QuantRS2-Core: Foundational Quantum Types

QuantRS2-Core is part of the QuantRS2 quantum computing framework, providing the foundational types and traits that form the basis of the entire ecosystem.

Features

• Type-Safe Qubit Identifiers: Zero-cost abstractions for qubit references
• Comprehensive Gate Definitions: Standard quantum gates with matrix representations
• Register Abstractions: Quantum register types with const generics for compile-time validation
• Robust Error Handling: Comprehensive error types and result wrappers

Usage

Basic Example

use quantrs2_core::prelude::*;

fn main() -> QuantRS2Result<()> {
    // Create a qubit identifier
    let qubit = QubitId::new(0);
    
    // Use a standard gate
    let x_gate = XGate::new();
    let matrix = x_gate.matrix();
    
    // Create a register (with 2 qubits)
    let register = Register::<2>::new();
    
    Ok(())
}

Creating Custom Gates

use quantrs2_core::prelude::*;
use num_complex::Complex64;

struct MyCustomGate;

impl GateOp for MyCustomGate {
    fn matrix(&self) -> Vec<Complex64> {
        // Define your custom gate matrix here
        // Example: custom rotation gate
        vec![
            Complex64::new(0.5, 0.0), Complex64::new(0.5, 0.5),
            Complex64::new(0.5, -0.5), Complex64::new(0.5, 0.0),
        ]
    }
    
    fn n_qubits(&self) -> usize {
        1 // This is a single-qubit gate
    }
}

Module Structure

• error.rs: Error types and result wrappers
• gate.rs: Gate trait definitions and standard gate implementations
• qubit.rs: Qubit identifier type
• register.rs: Quantum register abstractions

API Overview

Core Types

• QubitId: Type-safe wrapper around a qubit identifier
• Register<N>: Fixed-size quantum register using const generics
• QuantRS2Error: Error enumeration for all possible errors
• QuantRS2Result<T>: Convenient result type alias

Important Traits

• GateOp: Trait for quantum gates with matrix representation
• ControlledOp: Trait for controlled quantum operations
• StateVector: Trait for quantum state representations

Implementation Notes

• The QubitId type is a zero-cost abstraction using #[repr(transparent)]
• Gates are represented by their matrix form in column-major order
• Registers use Rust's const generics feature for compile-time qubit count validation
• Error handling follows Rust's standard practices with a custom error type

Future Plans

See TODO.md for planned improvements and features.

Integration with Other QuantRS2 Modules

This module is designed to work seamlessly with:

• quantrs2-circuit: Provides core types used in circuit construction
• quantrs2-sim: Provides matrix representations used in simulation

License

This project is licensed under either:

• Apache License, Version 2.0
• MIT License

at your option.