【作者】 王倩霞；

【导师】 吕燕伍；

【作者基本信息】 北京交通大学 ， 理论物理， 2010， 硕士

【摘要】 自旋压缩的研究受到广泛关注源于三方面的原因：海森堡不确定关系的普遍存在是量子测量器件精度提高的最根本障碍,如何抑制它对精度的影响有着巨大的应用前景；自旋压缩与量子纠缠的密切关系使得自旋压缩的研究对量子信息有着重要的意义；另外,量子纠缠是物理有待探索的基本问题之一,所以对自旋压缩的研究既有应用方面的意义,也有着基本理论方面的意义。本论文着重解决如下的问题：到目前为止无论是自旋压缩的定义还是判断标准都存在争议,就几种定义和判断标准在第二章作者提出了自己的看法；δJz是线性相互作用,不应对自旋压缩产生影响,所以这一项常被忽略,但有些情况下这一项确实存在,将这一项纳入哈密顿量进行计算时,由于对称性被破坏需要采用新的方法,而且这一项在某些情况下对自旋压缩的产生了影响,文中给出了合理的解释；时间关联函数表示二能级间的耦合,它是可以在实验中被观测的量,已发现一级关联函数与压缩系数之间有特定的关系,则可以利用这种关系将自旋压缩变成直接观测的现象,二级关联函数与之是否也有特定关系,这是计算二级关联函数的动机,计算发现,在特定的条件下二阶关联函数和压缩系数随时间的变化规律非常相似；有人提出新的纠缠态判断标准,论文的也计算了纠缠态的判断系数；粒子计数是物理实验中测量物理量最常用的手段,所以数压缩态的研究有着广泛的应用意义,文中最后研究了数压缩系数。更多还原

【Abstract】 There are three reasons for people’s extensive interest in spin squeezing. Firstly, the spin squeezing is an effective method to overcome the limit in precision improvement set by Heisenberg Uncertainty Principle. Secondly, because of the relationship between spin squeezing and entanglement, the research in spin squeezing is of importance for quantum information. Lastly but not the least, the entanglement is one of fundamental physics problems, so research in thespin squeezing has both practical and theoretical significance. Dispute on the definition and criteria for judgement still exists till now, author gives her own opinions in Chapter 2. Linear interaction is anticipated to bring no influence on spin squeezing, so the termδ(?)z is often neglected in calculation. Under some circumstance this term exists factually. In this thesis, it will be included in Hamiltonia to calculate. New method is introduce to solve problems because of symmetry breaking in some parameters afterδ(?)z added to Hamiltonian. After calculation, the author found that in some circumstance, this linear term brings some negative influence, reasonable explanation will be given in this thesis for this phenomenon. Particular relationship between squeezing parameter and the first-order correlated function has been found. Temporal correlated functions are measurable directly in experiment, so spin squeezing can be understood well with this relationship. What about the second-order function? Is there some particular relationship between them. That is the motivation of calculating second-order functions? After calculation, the answer is yes. New criteria for entanglement is provided recently, the squeezing parameter and the new entanglement criteria will be compared. It is meaningful to do research the number spin squeezing, for particle counting is such a popular measurement in experiment.更多还原