Probing the optical conductivity of trapped charge-neutral quantum gases

We study a harmonically confined atomic gas which is subjected to an additional external potential such as an optical lattice. Using a linear response formulation, we determine the response of the gas to a small, time-dependent displacement of the harmonic trap and derive a simple exact relation showing that the centre-of-mass position of the atomic cloud is directly related to the global optical conductivity of the system. We demonstrate the usefulness of this approach by calculating the optical conductivity of bosonic atoms in an optical lattice. In the Mott insulating phase, there is clear evidence of an optical Mott gap, providing a proof-of-principle demonstration that the global optical conductivity gives high-quality information about the exci- tations of strongly-correlated quantum gases.Comment: 6 pages, 2 figures. Published versio

Constraints on the energy spectrum of non-Hermitian models in open environments

Motivated by recent progress on non-Hermitian topological band theories, we study the energy spectrum of a generic two-band non-Hermitian Hamiltonian. We prove rigorously that the complex energy spectrum of such a non-Hermitian Hamiltonian is restricted to the lower complex plane, provided that the parameters of the Hamiltonian satisfy a certain constraint. Furthermore, we consider one specific scenario where such a non-Hermitian Hamiltonian can arise, namely a two-band model coupled to an environment, and show that this aforementioned constraint orignates from very general physical considerations. Our findings are relevant in the definition of the energy gap in non-Hermitian topological band theories and also have implications on simulations of such theories using quantum systems.Comment: 7 pages, 1 figur

Revenue Sharing and Control Rights in Team Production: Theories and Evidence from Joint Ventures.*

This paper presents a model of the joint venture that is grounded in the stylized facts we found from a sample of 200 joint venture contracts. The model incorporates the revenue-sharing contract into the incomplete contract frameworks of Grossman-Hart-Moore Property Rights Theory and the Transaction Cost Theory of the firm, and emphasizes the impact of expropriation. Joint control can be optimal as well as unilateral control. Our econometric analysis of the revenue-sharing and control arrangements o?ers strong support to our Property-Rights-Theory motivated model with self investment but rejects that with cooperative investment. The Transaction-Cost-Theory motivated model leaves some important empirical findings unexplained. Our findings also reject some of the existing theories of joint ownership.http://deepblue.lib.umich.edu/bitstream/2027.42/39948/2/wp563.pd