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Project-declaredLean 4.28.0 · mathlib@8f9d9cff6bd7

Sandwiched Renyi Entropy DPI eq one

sandwichedRenyiEntropy_DPI_eq_one

Plain-language statement

The Data Processing Inequality for the Sandwiched Rényi relative entropy (α > 1). Every CPTP map Φ satisfies D̃_α(Φρ‖Φσ) ≤ D̃_α(ρ‖σ). The proof uses the Stinespring representation (see CPTPMap.exists_purify): every CPTP map can be written as ancilla preparation + unitary conjugation + partial trace. Since the sandwiched Rényi divergence is invariant...

Exact Lean statement

theorem sandwichedRenyiEntropy_DPI_eq_one (ρ σ : MState d₁) (Φ : CPTPMap d₁ d₂) :
    D̃_ 1(Φ ρ‖Φ σ) ≤ D̃_ 1(ρ‖σ)

Formal artifact

Lean source

Canonical source
Full Lean sourceLean 4
theorem sandwichedRenyiEntropy_DPI_eq_one (ρ σ : MState d₁) (Φ : CPTPMap d₁ d₂) :    D̃_ 1(Φ ρ‖Φ σ)  D̃_ 1(ρ‖σ) := by  by_contra h_contra;  -- Since $\alpha \mapsto D_\alpha(\rho \| \sigma)$ is continuous on $(0, \infty)$, we can take the limit as $\alpha \to 1$.  have h_cont : Filter.Tendsto (fun α :  => D̃_ α(Φ ρ‖Φ σ)) (nhdsWithin 1 (Set.Ioi 1)) (nhds (D̃_ 1(Φ ρ‖Φ σ)))  Filter.Tendsto (fun α :  => D̃_ α(ρ‖σ)) (nhdsWithin 1 (Set.Ioi 1)) (nhds (D̃_ 1(ρ‖σ))) := by    exact  tendsto_nhdsWithin_of_tendsto_nhds ( by simpa using sandwichedRelRentropy.continuousOn ( Φ ρ ) ( Φ σ ) |> ContinuousOn.continuousAt <| Ioi_mem_nhds zero_lt_one ), tendsto_nhdsWithin_of_tendsto_nhds ( by simpa using sandwichedRelRentropy.continuousOn ρ σ |> ContinuousOn.continuousAt <| Ioi_mem_nhds zero_lt_one ) ;  exact h_contra <| le_of_tendsto_of_tendsto h_cont.1 h_cont.2 <| Filter.eventually_of_mem self_mem_nhdsWithin fun x hx => sandwichedRenyiEntropy_DPI_gt_one hx ρ σ Φ
Project
quantumInfo
License
MIT
Commit
56e83a9288a3
Source
QuantumInfo/Finite/Entropy/DPI.lean:1576-1582

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