0.70710678]
85+
[-0.70710678]]
86+
>>> qubit_states("1-") # doctest: +NORMALIZE_WHITESPACE
87+
Quantum object: dims = [[2, 2], [1, 1]], shape =
88+
(4, 1), type = ket
89+
Qobj data =
90+
[[ 0. ]
91+
[ 0. ]
92+
[ 0.70710678]
93+
[-0.70710678]]
94+
>>> import numpy as np
95+
>>> qubit_states([1.j/np.sqrt(2)]) # doctest: +NORMALIZE_WHITESPACE
96+
Quantum object: dims = [[2], [1]], shape = (2, 1), type = ket
97+
Qobj data =
98+
[[0.70710678+0.j ]
99+
[0. +0.70710678j]]
59100
"""
60-
state_list = []
61-
for i in range(N):
62-
if N > len(states) and i >= len(states):
63-
state_list.append(0)
64-
else:
65-
state_list.append(states[i])
101+
if all([np.issubdtype(type(s), np.integer) for s in states]):
102+
return qutip.basis([2] * len(states), states)
103+
104+
states_map = {
105+
0: qutip.basis(2, 0),
106+
1: qutip.basis(2, 1),
107+
"0": qutip.basis(2, 0),
108+
"1": qutip.basis(2, 1),
109+
"+": (qutip.basis(2, 0) + qutip.basis(2, 1)).unit(),
110+
"-": (qutip.basis(2, 0) - qutip.basis(2, 1)).unit(),
111+
}
66112

67-
return tensor([alpha * basis(2, 1) + sqrt(1 - alpha**2) * basis(2, 0)
68-
for alpha in state_list])
113+
states_list = []
114+
for s in states:
115+
if s in states_map:
116+
states_list.append(states_map[s])
117+
elif np.isscalar(s) and abs(s) <= 1:
118+
states_list.append(
119+
s * qutip.basis(2, 1) +
120+
np.sqrt(1 - abs(s)**2) * qutip.basis(2, 0)
121+
)
122+
else:
123+
raise TypeError(f"Invalid input {s}.")
124+
return qutip.tensor(states_list)
69125

70126

71127
def _find_reduced_indices(dims):

‎tests/test_optpulseprocessor.py‎

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -66,8 +66,8 @@ def test_simple_hadamard(self):
6666
qc, num_tslots=num_tslots, evo_time=evo_time, verbose=True)
6767

6868
# test run_state
69-
rho0 = qubit_states(1, [0])
70-
plus = (qubit_states(1, [0]) + qubit_states(1, [1])).unit()
69+
rho0 = qubit_states([0])
70+
plus = (qubit_states([0]) + qubit_states([1])).unit()
7171
result = test.run_state(rho0)
7272
assert_allclose(fidelity(result.states[-1], plus), 1, rtol=1.0e-6)
7373

@@ -112,8 +112,8 @@ def test_multi_qubits(self):
112112
qc = [tensor([identity(2), cnot()])]
113113
test.load_circuit(qc, num_tslots=num_tslots,
114114
evo_time=evo_time, min_fid_err=1.0e-6)
115-
rho0 = qubit_states(3, [1, 1, 1])
116-
rho1 = qubit_states(3, [1, 1, 0])
115+
rho0 = qubit_states([1, 1, 1])
116+
rho1 = qubit_states([1, 1, 0])
117117
result = test.run_state(
118118
rho0, options=Options(store_states=True))
119119
assert_(fidelity(result.states[-1], rho1) > 1-1.0e-6)

‎tests/test_processor.py‎

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -278,7 +278,7 @@ def testNoise(self):
278278
Test for Processor with noise
279279
"""
280280
# setup and fidelity without noise
281-
init_state = qubit_states(2, [0, 0, 0, 0])
281+
init_state = qubit_states([0, 0])
282282
tlist = np.array([0., np.pi/2.])
283283
a = destroy(2)
284284
proc = Processor(N=2)
@@ -287,15 +287,15 @@ def testNoise(self):
287287
proc.pulses[0].coeff = np.array([1])
288288
result = proc.run_state(init_state=init_state)
289289
assert_allclose(
290-
fidelity(result.states[-1], qubit_states(2, [0, 1, 0, 0])),
290+
fidelity(result.states[-1], qubit_states([0, 1])),
291291
1, rtol=1.e-7)
292292

293293
# decoherence noise
294294
dec_noise = DecoherenceNoise([0.25*a], targets=1)
295295
proc.add_noise(dec_noise)
296296
result = proc.run_state(init_state=init_state)
297297
assert_allclose(
298-
fidelity(result.states[-1], qubit_states(2, [0, 1, 0, 0])),
298+
fidelity(result.states[-1], qubit_states([0, 1])),
299299
0.981852, rtol=1.e-3)
300300

301301
# white random noise
@@ -336,7 +336,7 @@ def testDrift(self):
336336

337337
def testChooseSolver(self):
338338
# setup and fidelity without noise
339-
init_state = qubit_states(2, [0, 0, 0, 0])
339+
init_state = qubit_states([0, 0])
340340
tlist = np.array([0., np.pi/2.])
341341
a = destroy(2)
342342
proc = Processor(N=2)
@@ -345,7 +345,7 @@ def testChooseSolver(self):
345345
proc.pulses[0].coeff = np.array([1])
346346
result = proc.run_state(init_state=init_state, solver="mcsolve")
347347
assert_allclose(
348-
fidelity(result.states[-1], qubit_states(2, [0, 1, 0, 0])),
348+
fidelity(result.states[-1], qubit_states([0, 1])),
349349
1, rtol=1.e-7)
350350

351351
def test_no_saving_intermidiate_state(self):

‎tests/test_qubits.py‎

Lines changed: 13 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -30,11 +30,10 @@
3030
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
3131
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
3232
###############################################################################
33-
from numpy.testing import assert_, run_module_suite
3433
import numpy as np
3534
import pytest
3635
import qutip
37-
from qutip import (tensor, basis)
36+
from qutip import tensor, basis
3837
from qutip_qip.qubits import (
3938
qubit_states, truncate_to_qubit_state, expand_qubit_state)
4039

@@ -47,17 +46,18 @@ def testQubitStates(self):
4746
"""
4847
Tests the qubit_states function.
4948
"""
50-
psi0_a = basis(2, 0)
51-
psi0_b = qubit_states()
52-
assert_(psi0_a == psi0_b)
53-
54-
psi1_a = basis(2, 1)
55-
psi1_b = qubit_states(states=[1])
56-
assert_(psi1_a == psi1_b)
57-
58-
psi01_a = tensor(psi0_a, psi1_a)
59-
psi01_b = qubit_states(N=2, states=[0, 1])
60-
assert_(psi01_a == psi01_b)
49+
assert(qubit_states([0]) == basis(2, 0))
50+
assert(qubit_states([1]) == basis(2, 1))
51+
assert(qubit_states([0, 1]) == tensor(basis(2, 0), basis(2, 1)))
52+
plus = (basis(2, 0) + basis(2, 1)).unit()
53+
minus = (basis(2, 0) - basis(2, 1)).unit()
54+
assert(qubit_states("-+") == tensor(minus, plus))
55+
assert(qubit_states("0+") == tensor(basis(2, 0), plus))
56+
assert(qubit_states("+11") == tensor(plus, basis(2, 1), basis(2, 1)))
57+
assert(
58+
qubit_states([1.j/np.sqrt(2), 1.]) ==
59+
tensor(qutip.Qobj([[1/np.sqrt(2)], [1.j/np.sqrt(2)]]), basis(2, 1))
60+
)
6161

6262
@pytest.mark.parametrize(
6363
"state, full_dims",

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