Crate qvass 

A Rust library for building and running quantum circuit simulations.

This crate provides the tools to build, simulate, and measure quantum circuits. The primary entry point is the QuantumSimulator, which manages the state and execution of a Circuit. Circuits themselves are constructed from the fundamental building blocks defined in the Gate enum.

The simulator’s behavior is rigorously tested against Qiskit to ensure correctness.

Getting Started

Here is a quick example that creates a 3-qubit GHZ state ((|000⟩ + |111⟩)/√2), a classic example of quantum entanglement.

use rand::{rngs::SmallRng,  SeedableRng};

use qvass::{QuantumSimulator, Gate, QubitError};

fn main() -> Result<(), QubitError> {
    // 1. Create a simulator for a 3-qubit system.
    let mut sim = QuantumSimulator::new(3);

    // 2. Build the circuit to create the GHZ state.
    sim.add_gate(Gate::hadamard(), [0])?;
    sim.add_gate(Gate::cnot(), [0, 1])?;
    sim.add_gate(Gate::cnot(), [0, 2])?;

    // 3. Create a seeded RNG for reproducible measurements.
    // For a real simulation, you might seed this from the system time.
    let mut rng = SmallRng::seed_from_u64(123);

    // 4. Start from the |000⟩ state, run the simulation, and measure.
    sim.init_state(0);
    sim.run();
    let outcome = sim.measure(&mut rng);

    // After measurement, the state will be either |000⟩ (index 0)
    // or |111⟩ (index 7), with a 50/50 chance for each.
    println!("Measured state: |{}>", outcome);
    assert!(outcome == 0 || outcome == 7);

    Ok(())
}

Modules

qft

Provides a builder function for creating a Quantum Fourier Transform (QFT) circuit.

Structs

Circuit

Represents a quantum circuit as a sequence of gates

QuantumSimulator

Manages the state of a quantum system and the application of a circuit

Enums

Gate

Represents different types of quantum gates

QubitError

Represents errors that can occur during circuit construction