|
1 | | -# QKD Formalization Project |
| 1 | +# Quantum Key Distribution: High Fidelity Implies Low Entropy |
2 | 2 |
|
3 | | -Formalization of Peter Shor's certificate theorem for quantum key distribution in Lean 4. |
| 3 | +**Authors:** Ben Breen & Kfir Sulimany |
4 | 4 |
|
5 | | -## Project Structure |
| 5 | +Lean 4 formalization of Lemma 1 from [*Unconditional Security Of Quantum Key Distribution Over Arbitrarily Long Distances*](https://arxiv.org/abs/quant-ph/9802025) by Lo and Chau (1998). |
6 | 6 |
|
7 | | -``` |
8 | | -QKD/ |
9 | | -├── QKD/ |
10 | | -│ └── PeterShor.lean # Main formalization file |
11 | | -├── lakefile.lean # Lake build configuration |
12 | | -├── lean-toolchain # Lean version specification |
13 | | -└── README.md # This file |
14 | | -``` |
15 | | - |
16 | | -## Main Results |
| 7 | +**Blueprint:** [BenKBreen.github.io/QKD](https://BenKBreen.github.io/QKD) |
17 | 8 |
|
18 | | -This project formalizes: |
| 9 | +## Main Theorem |
19 | 10 |
|
20 | | -1. **Schur Convexity**: The function `f(x) = ∑ᵢ xᵢ log(xᵢ)` is Schur-convex |
21 | | -2. **High Fidelity Implies Low Entropy**: For a positive semidefinite density matrix ρ with trace 1, if there exists a unit vector achieving fidelity > 1-δ, then the von Neumann entropy is bounded |
22 | | - |
23 | | -### Key Theorem |
| 11 | +If a density matrix ρ has high fidelity (> 1-δ) with a pure state, then its von Neumann entropy is bounded: |
24 | 12 |
|
25 | 13 | ```lean |
26 | | -theorem high_fidelity_implies_low_entropy_equivalent |
27 | | - (R : ℕ) |
28 | | - (δ : ℝ) |
29 | | - (ρ : Matrix (Fin R) (Fin R) ℂ) |
30 | | - (hR : 1 < R) |
31 | | - (hδ_pos : 0 ≤ δ) |
32 | | - (hδ_lt_one : δ < 1) |
33 | | - (hδ_small : δ ≤ (R - 1 : ℝ) / R) |
34 | | - (hρ_pos : ρ.PosSemidef) |
35 | | - (trace_one : ∑ i, hρ_pos.isHermitian.eigenvalues i = 1) |
36 | | - (hv : ∃ v : EuclideanSpace ℂ (Fin R), norm v = 1 ∧ (⟪v, ρ *ᵥ v⟫_ℂ).re > 1 - δ) |
37 | | - : |
38 | | - (vonNeumannEntropy ρ).re ≤ -(1 - δ) * Real.log (1 - δ) - δ * Real.log (δ / (R - 1)) |
| 14 | +S(ρ) ≤ -(1-δ) log(1-δ) - δ log(δ/(R-1)) |
39 | 15 | ``` |
40 | 16 |
|
41 | | -## Building the Project |
42 | | - |
43 | | -### Prerequisites |
44 | | - |
45 | | -- Lean 4.25.0-rc2 |
46 | | -- Lake (comes with Lean) |
47 | | - |
48 | | -### Installation |
49 | | - |
50 | | -1. Install [elan](https://github.com/leanprover/elan): |
51 | | - ```bash |
52 | | - curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh |
53 | | - ``` |
54 | | - |
55 | | -2. Clone this repository: |
56 | | - ```bash |
57 | | - git clone <repository-url> |
58 | | - cd QKD |
59 | | - ``` |
60 | | - |
61 | | -3. Build the project: |
62 | | - ```bash |
63 | | - lake update |
64 | | - lake exe cache get # Download mathlib cache |
65 | | - lake build |
66 | | - ``` |
67 | | - |
68 | | -### Working with the Code |
69 | | - |
70 | | -To work on the formalization: |
| 17 | +## Building |
71 | 18 |
|
72 | 19 | ```bash |
73 | | -# Open in VS Code with Lean extension |
74 | | -code . |
75 | | - |
76 | | -# Or build specific files |
77 | | -lake build QKD.PeterShor |
| 20 | +lake update |
| 21 | +lake exe cache get |
| 22 | +lake build |
78 | 23 | ``` |
79 | 24 |
|
80 | | -## Key Definitions |
81 | | - |
82 | | -- **`vonNeumannEntropy`**: Von Neumann entropy S(ρ) = -tr(ρ log ρ) |
83 | | -- **`SchurConvex`**: A function is Schur-convex if it preserves the majorization ordering |
84 | | -- **`slope_comparison_tlogt`**: Key lemma showing t log t is a convex function |
85 | | - |
86 | | -## Dependencies |
87 | | - |
88 | | -- **Mathlib**: Lean's mathematical library |
89 | | -- Matrix theory, linear algebra, analysis |
90 | | -- Order theory (for Schur convexity) |
91 | | - |
92 | | -## References |
| 25 | +## Blueprint |
93 | 26 |
|
94 | | -This formalization is based on Peter Shor's work on quantum key distribution security proofs. |
| 27 | +Generate the documentation: |
95 | 28 |
|
96 | | -## License |
97 | | - |
98 | | -[Add appropriate license] |
99 | | - |
100 | | -## Contributing |
101 | | - |
102 | | -Contributions are welcome! Please feel free to submit pull requests or open issues. |
| 29 | +```bash |
| 30 | +cd blueprint |
| 31 | +leanblueprint web |
| 32 | +open web/index.html |
| 33 | +``` |
103 | 34 |
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