everett

A clean, zero-dependency statevector quantum simulator in Rust.

everett represents the quantum state of n qubits as a complex vector of 2^n amplitudes and applies gates in place over amplitude index-groups, never by materializing a full 2^n x 2^n matrix. The name is a nod to the many-worlds interpretation: a statevector holds the entire branching wavefunction at once.

Example

use everett::prelude::*;

// Bell state: (|00> + |11>) / sqrt(2)
let mut circuit = Circuit::new(2);
circuit.h(0).cnot(0, 1);

let exec = StateVectorBackend::run(&circuit)?;
let state = exec.state();
assert!((state.probability(0b00) - 0.5).abs() < 1e-12);
assert!((state.probability(0b11) - 0.5).abs() < 1e-12);
# Ok::<(), everett::Error>(())

Features

Three backends

Backend	State representation	Best for
StateVectorBackend	2^n amplitudes	general simulation up to ~30 qubits
DensityMatrixBackend	4^n density matrix	noise simulation, mixed states
StabilizerBackend	O(n^2) tableau	Clifford circuits on hundreds of qubits

Gate set -- single-qubit: H, X, Y, Z, S, T, Rx/Ry/Rz, Phase; two-qubit: CNOT, CZ, SWAP; plus arbitrary controlled gates.

Measurement -- projective measurement with Born-rule sampling and mid-circuit classically-controlled operations.

Noise -- uniform depolarizing, Kraus-operator channels, and readout errors via NoiseModel, applied through DensityMatrixBackend.

OpenQASM 3.0 -- import and export circuits with Circuit::from_qasm / Circuit::to_qasm.

Algorithms -- Bell/GHZ state preparation, quantum teleportation, superdense coding, quantum Fourier transform, phase estimation, and Hamiltonian simulation via Trotterization.

Optional: parallelism

Gate application can be parallelized across amplitude chunks with rayon. This is off by default to keep the core dependency-free and Miri-friendly.

everett = { version = "0.1", features = ["parallel"] }

Development

This project uses Nix flakes. The default shell provides the stable toolchain; separate shells provide nightly for Miri and the Kani verifier.

nix develop            # stable toolchain + rust-analyzer
nix flake check        # build, clippy, fmt, tests, doctests

nix develop .#miri     # nightly + miri
nix develop .#kani     # kani bounded formal verification

Without Nix, a standard cargo toolchain (1.85+) works for everything except Miri and Kani.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.