Entropy and specific heat for open systems in steady states

The fundamental assumption of statistical mechanics is that the system is equally likely in any of the accessible microstates. Based on this assumption, the Boltzmann distribution is derived and the full theory of statistical thermodynamics can be built. In this paper, we show that the Boltzmann distribution in general can not describe the steady state of open system. Based on the effective Hamiltonian approach, we calculate the specific heat, the free energy and the entropy for an open system in steady states. Examples are illustrated and discussed.Comment: 4 pages, 7 figure

Modulational instability criteria for two-component Bose-Einstein condensates

The stability of colliding Bose-Einstein condensates is investigated. A set of coupled Gross-Pitaevskii equations is thus considered, and analyzed via a perturbative approach. No assumption is made on the signs (or magnitudes) of the relevant parameters like the scattering lengths and the coupling coefficients. The formalism is therefore valid for asymmetric as well as symmetric coupled condensate wave states. A new set of explicit criteria is derived and analyzed. An extended instability region, in addition to an enhanced instability growth rate is predicted for unstable two component bosons, as compared to the individual (uncoupled) state.Comment: 4 pages, 1 figur

Geometric phase in dephasing systems

Beyond the quantum Markov approximation, we calculate the geometric phase of a two-level system driven by a quantized magnetic field subject to phase dephasing. The phase reduces to the standard geometric phase in the weak coupling limit and it involves the phase information of the environment in general. In contrast with the geometric phase in dissipative systems, the geometric phase acquired by the system can be observed on a long time scale. We also show that with the system decohering to its pointer states, the geometric phase factor tends to a sum over the phase factors pertaining to the pointer states.Comment: 4 page

The undergraduate research apprenticeship - improving the relevance of science teaching through authentic research experience.

The undergraduate experience is arguably the most important in shaping the future career trajectories of students. It is here that early exposure to the widest possible range of disciplines and practical experiences will have the most impact. In the face of a reduction in the number of students entering both undergraduate science and research as a career option, we must urgently initiate strategies to engage and retain students in science. This can be achieved by a research experience in a ‘mentored apprenticeship model’ in the context of an authentic laboratory/field during their formative undergraduate years. It is widely acknowledged that an interactive, enquiry-based approach to learning provides the most meaningful and lasting learning experience for students. It is similarly accepted that, within science, undergraduate research experiences are pivotal in providing context to student learning and providing a true sense of what it means to be a 'scientist'. In this discussion forum we will summarise research-based experiences currently available for Bachelor of Science (BSc) students at The University of Queensland (UQ). We will then look in detail at a proposed new ‘mentored apprenticeship model’, being examined for introduction into the UQ BSc from 2008 following the recent major review. The proposed model builds on the existing UQ Advanced Study Program in Science combined with the University of Michigan’s Undergraduate Research Opportunity Program and aims to: • achieve an increased level of student engagement to complement other strategies for motivating students who are in large first year classes • show students the functional/practical relevance of the core content of their course material • provide students with a personal experience of doing science so that they can plan their future studies from a more informed perspective • minimize the attrition rate from the first year science cohort • provide a mentored cohort experience to engage and support under-represented groups such as indigenous and international students • actively build on the tremendous investment in institutes at UQ by increasing the direct involvement of these research academics in the undergraduate science program (for example, places for 25 students have already been committed by one of the UQ research institutes) • increase the number of students proceeding to postgraduate education as the next step to a worthwhile and personally rewarding career trajectory in science. The proposed ‘mentored apprenticeship model’ provides a step-wise approach to a student’s growth as an apprentice scientist. As undergraduates progress through their degree-program their learning experiences in science should also progress closer and closer to those of a ‘scientist’ until, on graduation, they are fully-prepared for their science-related career. The new model achieves this through establishing strong working partnerships between students and research groups, supplementing traditional practical components of undergraduate courses by ‘doing’ more science and providing students with an opportunity to talk more about science. Within this forum participants will be asked to explore: • How are the theoretical frameworks of enquiry-based learning being translated into practical applications? • What are the outcomes of an undergraduate research opportunity? • How do we assess this learning? • What are the experiences of other institutions – how have they met the challenge of an authentic research experience, in a research-intensive university, for large numbers of students? • Are there discipline-specific variations to these approaches

Two-species magneto-optical trap with 40K and 87Rb

We trap and cool a gas composed of 40K and 87Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1x10^7 40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review

Binary Bose-Einstein Condensate Mixtures in Weakly and Strongly Segregated Phases

We perform a mean-field study of the binary Bose-Einstein condensate mixtures as a function of the mutual repulsive interaction strength. In the phase segregated regime, we find that there are two distinct phases: the weakly segregated phase characterized by a `penetration depth' and the strongly segregated phase characterized by a healing length. In the weakly segregated phase the symmetry of the shape of each condensate will not take that of the trap because of the finite surface tension, but its total density profile still does. In the strongly segregated phase even the total density profile takes a different symmetry from that of the trap because of the mutual exclusion of the condensates. The lower critical condensate-atom number to observe the complete phase segregation is discussed. A comparison to recent experimental data suggests that the weakly segregated phase has been observed.Comment: minor change

Decoherence in a Talbot Lau interferometer: the influence of molecular scattering

We study the interference of C70 fullerenes in a Talbot-Lau interferometer with a large separation between the diffraction gratings. This permits the observation of recurrences of the interference contrast both as a function of the de Broglie wavelength and in dependence of the interaction with background gases. We observe an exponential decrease of the fringe visibility with increasing background pressure and find good quantitative agreement with the predictions of decoherence theory. From this we extrapolate the limits of matter wave interferometry and conclude that the influence of collisional decoherence may be well under control in future experiments with proteins and even larger objects.Comment: 8 pages, 5 figure

Decoherence in a single trapped ion due to engineered reservoir

The decoherence in trapped ion induced by coupling the ion to the engineered reservoir is studied in this paper. The engineered reservoir is simulated by random variations in the trap frequency, and the trapped ion is treated as a two-level system driven by a far off-resonant plane wave laser field. The dependence of the decoherence rate on the amplitude of the superposition state is given.Comment: 4 pages, 2 figure