An Introduction To Q#

Introduction

In this article, I will be explaining about Q# – the new programming language introduced by Microsoft for quantum computing. We will understand the data type, expressions, and statements of Q# with the help of code snippets.

Prerequisites

Please visit my earlier article An Introduction To Quantum Computing to get a basic understanding of Quantum Computing and to also know how to install Quantum Development Kit in Visual Studio 2017.

What is Q#?

According to Microsoft, Q# is a scalable, multi-paradigm, domain-specific programming language for quantum computing.

So, what do these terms actually mean? Let us dive into the details.

• Scalable
  Q# allows us to write a code that can be executed on machines of varying computing abilities. We can use it to simulate a few Qubits on our local machine or even thousands of Qubits for an enterprise level application.
• Multi-paradigm
  Q# is a multi-paradigm programming language as it supports both, functional as well as imperative, programming styles. If you are new to the programming paradigm, I suggest you to please refer here.
• Domain-specific
  Q# is a programming language for quantum computing. It is to be used for writing algorithms/code snippets to be executed on quantum processors.

Validating Q# development environment on your machine

As this point in time, I assume that you have already installed Quantum Development Kit (QDK). If not, then please do it by referring to the prerequisites section.

Open VS 2017 and navigate to Team >> Manage Connections.

Select Clone under Local Git Repositories and enter the URL: – https://github.com/Microsoft/Quantum.git and click “Clone”.

The repository will be cloned on your local computer and Visual Studio will switch to the Solution Explorer displaying all the cloned libraries and samples.

Now, open QsharpLibraries.sln solution. If you are prompted with the “Install Missing Features” popup box, click “Install” to allow the installation of the necessary features. This will download and install F# and other tools used by some of the samples. Make sure that you are connected to the internet.

To execute a sample program, right-click on the TeleportationSample project in “Samples > 0.Introduction folder” of QsharpLibraries solution, and then click on “Set as Startup Project” and press F5.

If you can see an output screen similar to the one shown below, then congratulations, your VS 2017 is ready for Q# development.

Note that your output screen may vary because the data that is being teleported is random. But it should send 8 rounds of data with all being successfully teleported. 

Q# Type model

Let us understand what are the various type models provided by Q#

Primitive Type

• Int: – It represents the 64 -bit signed integer. Notice the upper case ‘I’. This is in contrast to int in C# with lower case ‘i’.
• Double: – It represents double-precision floating point number. This also has a upper case ‘D’ in contrast to double in C#.
• Bool: – It represents the Boolean type and can take two values – true or false.
• Qubit: – This represents the Quantum bit. Qubit is the fundamental unit of processing information in quantum computers, similar to a bit in classical computers.
• Pauli: – This type is used to denote the base operation for rotations and to specify the basis of a measurement. This can take four possible values PauliI, PauliX, PauliY, PauliZ
• Result: – This represents the result of a measurement. This can take two possible values Zero or One
• Range: – This represents a sequence of integers.
• String: – It represents a sequence of Unicode characters.

Array Type

operation AddInteger(a: Int, b: Int): Int {  
    body {  
        mutable c = 0;  
        set c = a + b;  
        return (c);  
    }  
} 

function ProductNumber(a: Double, b: Double): Double {  
    mutable c = 0.0;  
    set c = a * b;  
    return (c);  
} 

set i=10;  

for(num in 1..2..10)  
{  
   //Do something  
}  

repeat {  
    //do something  
}  
until boolean condition  
fixup {  
    // do something  
}  

if (num % 2 == 0) {  
    return true;  
} else {  
    return false;  
}  

if (num == 1) {  
    //do something  
}  
elif(num == 2) {  
    //do something  
}  
else {  
    //do something  
}