Quantum4Lean

Verified quantum computing in Lean 4. Bit-exact pure-Lean engine. Complete NISQ stack: StateVector, Observables, adaptive VQE, QAOA, Density Matrix + noise, Jordan-Wigner, quantum chemistry (exact H2), polynomial expansion to arbitrary degree, discrete topology with Hodge and Betti, declarative DSL, OpenQASM 3.0 exporter (including Gate.Unitary), verification tactics, intra-Lean fuzzer, FFI bridge to C++ CPU and Metal GPU engine for up to 30 qubits.

Status: v0.8.0 — 24 library modules, 7 playgrounds, 12 verified theorems, 208+ tests.

Build

cd Quantum4Lean
lake build quantum4lean-test && .lake/build/bin/quantum4lean-test

Zero external dependencies. Requires Lean 4.31.0 (lean-toolchain).

Architecture

Quantum4Lean (24 modules)
  Core, Error, Engine, Fuzz, Unitary, Observable, VQE, QAOA,
  Diophantine, Polynomial, Solver, Simp, Transpile, Clifford,
  Verify, DSL, Tactic, FFI, QASM, Density, Chemistry, Topology,
  Ansatz, Runner

Quantum4LeanPlayground (7 demos)
  Diophantine, Beal, Tijdeman, Riemann, TRDU, FFI, Mobius

Quantum4LeanBridge (C bridge)
  Quantum4LeanFFI.c/.h  -- Stable C API for FFI
buildCPU.sh buildFFI.sh buildMetal.sh  -- CPU/FFI/Metal build scripts

Quick Start

import Quantum4Lean
open Quantum4Lean
open Quantum4Lean.DSL.Shortcuts

-- Bell circuit with declarative DSL
def bell : Circuit 2 := circuit! {
  H q[0];
  CNOT q[0] q[1]
}

-- Run on the pure-Lean engine
#eval executeSim bell
-- Except.ok [1]

-- Verify semantic equivalence
#eval circuitsEquiv bell bell
-- true

-- circuit_equiv tactic (Clifford, no H)
example : circuitsEquiv
  (circuit fun c => (c.add (Gate.X q[0])).add (Gate.X q[0]))
  (Circuit.identity 2) := by
  circuit_equiv

API

DSL

-- Full names (always available)
def bell : Circuit 2 := circuit! {
  Gate.H q[0];
  Gate.CNOT q[0] q[1]
}

-- Short aliases (requires `open Quantum4Lean.DSL.Shortcuts`)
def ghz3 : Circuit 3 := circuit! {
  H q[0];
  CNOT q[0] q[1];
  CNOT q[1] q[2]
}

circuit_equiv Tactic

-- Works with native_decide for circuits without H (Pauli, CNOT, CZ, SWAP)
example : circuitsEquiv
  (circuit fun c => (c.add (Gate.X q[0])).add (Gate.X q[0]))
  (Circuit.identity 2) := by
  circuit_equiv

-- For circuits with H, use #eval
#eval circuitsEquiv
  (circuit fun c => (c.add (Gate.H q[0])).add (Gate.H q[0]))
  (Circuit.identity 2)

Clifford Verification (Z[i])

Formal proof of equivalences for the 7 Clifford gates (X, Y, Z, S, CNOT, CZ, SWAP) using integer arithmetic in Z[i]. No Float, no √2. 8 theorems proven with native_decide.

-- Formally proven (0 sorry)
theorem rule_X_X_eq_I : cliffordEquiv c (Circuit.identity 2) := by
  native_decide

-- Runtime verification for any Clifford circuit
#eval cliffordEquiv myCircuit otherCircuit

Diophantine Translator

Linear Diophantine equations (ax + by = c) to Ising Hamiltonians.

import Quantum4Lean

let eq : Diophantine := {
  vars := [
    { coeff := 3, name := "x", bits := 4 },
    { coeff := 5, name := "y", bits := 4 }
  ],
  constant := 22
}

let H := toIsing eq 4
let result := diophantineSolve eq 4
#eval checkSolution eq [("x", 4), ("y", 2)]  -- true (3*4 + 5*2 = 22)

Polynomial Translator

Polynomial expansion to any degree n. Z-mask representation with XOR for Z*Z=I. Generalizes the linear translator to multivariate monomials. Supports equations such as x^2 = y^3 + 1 (Tijdeman), x^3 + y^3 = z^3 (Fermat n=3), etc.

import Quantum4Lean

-- Equation: x^2 - y^3 = 1
let eq : PolyEquation := {
  monomials := [
    { coefficient := 1,  exponents := [(0, 2)] },
    { coefficient := -1, exponents := [(1, 3)] }
  ],
  constant := 1,
  varBits := [4, 4]
}

let H := polyToIsing eq    -- Ising Observable
let n := polyTotalQubits eq -- 8 qubits

FFI: C++/Metal Bridge (Apple Silicon)

External engine with GPU acceleration via Metal 3. CPU: up to 25 qubits (~1 GB). Metal GPU: Apple Silicon M2/M3 with unified memory.

Requires ../QuantumKit (sibling repository with the C++ engine). Setup:

bash setup.sh          # verify QuantumKit + build libs
# or step by step:
bash buildCPU.sh       # libQuantum4LeanCPU.a
bash buildMetal.sh     # libQuantum4LeanMetal.a

# Run CPU
LEAN_CC=clang lake build quantum4lean-ffi
.lake/build/bin/quantum4lean-ffi

# Run Metal GPU
LEAN_CC=clang lake build quantum4lean-ffi-metal
.lake/build/bin/quantum4lean-ffi-metal

import Quantum4Lean
open Quantum4Lean

-- FFI functions are in Quantum4Lean.FFI and helpers in the playground
-- Precompiled executable: .lake/build/bin/quantum4lean-ffi

FFI Architecture: Lean (@[extern] + unsafe) → C bridge (Quantum4LeanFFI.c) → C++ Engine (QuantumKitCore.mm) with embedded Metal JIT. Zero-copy via FloatArray (double*).

Playground

Advanced demonstrations extending the library. Independent import.

Diophantine Solver (QuantumPlaygroundDiophantine)

4 cases with exhaustive search via polyToIsing:

import Quantum4LeanPlayground
#eval Quantum4LeanPlayground.Diophantine.report

Cases: Tijdeman, Pillai n=2, Pillai n=3, Pythagoras.

Beal's Conjecture (QuantumPlaygroundBeal)

Massive counterexample search at 3 scales (9, 12, 19 qubits):

#eval Quantum4LeanPlayground.Beal.report

ADAM Optimizer

VQE with ADAM optimizer (momentum + adaptive learning rate).

let (energy, params, history) := adamVQE ansatz H initialParams 0.01 200

Quantum Tijdeman

#eval Quantum4LeanPlayground.Tijdeman.report
-- x^2 = y^3 + 1 via QAOA. Validated against formal proof.

Fuzzer

#eval runFullSuite { maxQubits := 5, numCircuits := 200 }
#eval reportToString (runFullSuite { numCircuits := 100 })

Bit-exactness with CoreQU4TRIX

Structure

Quantum4Lean/
+-- lakefile.lean
+-- Quantum4Lean.lean              -- Main module
+-- Quantum4Lean/
|   +-- Quantum4LeanCore.lean      -- Qubit, Gate, Circuit
|   +-- Quantum4LeanError.lean     -- QuantumError
|   +-- Quantum4LeanEngine.lean    -- StateVector, simulator
|   +-- Quantum4LeanFuzz.lean      -- Intra-Lean fuzzer
|   +-- Quantum4LeanUnitary.lean   -- Complex, UnitaryMatrix
|   +-- Quantum4LeanObservable.lean-- PauliString, expect
|   +-- Quantum4LeanVQE.lean       -- Parameter-shift, VQE
|   +-- Quantum4LeanQAOA.lean      -- Mixing layer, Ising
|   +-- Quantum4LeanDSL.lean       -- circuito!, q[i]
|   +-- Quantum4LeanTactic.lean    -- circuit_equiv, quantum_simp
|   +-- Quantum4LeanSimp.lean      -- Simplifier (12 rules)
|   +-- Quantum4LeanTranspile.lean -- Transpiler (8 theorems)
|   +-- Quantum4LeanClifford.lean  -- Clifford verification (Z[i])
|   +-- Quantum4LeanDiophantine.lean-- Linear Diophantine translator
|   +-- Quantum4LeanPolynomial.lean -- Polynomial translator
|   +-- Quantum4LeanRunner.lean    -- Test runner
+-- Quantum4LeanPlayground.lean    -- Playground root
+-- Quantum4LeanPlayground/
|   +-- QuantumPlaygroundDiophantine.lean
|   +-- QuantumPlaygroundBeal.lean
|   +-- QuantumPlaygroundTijdeman.lean
|   +-- QuantumPlaygroundRiemann.lean
|   +-- QuantumPlaygroundTRDU.lean
+-- Quantum4LeanBridge/            -- C bridge (FFI)
|   +-- Quantum4LeanFFI.h / .c
+-- buildCPU.sh buildFFI.sh buildMetal.sh  -- FFI scripts
+-- .github/workflows/ci.yml       -- CI
+-- README.md
+-- USER_MANUAL.md
+-- FOUNDATIONAL_MANUSCRIPT.md
+-- LICENSE
+-- CITATION.cff

License

Apache 2.0 — see LICENSE for full text.

Citation

If you use Quantum4Lean in your research, please cite:

@software{Quantum4Lean_v0.8.0,
  title   = {Quantum4Lean: Verified Quantum Computing on Apple Silicon},
  author  = {Izquierdo P\'erez, Bezalel},
  orcid   = {0009-0001-5993-4057},
  doi     = {10.5281/zenodo.21197538},
  year    = {2026},
  version = {v0.8.0},
  url     = {https://github.com/Alektronnik/Quantum4Lean}
}

See CITATION.cff for the full metadata.

Requirements

• Lean 4 (v4.31.0)
• macOS / Linux / Windows
• Apple Silicon + macOS 13+ (FFI/Metal optional, up to 25 qubits)
• RAM: 512 MB for 20 qubits, 4 GB for 25 qubits