🚧 quantr 🚧

This crate is not production ready and so should not be considered stable, nor produce correct answers. It is still under heavy development and requires many more optimisations. Hence, it's likely that near future updates will induce breaking changes. Please always check answers with other simulations if you are intending to use quantr for projects.

A Rust library crate that builds and simulates a quantum computer.

This crate allows the user to build a quantum circuit by adding columns of gates through various methods. Once the circuit has been built, then it can be simulated which attaches the register |00..0> to the circuit, resulting in a superposition that can be measured.

For a brief example of using quantr, see the quick start guide which walks through an implementation of the Grover's algorithm.

Defining features

• Aimed to be accessible to beginners in Rust.
• The distinction between physical observables and non-physical observables are made clear; but the latter is still made possible to retrieve.
• Prints the circuit diagram to the terminal, or saves it to a text file, as a UTF-8 string.
• Custom gates can be implemented easily by giving their explicit linear mappings on states. This allows the user to avoid representing the gates as matrices.
• Attempts to minimise memory consumption by not using matrices nor sparse matrices, and instead uses functions to represent the linear mapping of gates.
• Only safe Rust code is used, and the only dependency is the rand crate.

Limitations (currently)

• Inserting multiple n-gates by themselves or with other single gates causes an issue for the printer. For now, the user has to manually make sure that the n-gates are added by themselves, one column at a time. In the near future, this will be resolved.
• There is no noise consideration, or ability to introduce noise.
• There is no ability to add classical circuits.

Conventions

The ordering of the wires labelling the product states in the computational basis is defined as:

|a⟩ ──── 
|b⟩ ────  ⟺ |a,b,c,⋯⟩ ≡ |a⟩⊗|b⟩⊗|c⟩⊗⋯ 
|c⟩ ────
 ⋮    ⋮

When defining a custom function that depends on the position of control nodes to define gates (such as the CNot and Toffoli gates), it must be defined so that the most far right state of the product state, is assumed to be the gate that is 'activated'. In general, it is better to assume that the custom function doesn't define control nodes, but rather it extends the dimension of the function's domain.

Documentation

The Quantr Book is planned to serve as extended documentation to quantr, such as explaining the motivations behind chosen algorithms. For now, it only contains the start guide.

For the online code documentation, please refer to crates.io. This can also be built and opened in your favourite web browser locally by cloning the project, moving into the directory, and running cargo doc --open.

Other quantum computer simulators

As of 27th July 2023, the website Are We Quantum Yet lists all things quantum computing in Rust.

A useful and very practical simulator for learning quantum computing is Quirk. It's a real-time online simulator that interfaces via drag-and-drop gates. Note that Quirk uses the reverse ordering of labelling their states from the quantum circuit as defined here.

Licence

Quantr is licensed under the EUPL-1.2 or later. You may obtain a copy of the licence at https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12. A copy of the EUPL-1.2 licence in English is given in LICENCE.txt which is found in the root of this repository. Details of the licenses of third party software, and the quantr project, can be found in COPYRIGHT.txt.