Q Sharp

History

During a Microsoft Ignite Keynote on September 26, 2017, Microsoft announced that they were going to release a new programming language geared specifically towards quantum computers.^[3] On December 11, 2017, Microsoft released Q# as a part of the Quantum Development Kit.^[2]

At Build 2019, Microsoft announced that it is open-sourcing the Quantum Development Kit, including its Q# compilers and simulators.^[4]

Usage

Q# is available as a separately downloaded extension for Visual Studio,^[5] but it can also be run as an independent tool from the Command line or Visual Studio Code. The Quantum Development Kit ships with a quantum simulator which is capable of running Q#.

In order to invoke the quantum simulator, another .NET programming language, usually C#, is used, which provides the (classical) input data for the simulator and reads the (classical) output data from the simulator.

Features

A primary feature of Q# is the ability to create and use qubits for algorithms. As a consequence, some of the most prominent features of Q# are the ability to entangle and introduce superpositioning to qubits via Controlled NOT gates and Hadamard gates, respectively, as well as Toffoli Gates, Pauli X, Y, Z Gate, and many more which are used for a variety of operations; see the list at the article on quantum logic gates.

The hardware stack that will eventually come together with Q# is expected to implement Qubits as topological qubits. The quantum simulator that is shipped with the Quantum Development Kit today is capable of processing up to 32 qubits on a user machine and up to 40 qubits on Azure.

Documentation and resources

Currently, the resources available for Q# are scarce, but the official documentation is published: Microsoft Developer Network: Q#. Microsoft Quantum Github repository is also a large collection of sample programs implementing a variety of Quantum algorithms and their tests.

Microsoft has also hosted a Quantum Coding contest on Codeforces here: Microsoft Q# Coding Contest - Codeforces, and also provided related material to help answer the questions in the blog posts, plus the detailed solutions in the tutorials.

Microsoft hosts a set of learning exercises to help learn Q# on github: microsoft/QuantumKatas with links to resources, and answers to the problems.

Syntax

Q# is syntactically related to both C# and F# yet also has some significant differences.

Similarities with C#

• Uses namespace for code isolation
• All statements end with a ;
• Curly braces are used for statements of scope
• Single line comments are done using //
• Variable data types such as Int Double String and Bool are similar, although capitalised (and Int is 64-bit)^[6]
• Qubits are allocated and disposed inside a using block.
• Lambda functions using the => operator.
• Results are returned using the return keyword.

Similarities with F#

• Variables are declared using either let or mutable^[1]
• First-order functions
• Modules, which are imported using the open keyword
• The datatype is declared after the variable name
• The range operator ..
• for … in loops
• Every operation/function has a return value, rather than void. Instead of void, an empty Tuple () is returned.
• Definition of record datatypes (using the newtype keyword, instead of type).

Differences

• Functions are declared using the function keyword
• Operations on the quantum computer are declared using the operation keyword
• Lack of multiline comments
• Asserts instead of throwing exceptions
• Documentation is written in Markdown instead of XML-based documentation tags

References

External links

• Official documentation
• qsharp-language on GitHub