Spectral weight suppression in response functions of ultracold fermion-boson mixtures

We study the dynamical response of ultracold fermion-boson mixture in the Bogoliubov regime, where the interactions between fermionic impurities and bosonic excitations (phonons) are described by an effective Frohlich model under the Bogoliubov approximation. A characteristic suppression of the single-particle spectral weight is found in the small momentum region where the impurity band and phonon mode intersect. Using diagrammatic technique we compute the Bragg spectra as well as the momentum dependent force-force correlation function. We fnd that both of them are heavily affected by the spectral weight suppression effect at low impurity densities in both 1D and 2D systems. We show that the the spectral weight suppression feature in Bragg spectra, which was previously found in the quantum Monte Carlo simulations and which cannot be recovered by the random phase approximation, can be accurately reproduced with the help of vertex corrections.Comment: 14 pages, 10 figures. Final version with a new title, some revisions and a new figur

Gene specific co-regulation discovery: an improved approach

[Abstract]: Discovering gene co-regulatory relationships is a new but important research problem in DNA microarray data analysis. The problem of gene specific co-regulation discovery is to, for a particular gene of interest, called the target gene, identify its strongly co-regulated genes and the condition subsets where such strong gene co-regulations are observed. The study on this problem can contribute to a better understanding and characterization of the target gene. The existing method, using the genetic algorithm (GA), is slow due to its expensive fitness evaluation and long individual representation. In this paper, we propose an improved method for finding gene specific co-regulations. Compared with the current method, our method features a notably improved effciency. We employ kNN Search Table to substantially speed up fitness evaluation in the GA. We also propose a more compact representation scheme for encoding individuals in the GA, which contributes to faster crossover and mutation operations. Experimental results with a real-life gene mi-croarray data set demonstrate the improved effciency of our technique compared with the current method

Dynamical response of ultracold interacting fermion-boson mixtures

We analyze the dynamical response of a ultracold binary gas mixture in presence of strong boson-fermion couplings. Mapping the problem onto that of the optical response of a metal/semiconductor electronic degrees of freedom to electromagnetic perturbation we calculate the corresponding dynamic linear response susceptibility in the non-perturbative regimes of strong boson-fermion coupling using diagrammatic resummation technique as well as quantum Monte Carlo simulations. We evaluate the Bragg spectral function as well as the optical conductivity and find a pseudogap, which forms in certain parameter regimes.Comment: 32 pages, 13 figure

Pseudorandom States, Non-Cloning Theorems and Quantum Money

We propose the concept of pseudorandom states and study their constructions, properties, and applications. Under the assumption that quantum-secure one-way functions exist, we present concrete and efficient constructions of pseudorandom states. The non-cloning theorem plays a central role in our study---it motivates the proper definition and characterizes one of the important properties of pseudorandom quantum states. Namely, there is no efficient quantum algorithm that can create more copies of the state from a given number of pseudorandom states. As the main application, we prove that any family of pseudorandom states naturally gives rise to a private-key quantum money scheme.Comment: 20 page

The spatial coherence of weakly interacting one-dimensional non-equilibrium Bosonic quantum fluids

We present a theoretical analysis of spatial correlations in a one-dimensional driven-dissipative non-equilibrium condensate. Starting from a stochastic generalized Gross-Pitaevskii equation, we derive a noisy Kuramoto-Sivashinsky equation for the phase dynamics. For sufficiently strong interactions, the coherence decays exponentially in close analogy to the equilibrium Bose gas. When interactions are small on a scale set by the nonequilibrium condition, we find through numerical simulations a crossover between a Gaussian and exponential decay with peculiar scaling of the coherence length on the fluid density and noise strength.Comment: 5 pages, 2 figures, supplemental materia

Transnationals; or, the modern Frankenstein

“Learn from me, if not by my precepts, at least by my example, how dangerous is the acquirement of knowledge and how much happier that man is who believes his native town to be the world, than he who aspires to become greater than his nature will allow.” The title of this thesis is adapted from the title of Mary Shelley\u27s 1818 novel Frankenstein; or, The Modern Prometheus, and the quote above is said by the scientist in the novel. To associate the word “Frankenstein” with “transnationals” is not to refer to the transnational as the monster, but to explore the duality of the identity of Frankenstein: Dr. Victor Frankenstein, a privileged scientist who studies abroad and achieves a scientific breakthrough; and the Creature, a subject who experiences discrimination and oppression as the other in his assimilation into the world. Kai Ji’s written portion of his thesis is a short adaptation of Shelley’s original novel. The intention is to use the original characters of the novel to explore the identity of border-crossing transnationals and their relationship with nation states. Different from the original story, in the adaptation, the Creature’s body is submissive to Victor Frankenstein’s ambition, which demonstrates the interdependence between the maker and his creation. Based on this adaptation, two short experimental films are done on 16mm clear leader, with pigment on the film surface developed from the coating of M&Ms. The material choice of M&Ms speaks to Ji’s professional background as a former marketer of the brand