Q Sharp

Q# (pronounced as Q sharp) is a domain-specific programming language used for expressing quantum algorithms.[1] It was initially released to the public by Microsoft as part of the Quantum Development Kit.[2]

Q#
Paradigmmulti-paradigm: quantum, functional, imperative
Designed byMicrosoft Research (quantum architectures and computation group; QuArC)
DeveloperMicrosoft
First appearedDecember 11th, 2017
Typing disciplinestatic, strong
PlatformCommon Language Infrastructure
LicenseMIT License
Filename extensions.qs
WebsiteMicrosoft Quantum (GitHub)
Influenced by
C#, F#

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 and/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
  1. QuantumWriter. "The Q# Programming Language". docs.microsoft.com. Retrieved 2017-12-11.
  2. "Announcing the Microsoft Quantum Development Kit". Retrieved 2017-12-11.
  3. "Microsoft announces quantum computing programming language". Retrieved 2017-12-14.
  4. Microsoft is open-sourcing its Quantum Development Kit
  5. QuantumWriter. "Setting up the Q# development environment". docs.microsoft.com. Retrieved 2017-12-14.
  6. "Types in Q# - Microsoft Quantum". docs.microsoft.com.
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