Getting Started

Installation

To get started with JuliVQC.jl, you need to install both JuliVQC.jl and its dependency QuantumCircuits.jl. Note that these packages are not part of Julia's official package registry, so you need to install them directly from GitHub.

Step 1: Create a Dedicated Julia Environment (Highly Recommended)

We strongly recommend creating a dedicated Julia environment for JuliVQC.jl to prevent dependency conflicts with other projects. Follow these steps:

1. Open the Julia REPL.

2. Navigate to your project folder (or any desired directory).

3. Activate a new environment:

   pkg> activate .

   This command creates and activates a new Julia environment in the current folder. A Project.toml file will be generated automatically.

Step 2: Install QuantumCircuits.jl

⚠️ Important: The required QuantumCircuits.jl package is a custom version different from the official Julia package of the same name. Follow the steps below to avoid conflicts.

Install the custom version of QuantumCircuits.jl from the correct GitHub repository using the following command:

pkg> add https://github.com/weiyouLiao/QuantumCircuits.jl

This ensures you're installing the required custom version and avoiding conflicts with the official package.

Step 3: Install JuliVQC.jl

Once the correct version of QuantumCircuits.jl is installed, proceed to install JuliVQC.jl from its GitHub repository:

pkg> add https://github.com/weiyouLiao/JuliVQC.jl

Step 4: Verify Installation

After completing the above steps, verify the installation by loading JuliVQC.jl in the Julia REPL:

using JuliVQC

If no errors occur, the installation was successful, and you're ready to start building variational quantum circuits!

Quick Start

Here’s how you can get started with JuliVQC.jl:

Example 1: Create a Two-Qubit Bell State

using JuliVQC
using QuantumCircuits

# Create a 2-qubit quantum state
state = StateVector(2)

# Define a quantum circuit
circuit = QCircuit()
push!(circuit, HGate(1))         # Add a Hadamard gate on qubit 1
push!(circuit, CNOTGate(1, 2))   # Add a CNOT gate between qubits 1 and 2

# Apply the circuit to the quantum state
apply!(circuit, state)

# Perform quantum measurement
i, prob = measure!(state, 1)
println("Probability of qubit 1 being in state $i is $prob.")

Example 2: Build and Optimize a Variational Quantum Circuit

Constructing a variational quantum circuit is just as easy:

using JuliVQC
using QuantumCircuits
using Zygote

L = 3  # Number of qubits
state = StateVector(L)

# Define a variational quantum circuit
circuit = QCircuit()
for i in 1:L
    push!(circuit, RzGate(i, rand(), isparas=true))
    push!(circuit, RyGate(i, rand(), isparas=true))
    push!(circuit, RzGate(i, rand(), isparas=true))
end

for depth in 1:2
    for i in 1:L-1
        push!(circuit, CNOTGate(i, i+1))
    end
    for i in 1:L
        push!(circuit, RzGate(i, rand(), isparas=true))
        push!(circuit, RxGate(i, rand(), isparas=true))
        push!(circuit, RzGate(i, rand(), isparas=true))
    end
end

# Define a target state
target_state = StateVector([0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.1, 0.0])

# Define a loss function
loss(c) = distance(target_state, c * state)

# Compute the gradient of the loss function
v = loss(circuit)
grad = gradient(loss, circuit)