Flavor-twisted boundary condition for simulations of quantum many-body systems

We present an approximative simulation method for quantum many-body systems based on coarse graining the space of the momentum transferred between interacting particles, which leads to effective Hamiltonians of reduced size with the flavor-twisted boundary condition. A rapid, accurate, and fast convergent computation of the ground-state energy is demonstrated on the spin-1/2 quantum antiferromagnet of any dimension by employing only two sites. The method is expected to be useful for future simulations and quick estimates on other strongly correlated systems.Comment: 6 pages, 2 figure

Rabi oscillations of a qubit coupled to a two-level system

The problem of Rabi oscillations in a qubit coupled to a fluctuator and in contact with a heath bath is considered. A scheme is developed for taking into account both phase and energy relaxation in a phenomenological way, while taking full account of the quantum dynamics of the four-level system subject to a driving AC field. Significant suppression of the Rabi oscillations is found when the qubit and fluctuator are close to resonance. The effect of the fluctuator state on the read-out signal is discussed. This effect is shown to modify the observed signal significantly. This may be relevant to recent experiments by Simmonds et al. [Phys. Rev. Lett. 93, 077003 (2004)].Comment: 4 pages, 4 figure

PERLAKSANAAN DAN KEBERKESANAN KAEDAH LATTICE DALAM PENGAJARAN KEMAHIRAN MATEMATIK: SATU KAJIAN KES DI SEKOLAH RENDAH

Dalam pendidikan matematik, penguasaan pendaraban nombor merupakan salah satu kemahiran penting untuk matapelajaran matematik di sekolah rendah. Seandainya murid-murid tidak dapat menguasai kemahiran ini pada peringkat awal pembelajaran matematik, mereka bakal menghadapi pelbagai masalah dan cabaran dalam penguasaan kemahiran seterusnya yang memerlukan kemahiran pendaraban sebagai asas. Oleh yang demikian, satu kajian telah dijalankan untuk menilai sejauh manakah keberkesanan perlaksanaan kaedah Lattice dalam membantu meningkatkan kemahiran asas pendaraban, yang melibatkan pendaraban nombor dua dan tiga digit. Rekabentuk kajian yang digunakan ialah kajian kuasi-experimental yang melibatkan sampel murid sebanyak 15 orang murid darjah empat di Sekolah Jenis Kebangsaan Cina Chung Cheng, Batu Pahat, Johor. Ujian Pra dan Pos telah dilakukan bagi membandingkan tahap pencapaian sampel kajian sebelum dan selepas rawatan menerusi empat sesi intervensi. Secara keseluruhannya, hasil kajian telah mendapati peningkatan purata skor sebanyak 42.67 peratus selepas rawatan dengan penggunaan kaedah Lattice. Kesimpulannya, kaedah Lattice merupakan kaedah yang berkesan dalam meningkatkan pemahaman dan kemahiran responden dalam topik pendaraban

TOPICAL REVIEW: Slow light in semiconductor heterostructures

This paper presents an overview of slow light in semiconductor heterostructures. The focus of this paper is to provide a unified framework to summarize and compare various physical mechanisms of slow light proposed and demonstrated in the past few years. We expand and generalize the discussions on fundamental limitation of slow light and the delay–bandwidth product trade-off to include gain systems and other mechanisms such as injection locking. We derive the maximum fractional delay and compare the differences between material dispersion and waveguide dispersion based devices. The delay–bandwidth product is proportional to the square root of the device length for a material dispersion based device but has a linear relationship for a waveguide dispersion based device. Possible scenarios to overcome the delay–bandwidth product limitation are discussed. The prospects of slow light in various applications are also investigated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58125/2/d7_5_R01.pd

Origin of broad luminescence from site‐controlled InGaN nanodots fabricated by selective‐area epitaxy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106777/1/pssa201330362.pd

Molecular Evolution of the Substrate Utilization Strategies and Putative Virulence Factors in Mosquito-Associated Spiroplasma Species

Comparative genomics provides a powerful tool to characterize the genetic differences among species that may be linked to their phenotypic variations. In the case of mosquito-associated Spiroplasma species, such approach is useful for the investigation of their differentiations in substrate utilization strategies and putative virulence factors. Among the four species that have been assessed for pathogenicity by artificial infection experiments, Spiroplasma culicicola and S. taiwanense were found to be pathogenic, whereas S. diminutum and S. sabaudiense were not. Intriguingly, based on the species phylogeny, the association with mosquito hosts and the gain or loss of pathogenicity in these species appears to have evolved independently. Through comparison of their complete genome sequences, we identified the genes and pathways that are shared by all or specific to one of these four species. Notably, we found that a glycerol-3-phosphate oxidase gene (glpO) is present in S. culicicola and S. taiwanense but not in S. diminutum or S. sabaudiense. Because this gene is involved in the production of reactive oxygen species and has been demonstrated as a major virulence factor in Mycoplasma, this distribution pattern suggests that it may be linked to the observed differences in pathogenicity among these species as well. Moreover, through comparative analysis with other Spiroplasma, Mycoplasma, and Mesoplasma species, we found that the absence of glpO in S. diminutum and S. sabaudiense is best explained by independent losses. Finally, our phylogenetic analyses revealed possible recombination of glpO between distantly related lineages and local rearrangements of adjacent genes

Signatures of a Pressure-Induced Topological Quantum Phase Transition in BiTeI

We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through pz band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition, and are consistent with a recent theoretical proposal.Comment: revised final versio