Not achieves Rate gt log dim out
CPTPMap.not_achievesRate_gt_log_dim_out
Plain-language statement
A channel cannot achieve a rate greater than log2(D), where D is the output dimension.
Exact Lean statement
theorem not_achievesRate_gt_log_dim_out (Λ : CPTPMap d₁ d₂) {R : ℝ} (hR : Real.logb 2 (Fintype.card d₂) < R): ¬Λ.AchievesRate RFormal artifact
Lean source
theorem not_achievesRate_gt_log_dim_out (Λ : CPTPMap d₁ d₂) {R : ℝ} (hR : Real.logb 2 (Fintype.card d₂) < R): ¬Λ.AchievesRate R := by intro h; -- We show that the identity channel on the output space `d₂` emulates `Λ`. Since capacity is monotonic under emulation, `Q(Λ) ≤ Q(id_{d₂})`. have h_emulate : (CPTPMap.id (dIn := d₂)).Emulates Λ := by exact ⟨Λ, CPTPMap.id, by simp⟩ -- If `Λ` achieves rate `R`, then `id_{d₂}` achieves rate `R`. This follows because if `Λ^{\otimes n}` emulates `B`, and `id^{\otimes n}` emulates `Λ^{\otimes n}` (by functoriality of tensor product), then `id^{\otimes n}` emulates `B`. have h_id_achieves : (CPTPMap.id (dIn := d₂)).AchievesRate R := by intro ε hε_pos obtain ⟨n, hn, dimB, B, hB_emulate, hB_rate, hB_approx⟩ := h ε hε_pos have h_id_emulate : (CPTPMap.piProd (fun (_ : Fin n) => CPTPMap.id (dIn := d₂))).Emulates B := by -- Since `id_{d₂}` emulates `Λ`, we can use the fact that the tensor product of emulations is an emulation. have h_tensor_emulate : ∀ (n : ℕ), (CPTPMap.piProd (fun (_ : Fin n) => CPTPMap.id (dIn := d₂))).Emulates (CPTPMap.piProd (fun (_ : Fin n) => Λ)) := by intro n obtain ⟨E, D, hD⟩ := h_emulate use CPTPMap.piProd (fun (_ : Fin n) => E), CPTPMap.piProd (fun (_ : Fin n) => D); simp [ ← hD, ← CPTPMap.piProd_comp]; exact emulates_trans _ _ _ ( h_tensor_emulate n ) hB_emulate; exact ⟨ n, hn, dimB, B, h_id_emulate, hB_rate, hB_approx ⟩; refine not_le_of_gt hR <| not_lt.mp fun h => ?_ exact not_lt_of_ge ( le_of_not_gt fun h' => not_achievesRate_gt_log_dim_in _ h' h_id_achieves ) h- Project
- quantumInfo
- License
- MIT
- Commit
- 56e83a9288a3
- Source
- QuantumInfo/Finite/Capacity.lean:166-185
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Source project: quantumInfo
Person-level attribution pending.
Id achieves Rate log dim
CPTPMap.id_achievesRate_log_dim
Plain-language statement
The identity channel on D dimensional space achieves a rate of log2(D).
Source project: quantumInfo
Person-level attribution pending.