Q Sharp Explained

Q# (pronounced Q sharp) is a domain-specific programming language used for expressing quantum algorithms.^[3] It was initially released to the public by Microsoft as part of the Quantum Development Kit.^[4]

Q# works in conjunction with classical languages such as C#, Python and F#, and is designed to allow the use of traditional programming concepts in quantum computing, including functions with variables and branches as well as a syntax-highlighted development environment with a quantum debugger.^{[5] [6]}

History

Historically, Microsoft Research had two teams interested in quantum computing: the QuArC team based in Redmond, Washington,^[7] directed by Krysta Svore, that explored the construction of quantum circuitry, and Station Q initially located in Santa Barbara and directed by Michael Freedman, that explored topological quantum computing.^{[8] [9]}

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.^[10] On December 11, 2017, Microsoft released Q# as a part of the Quantum Development Kit.

At Build 2019, Microsoft announced that it would be open-sourcing the Quantum Development Kit, including its Q# compilers and simulators.^[11]

To support Q#, Microsoft developed Quantum Intermediate Representation (QIR) in 2023 as a common interface between programming languages and target quantum processors. The company also announced a compiler extension that generates QIR from Q#.^[12]

Bettina Heim currently leads the Q# language development effort.^{[13] [14]}

Usage

Q# is available as a separately downloaded extension for Visual Studio,^[15] but it can also be run as an independent tool from the command line or Visual Studio Code. Q# was introduced on Windows and is available on MacOS and Linux.^[16]

The Quantum Development Kit includes a quantum simulator capable of running Q# and simulated 30 logical qubits.^{[17] [18]}

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.^[19]

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.^[20]

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.^[21]

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, called 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 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 and are similar, although capitalised (and Int is 64-bit)^[22]
• Qubits are allocated and disposed inside a block.
• Lambda functions are defined using the => operator.
• Results are returned using the keyword.

Similarities with F#

• Variables are declared using either or
• First-order functions
• Modules, which are imported using the keyword
• The datatype is declared after the variable name
• The range operator
• loops
• Every operation/function has a return value, rather than . Instead of, an empty Tuple is returned.
• Definition of record datatypes (using the keyword, instead of).

Differences

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

Example

The following source code is a multiplexer from the official Microsoft Q# library repository.

// Copyright (c) Microsoft Corporation.// Licensed under the MIT License.

namespace Microsoft.Quantum.Canon

Notes and References

1. Web site: Microsoft’s Q# quantum programming language out now in preview . Ars Technica . 12 Dec 2017 . 2024-09-04. en-US.
2. Web site: Introduction to Q# . University of Washington.
3. Web site: The Q# Programming Language. QuantumWriter. docs.microsoft.com. en-us. 2017-12-11.
4. News: Announcing the Microsoft Quantum Development Kit. 2017-12-11. en-US.
5. Web site: Microsoft makes play for next wave of computing with quantum computing toolkit . 25 Sep 2017 . Ars Technica . 2024-09-04. en-US.
6. Web site: Quantum Computers Barely Exist—Here’s Why We’re Writing Languages for Them Anyway . 22 Dec 2017 . MIT Technology Review . 2024-09-04. en-US.
7. Web site: Solving the quantum many-body problem with artificial neural networks . Microsoft Azure Quantum . 15 February 2017.
8. [Scott Aaronson]
9. Web site: What are the Q# programming language & QDK? - Azure Quantum . learn.microsoft.com . 12 January 2024 . en-us.
10. News: Microsoft announces quantum computing programming language. 2017-12-14. en-US.
11. https://venturebeat.com/2019/05/06/microsoft-open-sourcing-quantum-development-kit/ Microsoft is open-sourcing its Quantum Development Kit
12. Web site: Microsoft taps LLVM for quantum computing . 2024-09-04 . 29 Sep 2020 . Krill . Paul . InfoWorld . en-US.
13. Web site: The Women of QuArC . 30 March 2019 .
14. Web site: Intro to Q# - Intro to Quantum Software Development . stem.mitre.org.
15. Web site: Setting up the Q# development environment. QuantumWriter. docs.microsoft.com. en-us. 2017-12-14.
16. Web site: Coppock . Mark . Microsoft’s quantum computing language is now available for MacOS . Digital Trends . 2024-09-04 . en . 26 Feb 2018.
17. Web site: Akdogan . Erman . Quantum computing is coming for finance & crypto . Medium . en . 23 October 2022.
18. Web site: Melanson . Mike . This Week in Programming: Get Quantum with Q Sharp . The New Stack . 2024-09-04 . en . 16 Dec 2017.
19. Web site: This Week in Programming: Get Quantum with Q Sharp . The New Stack . 16 December 2017.
20. Web site: Qubit Gate - an overview . www.sciencedirect.com.
21. Web site: Microsoft previews quantum computing development kit . CIO.
22. Web site: Types in Q# - Microsoft Quantum. docs.microsoft.com. 27 July 2022 .