No-relationship Between Impossibility of Faster-Than-Light Quantum Communication and Distinction of Ensembles with the Same Density Matrix  

作　　者：WANG Chuan LONG Gui-Lu SUN Yang 

机构地区：[1]Department of Physics and Key Laboratory for Quantum Information and Measurements, Tsinghua University, Beijing 100084, China [2]Key Laboratory for Atomic and Molecular NanoSciences, Tsinghua University, Beijing 100084, China [3]Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA

出　　处：《Communications in Theoretical Physics》2005年第4X期622-624,共3页理论物理通讯（英文版）

基　　金：国家重点基础研究发展计划(973计划)，the Hang-Tian Science Fund，高等学校博士学科点专项科研项目

摘　　要：It has been claimed in the literature that impossibility of faster-than-light quantum communication has an origin of indistinguishability of ensembles with the same density matrix. We show that the two concepts are not related.We argue that even with an ideal single-atom-precision measurement, it is generally impossible to produce two ensembles with exactly the same density matrix; or to produce ensembles with the same density matrix, classical communication is necessary. Hence the impossibility of faster-than-light communication does not imply the indistinguishability of ensembles with the same density matrix.

关 键 词：faster-than-light communication distinction of ensembles density matrix 

分 类 号：O431.2[机械工程—光学工程]