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@ -4,12 +4,13 @@ contributors:
- ["Vincent van Wingerden", "https://github.com/vivanwin"]
- ["Mariia Mykhailova", "https://github.com/tcNickolas"]
- ["Andrew Ryan Davis", "https://github.com/AndrewDavis1191"]
- ["Alex Hansen", "https://github.com/sezna"]
filename: LearnQSharp.qs
---
Q# is a high-level domain-specific language which enables developers to write quantum algorithms. Q# programs can be executed on a quantum simulator running on a classical computer and (in future) on quantum computers.
```c#
```qsharp
// Single-line comments start with //
@ -19,19 +20,20 @@ Q# is a high-level domain-specific language which enables developers to write qu
// The most important part of quantum programs is qubits.
// In Q# type Qubit represents the qubits which can be used.
// This will allocate an array of two new qubits as the variable qs.
using (qs = Qubit[2]) {
operation QuantumDataTypes() : Unit {
use qs = Qubit[2];
// The qubits have internal state that you cannot access to read or modify directly.
// You can inspect the current state of your quantum program
// if you're running it on a classical simulator.
// Note that this will not work on actual quantum hardware!
DumpMachine();
Std.Diagnostics.DumpMachine();
// If you want to change the state of a qubit
// you have to do this by applying quantum gates to the qubit.
H(qs[0]); // This changes the state of the first qubit
// from |0⟩ (the initial state of allocated qubits)
// to (|0⟩ + |1⟩) / sqrt(2).
H(qs[0]); // This changes the state of the first qubit
// from |0⟩ (the initial state of allocated qubits)
// to (|0⟩ + |1⟩) / sqrt(2).
// qs[1] = |1⟩; - this does NOT work, you have to manipulate a qubit by using gates.
// You can apply multi-qubit gates to several qubits.
@ -58,96 +60,101 @@ using (qs = Qubit[2]) {
/////////////////////////////////////
// 2. Classical data types and operators
// Numbers in Q# can be stored in Int, BigInt or Double.
let i = 1; // This defines an Int variable i equal to 1
let bi = 1L; // This defines a BigInt variable bi equal to 1
let d = 1.0; // This defines a Double variable d equal to 1
function ClassicalDataTypes() : Unit {
// Numbers in Q# can be stored in Int, BigInt or Double.
let i = 1; // This defines an Int variable i equal to 1
let bi = 1L; // This defines a BigInt variable bi equal to 1
let d = 1.0; // This defines a Double variable d equal to 1
// Arithmetic is done as expected, as long as the types are the same
let n = 2 * 10; // = 20
// Q# does not have implicit type cast,
// so to perform arithmetic on values of different types,
// you need to cast type explicitly
let nd = IntAsDouble(2) * 1.0; // = 20.0
// Arithmetic is done as expected, as long as the types are the same
let n = 2 * 10; // = 20
// Q# does not have implicit type cast,
// so to perform arithmetic on values of different types,
// you need to cast type explicitly
let nd = Std.Convert.IntAsDouble(2) * 1.0; // = 20.0
// Boolean type is called Bool
let trueBool = true;
let falseBool = false;
// Boolean type is called Bool
let trueBool = true;
let falseBool = false;
// Logic operators work as expected
let andBool = true and false;
let orBool = true or false;
let notBool = not false;
// Logic operators work as expected
let andBool = true and false;
let orBool = true or false;
let notBool = not false;
// Strings
let str = "Hello World!";
// Strings
let str = "Hello World!";
// Equality is ==
let x = 10 == 15; // is false
// Equality is ==
let x = 10 == 15; // is false
// Range is a sequence of integers and can be defined like: start..step..stop
let xi = 1..2..7; // Gives the sequence 1,3,5,7
// Range is a sequence of integers and can be defined like: start..step..stop
let xi = 1..2..7; // Gives the sequence 1,3,5,7
// Assigning new value to a variable:
// by default all Q# variables are immutable;
// if the variable was defined using let, you cannot reassign its value.
// Assigning new value to a variable:
// by default all Q# variables are immutable;
// if the variable was defined using let, you cannot reassign its value.
// When you want to make a variable mutable, you have to declare it as such,
// and use the set word to update value
mutable xii = true;
set xii = false;
// When you want to make a variable mutable, you have to declare it as such,
// and use the set word to update value
mutable xii = true;
set xii = false;
// You can create an array for any data type like this
let xiii = new Double[10];
// You can create an array for any data type like this
let xiii = [0.0, size = 10];
// Getting an element from an array
let xiv = xiii[8];
// Getting an element from an array
let xiv = xiii[8];
// Assigning a new value to an array element
mutable xv = new Double[10];
set xv w/= 5 <- 1;
// Assigning a new value to an array element
mutable xv = [0.0, size = 10];
set xv w/= 5 <- 1.0;
}
/////////////////////////////////////
// 3. Control flow
// If structures work a little different than most languages
if (a == 1) {
// ...
} elif (a == 2) {
// ...
} else {
// ...
}
operation ControlFlow() : Unit {
let a = 1;
// If expressions support a true branch, elif, and else.
if (a == 1) {
// ...
} elif (a == 2) {
// ...
} else {
// ...
}
use qubits = Qubit[2];
// Foreach loops can be used to iterate over an array
for (qubit in qubits) {
X(qubit);
}
// For loops can be used to iterate over an array
for qubit in qubits {
X(qubit);
}
// Regular for loops can be used to iterate over a range of numbers
for (index in 0 .. Length(qubits) - 1) {
X(qubits[index]);
}
// Regular for loops can be used to iterate over a range of numbers
for index in 0..Length(qubits) - 1 {
X(qubits[index]);
}
// While loops are restricted for use in classical context only
mutable index = 0;
while (index < 10) {
set index += 1;
}
// While loops are restricted for use in classical context only
mutable index = 0;
while (index < 10) {
set index += 1;
}
// Quantum equivalent of a while loop is a repeat-until-success loop.
// Because of the probabilistic nature of quantum computing sometimes
// you want to repeat a certain sequence of operations
// until a specific condition is achieved; you can use this loop to express this.
repeat {
// Your operation here
let success_criteria = true;
// Quantum equivalent of a while loop is a repeat-until-success loop.
// Because of the probabilistic nature of quantum computing sometimes
// you want to repeat a certain sequence of operations
// until a specific condition is achieved; you can use this loop to express this.
repeat {
// Your operation here
} until (success_criteria) // This could be a measurement to check if the state is reached
fixup {
// Resetting to the initial conditions, if required
}
}
until (success criteria) // This could be a measurement to check if the state is reached
fixup {
// Resetting to the initial conditions, if required
}
/////////////////////////////////////
// 4. Putting it all together
@ -161,7 +168,7 @@ operation ApplyXGate(source : Qubit) : Unit {
// adjoint and controlled variants of it.
// The easiest way to do that is to add "is Adj + Ctl" after Unit.
// This will tell the compiler to generate the variants automatically.
operation ApplyXGateCA (source : Qubit) : Unit is Adj + Ctl {
operation ApplyXGateCA(source : Qubit) : Unit is Adj + Ctl {
X(source);
}
@ -169,20 +176,21 @@ operation ApplyXGateCA (source : Qubit) : Unit is Adj + Ctl {
// To run Q# code, you can put @EntryPoint() before the operation you want to run first
@EntryPoint()
operation XGateDemo() : Unit {
using (q = Qubit()) {
ApplyXGate(q);
}
use q = Qubit();
ApplyXGate(q);
}
// Here is a simple example: a quantum random number generator.
// We will generate a classical array of random bits using quantum code.
@EntryPoint()
operation QRNGDemo() : Unit {
mutable bits = new Int[5]; // Array we'll use to store bits
using (q = Qubit()) { // Allocate a qubit
for (i in 0 .. 4) { // Generate each bit independently
// Callables (functions or operations) named `Main` are used as entry points.
operation Main() : Unit {
mutable bits = [0, size = 5]; // Array we'll use to store bits
use q = Qubit();
{
// Allocate a qubit
for i in 0..4 {
// Generate each bit independently
H(q); // Hadamard gate sets equal superposition
let result = M(q); // Measure qubit gets 0|1 with 50/50 prob
let bit = result == Zero ? 0 | 1; // Convert measurement result to integer
@ -196,9 +204,6 @@ operation QRNGDemo() : Unit {
## Further Reading
The [Quantum Katas][1] offer great self-paced tutorials and programming exercises to learn quantum computing and Q#.
The Quantum Katas ([repo](https://github.com/microsoft/qsharp/tree/main/katas) [hosted tutorials](https://quantum.microsoft.com/en-us/tools/quantum-katas) offer great self-paced tutorials and programming exercises to learn quantum computing and Q#.
[Q# Documentation][2] is official Q# documentation, including language reference and user guides.
[1]: https://github.com/microsoft/QuantumKatas
[2]: https://docs.microsoft.com/quantum/
[Q# Documentation](https://docs.microsoft.com/quantum/) is official Q# documentation, including language reference and user guides.