Level attraction in a microwave optomechanical circuit

Level repulsion - the opening of a gap between two degenerate modes due to coupling - is ubiquitous anywhere from solid state theory to quantum chemistry. In contrast, if one mode has negative energy, the mode frequencies attract instead. They converge and develop imaginary components, leading to an instability; an exceptional point marks the transition. This, however, only occurs if the dissipation rates of the two modes are comparable. Here we expose a theoretical framework for the general phenomenon and realize it experimentally through engineered dissipation in a multimode superconducting microwave optomechanical circuit. Level attraction is observed for a mechanical oscillator and a superconducting microwave cavity, while an auxiliary cavity is used for sideband cooling. Two exceptional points are demonstrated that could be exploited for their topological properties.Comment: 5 pages, 4 figures; includes Supplementary informatio

Thermodynamics of the three-dimensional Hubbard model: Implications for cooling cold atomic gases in optical lattices

We present a comprehensive study of the thermodynamic properties of the three-dimensional fermionic Hubbard model, with application to cold fermionic atoms subject to an optical lattice and a trapping potential. Our study is focused on the temperature range of current experimental interest. We employ two theoretical methods - dynamical mean-field theory and high-temperature series - and perform comparative benchmarks to delimitate their respective range of validity. Special attention is devoted to understand the implications that thermodynamic properties of this system have on cooling. Considering the distribution function of local occupancies in the inhomogeneous lattice, we show that, under adiabatic evolution, the variation of any observable (e.g., temperature) can be conveniently disentangled into two distinct contributions. The first contribution is due to the redistribution of atoms in the trap during the evolution, while the second one comes from the intrinsic change of the observable. Finally, we provide a simplified picture of the cooling procedure recently proposed in J.-S. Bernier et al., Phys. Rev. A 79, 061601 (2009) by applying this method to an idealized model.Comment: 17 pages, 27 figures, version published in PR

Biaxial spin-nematic phase of two dimensional disordered rotor models and spin-one bosons in optical lattices

We show that the ground state of disordered rotor models with quadrupolar interactions can exhibit biaxial nematic ordering in the disorder-averaged sense. We present a mean-field analysis of the model and demonstrate that the biaxial phase is stable against small quantum fluctuations. We point out the possibility of experimental realization of such rotor models using ultracold spin-one Bose atoms in a spin-dependent and disordered optical lattice in the limit of a large number of atoms per site and also suggest an imaging experiment to detect the biaxial nematicity in such systems.Comment: revtex file 7 pages, 2 figures, version published in PR

Mott phases and superfluid-insulator transition of dipolar spin-three bosons in an optical lattice: implications for <SUP>52</SUP>Cr atoms

We study the Mott phases and superfluid-insulator transition of spin-three bosons in an optical lattice with an anisotropic two-dimensional optical trap. We chart out the phase diagrams for Mott states with n=1 and n=2 atoms per lattice site. It is shown that the long-range dipolar interaction stabilizes a state where the chains of the ferromagnetically aligned spins run along the longer trap direction while the spin ordering is staggered between nearby chains, leading to an antiferromagnetic ordering along the shorter trap direction. We also obtain the mean-field phase boundary for the superfluid-insulator transition in these systems and study the nature of spin ordering in the superfluid state near the transition. We show that, inside the superfluid phase and near the superfluid-insulator phase boundary, the system undergoes a first-order antiferromagnetic-ferromagnetic spin ordering transition. We discuss implications of our results for 52Cr atoms and suggest possible experiments to detect different phases in such systems

Neoliberalism and the Environmental Movement: Contemporary Considerations for the Counter Hegemonic Struggle

This thesis proposes a conceptual framework for understanding how neoliberalism has decreased the ability of environmental movements to manifest changes in political economic structure or spur state action on environmental issues that might be antagonistic to the neoliberal order. Karl Marx and Karl Polanyi have developed reputable theories that describe social movements as exercising a degree of control over political economy. However, the problems with Marxist and Polanyian theory are twofold: first, they offer vague and homogenous descriptions of the social movements to which they refer. Second, a large shift in economic-political context towards neoliberalism since the 1970’s has drastically altered the political opportunity structure of social movements. In the modern day, many social movements have rallied around environmental issues in response to an impending environmental crisis. The antipathy of neoliberal hegemony towards environmental regulation has set it in opposition with environmental movements and as such many factions of the movement can be described as ‘counter hegemonic’. As neoliberalism constricts the political opportunity structure of these movements through domestic and international legislation and treaties, assimilation of loci of dissent into a neoliberal framework, and powerful financial coercion, limitations on environmental movement influence may yield dire consequences for the global environment