def single_displacement_matrix(r, phi, cutoff, dtype=def_type.as_numpy_dtype):
"""creates a single mode displacement matrix"""
r = r.numpy()
phi = phi.numpy()
gate = displacement_tw(r, phi, cutoff, dtype)
# NOTE: tested when testing the gate and its gradients; also tested independently in thewalrus
def grad(dy): # pragma: no cover
Dr, Dphi = grad_displacement_tw(gate, r, phi)
grad_r = tf.math.real(tf.reduce_sum(dy * tf.math.conj(Dr)))
grad_phi = tf.math.real(tf.reduce_sum(dy * tf.math.conj(Dphi)))
return grad_r, grad_phi, None
return gate, grad
def displacement(r, phi, trunc):
r"""The displacement operator :math:`D(\alpha)`.
Uses the `displacement operation from The Walrus`_ to calculate the displacement.
.. _`displacement operation from The Walrus`: https://the-walrus.readthedocs.io/en/latest/code/api/thewalrus.fock_gradients.displacement.html
Args:
r (float): the displacement amplitude
phi (float): the displacement angle
trunc (int): the Fock cutoff
"""
ret = displacement_tw(r, phi, cutoff=trunc)
return ret