What does decoherence mean?
Decoherence is the process by which a quantum system ceases to behave quantum-mechanically and starts behaving classically, as a result of unavoidable interaction with its surrounding environment. When a particle or qubit becomes entangled with air molecules, photons, or other external influences, the delicate phase relationships that allow it to exist in multiple states at once are rapidly destroyed, leaving only an ordinary probability mixture. First articulated as a concept in the 1970s and 1980s through work by physicists such as H. Dieter Zeh and Wojciech Zurek, decoherence is now considered central to understanding the quantum-to-classical transition — why we never see everyday objects in superposition. It also poses the chief practical obstacle to building quantum computers, since computation depends on preserving coherence long enough to perform operations. The term appears mainly in scientific literature, where phrases such as 'quantum decoherence' and 'decoherence time' are standard.
nounThe process by which a quantum system loses its coherent quantum behaviour through interaction with its environment, causing superposed states to decay into ordinary classical mixtures. It is regarded as the principal mechanism explaining why quantum superpositions are not observed in everyday macroscopic objects.
- (physics) The loss of quantum coherence in a system due to entanglement with its environment, converting superpositions into classical statistical mixtures.
"Decoherence destroys the delicate superposition of the qubit within microseconds, long before any measurement is made."
"Researchers must isolate the processor from thermal noise because even stray electromagnetic fields accelerate decoherence."
"The decoherence timescale of trapped ions can extend to several seconds, making them attractive candidates for quantum memory."
Rarely used in the plural; 'decoherence' is normally treated as an uncountable mass noun referring to the process in general.
"The paper compares decoherences arising from different environmental models."
Decoherence is why Schrödinger's cat is never both alive and dead in practice — the universe itself constantly 'measures' quantum systems by letting them leak information into their surroundings.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of decoherence
Decoherence derives from the prefix 'de-' combined with 'coherence', which traces back through French to the Latin verb 'cohaerere', meaning 'to stick together' or 'to cling', formed from 'com-' ('together') and 'haerere' ('to adhere'). The word emerged in twentieth-century physics as scientists needed a name for the reverse of coherence: the falling-apart of unified quantum states into classical ones. Its cognates include 'cohere', 'coherent', 'incoherent', and 'adhere', all descendants of the same Latin root 'haerere'.
How decoherence is actually used
A technical term used almost exclusively in physics, particularly quantum mechanics and quantum computing; it is rare outside scientific writing and carries no informal or figurative use. Plural 'decoherences' exists but is uncommon.
Easily confused with decoherence
Incoherence means a lack of logical connection or clarity (as in speech or thought), while decoherence specifically denotes the physical process by which quantum systems lose their coherent superposition.