def test_ghz_4_7(self):
r"""
The following generates the following GHZ state in `(C^4)^{\otimes 7}`.
`1/sqrt(30) * (|0000000> + 2|1111111> + 3|2222222> + 4|3333333>)`.
"""
e0_4 = np.array([[1], [0], [0], [0]])
e1_4 = np.array([[0], [1], [0], [0]])
e2_4 = np.array([[0], [0], [1], [0]])
e3_4 = np.array([[0], [0], [0], [1]])
expected_res = (
1
/ np.sqrt(30)
* (
tensor(e0_4, e0_4, e0_4, e0_4, e0_4, e0_4, e0_4)
+ 2 * tensor(e1_4, e1_4, e1_4, e1_4, e1_4, e1_4, e1_4)
+ 3 * tensor(e2_4, e2_4, e2_4, e2_4, e2_4, e2_4, e2_4)
+ 4 * tensor(e3_4, e3_4, e3_4, e3_4, e3_4, e3_4, e3_4)
)
)
res = ghz(4, 7, np.array([1, 2, 3, 4]) / np.sqrt(30)).toarray()
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_ghz_2_3(self):
"""Produces the 3-qubit GHZ state: `1/sqrt(2) * (|000> + |111>)`."""
e_0, e_1 = ket(2, 0), ket(2, 1)
expected_res = 1 / np.sqrt(2) * (tensor(e_0, e_0, e_0) + tensor(e_1, e_1, e_1))
res = ghz(2, 3).toarray()
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_w_state_3(self):
"""The 3-qubit W-state."""
e_0, e_1 = ket(2, 0), ket(2, 1)
expected_res = (
1
/ np.sqrt(3)
* (tensor(e_1, e_0, e_0) + tensor(e_0, e_1, e_0) + tensor(e_0, e_0, e_1))
)
res = w_state(3)
bool_mat = np.isclose(res, expected_res, atol=0.2)
self.assertEqual(np.all(bool_mat), True)
def test_counterfeit_attack_wiesner_money(self):
"""Probability of counterfeit attack on Wiesner's quantum money."""
e_0, e_1 = ket(2, 0), ket(2, 1)
e_p = (e_0 + e_1) / np.sqrt(2)
e_m = (e_0 - e_1) / np.sqrt(2)
e_000 = tensor(e_0, e_0, e_0)
e_111 = tensor(e_1, e_1, e_1)
e_ppp = tensor(e_p, e_p, e_p)
e_mmm = tensor(e_m, e_m, e_m)
q_a = (1 / 4 * (e_000 * e_000.conj().T + e_111 * e_111.conj().T +
e_ppp * e_ppp.conj().T + e_mmm * e_mmm.conj().T))
res = counterfeit_attack(q_a)
self.assertEqual(np.isclose(res, 3 / 4), True)
def test_tensor_n_0(self):
"""Test tensor n=0 times."""
e_0 = ket(2, 0)
expected_res = None
res = tensor(e_0, 0)
self.assertEqual(res, expected_res)
def test_tensor_n_3(self):
"""Test tensor n=3 times."""
e_0 = ket(2, 0)
expected_res = np.kron(np.kron(e_0, e_0), e_0)
res = tensor(e_0, 3)
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_tensor_n_1(self):
"""Test tensor n=1 times."""
e_0 = ket(2, 0)
expected_res = e_0
res = tensor(e_0, 1)
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_tensor_list_3(self):
"""Test tensor list with three items."""
e_0, e_1 = ket(2, 0), ket(2, 1)
expected_res = np.kron(np.kron(e_0, e_1), e_0)
res = tensor([e_0, e_1, e_0])
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_tensor_list_1(self):
"""Test tensor list with one item."""
e_0 = ket(2, 0)
expected_res = e_0
res = tensor([e_0])
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_tensor(self):
"""Test standard tensor on vectors."""
e_0 = ket(2, 0)
expected_res = np.kron(e_0, e_0)
res = tensor(e_0, e_0)
bool_mat = np.isclose(res, expected_res)
self.assertEqual(np.all(bool_mat), True)
def test_generalized_w_state(self):
"""Generalized 4-qubit W-state."""
e_0, e_1 = ket(2, 0), ket(2, 1)
expected_res = (
1
/ np.sqrt(30)
* (
tensor(e_1, e_0, e_0, e_0)
+ 2 * tensor(e_0, e_1, e_0, e_0)
+ 3 * tensor(e_0, e_0, e_1, e_0)
+ 4 * tensor(e_0, e_0, e_0, e_1)
)
)
coeffs = np.array([1, 2, 3, 4]) / np.sqrt(30)
res = w_state(4, coeffs)
bool_mat = np.isclose(res, expected_res, atol=0.2)
self.assertEqual(np.all(bool_mat), True)
def counterfeit_attack(q_a: np.ndarray, num_reps: int = 1) -> float:
r"""
Compute probability of counterfeiting quantum money [MVW12]_.
The primal problem for the :math:`n`-fold parallel repetition is given as
follows:
.. math::
\begin{equation}
\begin{aligned}
\text{maximize:} \quad & \langle W_{\pi} \left(Q^{\otimes n}
\right) W_{\pi}^*, X \rangle \\
\text{subject to:} \quad & \text{Tr}_{\mathcal{Y}^{\otimes n}
\otimes \mathcal{Z}^{\otimes n}}(X)
= \mathbb{I}_{\mathcal{X}^{\otimes
n}},\\
& X \in \text{Pos}(
\mathcal{Y}^{\otimes n}
\otimes \mathcal{Z}^{\otimes n}
\otimes \mathcal{X}^{\otimes n})
\end{aligned}
\end{equation}
The dual problem for the :math:`n`-fold parallel repetition is given as
follows:
.. math::
\begin{equation}
\begin{aligned}
\text{minimize:} \quad & \text{Tr}(Y) \\
\text{subject to:} \quad & \mathbb{I}_{\mathcal{Y}^{\otimes n}
\otimes \mathcal{Z}^{\otimes n}} \otimes Y \geq W_{\pi}
\left( Q^{\otimes n} \right) W_{\pi}^*, \\
& Y \in \text{Herm} \left(\mathcal{X}^{\otimes n} \right)
\end{aligned}
\end{equation}
Examples
==========
Wiesner's original quantum money scheme [Wies83]_ was shown in [MVW12]_ to
have an optimal probability of 3/4 for succeeding a counterfeiting attack.
Specifically, in the single-qubit case, Wiesner's quantum money scheme
corresponds to the following ensemble:
.. math::
\left{
\left( \frac{1}{4}, |0\rangle \right),
\left( \frac{1}{4}, |1\rangle \right),
\left( \frac{1}{4}, |+\rangle \right),
\left( \frac{1}{4}, |-\rangle \right)
\right},
which yields the operator
.. math::
Q = \frac{1}{4} \left(
|000\rangle + \langle 000| + |111\rangle \langle 111| +
|+++\rangle + \langle +++| + |---\rangle \langle ---|
\right)
We can see that the optimal value we obtain in solving the SDP is 3/4.
>>> from toqito.states.operations.tensor import tensor
>>> from toqito.core.ket import ket
>>> import numpy as np
>>> e_0, e_1 = ket(2, 0), ket(2, 1)
>>> e_p = (e_0 + e_1) / np.sqrt(2)
>>> e_m = (e_0 - e_1) / np.sqrt(2)
>>>
>>> e_000 = tensor(e_0, e_0, e_0)
>>> e_111 = tensor(e_1, e_1, e_1)
>>> e_ppp = tensor(e_p, e_p, e_p)
>>> e_mmm = tensor(e_m, e_m, e_m)
>>>
>>> q_a = 1 / 4 * (e_000 * e_000.conj().T + e_111 * e_111.conj().T + \
>>> e_ppp * e_ppp.conj().T + e_mmm * e_mmm.conj().T)
>>> print(counterfeit_attack(q_a))
0.749999999967631
References
==========
.. [MVW12] Abel Molina, Thomas Vidick, and John Watrous.
"Optimal counterfeiting attacks and generalizations for Wiesner’s
quantum money."
Conference on Quantum Computation, Communication, and Cryptography.
Springer, Berlin, Heidelberg, 2012.
https://arxiv.org/abs/1202.4010
.. [Wies83] Stephen Wiesner
"Conjugate coding."
ACM Sigact News 15.1 (1983): 78-88.
https://dl.acm.org/doi/pdf/10.1145/1008908.1008920
:param q_a: The fixed SDP variable.
:param num_reps: The number of parallel repetitions.
:return: The optimal probability with of counterfeiting quantum money.
"""
# The system is over:
# Y_1 ⊗ Z_1 ⊗ X_1, ... , Y_n ⊗ Z_n ⊗ X_n.
num_spaces = 3
# In the event of more than a single repetition, one needs to apply a
# permutation operator to the variables in the SDP to properly align
# the spaces.
if num_reps == 1:
pperm = np.array([1])
else:
# The permutation vector `perm` contains elements of the
# sequence from: https://oeis.org/A023123
q_a = tensor(q_a, num_reps)
perm = []
for i in range(1, num_spaces + 1):
perm.append(i)
var = i
for j in range(1, num_reps):
perm.append(var + num_spaces * j)
pperm = permutation_operator(2, perm)
return dual_problem(q_a, pperm, num_reps)
def test_tensor_list_0(self):
"""Test tensor empty list."""
expected_res = None
res = tensor([])
self.assertEqual(res, expected_res)
def pauli(ind: Union[int, str, List[int], List[str]],
is_sparse: bool = False) -> Union[np.ndarray, sparse.csr_matrix]:
r"""
Produce a Pauli operator [WIKPAU]_.
Provides the 2-by-2 Pauli matrix indicated by the value of `ind`. The
variable `ind = 1` gives the Pauli-X operator, `ind = 2` gives the Pauli-Y
operator, `ind =3` gives the Pauli-Z operator, and `ind = 0`gives the
identity operator. Alternatively, `ind` can be set to "I", "X", "Y", or "Z"
(case insensitive) to indicate the Pauli identity, X, Y, or Z operator.
The 2-by-2 Pauli matrices are defined as the following matrices:
.. math::
\begin{equation}
\begin{aligned}
X = \begin{pmatrix}
0 & 1 \\
1 & 0
\end{pmatrix}, \quad
Y = \begin{pmatrix}
0 & -i \\
i & 0
\end{pmatrix}, \quad
Z = \begin{pmatrix}
1 & 0 \\
0 & -1
\end{pmatrix}, \quad
I = \begin{pmatrix}
1 & 0 \\
0 & 1
\end{pmatrix}.
\end{aligned}
\end{equation}
Examples
==========
Example for identity Pauli matrix.
>>> from toqito.linear_algebra.matrices.pauli import pauli
>>> pauli("I")
array([[1., 0.],
[0., 1.]])
Example for Pauli-X matrix.
>>> from toqito.linear_algebra.matrices.pauli import pauli
>>> pauli("X")
array([[0, 1],
[1, 0]])
Example for Pauli-Y matrix.
>>> from toqito.linear_algebra.matrices.pauli import pauli
>>> pauli("Y")
array([[ 0.+0.j, -0.-1.j],
[ 0.+1.j, 0.+0.j]])
Example for Pauli-Z matrix.
>>> from toqito.linear_algebra.matrices.pauli import pauli
>>> pauli("Z")
array([[ 1, 0],
[ 0, -1]])
References
==========
.. [WIKPAU] Wikipedia: Pauli matrices
https://en.wikipedia.org/wiki/Pauli_matrices
:param ind: The index to indicate which Pauli operator to generate.
:param is_sparse: Returns a sparse matrix if set to True and a non-sparse
matrix if set to False.
"""
if isinstance(ind, (int, str)):
if ind in ("x", "X", 1):
pauli_mat = np.array([[0, 1], [1, 0]])
elif ind in ("y", "Y", 2):
pauli_mat = np.array([[0, -1j], [1j, 0]])
elif ind in ("z", "Z", 3):
pauli_mat = np.array([[1, 0], [0, -1]])
else:
pauli_mat = np.identity(2)
if is_sparse:
pauli_mat = sparse.csr_matrix(pauli_mat)
return pauli_mat
num_qubits = len(ind)
pauli_mats = []
for i in range(num_qubits - 1, -1, -1):
pauli_mats.append(pauli(ind[i], is_sparse))
return tensor(pauli_mats)
