def beamsplitter(theta, phi, trunc):
r"""The beamsplitter :math:`B(\theta, \phi)`.
Uses the `beamsplitter operation from The Walrus`_ to calculate the beamsplitter.
.. _`beamsplitter operation from The Walrus`: https://the-walrus.readthedocs.io/en/latest/code/api/thewalrus.fock_gradients.beamsplitter.html
"""
BS_tw = beamsplitter_tw(theta, phi, cutoff=trunc)
# Transpose needed because of different conventions in SF and The Walrus.
return BS_tw.transpose((0, 2, 1, 3))
def single_beamsplitter_matrix(theta, phi, cutoff, dtype=def_type.as_numpy_dtype):
"""creates a single mode beamsplitter matrix"""
theta = theta.numpy()
phi = phi.numpy()
gate = beamsplitter_tw(theta, phi, cutoff, dtype)
gate = np.transpose(gate, [0, 2, 1, 3])
def grad(dy):
Dtheta, Dphi = grad_beamsplitter_tw(np.transpose(gate, [0, 2, 1, 3]), theta, phi)
Dtheta = np.transpose(Dtheta, [0, 2, 1, 3])
Dphi = np.transpose(Dphi, [0, 2, 1, 3])
grad_theta = tf.math.real(tf.reduce_sum(dy * tf.math.conj(Dtheta)))
grad_phi = tf.math.real(tf.reduce_sum(dy * tf.math.conj(Dphi)))
return grad_theta, grad_phi, None
return gate, grad