estimate_dfe¶

forest.benchmarking.direct_fidelity_estimation.
estimate_dfe
(results: List[forest.benchmarking.observable_estimation.ExperimentResult], kind: str) → Tuple[float, float]¶ Analyse data from experiments to obtain a direct fidelity estimate (DFE).
State fidelity between the experimental state σ and the ideal (pure) state ρ (both states represented by density matrices) is defined as F(σ,ρ) = tr σ⋅ρ [Joz].
The direct fidelity estimate for a state is given by the average expected value of the Pauli operators in the stabilizer group of the ideal pure state (i.e., Eqn. 1 of [DFE1]).
The average gate fidelity between the experimental process ℰ and the ideal (unitary) process 𝒰 is defined as F(ℰ,𝒰) = (tr ℰ 𝒰⁺ + d)/(d^2+d) where the processes are represented by linear superoperators acting of vectorized density matrices, and d is the dimension of the Hilbert space ℰ and 𝒰 act on (and where ⁺ represents the Hermitian conjugate). See [Nie] for details.
The average gate fidelity can be rewritten a F(ℰ,𝒰)=(d^2 tr J(ℰ)⋅J(𝒰) + d)/(d^2+d) where J() is the ChoiJamiolkoski representation of the superoperator in the argument. Since the ChoiJamiolkowski representation is given by a density operator, the connection to the calculation of state fidelity becomes apparent: F(J(ℰ),J(𝒰)) = tr J(ℰ)⋅J(𝒰) is the state fidelity between ChoiJamiolkoski states.
Noting that the ChoiJamiolkoski state is prepared by acting on half of a maximally entangled state with the process in question, the direct fidelity estimate of the ChoiJamiolkoski state is given by the average expected value of a Pauli operator resulting from applying the ideal unitary 𝒰 to a Pauli operator Pᵢ, for the state resulting from applying the ideal unitary to a stabilizer state that has Pᵢ in its stabilizer group (one must be careful to prepare states that have both +1 and 1 eigenstates of the operator in question, to emulate the random state preparation corresponding to measuring half of a maximally entangled state).
[Joz] Fidelity for Mixed Quantum States. Jozsa. Journal of Modern Optics. 41:12, 23152323 (1994). DOI: 10.1080/09500349414552171 https://doi.org/10.1080/09500349414552171 [Nie] A simple formula for the average gate fidelity of a quantum dynamical operation. Nielsen. Phys. Lett. A 303 (4): 249252 (2002). https://doi.org/10.1016/S03759601(02)012720 https://arxiv.org/abs/quantph/0205035 Parameters:  results – A list of ExperimentResults from running a DFE experiment
 kind – A string describing the kind of DFE data being analysed (‘state’ or ‘process’)
Returns: the estimate of the mean fidelity along with the associated standard err