# Decoherence The loss of quantum properties ([[Superposition]] and [[Entanglement]]) through interaction with the environment. The engineering enemy of [[Quantum Computing]]: every [[Qubit]] technology fights decoherence differently, and error rates from decoherence are what keeps current quantum computers from practical use. A qubit in superposition is exquisitely sensitive to its surroundings — thermal vibrations, electromagnetic noise, even stray photons can cause it to "decohere" into a classical state, losing the quantum information it carried. This is why superconducting qubits operate at temperatures colder than outer space (15 millikelvins), trapped ion qubits are isolated in vacuum chambers, and the entire field of [[Quantum Error Correction]] exists to detect and fix decoherence-induced errors. Coherence time — how long a qubit maintains its quantum state before decohering — is one of the key metrics for quantum hardware. Superconducting qubits maintain coherence for microseconds to milliseconds; trapped ions can last seconds to minutes. The practical consequence: a quantum computation must complete before its qubits decohere, creating a race between algorithm speed and hardware stability. ## See Also - [[Qubit]] — what decoheres - [[Superposition]] — what gets destroyed - [[Entanglement]] — what gets broken - [[Quantum Error Correction]] — the countermeasure - [[Technology Lexicon]] — the full vocabulary (quantum computing section)