Atom-molecule coexistence and collective dynamics near a Feshbach resonance of cold fermions

Degenerate Fermi gas interacting with molecules near Feshbach resonance is unstable with respect to formation of a mixed state in which atoms and molecules coexist as a coherent superposition. Theory of this state is developed using a mapping to the Dicke model, treating molecular field in the single mode approximation. The results are accurate in the strong coupling regime relevant for current experimental efforts. The exact solution of the Dicke model is exploited to study stability, phase diagram, and nonadiabatic dynamics of molecular field in the mixed state.Comment: 5 pages, 2 figure

Connecting your Mobile Shopping Cart to the Internet-of-Things

International audienceOnline shopping has reached an unforeseen success during the last decade thanks to the explosion of the Internet and the development of dedicated websites. Nonetheless, the wide diversity of e-commerce websites does not really foster the sales, but rather leaves the customer in the middle of dense jungle. In particular, finding the best offer for a specific product might require to spend hours browsing the Internet without being sure of finding the best deal in the end. While some websites are providing comparators to help the customer in finding the best offer meeting her/his requirements, the objectivity of these websites remains questionable, the comparison criteria are statically defined, while the nature of products they support is restricted to specific categories (e.g., electronic devices). In this paper, we introduce MACCHIATO as a user-centered platform leveraging online shopping. MACCHIATO implements the principles of the Internet-of-Things by adopting the REST architectural style and semantic web standards to navigate product databases exposed on the Internet. By doing so, customers keep the control of their shopping process by selecting the stores and comparing the offers according to their own preferences

A Dicke Type Model for Equilibrium BEC Superradiance

We study the effect of electromagnetic radiation on the condensate of a Bose gas. In an earlier paper we considered the problem for two simple models showing the cooperative effect between Bose-Einstein condensation and superradiance. In this paper we formalise the model suggested by Ketterle et al in which the Bose condensate particles have a two level structure. We present a soluble microscopic Dicke type model describing a thermodynamically stable system. We find the equilibrium states of the system and compute the thermodynamic functions giving explicit formulae expressing the cooperative effect between Bose-Einstein condensation and superradiance

The role of infrared divergence for decoherence

Continuous and discrete superselection rules induced by the interaction with the environment are investigated for a class of exactly soluble Hamiltonian models. The environment is given by a Boson field. Stable superselection sectors emerge if and only if the low frequences dominate and the ground state of the Boson field disappears due to infrared divergence. The models allow uniform estimates of all transition matrix elements between different superselection sectors.Comment: 11 pages, extended and simplified proo

Quantum control without access to the controlling interaction

In our model a fixed Hamiltonian acts on the joint Hilbert space of a quantum system and its controller. We show under which conditions measurements, state preparations, and unitary implementations on the system can be performed by quantum operations on the controller only. It turns out that a measurement of the observable A and an implementation of the one-parameter group exp(iAr) can be performed by almost the same sequence of control operations. Furthermore measurement procedures for A+B, for (AB+BA), and for i[A,B] can be constructed from measurements of A and B. This shows that the algebraic structure of the set of observables can be explained by the Lie group structure of the unitary evolutions on the joint Hilbert space of the measuring device and the measured system. A spin chain model with nearest neighborhood coupling shows that the border line between controller and system can be shifted consistently.Comment: 10 pages, Revte

A comparative study of the neutrino-nucleon cross section at ultra high energies

The high energy neutrino cross section is a crucial ingredient in the calculation of the event rate in high energy neutrino telescopes. Currently there are several approaches which predict different behaviours for its magnitude for ultrahigh energies. In this paper we present a comparison between the predictions based on linear DGLAP dynamics, non-linear QCD and in the imposition of a Froissart-like behaviour at high energies. In particular, we update the predictions based on the Color Glass Condensate, presenting for the first time the results for $\sigma_{\nu N}$ using the solution of the running coupling Balitsky-Kovchegov equation. Our results demonstrate that the current theoretical uncertainty for the neutrino-nucleon cross section reaches a factor three for neutrinos energies around $10^{11}$ GeV and increases to a factor five for $10^{13}$ GeV.Comment: 6 pages, 3 figure

Renormalizing the Schwinger-Dyson equations in the auxiliary field formulation of λϕ4\lambda \phi^4 field theory

In this paper we study the renormalization of the Schwinger-Dyson equations that arise in the auxiliary field formulation of the O(N) $\phi^4$ field theory. The auxiliary field formulation allows a simple interpretation of the large-N expansion as a loop expansion of the generating functional in the auxiliary field $\chi$, once the effective action is obtained by integrating over the $\phi$ fields. Our all orders result is then used to obtain finite renormalized Schwinger-Dyson equations based on truncation expansions which utilize the two-particle irreducible (2-PI) generating function formalism. We first do an all orders renormalization of the two- and three-point function equations in the vacuum sector. This result is then used to obtain explicitly finite and renormalization constant independent self-consistent S-D equations valid to order~1/N, in both 2+1 and 3+1 dimensions. We compare the results for the real and imaginary parts of the renormalized Green's functions with the related \emph{sunset} approximation to the 2-PI equations discussed by Van Hees and Knoll, and comment on the importance of the Landau pole effect.Comment: 20 pages, 10 figure

Continuity of the four-point function of massive ϕ44\phi_4^4-theory above threshold

In this paper we prove that the four-point function of massive \vp_4^4-theory is continuous as a function of its independent external momenta when posing the renormalization condition for the (physical) mass on-shell. The proof is based on integral representations derived inductively from the perturbative flow equations of the renormalization group. It closes a longstanding loophole in rigorous renormalization theory in so far as it shows the feasibility of a physical definition of the renormalized coupling.Comment: 23 pages; to appear in Rev. Math. Physics few corrections, two explanatory paragraphs adde