Young Researchers Conference 2008

While analogue models for gravity have so far provided some insights on the kinematical aspects of general relativity, the emergence of gravitational dynamics is still unclear. In this talk I will present two models which aim at filling this gap. In the first one a BEC model is considered, to uncover the gravitational dynamics hidden in these systems. In particular, the emergence of a modified Newtonian dynamics and of the cosmological constant will be discussed. A second model will be used to show how Nordstrom theory of gravity emerges from a system defined in Minkowski spacetime, showing how background independent theories of gravity could emerge from background dependent models.

I will review the present status of the black hole entropy computation in Loop Quantum Gravity within the isolated horizon framework. Starting from the recently discovered discretization effect, I will give an overview of the subsequent developments that have been obtained motivated by it. Through this further analysis of the problem I will present some new related results and the promising new open windows that they give rise to.

The AdS/CFT correspondence has recently been extended to field theories satisfying the non-relativistic generalization of conformal symmetry, the Schroedinger symmetry. These holographic descriptions offer the potential to do calculations in the strong coupling regime of experimentally-realized condensed matter systems, such as fermions at unitarity. In this talk, we will outline the holographic formulation of such NRCFTs at zero temperature. We will then discuss the embedding of the appropriate geometry into IIB supergravity, and the finite temperature generalization that results. We will conclude with a brief discussion of the holographic description of non-relativistic conformal hydrodynamics and current research projects.

I will discuss a simple two-dimensional theory, whose unparticle sector is a modification of the Schwinger model, that gives new insights into the qualitative features of unparticle physics. I will analyze the transition between the short-distance perturbative physics and large-distance unparticle behavior. Then I will show how to compute processes that involve unparticle self-interactions, for which nontrivial higher n-point functions of the conformal theory are essential.

Extension of the minimal supersymmetric standard model (MSSM) that include a U(1)\' gauge symmetry are motivated by top-down constructions and offer an elegant solution to the MSSM mu problem. In this talk I will describe some of the opportunities that such models offer, such as a new mechanism for mediation of supersymmetry breaking, as well as some of the challenges in constructing viable supersymmetric U(1)\' models.

We present a method which can be used to convert certain single photon sources, such as quantum dots, into devices capable of emitting large strings of photonic cluster states in a controlled and pulsed “on demand” manner. Such sources greatly alleviate the resources required to achieve linear optical quantum computation. Standard spin errors, such as dephasing, are shown to affect only 1 or 2 of the emitted photons at a time. This allows for the use of standard fault tolerance techniques, and shows that the machine gun can be fired for arbitrarily long times. Using realistic parameters for current semiconductor quantum dot sources, we conclude high entangled-photon emission rates are achievable, with Pauli-error rates less than 0.2%.

A quantum channel models a physical process which adds noise to a quantum system by interacting with the environment. Protecting quantum systems from such noise can be viewed as an extension of the classical communication problem introduced by Shannon sixty years ago. A fundamental quantity of interest is the quantum capacity of a given channel. It measures the amount of quantum information that can be transmitted with vanishing error, in the limit of many independent transmissions over that channel. In this talk, I will show that certain pairs of channels, each with a capacity of zero, can have a strictly positive capacity when used together. This unveils a rich structure in the theory of quantum communication that is absent from Shannon\'s classical theory. This is joint work with Graeme Smith (IBM) which was published in the Sept. 26 issue of Science.

Instead of adding another dark component to the energy budget of the Universe in trying to explain the accelerated expansion, one can ask whether the cause is in fact the laws of gravity itself on the largest scales. In this talk, I will consider a sub-class of so-called f(R) gravity theories which closely follow the LambdaCDM expansion history, while at the same time evading tight Solar System constraints on gravity. I will present new results from cosmological N-body simulations which consistently solve for the modified gravitational force. In particular, I will discuss the effects of modified gravity on structure formation, dark matter halo properties, and cosmological observables.