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diff --git a/qsharp.html.markdown b/qsharp.html.markdown new file mode 100644 index 00000000..b4a55d14 --- /dev/null +++ b/qsharp.html.markdown @@ -0,0 +1,192 @@ +--- +language: Q# +contributors: + - ["Vincent van Wingerden", "https://github.com/vivanwin"] + - ["Mariia Mykhailova", "https://github.com/tcNickolas"] +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. + +This is the new outline +```C# +// Single-line comments start with // + +///////////////////////////////////// +// 1. Quantum data types and operators + +// 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]) { + + // 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(); + + // If you want to change the state of a qubit, you have to do this by applying quantum gates to the qubit. + H(q[0]); // This changes the state of the first qubit from |0⟩ (the initial state of allocated qubits) to (|0⟩ + |1⟩) / sqrt(2). + // q[1] = |1⟩; - this does NOT work, you have to manipulate a qubit by using gates. + + // You can apply multi-qubit gates to several qubits. + CNOT(qs[0], qs[1]); + + // You can also apply a controlled version of a gate: a gate that is applied if all control qubits are in |1⟩ state. + // The first argument is an array of control qubits, the second argument is the target qubit. + Controlled Y([qs[0]], qs[1]); + + // If you want to apply an anti-controlled gate (a gate that is applied if all control qubits are in |0⟩ state), you can use a library function. + ApplyControlledOnInt(0, X, [qs[0]], qs[1]); + + // To read the information from the quantum system, you use measurements. + // Measurements return a value of Result data type: Zero or One. + // You can print measurement results as a classical value. + Message($"Measured {M(qs[0])}, {M(qs[1])}"); +} + + +///////////////////////////////////// +// 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 + +// 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 + +// 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; + +// Strings +let str = "Hello World!"; + +// 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 + +// 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; + +// You can create an array for any data type like this +let xiii = new Double[10]; + +// 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; + + +///////////////////////////////////// +// 3. Control flow + +// If structures work a little different than most languages +if (a == 1) { + // ... +} elif (a == 2) { + // ... +} else { + // ... +} + +// Foreach 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]); +} + +// 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 +} +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 + +// Q# code is written in operations and functions +operation ApplyXGate(source : Qubit) : Unit { + X(source); +} + +// If the operation implements a unitary transformation, you can define +// 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 { + X(source); +} + +// Now you can call Adjoint ApplyXGateCA and Controlled ApplyXGateCA. + + +// 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); + } +} + +// 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 + H(q); // Apply Hadamard gate to prepare equal superposition + let result = M(q); // Measure the qubit to get Zero or One with 50/50 probability + let bit = result == Zero ? 0 | 1; // Convert measurement result to an integer + set bits w/= i <- bit; // Write generated bit to an array + } + } + Message($"{bits}"); // Print the result +} +``` + + +## Further Reading + +The [Quantum Katas][1] 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/
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