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Quantum 101What is a Qubit? Understanding the Building Block of Quantum Computing
By Dr. Sarah Chen 8 min read 5427 views 89
AI Summary
A qubit is the quantum equivalent of a classical bit. Unlike bits (0 or 1), qubits can exist in superposition — both states at once — enabling quantum computers to process vast possibilities simultaneously.
Introduction
A qubit (quantum bit) is the fundamental unit of quantum information. While a classical bit can be either 0 or 1, a qubit can exist in a superposition of both states simultaneously.
Classical vs Quantum Bits
A classical bit is like a light switch — it's either on or off. A qubit is more like a spinning coin — it's in a blend of both heads and tails until you stop it (measure it).
The Bloch Sphere
We visualize qubit states using the Bloch sphere, where:
- ▸The north pole represents |0⟩
- ▸The south pole represents |1⟩
- ▸Any point on the surface represents a superposition
Key Properties
- ▸Superposition: A qubit can be in both |0⟩ and |1⟩ simultaneously
- ▸Measurement: Observing a qubit collapses it to 0 or 1
- ▸Entanglement: Qubits can be correlated in ways classical bits cannot
Why It Matters
With n qubits, a quantum computer can represent 2ⁿ states simultaneously, enabling exponential speedups for certain problems.
qubit
basics
superposition
bloch-sphere
References
- • Nielsen & Chuang, Quantum Computation and Quantum Information
- • IBM Quantum Learning
- • Qiskit Textbook