🚧 quantr 🚧

This crate is not production ready, and so should not be considered stable, nor produce correct answers. It is still heavily under development and major optimsations are still needed, most likely requiring major breaking updates in the near future. Please always check your answers with other simulations if you are intending to use this for projects.

A Rust crate that simulates a quantum computer.

This crate simulates a quantum computer by allowing the user to build a quantum circuit by adding columns of gates so that a quantum register can be constructed (see the quick start guide). Measurements can then be performed on this circuit to return observables.

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 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 or with other single gates causes an issue for the printer. For now, the user has to manually make sure that 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 states labelling the product states of the circuit 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 "activiated". In general, it is better to assume that the custom function doesn't define control nodes, but rather that it extends the dimension of its domain.

Documentation

There are plans to create a mdBook that gives the background and theory behind quantr.

For the online code documentation, please refer to crates.io. This can also be built and opened in your favourite webrowser 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 in learning quantum computing is Quirk. It's a real-time online simulator that inerfaces 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.