Quantum entropy and the Holevo bound
Research context
postgraduate concept · established · As of 2026-10-10
Von Neumann entropy is −tr rho log2 rho and equals Shannon entropy of the density operator's eigenvalues.
Key knowledge
Von Neumann entropy is −tr rho log2 rho and equals Shannon entropy of the density operator's eigenvalues. For an ensemble {p-x,rho-x}, accessible classical mutual information from a measurement is bounded by chi=S(sum p-x rho-x)−sum p-x S(rho-x). Nonorthogonal states limit distinguishability. Entanglement and conditional quantum entropy produce behavior absent from ordinary classical conditional entropy; one formula cannot replace every quantum resource capacity.
Values and equations
I(X;Y_measurement)≤chi=S(rho_bar)−sum_x p_x S(rho_x)
- rho_bar
- Average density operator
- X
- Classical ensemble label
- Y_measurement
- Classical measurement outcome
- S
- Von Neumann entropy in bits
Conditions and scope
- The Holevo bound concerns classical labels encoded into a quantum ensemble and a subsequent measurement.
- The logarithm base is two, yielding bits; specify the ensemble and available side information.
Sources · 2
References
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Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: Qubits, density operators, ensembles, von Neumann entropy and no-cloning; Holevo bound, coherent information and regularized quantum capacity; entanglement assistance. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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- research-info-quantum-entropy-holevo
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- Postgraduate & research reference