Completely positive channels and environment assumptions
Research context
postgraduate concept · established · As of 2026-10-10
A quantum channel Φ(ρ)=Σ_kK_kρK_k† with Σ_kK_k†K_k=I remains positive when extended by an identity map on an arbitrary ancilla.
Key knowledge
A quantum channel Φ(ρ)=Σ_kK_kρK_k† with Σ_kK_k†K_k=I remains positive when extended by an identity map on an arbitrary ancilla. This complete positivity is stronger than positivity on isolated inputs. A fixed unitary interaction with an initially uncorrelated environment and subsequent partial trace supplies such a channel.
Values and equations
Φ(ρ)=Σ_kK_kρK_k†; Σ_kK_k†K_k=I
- Φ
- Trace-preserving completely positive map
- K_k
- Dimensionless Kraus operators
- ρ,I
- Density matrix and identity
Conditions and scope
- Finite-dimensional channel acting on all allowed system states; Kraus representations are not unique.
- Initially correlated system–environment assignments can restrict the allowed input domain. Do not infer an unrestricted CPTP reduced map from every correlated preparation.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Inspected §§3.1.2, 3.2.1, 3.2.4, 3.2.6, 3.5 and 3.6: probabilities, operations, complete positivity, semigroups and coloured noise; source check dated 2026-10-10. Scope is limited to the cited statements, equations and assumptions, not the whole publication.
2026-10-10 · Author source inspection of the displayed claim, model assumptions and equations; independent exact-content and branch-inventory review is a separate gate. Contemporary status is a dated snapshot, not a promise of ongoing monitoring.
Entry details
Permanent link to this entry ↗- Record identity
- research-physics-cptp-channels
- Revision
- research.1
- Structured reference record
- Postgraduate & research reference