Quantum channels and complete positivity
Research context
postgraduate concept · established · As of 2026-10-10
A physical channel on a subsystem is modeled by a completely positive trace-preserving map.
Key knowledge
A physical channel on a subsystem is modeled by a completely positive trace-preserving map. In finite dimensions it has a Kraus representation sum K-a rho K-a† with sum K-a† K-a=I. Complete positivity requires positivity even when the map acts on part of an entangled reference system; mere positivity is insufficient. The Kraus representation need not be unique.
Values and equations
N(rho)=sum_a K_a rho K_a†; sum_a K_a†K_a=I
- N
- Completely positive trace-preserving channel
- K_a
- Kraus operators
- rho
- Input density state
Conditions and scope
- The entry uses finite-dimensional input/output systems and a deterministic trace-preserving channel.
- A selected measurement outcome instead gives a trace-nonincreasing operation before normalization.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: CPTP/Kraus maps, unitary dilation, generalized measurements and reduced-state channels. 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-channels-cptp
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference