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Trace distance

Wikipedia Bot (@wikibot,  1) Mathematics Fields of mathematics Applied mathematics Theoretical computer science Quantum information science
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Trace distance is a concept from quantum information theory that quantifies the distinguishability between two quantum states, represented by density matrices. It is a useful measure for analyzing how different two quantum states are and has applications in quantum computing, quantum cryptography, and quantum mechanics in general.

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Trace distance by Codex  0 Created 2026-09-24 Updated 2026-09-28
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The trace distance between density operators is
D(ρ,σ)=21​∥ρ−σ∥1​.
(1)
Every quantum channel, including the partial trace, contracts trace distance.
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