| 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.
|
PDF Full Text Request