def u2_ex_gate(phi, wires=None):
r"""Implements the two-qubit exchange gate :math:`U_{2,\mathrm{ex}}` proposed in
`arXiv:1805.04340 <https://arxiv.org/abs/1805.04340>`_ to build particle-conserving VQE ansatze
for Quantum Chemistry simulations.
The unitary matrix :math:`U_{2, \mathrm{ex}}` acts on the Hilbert space of two qubits
.. math::
U_{2, \mathrm{ex}}(\phi) = \left(\begin{array}{cccc}
1 & 0 & 0 & 0 \\
0 & \mathrm{cos}(\phi) & -i\;\mathrm{sin}(\phi) & 0 \\
0 & -i\;\mathrm{sin}(\phi) & \mathrm{cos}(\phi) & 0 \\
0 & 0 & 0 & 1 \\
\end{array}\right).
Args:
phi (float): angle entering the controlled-RX operator :math:`CRX(2\phi)`
wires (list[Wires]): the two wires ``n`` and ``m`` the circuit acts on
"""
CNOT(wires=wires)
CRX(2 * phi, wires=wires[::-1])
CNOT(wires=wires)
def KwargTemplateDouble(par, wires, a=True):
if a:
T(wires=wires[0])
CRX(par, wires=wires)
def ParametrizedTemplateDouble(par1, par2, wires):
CRX(par1, wires=wires)
RY(par2, wires=wires[0])