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fix p_z probability for thermal_relaxation_error

This commit is contained in:
cjwood 2018-12-14 12:03:39 -05:00
parent 4b0cddda0b
commit 748a9d2cf8
1 changed files with 14 additions and 12 deletions
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26
qiskit_aer/noise/errors/standard_errors.py
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@ -328,26 +328,28 @@ def thermal_relaxation_error(t1, t2, time, excited_state_population=0):
# T1 relaxation rate
if t1 == np.inf:
rate1 = 0
p_reset = 0
else:
rate1 = 1 / t1
p_reset = 1 - np.exp(-time * rate1)
# T2 dephasing rate
if t2 == np.inf:
rate2 = - rate1
rate2 = 0
exp_t2 = 1
else:
rate2 = 2 / t2 - rate1
# Relaxation probabilities
pr = 1 - np.exp(-rate1 * time)
rate2 = 1 / t2
exp_t2 = np.exp(-time * rate2)
# Qubit state equilibrium probabilities
p0 = 1 - excited_state_population
p1 = excited_state_population
if t2 > t1:
# If T_2 > T_1 we must express this as a Kraus channel
# We start with the Choi-matrix representation:
p2 = np.exp(-0.5 * (rate1 + rate2) * time)
choi = np.array([[1 - p1 * pr, 0, 0, p2],
[0, p1 * pr, 0, 0],
[0, 0, p0 * pr, 0],
[p2, 0, 0, 1 - p0 * pr]])
choi = np.array([[1 - p1 * p_reset, 0, 0, exp_t2],
[0, p1 * p_reset, 0, 0],
[0, 0, p0 * p_reset, 0],
[exp_t2, 0, 0, 1 - p0 * p_reset]])
# Find canonical Kraus operators by eigendecomposition of Choi-matrix
kraus = choi2kraus(choi)
return QuantumError(kraus)
@ -360,9 +362,9 @@ def thermal_relaxation_error(t1, t2, time, excited_state_population=0):
[{'name': 'reset', 'qubits': [0]}],
[{'name': 'reset', 'qubits': [0]}, {'name': 'x', 'qubits': [0]}]]
# Probability
p_reset0 = pr * p0
p_reset1 = pr * p1
p_z = 0.5 * (1 - pr) * (1 - np.exp(-0.5 * (rate2 - rate1) * time))
p_reset0 = p_reset * p0
p_reset1 = p_reset * p1
p_z = (1 - p_reset) * (1 - np.exp(-time * (rate2 - rate1))) / 2
p_identity = 1 - p_z - p_reset0 - p_reset1
probabilities = [p_identity, p_z, p_reset0, p_reset1]
return QuantumError(zip(circuits, probabilities))