Hello Quantum World! – Writing and Running Your First Quantum Program from Start to Finish

H Hannan

Updated on:

Hello Quantum World! - Writing and Running Your First Quantum Program from Start to Finish
Back to The Qiskit Home Page

Introduction

Quantum computing represents one of the most transformative emerging technologies of our time. By leveraging exotic quantum mechanical phenomena like superposition, entanglement, and quantum parallelism, quantum computers promise exponential leaps in processing power compared to classical binary machines.

Superposition allows quantum bits or qubits to represent multiple states simultaneously. Entanglement links qubits in ways that defy classical physics. Parallelism then enables operating on these massive superposed states for certain tasks believed classically intractable.

Realizing this enormous potential requires mastering quantum programming techniques. In this comprehensive guide, we will cover everything involved in writing and executing your first quantum program using Qiskit – from environment setup to simulation, visualization and even running on real quantum chips!

Setting Up Your Qiskit Quantum Programming Environment

Before we can begin quantum coding, we need to configure our environment with Qiskit and its dependencies. Qiskit offers an open-source Python framework for working with quantum programs and hardware.

Installing Qiskit

The easiest way to install Qiskit is via the pip package manager. Ensure you have pip installed, then run:

pip install qiskit

This will handle installing Qiskit along with all its necessary dependencies like NumPy, SciPy, Matplotlib etc.

For alternative installation options, check out this easy-to-follow Setup Guide.

Importing Key Qiskit Modules

With Qiskit installed, we can now import the modules needed for quantum programming:

from qiskit import QuantumCircuit, execute, Aer
from qiskit.visualization import plot_histogram

This imports:

  • QuantumCircuit: Enables building quantum circuit diagrams.
  • execute: Allows running circuits on backends.
  • Aer: Provides simulator backends.
  • plot_histogram: Visualizes output histograms.

Later we will import additional functionality like transpile() and assemble() to compile circuits.

Constructing Your First Quantum Circuit in Qiskit

Now we can start building quantum circuits using Qiskit programming constructs. Qiskit represents quantum computations as circuits consisting of qubits, classical bits, and quantum operations. Let’s initialize the components of our first circuit.

Creating Quantum and Classical Registers

Qiskit circuits require:

  • Quantum registers – To hold qubits
  • Classical registers – To hold regular bits
qr = QuantumRegister(2) # 2 qubit quantum register
cr = ClassicalRegister(2) # 2 bit classical register

Registers are combined into a QuantumCircuit object:

circuit = QuantumCircuit(qr, cr) # Create circuit

Adding Quantum Gates and Operations

With registers defined, we can now add gates that manipulate the qubits:

circuit.h(qr[0]) # Apply Hadamard Gate to qubit 0
circuit.cx(qr[0], qr[1]) # Apply CX (CNOT) Gate
circuit.measure(qr, cr) # Quantum Measurement

The h gate puts a qubit into superposition. The cx gate entangles a control and target qubit. measure collapses the qubit state into a classical state.

We can also visualize the circuit using circuit.draw(). This outputs the quantum logic diagram. Feel free to experiment with adding more gates and qubits!

Simulating Quantum Circuits Using Qiskit Aer

To understand this quantum circuit’s behaviour before running it on real hardware, we will simulate it using Qiskit Aer, which provides high-performance simulators.

Compiling and Simulating Circuits

Qiskit requires two steps to simulate circuits – transpilation and assembly:

backend = Aer.get_backend('qasm_simulator') # Choose a simulator
compiled_circuit = transpile(circuit, backend) # Optimization
qobj = assemble(compiled_circuit) # Assembly

We then run the simulation:

result = backend.run(qobj).result()

Extracting and Visualizing Simulation Results

With the simulation complete, we can extract the results and visualize them:

counts = result.get_counts(circuit)
plot_histogram(counts)

This plots a histogram showing the probability distribution of qubit states at the end of the circuit. By inspecting these output states, we can understand how our circuit transformed an input state as expected.

Simulators thus allow iteratively developing and debugging quantum programs before running them on actual hardware. Once satisfied, we will deploy our code to a real quantum processor next!

Executing Your First Real Quantum Circuit

Once you have simulated your quantum circuit extensively, it’s time to run it on actual quantum hardware! We will leverage IBM Quantum services to deploy our program on a real chip.

Configuring IBM Quantum Experience

To access the quantum devices, we first configure IBM Quantum Experience:

from qiskit import IBMQ

IBMQ.load_account() # Load IBMQ account details
provider = IBMQ.get_provider('ibm-q') # Get provider
backend = provider.get_backend('ibmq_16_melbourne') # Pick device

Compiling and Executing Circuits on Real Chips

With the backend initialized, we compile and run our circuit:

job = execute(circuit, backend, shots=1024) # Execute circuit on backend
result = job.result() # Retrieve results
counts = result.get_counts(circuit) # Get histogram data

The shots argument enables sampling multiple runs to recover probabilistic qubit results. We set shots higher to improve accuracy.

Analyzing Results from Real Hardware

Finally, we can visualize the results just like with simulation:

plot_histogram(counts)

The histogram may differ more from ideal case due to real hardware noise. By comparing sim versus real results, we can fine-tune circuits to counter noise through error mitigation and other techniques.

Accessing real quantum systems provides invaluable practical quantum programming experience today. IBM Quantum services and other cloud platforms represent a profound democratization of quantum computing for education and research.

Where To Go From Here? Expanding Your Quantum Skills

Congratulations! In this guide you have accomplished the vital milestone of programming your first quantum circuit from start to finish – culminating in execution on a real quantum chip!

This marks just the beginning of your quantum journey. Some recommended next steps to build on these foundations include:

The most valuable way forward is to let curiosity guide your quantum adventures. Bring a passion for learning and use cases relevant to your interests. Quantum programming skills are in demand, and will only grow as the field matures.

Buckle up, the quantum era is here! With Qiskit powering your quantum development, a world of inspirational possibilities awaits. Step forward with your imagination to start shaping our quantum future today. The next breakthrough begins with you!

Leave a Comment