Qubit.NET

🧠 C# Quantum Computing Simulation Library

Qubit.NET is a lightweight quantum circuit simulation library written in C#. It allows users to simulate quantum circuits up to 30 qubits, initialize qubits, apply common quantum gates, and measure results — all using a classical computer. Perfect for learning, prototyping, or integrating quantum logic into .NET applications.

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✅ Requirements

• .NET 6.0 or newer
• System.Numerics (for complex numbers — included in .NET)

📥 Setup

Clone or download the repository:

git clone https://github.com/InfoTCube/Qubit.Net.git
cd Qubit.NET

Add the project to your solution or include the .cs files (QuantumCircuit.cs, QuantumGates.cs, etc.) in your C# project.

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🚀 Quick Start

using Qubit.Net;

//qubits are created in 0 state
var qc = new QuantumCircuit(2);

// Apply Hadamard to qubit 0
qc.H(0);

// Apply CNOT (qubit 0 → control, qubit 1 → target)
qc.CNOT(0, 1);

// Draw a circuit
qc.Draw();

// Measure full state
Console.WriteLine($"Measured: {qc.Measure()}"); // Possible: 00 or 11

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🧰 Features

🧩 Qubit Initialization

You can initialize any qubit to one of the predefined basis states:

• |0⟩ → State.Zero
• |1⟩ → State.One
• |+⟩ → State.Plus
• |−⟩ → State.Minus

qc.Initialize(0, State.Minus);

or in any custom state

qc.Initialize(0, new Complex(1, 1), new Complex(2, 2));

⚠️ Initialization can only be done before any gate is applied to that qubit.
This is internally tracked using a private _isQubitModified array.

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🌀 Gate Application

Qubit.NET includes several built-in quantum gates:

✅ Single-Qubit Gates

Method	Description
I(q)	Identity
H(q)	Hadamard
X(q)	Pauli-X (NOT)
Y(q)	Pauli-Y
Z(q)	Pauli-Z
S(q)	Phase gate (√Z)
Sdag(q)	Conjugate transpose of S (S†)
T(q)	T gate (fourth root of Z)
Tdag(q)	Conjugate transpose of T (T†)
Rx(q, θ)	Rotation around X-axis by angle θ
Ry(q, θ)	Rotation around Y-axis by angle θ
Rz(q, θ)	Rotation around Z-axis by angle θ
SX(q)	Square-root of Pauli-X (√X)
SY(q)	Square-root of Pauli-Y (√Y)
SZ(q)	Square-root of Pauli-Z (√Z), aka S gate
U3(q, θ, φ, λ)	General single-qubit rotation gate

qc.H(0);
qc.X(1);

✅ Two-Qubit Gates

Method	Description
CNOT(c, t)	Controlled-NOT gate
CY(c, t)	Controlled-Y gate
CZ(c, t)	Controlled-Z gate
CH(c, t)	Controlled-Hadamard gate
CRx(c, t, θ)	Controlled-Rx gate
CRy(c, t, θ)	Controlled-Ry gate
CRz(c, t, θ)	Controlled-Rz gate
CU3(c, t, θ, φ, λ)	Controlled-U3 gate
SWAP(q1, q2)	SWAP gate (exchanges qubits)

qc.CNOT(0, 1);

✅ Three-Qubit Gates

Method	Description
Toffoli(c1, c2, t)	Toffoli (CC-NOT) gate
Fredkin(c, t1, t2)	Fredkin (C-SWAP) gate

qc.Toffoli(0, 1, 2);
qc.Fredkin(0, 1, 2);

✅ Custom Gate Support

You can custom gates for 1-4 qubits. Remember that matrix must be a square matrix of size 2^n x 2^n, where n is number of qubits involved. The matrix must be unitary — 𝑈†𝑈 = 𝐼

// Equivalent to CNOT(0, 1)

var cx = new Complex[,]
{
    { 1, 0, 0, 0 },
    { 0, 1, 0, 0 },
    { 0, 0, 0, 1 },
    { 0, 0, 1, 0 }
};

qc.Custom(cx, 0, 1);

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📏 Measurement

Measure the entire quantum system and get a classical bitstring (e.g. "00", "11"). You can get one result using basic vector state real-time simulator. You can also perform partial measurements to observe only selected qubits, yielding a shorter bitstring corresponding to the measured subset - the bits in the result are ordered exactly as the qubit indices are listed in the argument.

string result = qc.Measure();

string result = qc.Measure(0, 2);

The measurement collapses the quantum state probabilistically based on the amplitudes.

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⚙️ Simulation

The Simulator class provides functionality to simulate quantum circuits and measure the results. It allows you to run a quantum circuit multiple times and analyze the measurement outcomes. It returns an array of measurments for each qc.Measure()

Example:

QuantumCircuit qc = new QuantumCircuit(2);
qc.H(0);
qc.CNOT(0, 1);
qc.Measure();

string results = Simulator.Run(qc, 1000)[0].GetStringResult();
Console.WriteLine(results);

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🎲 Randomness source

Qubit.NET uses a pluggable randomness system through the IRandomSource interface. By default, it uses a pseudo-random generator (PseudoRandomSource). You can swap this out for your custom implementation.

using Qubit.NET.Utilities;

public class FixedRandomSource : IRandomSource
{
    public double NextDouble() => 0.42; // Always returns the same value
}

Then you can use it in QuantumCircuit:

QuantumCircuit qc = new QuantumCircuit(2);
qc.RandomSource = new FixedRandomSource();

📌 Future Roadmap

• Entanglement entropy measurements
• Noise simulation (decoherence, damping)
• Circuit export in QASM

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💡 Contributions

Pull requests, suggestions, and feature requests are welcome!
Feel free to fork and extend the library.

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👤 Author

Created by Tymoteusz Marzec
Find me on GitHub: @InfoTCube