基于冷原子系统的量子纠缠态产生与存储

发布时间：2018-01-05 04:21

本文关键词：基于冷原子系统的量子纠缠态产生与存储　出处：《山西大学》2016年博士论文　论文类型：学位论文

【摘要】：量子中继器是量子信息中重要的组成环节。在量子网络中,脆弱的量子信息从发射方传递到接收方,不可避免的要经历退相干过程,其中包括光纤损耗和环境干扰。由此量子信息传递的直接距离被限制在约200km之内,而量子中继器就是用来扩展量子信息传递距离的重要仪器。一般量子中继包含量子纠缠交换,量子存储和量子纠缠纯化三个部分。其中量子纠缠的交换用来联结纠缠子区间,以避免长距离传输的光子数损耗,量子存储用来解决概率性事件带来的资源指数消耗,量子纠缠纯化用来解决退相干过程带来纠缠品质的下降。本论文的主要内容是基于冷原子系综的量子中继器的研究,其中包括以下几个方面的研究内容：(1)窄带纠缠光源的产生：利用自发拉曼散射的办法,在冷原子系综中同时产生两对光和原子的纠缠态,通过对其中的这两个光子进行Bell测量,我们将存储中的两个自旋波投影到一个Bell态上,形成一对偏振纠缠光子对的存储。在一段存储时间之后,可预言的读出一对偏振纠缠光子对,利用双光子量子态Tomography和Bell测量等方法验证了产生的纠缠光的品质。利用类似的实验方法,还可以实现三光子GHZ态的建立。这样,我们在实验上实现了窄带的纠缠光的制备。(2)任意偏振单光子存储：在冷原子系综上施加一个中等强度的轴向磁场,将原子的Zeeman简并态分离,经过光泵浦过程,建立两互相正交的磁不敏感态。利用电磁感应透明过程,将任意偏振的单光子量级信号光,存储为冷原子系综中的自旋波叠加态。利用自制的滤波系统(模清洁器等),对控制光进行高效的噪声抑制,对信号光进行高信噪比的滤波。实现了长存储寿命高保真度的量子存储。在4.5ms的存储时间,量子偏振态保真度为78.4%。(3)动力学退耦合延长量子信息在冷原子系综中的寿命：利用Raman双光子跃迁过程,对存储在冷原子系综中的自旋波叠加态施加CPMG序列的退耦合操控。量子过程保真度在8001μs的存储时间依然大于80%,相比于没有施加退耦合操控的存储寿命提高了3.4倍。
[Abstract]:Quantum repeater is an important part of quantum information. In quantum network, the fragile quantum information is transferred from the emitter to the receiver, and it is inevitable to undergo the process of decoherence. This includes optical fiber loss and environmental interference. The direct distance of quantum information transmission is limited to about 200 km. Quantum repeater is an important instrument to extend the transmission distance of quantum information. Generally quantum relay contains quantum entanglement exchange. Quantum storage and quantum entanglement purification, in which the exchange of quantum entanglement is used to link the entangled sub-region to avoid the loss of photon number in long distance transmission. Quantum storage is used to solve the resource exponent consumption caused by probabilistic events. Quantum entanglement purification is used to solve the degradation of entanglement quality caused by decoherence. The main content of this thesis is based on the research of quantum repeater with cold atom ensemble. It includes the following aspects: the generation of narrowband entangled light sources: using the method of spontaneous Raman scattering, the entangled states of two pairs of light and atoms are produced simultaneously in cold atomic ensemble. By Bell measurements of these two photons, we project the two spin waves onto a Bell state to form a pair of polarization-entangled photons, after a period of storage time. A pair of polarization-entangled photon pairs can be read out predictably. The quality of the generated entangled light is verified by two-photon quantum state Tomography and Bell measurements. Similar experimental methods are used. It is also possible to establish a three-photon GHZ state. We have experimentally realized the fabrication of narrow band entangled light. 2) arbitrary polarization single photon storage: applying a medium intensity axial magnetic field to the cold atomic system to separate the Zeeman states of atoms. Two mutually orthogonal magnetically insensitive states are established through the optical pumping process, and the arbitrary polarization of single-photon signal light is obtained by using the electromagnetic induction transparency process. It is stored as the superposition state of spin wave in the cold atomic ensemble. The noise suppression of the control light is carried out efficiently by using the self-made filter system (mode cleaner, etc.). The signal light is filtered with high signal-to-noise ratio (SNR). Quantum storage with long storage life and high fidelity is realized. The storage time is 4.5 Ms. The fidelity of quantum polarization state is 78.4%.) Kinetic decoupling prolongs the lifetime of quantum information in cold atomic ensemble: using Raman two-photon transition process. The decoupling operation of the CPMG sequence is applied to the spin wave superposition state stored in the cold atomic ensemble. The storage time of the quantum process fidelity at 8001 渭 s is still greater than 80%. The storage life is 3.4 times longer than that without decoupling control.
【学位授予单位】：山西大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O413

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