反铁磁链中Dzyaloshinskii–Moriya机制驱动矢量自旋手征束缚态的研究

Dzyaloshinskii-Moriya(DM)相互作用驱动的矢量自旋手征态,能和声子发生耦合,具备非常丰富的物理现象.本论文以一维反铁磁链中自旋手征-声子耦合模型为基础,研究不同声子环境下,耦合强度对自旋手征动力学演化过程的影响规律.结果表明,对自旋S=1/2的系统,在不同的声子浴(sub-Ohmic(0 1))中,均会在非相干到相干自旋涨落过程中产生无能隙一级相变,其来源是自旋手征束缚态的形成.相变发生的临界自旋-声子耦合强度正比于自旋涨落大小,反比于系统德拜频率.当自旋-声子耦合强度超过其临界值时,自旋手征束缚态的产生将极大地抑制非相干自旋涨落.     

海森堡XYZ自旋链系统的热纠缠与局域量子不确定性研究

研究了热平衡温度,自旋交换相互作用,Dzyaloshinskii-Moriya(DM)相互作用及外加非一致性磁场对两比特海森堡XYZ自旋链量子系统的热纠缠与局域量子不确定度的影响,对比分析了并发度量子纠缠与局域量子不确定度描述自旋链系统量子关联的差别.结果表明自旋链系统的量子纠缠在热平衡温度,DM相互作用及外加磁场的非一致性参数的变化情况下均会出现纠缠突然死亡的再生现象,而自旋链系统的局域量子不确定度随着这些参数呈连续变化现象.并且,自旋交换相互作用,DM相互作用及外加横向磁场作用强度较小时,他们的变化对自旋链系统的量子纠缠与局域量子不确定度的影响有着明显的差别.     

Splitting an Arbitrary Three-Qubit State via a Five-Qubit Cluster State and a Bell State

Quantum information splitting (QIS) provides an idea for transmitting the quantum state through a classical channel and a preshared quantum entanglement resource. This paper presents a new scheme for QIS based on a five-qubit cluster state and a Bell state. In this scheme, the sender transmits the unknown three-qubit secret state to two agents by the quantum channel with the Bell basis measurement three times and broadcasts the measurement results to the agents through the classical channel. The agent who restores the secret state can successfully recover the initial information to be transmitted through the appropriate unitary operation with the help of the other party. Firstly, our scheme’s process can be accurately realized by performing the applicable Bell basis measurement, single-qubit measurement, and local unitary operation instead of a multiparticle joint measurement. The splitting process of quantum information is realized through a convenient operation. Secondly, compared with some previous schemes, the efficiency of the total scheme has been improved in principle, and the qubit consumption is reduced. Finally, the security of the quantum information splitting scheme is analyzed from the perspectives of external attacks and participant attacks. It is proved that our scheme can effectively resist internal participant attacks and external eavesdropper attacks.     

Memory Effects in High-Dimensional Systems Faithfully Identified by Hilbert–Schmidt Speed-Based Witness

A witness of non-Markovianity based on the Hilbert–Schmidt speed (HSS), a special type of quantum statistical speed, has been recently introduced for low-dimensional quantum systems. Such a non-Markovianity witness is particularly useful, being easily computable since no diagonalization of the system density matrix is required. We investigate the sensitivity of this HSS-based witness to detect non-Markovianity in various high-dimensional and multipartite open quantum systems with finite Hilbert spaces. We find that the time behaviors of the HSS-based witness are always in agreement with those of quantum negativity or quantum correlation measure. These results show that the HSS-based witness is a faithful identifier of the memory effects appearing in the quantum evolution of a high-dimensional system with a finite Hilbert space.     

水溶性ZnO量子点制备及其光学性质

利用3-巯丙基三乙氧基硅烷对ZnO进行表面修饰后沉积SiO2, 制备出水溶性SiO2包覆ZnO的量子点. 与直接采用正硅酸乙酯沉积包覆SiO2的ZnO量子点相比, 362 nm处的激子荧光发射峰的强度提高了将近4倍. 由于表面引入了巯基官能团, 量子点的水溶性明显提高, 稳定性增强, 即使在较高的盐浓度下也不会团聚. 通过改变条件, 制备出了发光波长在420 nm的蓝色荧光量子点.     

热囚禁离子系统中的两量子比特条件相位门的简单方案

提出了一个实现两离子量子逻辑门的简单方案。本方案使用了两个囚禁于线性阱的三能级离子。本方案不使用振动模作为数据总线,仅需要激光与离子的单个相互作用,因而相互作用时间变短,这点从退相干的角度看是很重要的,而且本方案对振动模的加热不敏感。     

Encapsulation of nanocrystals with responsive gels for spatial optical identification

A tripeptide (β-AspFF) gelator was designed and synthesised using solid-phase peptide synthesis. The as-prepared gelator formed a stable and clear multi-responsive gel in toluene solution. Encapsulating the quantum dots with β-AspFF effectively increased stability and antioxidisation ability which are beneficial for optical identification.