Optical realization of the two-site Bose-Hubbard model in waveguide lattices

A classical realization of the two-site Bose-Hubbard Hamiltonian, based on light transport in engineered optical waveguide lattices, is theoretically proposed. The optical lattice enables a direct visualization of the Bose-Hubbard dynamics in Fock space.Comment: to be published, J Phys. B (Fast Track Communication

Low-temperature lattice effects in the spin-liquid candidate κ\kappa-(BEDT-TTF)2_2Cu2_2(CN)3_3

The quasi-two-dimensional organic charge-transfer salt $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ is one of the prime candidates for a quantum spin-liquid due the strong spin frustration of its anisotropic triangular lattice in combination with its proximity to the Mott transition. Despite intensive investigations of the material's low-temperature properties, several important questions remain to be answered. Particularly puzzling are the 6\,K anomaly and the enigmatic effects observed in magnetic fields. Here we report on low-temperature measurements of lattice effects which were shown to be particularly strongly pronounced in this material (R. S. Manna \emph{et al.}, Phys. Rev. Lett. \textbf{104}, 016403 (2010)). A special focus of our study lies on sample-to-sample variations of these effects and their implications on the interpretation of experimental data. By investigating overall nine single crystals from two different batches, we can state that there are considerable differences in the size of the second-order phase transition anomaly around 6\,K, varying within a factor of 3. In addition, we find field-induced anomalies giving rise to pronounced features in the sample length for two out of these nine crystals for temperatures $T <$ 9 K. We tentatively assign the latter effects to $B$-induced magnetic clusters suspected to nucleate around crystal imperfections. These $B$-induced effects are absent for the crystals where the 6\,K anomaly is most strongly pronounced. The large lattice effects observed at 6\,K are consistent with proposed pairing instabilities of fermionic excitations breaking the lattice symmetry. The strong sample-to-sample variation in the size of the phase transition anomaly suggests that the conversion of the fermions to bosons at the instability is only partial and to some extent influenced by not yet identified sample-specific parameters

Nonlinear Self-Trapping of Matter Waves in Periodic Potentials

We report the first experimental observation of nonlinear self-trapping of Bose-condensed 87Rb atoms in a one dimensional waveguide with a superimposed deep periodic potential . The trapping effect is confirmed directly by imaging the atomic spatial distribution. Increasing the nonlinearity we move the system from the diffusive regime, characterized by an expansion of the condensate, to the nonlinearity dominated self-trapping regime, where the initial expansion stops and the width remains finite. The data are in quantitative agreement with the solutions of the corresponding discrete nonlinear equation. Our results reveal that the effect of nonlinear self-trapping is of local nature, and is closely related to the macroscopic self-trapping phenomenon already predicted for double-well systems.Comment: 5 pages, 4 figure

Quantum dynamics of a binary mixture of BECs in a double well potential: an Holstein-Primakoff approach

We study the quantum dynamics of a binary mixture of Bose-Einstein condensates (BEC) in a double-well potential starting from a two-mode Bose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is very large, a mapping onto a SU(2) spin problem together with a Holstein-Primakoff transformation is performed. The quantum evolution of the number difference of bosons between the two wells is investigated for different initial conditions, which range from the case of a small imbalance between the two wells to a coherent spin state. The results show an instability towards a phase-separation above a critical positive value of the interspecies interaction while the system evolves towards a coherent tunneling regime for negative interspecies interactions. A comparison with a semiclassical approach is discussed together with some implications on the experimental realization of phase separation with cold atoms.Comment: 12 pages, 7 figures, accepted for publication in J. Phys.

Efficiency of Wastewater Treatment System and Its Use for Irrigation - A Case Study of a private University in Ghana

The reuse or utilization of treated wastewater for irrigation is conventionally considered as a means of mitigating water shortage or abating water pollution. Wastewater treatment plants designed for reuse in irrigation are more appropriate for developing countries striving to enhance access to improved sanitation. It is well known that successive stages of treatment of sewage effluent reduces the quantity of suspended solids, organic matter and nutrient load, bacteria population as well as biological oxygen demand to the extent that the final treated effluent contains virtually a small fraction compared to the influent sewage. A short-term assessment of the decentralised reuse-oriented effluent system of a private University (in Ghana) was carried out to determine its effluent quality for the purpose of irrigating its landscape. The investigation showed that Total Coliform, E. coli and Vibrio spp. were significantly reduced, through the treatment stages, but not to within Internationally accepted guideline values. Salmonella spp. was not significantly reduced. Physical parameters, nutrients as well as biological oxygen demand did not show any variation along the treatment stages. Suspended solids, optimum temperature and pH were identified as contributing to treatment inefficiency of the plant. It is therefore recommended the treated wastewater, prior to disinfection, should be filtered to reduce suspended solids. This will enhance effective chlorination and by extension, significantly reduce bacteria population. Furthermore Regular monitoring and laboratory analysis of the recycled effluent from the plant should be carried out by the EPA or other professional organisation to ensure compliance. Keywords: Reuse, Wastewater, Irrigation, Chlorinatio

Analisis Perbandingan Kapasitas Balok Komposit Baja-Beton dengan Steel Headed Stud dan UNP Stud

Penghubung geser atau stud memiliki peranan penting dalam menghasilkan perilaku komposit baja-beton. Terdapat dua jenis stud yang direkomendasikan, yaitu steel headed stud atau paku berkepala dan UNP stud atau kanal. Penelitian ini menganalisis perbandingan kapasitas balok komposit baja-beton dengan penghubung geser jenis steel headed stud dan UNP stud. Pemodelan menggunakan program elemen hingga dipilih sebagai metode dalam analisis perilaku non-linier. Luas permukaan kedua jenis penghubung geser dibuat sama sehingga kuat nominal, jumlah, dan jarak pemasangan penghubung geser pun juga akan sama untuk kedua jenis pemodelan ini. Kapasitas yang ditinjau meliputi tegangan pada balok baja WF, tegangan pelat beton, tegangan pada stud, konsentrasi tegangan pada balok baja dan pelat beton, serta defleksi pada balok komposit. Sebelum melakukan pemodelan dengan program elemen hingga, proses desain sesuai SNI 1727:2015 dilakukan terlebih dahulu untuk menentukan dimensi struktur yang akan digunakan. Validasi diperlukan untuk melihat tingkat keakuratan pemodelan yang dilakukan. Metode validasi dilakukan dengan membandingkan nilai tegangan lentur pada serat bagian bawah dan atas balok komposit baja-beton. Persentase pemodelan mencapai 86,95% untuk model steel headed stud dan 87,4% untuk UNP stud. Hasil pemodelan menunjukkan bahwa balok komposit dengan UNP stud memilik kapasitas yang lebih baik karena menghasilkan nilai tegangan-tegangan dan defleksi yang lebih kecil. Tegangan lentur balok baja UNP stud dan steel headed stud adalah 19,129 MPa dan 19,556 MPa (perbedaan 2,18 %). Tegangagan lentur pelat beton UNP stud dan steel headed stud adalah 1,21 MPa dan 1,194 MPa (perbedaan 1,34 %). Defleksi balok komposit dengan UNP stud dan steel headed stud adalah 0.478 mm dan 0,435 mm (perbedaan 8,99 %)

Control of unstable macroscopic oscillations in the dynamics of three coupled Bose condensates

We study the dynamical stability of the macroscopic quantum oscillations characterizing a system of three coupled Bose-Einstein condensates arranged into an open-chain geometry. The boson interaction, the hopping amplitude and the central-well relative depth are regarded as adjustable parameters. After deriving the stability diagrams of the system, we identify three mechanisms to realize the transition from an unstable to stable behavior and analyze specific configurations that, by suitably tuning the model parameters, give rise to macroscopic effects which are expected to be accessible to experimental observation. Also, we pinpoint a system regime that realizes a Josephson-junction-like effect. In this regime the system configuration do not depend on the model interaction parameters, and the population oscillation amplitude is related to the condensate-phase difference. This fact makes possible estimating the latter quantity, since the measure of the oscillating amplitudes is experimentally accessible.Comment: 25 pages, 12 figure