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arXiv 1706.07464quant-phmath.QA
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偏振模色散量子信道的有效纠缠蒸馏

Efficient Entanglement Distillation for Quantum Channels with Polarization Mode Dispersion

Liangzhong Ruan, Brian T. Kirby, Michael Brodsky, Moe Z. Win

摘要:

由远程网络节点共享的量子纠缠在分布式计算、密码学和传感等领域具有广阔的应用前景。然而,由于光纤中的各种退相干机制,通过光纤路由分配高质量的纠缠可能是具有挑战性的。特别地,光纤中的主要偏振退相干机制之一是偏振模色散(PMD),其是由系统中随机变化的双折射引起的光脉冲的失真。为了减轻纠缠粒子的退相干效应,人们提出了量子纠缠蒸馏(QED)算法。有一类特殊的算法,即递归QED算法,因为它对所涉及的量子线路的大小和粒子纠缠的初始质量都有相对宽松的要求而脱颖而出。然而,由于所需的粒子数量随着蒸馏轮数呈指数增长,因此有效的递归算法需要快速收敛。我们提出了一个递归QED算法设计的光子量子比特对PMD退化的通道。我们提出的算法实现了最佳的保真度以及最佳的成功概率(条件是实现最佳保真度)在每一轮蒸馏。最佳保真度的实现提高了从线性到二次的蒸馏轮次的保真度的收敛速度,因此显著减少了蒸馏轮次的数量。结合最佳成功概率的实现,该算法提供了一种有效的方法来分配纠缠态的高保真度通过光纤。

英文摘要:

Quantum entanglement shared by remote network nodes serves as a valuable resource for promising applications in distributed computing, cryptography, and sensing. However, distributing entanglement with high-quality via fiber optic routes could be challenging due to the various decoherence mechanisms in fibers. In particular, one of the primary polarization decoherence mechanisms in optical fibers is polarization mode dispersion (PMD), which is the distortion of optical pulses by randomly varying birefringences in the system. To mitigate the effect of decoherence in entangled particles, quantum entanglement distillation (QED) algorithms have been proposed. One particular class, the recurrence QED algorithms, stands out because it has relatively relaxed requirements on both the size of the quantum circuits involved and on the initial quality of entanglement in particles. However, because the number of particles required grows exponentially with the number of rounds of distillation, an efficient recurrence algorithm needs to converge quickly. We present a recurrence QED algorithm designed for photonic qubit pairs affected by PMD-degraded channels. Our proposed algorithm achieves the optimal fidelity as well as the optimal success probability (conditional on the optimal fidelity being achieved) in every round of distillation. The attainment of optimal fidelity improves the convergence speed of fidelity with respect to the rounds of distillation from linear to quadratic, and hence significantly reduces the number of distillation rounds. Combined with the fact that the optimal success probability is achieved, the proposed algorithm provides an efficient method to distribute entangled states with high fidelity via optic fibers.

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