Introduction to Quantum Physics with Qiskit

Quantum physics is a fascinating field that explores the behavior of matter and energy at the smallest scales. In this introduction, we'll explore some key concepts of quantum physics and demonstrate them using Qiskit, an open-source framework for quantum computing.

What is Quantum Physics?

Quantum physics, also known as quantum mechanics, is a fundamental theory in physics that describes nature at the smallest scales of energy levels of atoms and subatomic particles. It's a complex and often counterintuitive field, but it's also incredibly powerful and has led to many technological advancements.

Key Concepts in Quantum Physics

1. Superposition
2. Entanglement
3. Quantum Measurement

Let's explore these concepts with some Qiskit code examples.

Superposition

Superposition is a fundamental principle of quantum mechanics. It states that a quantum system can exist in multiple states simultaneously until it is measured.

from qiskit import QuantumCircuit, execute, Aer
 
# Create a quantum circuit with one qubit
qc = QuantumCircuit(1, 1)
 
# Apply a Hadamard gate to put the qubit in superposition
qc.h(0)
 
# Measure the qubit
qc.measure(0, 0)
 
# Execute the circuit on a simulator
simulator = Aer.get_backend('qasm_simulator')
job = execute(qc, simulator, shots=1000)
result = job.result()
 
# Get the measurement counts
counts = result.get_counts(qc)
print("Measurement results:", counts)

This code creates a single qubit, puts it in superposition using a Hadamard gate, and then measures it. You'll see that the measurement results are approximately 50% |0⟩ and 50% |1⟩.

Entanglement

Quantum entanglement is a phenomenon where two or more quantum particles are connected in such a way that the quantum state of each particle cannot be described independently.

from qiskit import QuantumCircuit, execute, Aer
 
# Create a quantum circuit with two qubits
qc = QuantumCircuit(2, 2)
 
# Apply Hadamard gate to the first qubit
qc.h(0)
 
# Apply CNOT gate to entangle the qubits
qc.cx(0, 1)
 
# Measure both qubits
qc.measure([0, 1], [0, 1])
 
# Execute the circuit on a simulator
simulator = Aer.get_backend('qasm_simulator')
job = execute(qc, simulator, shots=1000)
result = job.result()
 
# Get the measurement counts
counts = result.get_counts(qc)
print("Measurement results:", counts)

This code creates an entangled state known as a Bell state. You'll see that the measurement results are approximately 50% |00⟩ and 50% |11⟩, demonstrating the correlated nature of entangled qubits.

Quantum Measurement

In quantum mechanics, measurement plays a crucial role. The act of measurement causes the quantum state to collapse into one of its possible classical states.

from qiskit import QuantumCircuit, execute, Aer
from qiskit.visualization import plot_histogram
 
# Create a quantum circuit with one qubit
qc = QuantumCircuit(1, 1)
 
# Apply a rotation to the qubit
qc.ry(1.2, 0)
 
# Measure the qubit
qc.measure(0, 0)
 
# Execute the circuit on a simulator
simulator = Aer.get_backend('qasm_simulator')
job = execute(qc, simulator, shots=1000)
result = job.result()
 
# Get the measurement counts
counts = result.get_counts(qc)
print("Measurement results:", counts)
 
# Plot the results
plot_histogram(counts)

This code applies a rotation to a qubit and then measures it. The measurement results will depend on the rotation angle, demonstrating how measurement collapses the quantum state.

Conclusion

Quantum physics opens up a whole new world of possibilities in computing and technology. While these examples just scratch the surface, they provide a glimpse into the power and peculiarity of quantum mechanics. As you delve deeper into quantum physics and quantum computing, you'll discover even more fascinating phenomena and applications.