Editing Quantum channel (section)

{{Short description|Foundational object in quantum communication theory}}
{{More footnotes needed|date=December 2024}}
In [[quantum information theory]], a '''quantum channel''' is a communication channel that can transmit [[quantum information]], as well as classical information.  An example of quantum information is the general dynamics of a [[qubit]].  An example of classical information is a text document transmitted over the [[Internet]].

Terminologically, quantum channels are [[completely positive]] (CP) trace-preserving maps between spaces of operators.  In other words, a quantum channel is just a [[quantum operation]] viewed not merely as the [[reduced dynamics]] of a system but as a pipeline intended to carry quantum information.  (Some authors use the term "quantum operation" to include trace-decreasing maps while reserving "quantum channel" for strictly trace-preserving maps.<ref name="weedbrook">{{Cite journal | doi=10.1103/RevModPhys.84.621| title=Gaussian quantum information| year=2012| last1=Weedbrook| first1=Christian| last2=Pirandola| first2=Stefano| last3=García-Patrón| first3=Raúl| last4=Cerf| first4=Nicolas J.| last5=Ralph| first5=Timothy C.| last6=Shapiro| first6=Jeffrey H.| last7=Lloyd| first7=Seth| journal=Reviews of Modern Physics| volume=84| issue=2| pages=621–669| arxiv=1110.3234| bibcode=2012RvMP...84..621W| s2cid=119250535}}</ref>)