BCS-BEC过渡区原子费米气体的动态性研究

研究BCS-BEC过渡区原子费米气体依赖时间的Ginzburg-Landau方程的平面波解及其动态性。主要研究该方程各个系数a、b、c、d 之间的关系,以及原子费米气体的化学势？和能量阀值2v ,温度T 和极化率h之间的关系。     

弱相互作用对束缚的玻色气体的影响

在半经典近似下,考虑了弱相互作用对幂型势阱中玻色—爱因斯坦凝聚体的影响。从结果中发现,相对于理想玻色气体,排斥力会使得临界温度升高,其偏移量正比于s-波散射长度α,而相互作用能和比热则是相应的减小。对弱相互作用下绝热冷却的研究表明,玻色气体之间的相互作用越强,其对外场的敏感性越弱。     

Entangled states of trapped atomic ions

To process information using quantum-mechanical principles, the states of individual particles need to be entangled and manipulated. One way to do this is to use trapped, laser-cooled atomic ions. Attaining a general-purpose quantum computer is, however, a distant goal, but recent experiments show that just a few entangled trapped ions can be used to improve the precision of measurements. If the entanglement in such systems can be scaled up to larger numbers of ions, simulations that are intractable on a classical computer might become possible.     

准二维谐振势阱中有限尺度的非理想玻色气体

研究了准二维谐振势阱中粒子数有限的非理想玻色气体的热力学性质。利用巨正则系综的求和方法与平均场理论，给出了有限粒子数与原子间相互作用对系统势力学性质的共同修正；并将所得结果与三维时的情况进行了比较。结果表明：降低维数不能提高系统的临界温度；在准二维谐振系统中，有限粒子数对系统的影响随着粒子数的增大而减小直至消失，而相互作用的影响与粒子数无关，因此可以通过增大粒子数来提高准二维谐振系统的临界温度。     

囚禁有限unitary费米气体的压强与状态方程

目的研究非对称与球对称简谐势阱中有限unitary费米气体的压强与状态方程。方法运用分数不相容统计法。结果求出了非对称与球对称简谐势阱中有限unitary费米气体的压强张量以及压强与内能的关系,导出了球对称势阱中的状态方程并给出了低温强简并近似和高温弱简并近似。结论揭示了有限unitary费米气体系统压强的有限尺度效应,给出了有限尺度效应判据。指出了球对称简谐势阱中有限unitary费米气体的压强在空间3个方向上各向同性与非对称势阱中压强张量在空间3个方向各向异性的特征,阐明了非对称势阱中沿着势阱圆频率低的方向压强张量高,沿着势阱圆频率高的方向压强张量低的规律,揭示了压强张量在空间3个方向各向异性的物理本质。     

Measurement of the spatial coherence of a trapped Bose gas at the phase transition

The experimental realization of Bose-Einstein condensates of dilute gases has allowed investigations of fundamental concepts in quantum mechanics at ultra-low temperatures, such as wave-like behaviour and interference phenomena. The formation of an interference pattern depends fundamentally on the phase coherence of a system; the latter may be quantified by the spatial correlation function. Phase coherence over a long range is the essential factor underlying Bose-Einstein condensation and related macroscopic quantum phenomena, such as superconductivity and superfluidity. Here we report a direct measurement of the phase coherence properties of a weakly interacting Bose gas of rubidium atoms. Effectively, we create a double slit for magnetically trapped atoms using a radio wave field with two frequency components. The correlation function of the system is determined by evaluating the interference pattern of two matter waves originating from the spatially separated 'slit' regions of the trapped gas. Above the critical temperature for Bose-Einstein condensation, the correlation function shows a rapid gaussian decay, as expected for a thermal gas. Below the critical temperature, the correlation function has a different shape: a slow decay towards a plateau is observed, indicating the long-range phase coherence of the condensate fraction.     

一维Bose-Einstein凝聚中的孤波

 导出了在一维原子玻色-爱因斯坦凝聚(BEC)中,原子被约束在谐和柱形陷阱中时的孤波的有关性质.     

谐振势中相互作用费米子的稳定性条件

在局域密度近似的框架内（其中气体在每一点都可以看成是局域均匀的）,得到谐振势中相互作用费米气体的能量密度.在这些表达式的基础上,研究了零温时约束气体的热力学稳定性条件,给出了一维、二维、三维系统稳定条件的解析表达式.此外,绘出了不同维度系统的稳定性相图.结果表明：在本研究中的所有维度中,在特定粒子数密度的条件下,排斥相互作用或无相互作用系统是稳定的.然而,对于吸引相互作用系统,只有在相互作用很弱的条件下,系统才是稳定的.对于一维和三维系统来说,相互作用强度的临界值与粒子数密度紧密相关,而对于二维系统而言,相应的临界值同粒子数密度不存在明显关联性.     

一种新型陷波镜像波导的色散特性

论文提出一种适用于毫米波集成电路的新型陷波镜像波导结构。文中运用有效介电常数和横向谐振条件,将该新型结构等效成简化模型,并推导了新型陷波镜像波导相移常数的计算公式;最后给出2个计算实例,计算结果与Ansoft HFSS仿真结果吻合较好,说明该方法是行之有效的。     

Observation of entanglement between a single trapped atom and a single photon

An outstanding goal in quantum information science is the faithful mapping of quantum information between a stable quantum memory and a reliable quantum communication channel. This would allow, for example, quantum communication over remote distances, quantum teleportation of matter and distributed quantum computing over a 'quantum internet'. Because quantum states cannot in general be copied, quantum information can only be distributed in these and other applications by entangling the quantum memory with the communication channel. Here we report quantum entanglement between an ideal quantum memory--represented by a single trapped 111Cd+ ion--and an ideal quantum communication channel, provided by a single photon that is emitted spontaneously from the ion. Appropriate coincidence measurements between the quantum states of the photon polarization and the trapped ion memory are used to verify their entanglement directly. Our direct observation of entanglement between stationary and 'flying' qubits is accomplished without using cavity quantum electrodynamic techniques or prepared non-classical light sources. We envision that this source of entanglement may be used for a variety of quantum communication protocols and for seeding large-scale entangled states of trapped ion qubits for scalable quantum computing.     

Resonant quantum transitions in trapped antihydrogen atoms

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.     

V-型原子系统中慢光孤子研究

研究有自发辐射诱导相干效应的寿命拓宽的V-型原子与一个弱探测光场共振相互作用的情况。研究表明在激光与原子介质高度共振情况下。选择合适的参量．该系统中有暗孤子产生。同时孤子的群速度是慢光速。     

囚禁在光格中的波色-爱因斯坦凝聚体孤子

利用数值模拟解Gross-Pitaevskii方程来研究囚禁在光格中的波色-爱因斯坦凝聚体明孤子，发现周期性光格可被用作为可控的物质波分裂器，其分裂效果与孤子在光格中的初始位置、势阱中的原子数、以及光格电势的幅度、波矢有关。     

双光束信号在四能级原子系统中的传输

目的 研究双-Λ型四能级原子介质中信号的传输问题.方法 对信号场和原子的运动方程做数值模拟.结果 数值模拟展示了2个信号在介质中传输的几种新效应.结论 可以在四能级原子系统中操控双光束信号.     

驻涡燃烧室内涡系分布研究

为清晰了解驻涡燃烧室内流场的涡系分布,对中心驻体为67%燃烧室当量宽度的驻涡燃烧室流场,在驻涡腔无喷射和有喷射两种状况下分别进行冷态数值模拟,详细研究流场内旋涡分布情况.结果表明:流道前部存在4个影响很小、沿流动方向运动、分布于驻体与端壁角区的螺旋状旋涡;流道后部存在1个由2个旋涡构成、面积较大的回流区;流道中部的驻涡区旋涡情况复杂,在驻涡腔无喷射情况下,主流与驻涡区之间悬挂驻留2个稳定的驻涡,驻涡腔内存在不稳定且数目不确定的旋涡;当驻涡腔前驻体有喷射存在时,驻涡腔内形成4个均匀且稳定的旋涡.