Quantum Coherence: The Resource Behind Interference
Quantum coherence is the ability of a state to show interference. Where it comes from, how it is lost and why computing and sensing depend on it.
BasicsAlgorithmsHardwareError CorrectionCryptographyMachine LearningInformation TheoryPhysics & SimulationApplicationsIndustry & Careers
All Articles
Every explainer on QuantumExplainer.com, newest first. Use the pillars above to jump straight to a topic.
739 articles
Quantum Fidelity: How Close Two States Are
Fidelity measures how close two quantum states are. How it is computed and why it is used to judge gates, error correction and protocols.
Quantum Information Distance Between States
Measures of distance between quantum states and channels, such as trace distance, fidelity and diamond norm, and where each is used.
Quantum Shannon Theory: Coding for Quantum Channels
Quantum Shannon theory extends Shannon’s information theory to quantum channels: compression, capacities, coding and entanglement.
The Holevo Bound: How Much a Qubit Can Carry
The Holevo bound, proved by Alexander Holevo in 1973, limits how much classical information can be read from qubits. Its statement and consequences.
Quantum Relative Entropy as a Distinguishability Measure
Quantum relative entropy measures how distinguishable two states are and is never negative. Properties, uses and link to hypothesis testing.
Quantum Mutual Information Between Subsystems
Quantum mutual information measures total correlations between two subsystems, classical and quantum. Its definition, properties and uses.
Von Neumann Entropy and What It Counts
Von Neumann entropy extends Shannon entropy to quantum states via the density matrix. Its definition, properties and uses in quantum information.
Quantum Entropy: Measuring Uncertainty in a State
Quantum entropy measures uncertainty in a quantum state. Von Neumann entropy, its relation to classical entropy, and uses in physics and computing.
Error-Correcting Codes in Quantum Cryptography
How error-correcting codes are used in quantum cryptography, from reconciliation in QKD to codes that protect quantum states.
Quantum Network Security: Threats and Controls
Threats to network security from quantum computers and the controls available: QKD, post-quantum protocols and quantum hacking countermeasures.
Quantum Data Privacy: What Qubits Can Protect
What quantum technologies can and cannot do for data privacy: QKD, quantum-safe algorithms and the post-quantum migration challenge.