Merge pull request #172 from johnny-sa/master

Implementation of Black-body radiation shift to atomic state

arc/alkali_atom_functions.py

@@ -1609,6 +1609,111 @@ def updateDipoleMatrixElementsFile(self):
  )
  print(e)
 
+ def getFarleyWing(self, n1, l1, j1, n2, l2, j2, temperature=0.0):
+ """
+ Calculates the Farley Wing function in the context of a BBR shift, uses a closed
+ form for the integral (which has a singularity, need Cauchy principal value)
+
+ References:
+ (Farley, John W., and William H. Wing. Physical Review A 23.5 (1981): 2397
+ doi = {10.1103/PhysRevA.23.2397}
+
+ (A.A. Kamenski et al 2019 Quantum Electron. 49 464, DOI:10.1070/QEL17000 )
+
+ """
+ if temperature == 0:
+ temperature = 1e-10 ###avoid zero error 
+
+ transition_frequency = self.getTransitionFrequency(n1, l1, j1, n2, l2, j2)
+ y = scipy.constants.h * transition_frequency / (scipy.constants.Boltzmann * temperature)
+
+
+ z = 1j * y
+ a = 0.5 * (np.log(z / (2 * np.pi)) - np.pi / z - mpmath.digamma(z / (2 * np.pi)))
+ return float(-(np.pi**2) * y / 3 - 2 * y**3 * mpmath.re(a))
+
+ def getBBRshift(self, n, l, j, includeLevelsUpTo=0, temperature=0.0, s=0.5):
+ """
+ Frequency shift of an atomic state induced by black-body radiation
+ using the Farley-Wing function. 
+ Uses getFarleyWing as part of the calculation.
+
+ n, l, j (int,int,float): specifies state whose shift we are
+ calculating
+ temperature : optional. Temperature at which the atom
+ environment is, measured in K. If this parameter
+ is non-zero, user has to specify transitions up to
+ which state (due to black-body decay) should be included
+ in calculation.
+ includeLevelsUpTo (int): optional and not needed for atom
+ lifetimes calculated at zero temperature. At non zero
+ temperatures, this specify maximum principal quantum number
+ of the state to which black-body induced transitions will
+ be included. Minimal value of the parameter in that case is
+ :math:`n+1`
+
+ Returns:
+ float:
+ Energy shift in units of frequency (Hz)
+
+ See also:
+ :obj:`getFarleyWing` which is used in calculation.
+
+ References:
+ (Farley, John W., and William H. Wing. Physical Review A 23.5 (1981): 2397
+ doi = {10.1103/PhysRevA.23.2397}
+)
+
+ """
+
+ n = int(n)
+ l = int(l)
+
+ DeltaE = 0
+
+ factor = (-(physical_constants["Bohr radius"][0] * scipy.constants.e) ** 2 /
+ (6 * scipy.constants.epsilon_0 * np.pi ** 2 * scipy.constants.c ** 3) *
+ (scipy.constants.Boltzmann * temperature / scipy.constants.hbar) ** 3 /
+ scipy.constants.h)
+
+ # Precompute commonly used values
+ max_ground_state_n = max(self.groundStateN, l)
+
+ def compute_deltaE(n, l, j, nto, lto, jto):
+ prefactor = (2*jto + 1)*Wigner6j(l,j,s,jto,lto,1)**2
+ radial_matrix_element = self.getRadialMatrixElement(n, l, j, nto, lto, jto)
+ farley_wing = self.getFarleyWing(n, l, j, nto, lto, jto, temperature)
+ max_l = max(l, lto)
+ return prefactor*(max_l) * (radial_matrix_element ** 2) * farley_wing
+
+ # Sum over all l-1
+ if l > 0:
+ lto = l - 1
+ for nto in range(max_ground_state_n, includeLevelsUpTo + 1):
+ if lto > j - s - 0.1:
+ jto = j
+ DeltaE += compute_deltaE(n, l, j, nto, lto, jto)
+ jto = j - 1.0
+ if jto > 0:
+ DeltaE += compute_deltaE(n, l, j, nto, lto, jto)
+
+ # Sum over all l+1
+ lto = l + 1
+ for nto in range(max(self.groundStateN, l + 2), includeLevelsUpTo + 1):
+ if lto - s - 0.1 < j:
+ jto = j
+ DeltaE += compute_deltaE(n, l, j, nto, lto, jto)
+ jto = j + 1
+
+ DeltaE += compute_deltaE(n, l, j, nto, lto, jto)
+
+ # Sum over additional states
+ for state in self.extraLevels:
+ if (abs(j - state[2]) < 1.1 and abs(state[1] - l) < 1.1 and abs(state[1] - l) > 0.9):
+ DeltaE += compute_deltaE(n, l, j, state[0], state[1], state[2])
+
+ return factor * DeltaE
+
  def getTransitionRate(self, n1, l1, j1, n2, l2, j2, temperature=0.0, s=0.5):
  """
  Transition rate due to coupling to vacuum modes