Qiskit Framework

Qiskit Framework

Qiskit is IBM's open-source SDK for quantum computing. It provides a programmatic abstraction for designing quantum circuits, compiling them for specific architectures, and executing them on simulators or physical QPUs.

Theoretical Foundation & Architecture

Quantum circuits in Qiskit are represented as DAGs (Directed Acyclic Graphs). A QuantumCircuit instance holds QuantumRegister and ClassicalRegister objects. Unitary operations (gates) manipulate the quantum state space $\mathbb{C}^{2^n}$, while measurements collapse the state onto the computational basis, recording outcomes in classical bits.

Actionable Execution

1. Initialization: Instantiate QuantumCircuit(n, m) with $n$ qubits and $m$ classical bits. All qubits initialize to $|0\rangle$.
2. Gate Application:
   • Apply single-qubit gates (e.g., qc.h(0), qc.rx(theta, 0)).
   • Apply entangling two-qubit gates (e.g., qc.cx(0, 1) for CNOT).
3. Measurement: Map quantum states to classical registers (qc.measure(qubit_index, bit_index)).
4. Execution: Transpile the circuit for a target backend and invoke run().

Execution Flow

%%{init: {"theme": "default", "flowchart": {"useMaxWidth": true}}}%%
flowchart TD
    A[Start] --> B[Initialize QuantumCircuit]
    B --> C[Allocate Quantum and Classical Registers]
    C --> D[Apply Unitary Gates]
    D --> E[Apply Entangling Operations]
    E --> F[Add Measurement Operations]
    F --> G[Transpile Circuit for Backend]
    G --> H[Execute on Simulator or QPU]
    H --> I[Analyze Results/Counts]
    I --> J[End]