Macroscopic Quantum States and Quantum Phase Transition in the Dicke Model

The energy spectrum of Dicke Hamiltonians with and without the rotating wave approximation for an arbitrary atom number is obtained analytically by means of the variational method,in which the effective pseudo-spin Hamiltonian resulting from the expectation value in the boson-field coherent state is diagonalized by the spincoherent-state transformation.In addition to the ground-state energy,an excited macroscopic quantum-state is found corresponding to the south- and north-pole gauges of the spin-coherent states,respectively.Our results of ground-state energies in exact agreement with various approaches show that these models exhibit a zerotemperature quantum phase transition of the second order for any number of atoms,which was commonly considered as a phenomenon of the thermodynamic limit with the atom number tending to infinity.The critical behavior of the geometric phase is analyzed.

视觉遮挡下猕猴皮质内峰电位信号的感觉解码

目的研究猕猴执行抓握运动时视觉信息对不同脑功能区的神经元发放机制和神经信号解码准确率的影响。方法设计一种实验装置,可有效训练猕猴在无视觉遮挡和视觉遮挡两种条件下分辨3种不同形状物体。在猕猴大脑初级运动皮质(M1)、初级感觉皮质(S1)和后顶叶皮质(PPC)植入浮动微电极阵列(FMA),通过神经数据采集系统记录猕猴执行不同形状物体抓握任务中皮质内神经信号。对猕猴的行为学数据、峰电位数据进行统计分析,采用线性判别分析(LDA)、支持向量机(SVM)和胶囊网络(CAPSNET)3种算法对神经信号进行解码。结果视觉遮挡可增加猕猴抓握过程中形状辨别的时间,3种目标抓握辨别的时间分别延长19.48%、39.71%及14.29%;CAPSNET解码器最高可实现98.21%的多脑区解码准确率,以及97.52%的单脑区解码准确率;视觉遮挡对不同脑功能区的解码准确率可产生显著影响。结论视觉遮挡可引起不同脑功能区解码准确率的改变,视觉遮挡后触觉相关脑区的功能性会增强,而视觉相关脑区的功能性则会减弱。