The quantum controlled-NOT (CNOT) gate is a prototypical two-qubit quantum logic gate that provides the basic controlled logic for a set of gates for universal quantum computation. It has been shown that parity checking devices can be used to construct CNOT gates, and the fidelity of a CNOT operation is highly constrained by the fidelity of parity detection with this strategy. In this paper, a scheme to implement a CNOT operation on two stationary electron spins confined in quantum dots (QDs) inside double-sided optical microcavities is presented, based on the faithful parity detection achieved by a heralded and robust two-electron-spin quantum nondemolition (QND) parity detector. The QND parity detector is considerably different from previous implementations and experimentally more realizable, and works in the heralded and repeat-until-success fashion with robust fidelity, which enables our CNOT gate to be implemented deterministically with unity fidelity. Moreover, based on the features of the QND parity detector, a complete Bell-state analysis on two QD-confined electron spins can be realized without wrong judgment or any destruction of the analyzed entangled state. The efficiency of parity detection is also discussed by considering currently achievable system parameters.

中文翻译：

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基于忠实的量子非爆破奇偶性检测的量子点受限电子自旋的确定性CNOT门和完整的贝尔状态分析仪

量子受控NOT（CNOT）门是典型的两量子位量子逻辑门，它为通用量子计算的一组门提供基本的受控逻辑。已经表明，奇偶校验装置可以用来构造CNOT门，并且用这种策略的奇偶校验检测的保真度在很大程度上限制了CNOT操作的保真度。本文提出了一种基于对双电子自旋量子的稳健检测实现的忠实奇偶校验检测的方案，该方案用于对双面光学微腔内的量子点（QD）内的两个固定电子自旋实施CNOT操作。不可拆卸（QND）奇偶校验检测器。QND奇偶校验检测器与以前的实现有很大不同，并且在实验上更易于实现，并以可靠的保真度以预告和重复直到成功的方式工作，这使我们的CNOT门能够确定性地实现保真度。而且，基于QND奇偶检测器的特征，可以实现对两个QD限制的电子自旋的完整贝尔状态分析，而不会错误判断或分析的纠缠态发生任何破坏。还通过考虑当前可实现的系统参数来讨论奇偶校验检测的效率。