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qiskit.quantum_info.hellinger_fidelity

hellinger_fidelity(dist_p, dist_q)[source]

Computes the Hellinger fidelity between two counts distributions.

The fidelity is defined as \(\left(1-H^{2}\right)^{2}\) where H is the Hellinger distance. This value is bounded in the range [0, 1].

This is equivalent to the standard classical fidelity \(F(Q,P)=\left(\sum_{i}\sqrt{p_{i}q_{i}}\right)^{2}\) that in turn is equal to the quantum state fidelity for diagonal density matrices.

Parameters
  • dist_p (dict) – First dict of counts.

  • dist_q (dict) – Second dict of counts.

Returns

Fidelity

Return type

float

Example

from qiskit import QuantumCircuit, execute, BasicAer
from qiskit.quantum_info.analysis import hellinger_fidelity

qc = QuantumCircuit(5, 5)
qc.h(2)
qc.cx(2, 1)
qc.cx(2, 3)
qc.cx(3, 4)
qc.cx(1, 0)
qc.measure(range(5), range(5))

sim = BasicAer.get_backend('qasm_simulator')
res1 = execute(qc, sim).result()
res2 = execute(qc, sim).result()

hellinger_fidelity(res1.get_counts(), res2.get_counts())
0.9994506647234539

References

Quantum Fidelity @ wikipedia Hellinger Distance @ wikipedia