Salimian S, Tavassoly M K, Ghasemi M
Laser and Optics Group, Faculty of Physics, Yazd University, Yazd, Iran.
Sci Rep. 2023 Sep 28;13(1):16342. doi: 10.1038/s41598-023-43592-y.
In recent decades the entangled state generation is of great importance in the quantum information processing and technologies. In this paper, producing the distributed entangled state of superconducting (SC) qubits is considered using an entanglement swapping protocol in three successive stages. The SC qubit pairs [Formula: see text] with [Formula: see text], where each pair of the qubits has been placed on a separate chip, are initially prepared in maximally entangled states. The external magnetic fields on capacitively coupled pairs [Formula: see text] and [Formula: see text] are implemented for modulating the frequency of qubits. Then, the SC qubits [Formula: see text] and [Formula: see text] are converted into entangled states via operating proper measurements instead of Bell state measurement (which is generally a hard task). Finally, the distributed entangled state of target SC qubits [Formula: see text] can be obtained by applying external magnetic fields on qubits [Formula: see text] and via operating suitable measurements. This process is studied in the absence and presence of thermal decoherence effects. The concurrence, as a measure of entanglement between two target qubits, success probability of the distributed entangled states and the corresponding fidelities are evaluated, by which we find that the state of target SC qubits [Formula: see text] is converted to Bell state with maximum entanglement at some moments of time. Under appropriate conditions the maximum of success probability of the obtained states in each stage approaches 1. However, the maxima of concurrence and success probability gradually decrease due to the thermal noise as time goes on. Moreover, compelling amounts of fidelity, success probability and entanglement can be obtained for the achieved entangled states.
近几十年来，纠缠态的产生在量子信息处理和技术中具有极其重要的意义。本文考虑使用纠缠交换协议，分三个连续阶段来产生超导（SC）量子比特的分布式纠缠态。超导量子比特对[公式：见原文]，其中[公式：见原文]，且每对量子比特都放置在单独的芯片上，最初被制备为最大纠缠态。对电容耦合对[公式：见原文]和[公式：见原文]施加外部磁场，以调制量子比特的频率。然后，通过进行适当的测量而非贝尔态测量（这通常是一项艰巨的任务），将超导量子比特[公式：见原文]和[公式：见原文]转换为纠缠态。最后，通过对量子比特[公式：见原文]施加外部磁场并进行适当的测量，可以获得目标超导量子比特[公式：见原文]的分布式纠缠态。在有无热退相干效应的情况下对这一过程进行了研究。计算了作为两个目标量子比特之间纠缠度量的并发度、分布式纠缠态的成功概率以及相应的保真度，据此我们发现目标超导量子比特[公式：见原文]的状态在某些时刻会转换为具有最大纠缠的贝尔态。在适当条件下，每个阶段所获得状态的成功概率最大值接近1。然而，随着时间的推移，由于热噪声的影响，并发度和成功概率的最大值会逐渐降低。此外，对于所实现的纠缠态，可以获得相当可观的保真度、成功概率和纠缠量。
