def apply_dephasing(number_of_spins, alpha, B,fm_str = 'AFM',kT = 0.0):
'''
takes number of spins, alpha, and the magnetic field and returns the
hamiltonian along with its ground state and the dephased ground state
choose fm_str = 'FM' for ferromagnetic interaction, and 'AFM' for anti-ferromagnetic
'''
if fm_str == 'FM':
calc = ising_calculator_FM(number_of_spins, alpha, B)
elif fm_str == 'AFM':
calc = ising_calculator_AFM(number_of_spins, alpha, B)
H = calc.get_H()
if kT == 0.0:
energy,groundstate = H.groundstate()
dm_groundstate = ket2dm(groundstate)
else:
Hdata = H.data.todense()
arr_mp = mp.matrix(-Hdata /kT)
exp_mp = mp.expm(arr_mp)
trace = np.array(exp_mp.tolist()).trace()
normalized_mp = exp_mp / trace
normalized_np = np.array(normalized_mp.tolist(), dtype = np.complex)
dm_groundstate = Qobj(normalized_np, dims = 2 * [number_of_spins*[2]])
dephased = do_dephasing_dm(dm_groundstate, number_of_spins)
return H, dm_groundstate, dephased
def expM(Q):
"""Uses mpmath's exp computation
"""
return mp.expm(Q)
mpmath.mpf.shape = ()
mpmath.mpc.shape = ()
# Observe that our E7-definitions have 'numerically exact' structure constants.
#
# So, it actually makes sense to take these as defined, and lift them to mpmath.
#
# >>> set(e7.t_a_ij_kl.reshape(-1))
# >>> {(-2+0j), (-1+0j), -2j, -1j, 0j, 1j, 2j, (1+0j), (2+0j)}
# `mpmath` does not work with numpy.einsum(), so for that reason alone,
# we use opt_einsum's generic-no-backend alternative implementation.
mpmath_scalar_manifold_evaluator = scalar_sector.get_scalar_manifold_evaluator(
frac=lambda p, q: mpmath.mpf(p) / mpmath.mpf(q),
to_scaled_constant=(
lambda x, scale=1: numpy.array(
x, dtype=mpmath.ctx_mp_python.mpc) * scale),
# Wrapping up `expm` is somewhat tricky here, as it returns a mpmath
# matrix-type that numpy does not understand.
expm=lambda m: numpy.array(mpmath.expm(m).tolist()),
einsum=lambda spec, *arrs: opt_einsum.contract(spec, *arrs),
# trace can stay as-is.
eye=lambda n: numpy.eye(n) + mpmath.mpc(0),
complexify=lambda a: a + mpmath.mpc(0),
# re/im are again tricky, since numpy.array(dtype=object)
# does not forward .real / .imag to the contained objects.
re=lambda a: numpy.array([z.real for z in a.reshape(-1)]).reshape(a.shape),
im=lambda a: numpy.array([z.imag for z in a.reshape(-1)]).reshape(a.shape))
