Dynamics of Two-Component Bose-Einstein Condensates Coupled with Environment

We investigate the dynamics of an open Bose-Einstein condensate system consisting of two hyperfine states of the same atomic species which are coupled by tunable Raman laser. It is already suggested that the detuning between the laser frequency and transition frequency affect significantly on the dynamics of the pure condensate. Here we show that the detuning effect is suppressed by noise and dissipation caused by the environment. The increase of coherence and purity are also displayed for specific parameters. As a verification to the lowest-order approximation we derive the hierarchy of motion equations in the second-order approximation. It turns out that the former one can describe the dynamical evolution qualitatively for weak noise and dissipation and quantitatively for strong noise and dissipation.Comment: 7 pages,8 figure

Dissipation effect in the double-well Bose-Einstein Condensate

Dynamics of the double-well Bose-Einstein condensate subject to energy dissipation is studied by solving a reduced one-dimensional time-dependent Gross-Pitaevskii equation numerically. We first reproduce the phase space diagram of the system without dissipation systematically, and then calculate evolutionary trajectories of dissipated systems. It is clearly shown that the dissipation can drive the system to evolve gradually from the $\pi$-mode quantum macroscopic self-trapping state, a state with relatively higher energy, to the lowest energy stationary state in which particles distribute equally in the two wells. The average phase and phase distribution in each well are discussed as well. We show that the phase distribution varies slowly in each well but may exhibit abrupt changes near the barrier. This sudden change occurs at the minimum position in particle density profile. We also note that the average phase in each well varies much faster with time than the phase difference between two wells.Comment: 7 pages, 7 figures, to be published in Euro. Phys. J.

Controlling two-phase flow in microfluidic systems using electrowetting

Electrowetting (EW)-based digital microfluidic systems (DMF) and droplet-based\ud two-phase flow microfluidic systems (TPF) with closed channels are the most\ud widely used microfluidic platforms. In general, these two approaches have been\ud considered independently. However, integrating the two technologies into one\ud allows to combine the advantages of both worlds: (i) high throughput (from TPF)\ud and (ii) precise control over each individual drop (from EW). Thus the aim of this\ud thesis was to investigate the combination of EW technology and the droplet-based\ud TPF platform. Hence we designed and developed several of such hybrid microfluidic\ud chips, using different approaches and microfabrication technologies. We\ud demonstrated the new functionalities of the developed devices and explored the\ud physics ingredients based on our observations

Studentification in China: changing geographies of Haidian district, Beijing

Processes of studentification encompass socio-economic, cultural and physical changes which are tied to seasonal population movements of university students. To date, most empirical investigations of studentification have tended to take place in Anglophone contexts. This thesis extends the lens of study to China, and shows the salience of the concept for understanding urban transformations which have unfolded since the introduction of a new state policy in 1999 for the expansion of higher education. Using the case study of Haidian District (Beijing), and focussing on Peking University students, the thesis makes original contributions to academic knowledge. First, it argued that the concept of studentification can be transposed to the Chinese context, and that social, cultural, economic and physical signifiers of studentification are evident in Beijing. Second, four main geographies of studentification are revealed, which concur with Smith and Hubbard s (2014) discussion of the co-existence of diverse geographies of studentification in the UK. These include: on-campus, university-managed dormitories (Yanyuan and Shaoyuan by Peking University); off-campus, university-managed dormitories (Wanliu, Changchunyuan/Changchunxinyuan, and Global Village); off-campus, Housing in Multiple Occupation (Haidianlu), and; off-campus, Purpose-built student accommodation (Wudaokou). By contrast to the UK, it is shown that all geographies of studentification are gated . Yet, differential residential and socio-cultural experiences are highlighted, in part, influenced by state regulations for Chinese students to reside within university-managed dormitories, or acquire permission to live off-campus; contrary to less-regulated accommodation patterns of International students. This division marks a conceptual difference between studentification in China and UK, with international students more aligned to stereotypical cultural/lifestyle traits of UK students (e.g. noise, partying), as opposed to Chinese counterparts residing in regulated (study-oriented) spaces on-campus. The thesis presents a redefined conceptualisation of studentification for pining down the diverse geographies of student housing in Beijing, to meet the differential demands of Chinese and international students in an expanded system of higher education