基于非对称量子信道的非局域N-qubit受控幺正门的网络设计与优化  

Quantum networks for implementing effiently a nonlocal N-qubit controlled unitary gate via non-symmetric quantum channels: Designing and optimizing

作　　者：陈立冰[1] 路洪[1] 

机构地区：[1]佛山科学技术学院光电子与物理学系,佛山528000

出　　处：《中国科学：物理学、力学、天文学》2017年第12期36-46,共11页Scientia Sinica Physica,Mechanica & Astronomica

基　　金：广东省自然科学基金(编号:06029431)资助

摘　　要：本文提出在非对称量子信道辅助下有效地实现非局域N-qubit受控幺正门的局域操作方案.分别设计两个量子网络去实现该非局域门.方案一用(N–2)个对称的qubit-qubit Bell态和一个非对称的qubit-qudit Bell态作为量子信道.它利用qubit-qudit Bell态中qudit的(N–2)个附加能级将(N–1)个非局域控制态的多个计算基态"隐藏"起来,简化了该非局域门的操作.该方案的缺陷是,qudit的能级和所耗费的1-qudit门随N增加.在不改变网络功能的条件下,方案二用(N–1)个非对称的qubit-qutrit Bell态作为量子信道,对方案一进行了优化.该方案分别利用(N–1)个qutrit的第3能级仅将(N–1)个非局域控制态的某个计算基态"暴露"于随后的操作,进一步降低了网络的复杂度,提高了操控速度.值得注意的是,两个方案在不使用辅助系统的条件下所需的局域二体门仅为(3N–4)个.We show how a nonlocal N-qubit controlled unitary gate can be implemented locally and effectively by using non-symmetric quantum channels. We construct respectively two quantum networks for realizing conclusively this nonlocal quantum gate. The first one hires （N–2） symmetric qubit-qubit Bell states and a non-symmetric qubit-qudit Bell state as quantum channels. The basic idea of this scheme is to use （N–2） additional levels of this qudit to ＂hide＂ certain computational states of （N–1） nonlocal control states from the conditional dynamics, which results in an effective nonlocal N-qubit controlled unitary gate design. In this scheme, however, either the number of the additional levels or that of 1-qudit gates needs to increase with N. The other one can improve significantly the local implementation of this nonlocal gate if we harness （N–1） non-symmetric qubit-qutrit Bell states as quantum channels. This scheme uses respectively （N–1） qutrits’s additional levels to expose one and only one initial computational state of （N–1） nonlocal control states to the conditional dynamics. In comparison with the first one, the procedure is greatly simplified, and the total gate time is reduced. The fact that the quantum network that does the proposed implementation is built entirely of local single-body and two-body gates, and has only （3N–4） two-body gates is notable.

关 键 词：N能级量子系统 3能级量子系统 非局域N-qubit受控幺正门 量子网络 优化 

分 类 号：O413[理学—理论物理]