Entangled qubits transported through space is a key element in many prospective quantum information systems, from long-distance quantum communication to large modular quantum processors. The moving qubits are decohered by time- and space-dependent noises with finite extent of correlations. Since the qubit paths are interrelated, the phase fluctuations experienced by the qubits exhibit peculiar correlations, which are difficult to analyze with the conventional theory of random processes. We propose an approach to this problem based on the concept of trajectories on random sheets. We establish its efficacy with a specific example of the electron spins shuttled in semiconductor structures, and derive explicit solutions, revealing the role of unusual noise correlations. We also demonstrate how the analysis of noise correlations can enhance the shuttling fidelity, by studying transport of two entangled spins encoding a logical qubit. The proposed approach enabled us to specify the favorable conditions for this encoding, and find a particularly beneficial shuttling regime. We also describe application of this approach to other shuttling scenarios, and explain its utility for analysis of other types of systems, such as atomic qubits and photons in quantum networks.
Decoherence of Einstein-Podolsky-Rosen pairs in a noisy Andreev entangler
研究了量子噪声对非定域库珀对在Andreev纠缠器中输运的影响。Andreev纠缠器是由一个s波超导体与两个小量子点共振耦合而成的，两个小量子点又与正常引线耦合。由于栅极引线中的有限电阻或耦合到点的任何电阻性引线电容的结果，驻留在两个点上的电子感受到电压波动，因此出现噪声。在理想的无噪声情况下，该设置提供了移动和非局域自旋纠缠电子的可靠来源，并且传输由两粒子Breit-Wigner共振主导，其允许两个自旋纠缠电子以相同能量注入到不同的引线中[P. Recher，E. V. Sukhorukov和D. Loss，Phys.Rev.B63，165314（2001）]。我们试图重新审视这些非本地的库珀对的运输，以及这样的Andreev纠缠的效率时，包括量子噪声（退相干）。
