摘要:
量子信息技术主要基于量子纠缠，量子纠缠源作为重要的相干叠加态，其相干性很容易受到环境的影响而变得非常脆弱，甚至导致量子信息处理的失败。因此，全面揭示不同噪声环境和不同噪声信道下量子纠缠源演化规律，进而探寻抑制退相干的方法就显得至关重要。本文以量子信息最基本的单元-两比特纠缠对作为研究对象，实验上利用线性光学系统模拟了比特翻转和相移噪声(集体和非集体)，研究了纠缠源在不同噪声环境及单、双和混合噪声信道下保真度的变化规律。实验结果表明：对同一种噪声类型，当纠缠比特经过双通道噪声环境时，其纠缠特性破坏得快；当纠缠比特经过非集体环境时，其纠缠特性消失得快。对不同噪声类型比较，结果表明比特翻转噪声相对于相移噪声更容易破坏纠缠特性。所得结论对纠缠退相干的理论和实验研究具有重要的借鉴意义，同时对基于非线性光学系统的量子信息处理技术具有重要的应用价值。
Abstract:
Quantum information technology is mainly based on quantum entanglement. As an important coherent superposi-tion state, the coherence of quantum entanglement source is easily affected by environment and becomes fragile, which will lead to the failure of the quantum information processing. Thus, it is critical to reveal the evolutions of quantum entanglement source under different noisy environments and different noisy channels. Firstly, we experimentally prepare a high-fidelity two-bit entangled state by several technical methods. The fidelity observed for the state prepared in our experiment is 0.993 and the signal-to-noise ratio can reach up to 299. Then, we simulate the bit-flip noise and phase-shift noise (collective and non-collective) using the all-optical experimental setup. Finally, based on the entanglement qubit state, we experimentally study the evolutions of entanglement characteristic under different noisy environments and the single, double and mixed noisy channels. The experimental results show that for the same type of noise, the entanglement properties disappear fast when entangled qubit passes through dual channel noisy environment. The upper bounds of noise intensity to destroy the entanglement property are 0.25 and 0.26 for the single bit-flip noise and phase-shift noisy channels, respectively. The comparison between the two different kinds of noisy environments shows that the entan-glement properties disappear fast when entangled bit passes through non-collective environment. The upper bounds of noise intensity are 0.08 and 0.14 for non-collective bit-flip and phase-shift noise to destroy the entanglement property, while the noise intensities are 0.14 and 0.23 for collective bit-flip and phase-shift noise, respectively. For different kinds of noises, the results show that bit-flip noise is more likely to destroy the entanglement properties than the phase-shift. Our results have great significance for the theoretical and experimental studies of entanglement decoherence and have important application value for quantum information processing technology based on the nonlinear optical system.
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